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Phil. Trans. R. Soc. A (2012) 370, 2216–2239
doi:10.1098/rsta.2011.0602
Indo-Gangetic river systems, monsoon
and malaria
BY ELIZABETH WHITCOMBE*,†
Earth System Science Interdisciplinary Center (ESSIC), University of
Maryland, College Park, MD 20740, USA
The history of the Indo-Gangetic river systems from the late nineteenth to the early
twentieth centuries can be reconstructed from the meticulous official records of the
survey, meteorological and medical departments of the British Government of India.
In contrast with the grand sweep of the geological evidence, these records indicate
a complex narrative of floods, droughts and channel shifts. Similarly, the cumulative
growth of the Ganges–Brahmaputra and Indus deltas was overprinted by the effects
of the annual monsoon cycle on precipitation, temperature and winds. Malaria, the
principal vector-borne disease of the Indian subcontinent, and the deadliest, displayed
epidemiological types that ranged between the extremes of stable–endemic to unstable–
epidemic as defined in the classic theory of equilibrium of George Macdonald. Variations
in its transmission, incidence and prevalence were closely tied to the different deltaic
environments of the Bengal and Indus basins and to the short-sightedness of many
irrigation and related engineering schemes.
Keywords: Indo-Gangetic deltas; monsoon; malaria
1. Introduction
To H. F. Blanford, FGS, FRS (1834–1893), palaeontologist with the Geological
Survey of India from 1855 to 1862 and Meteorological Reporter to the
Government of India from 1874 to 1888, the subcontinent offered ‘many peculiar
advantages’ for scientific enquiry. As a region defined, to the north, by the
Himalaya and to the west and east by the Arabian Sea and Indian Ocean, it
presented ‘in its different parts extreme modifications of climate and geographic
features’ [1, pp. 563–564]. From the mid-1870s, systematic observations on
geological phenomena and meteorological events were published in the surveys’
annual reports. Meanwhile, under the Registration Act of 1865, the district
medical officers of the provincial Sanitary Commissioners’ departments collected
monthly observations on births and deaths, with specific reference to climate
and physiographic conditions. Deaths were registered inter alia by principal
cause—chiefly fevers, of which upwards of one-third were ‘malarious’.
*[email protected]
† Visiting Senior Research Scholar.
One contribution of 10 to a Theme Issue ‘River history’.
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This journal is © 2012 The Royal Society
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Indian rivers, monsoon and malaria
2217
Nowhere in British India was the range of variation in physiography and
climate more striking, nor more closely observed, than in the north, in the great
river basins of the Ganges–Brahmaputra system to the east and the Indo-Gangetic
system to the west. Against a background of the geological past of these great river
systems, as established by advances in geoscience, it is possible to reconstruct a
recent history, from the mid-nineteenth century, of fluvial processes, their climate
and their environmental diseases from technical records of the British Government
of India, unique in their calibre and consistency.
Malaria was British India’s most deadly and debilitating disease.
Predominantly a disease afflicting the rural poor, malaria was ‘responsible
directly’ for at least 1 000 000 deaths each ordinary year, increased, in epidemic
years, by another 25 000. At least 100 000 000 suffered from malaria each year.
It probably accounted for an ‘additional indirect morbidity’ of 25–75 000 000. It
had a marked adverse effect on the birth rate, and was ‘probably the greatest
single cause in retarding the natural increase of the population’ and ‘the greatest
factor in lowering the health, vitality and physical development of the people’
where it prevailed. Malaria accounted for annual financial losses ca £80 000 000
to the individual and the family alone. While direct and indirect losses could not
be accurately evaluated, there was ‘little reason to doubt that they must run into
unbelievable millions of pounds sterling each year’ [2, p. 158].
When systematic registration of mortality began in 1865, environmental
conditions—dampness, defective drainage, waterlogging and swamps—had long
been regarded as the direct cause of ‘malarious fevers’, and were given prominence
accordingly in the Sanitary Commissioners’ reports. Laveran’s identification
of the parasite Oscilleria (later renamed Plasmodium) malariae as causative
organism in Algeria, in December 1880, established an intermediate step
between environment and human host. By the end of the decade, two further
plasmodia had been discovered in the blood of malarious patients and the
association of each species with periodicity of malarial fever—Plasmodium vivax
with benign tertian, P. falciparum with malignant tertian and P. malariae
with quartan—determined. The passage of plasmodium to host, and the role
of environmental conditions, awaited elucidation. In China, in 1878, Patrick
Manson, parasitologist—the ‘father of tropical medicine’—had shown how the
agent of filariasis, the parasitic worm, Filaria sanguinis hominis, was transmitted
by Anopheles mosquito—the female, since ‘the anatomical arrangement of the
male’s proboscis and appendages prevented it from penetrating the skin’. The
mosquito ingested the filarial embryos, ‘nursed’ them to maturation, then
reinjected them into the animal host [3]. Might not the female Anopheles, favoured
by the environmental conditions long associated with malarious fevers, be the
‘nurse’ of the malarial parasite? In discussions from 1894 to 1897, Manson
discussed his hypothesis with Surgeon-Major Ronald Ross, Indian Medical
Service, physician, artist and mathematician. In Calcutta, in August 1897, Ross
demonstrated, by experiments of an elegance to match Manson’s hypothesis, the
transmission of the plasmodium associated with benign tertian malaria (P. vivax)
by the female Anopheles mosquito to an avian host [4–6]. In 1900, Manson, in
association with Italian colleagues, confirmed by experiment the transmission of
plasmodium by Anopheles to human host—his physician son, whose recording
of his symptoms of benign tertian malaria daily and in detail perfected the
demonstration [7].
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Subsequent investigations into the parasitology and transmission of malaria,
the environmental conditions that favoured it and pioneering efforts at control
and prevention are described by Bruce-Chwatt [8].
Distilling field and experimental observations on malaria as the prototype of
vector-borne disease into a probabilistic theory of transmissibility, generalized as
‘pathometry’, Ross [9,10] laid the foundations of the mathematical epidemiology
of vector-borne disease.
Some 40 years later, George Macdonald, malariologist and mathematician,
followed Ross’ probabilistic method in his classic paper on theory of equilibrium in
malaria [11]. His theory was derived from half a century’s field and experimental
observations, given mathematical expression and translated back into
epidemiological terms.
Macdonald [11] identified three factors as essential to the epidemiology of
malaria: (i) the duration of the extrinsic cycle of the parasite (in the vector); (ii)
the vector’s biting habit—specifically, the frequency with which it fed on man;
and (iii) the vector’s normal longevity. Factors (ii) and (iii) could be related as the
average number of feeds on man that an insect took in its lifetime. These factors
affected ‘the probability of an insect becoming infected and thus the density of
insects needed to maintain continuous transmission’: they determined the ‘critical
density of insects in relation to man, below which the disease tends to disappear’.
If the critical density was exceeded, then Macdonald considered that these factors
would act to curb ‘progressive multiplication of human cases’.
Macdonald [11, p. 824] described the variability of transmission of malaria
between vector and host as a dynamic equilibrium, continually adjusted between
stability and instability (see table 1):
according to the degree of the controlling factors, the epidemiology of the resultant malaria
corresponds to some point on the scale between the extremes described as stable and unstable
malaria.
In stable–endemic areas, transmission of malaria was more or less constant,
building up a firm immunity in the host population and thus preventing
epidemics. In areas prone to epidemics, transmission was interrupted and
immunity fell. The resumption of transmission led to an epidemic, followed by
a significant level of immunity for several years [11]. It was well recognized that
endemic malaria, despite its relatively low death rate, sapped the strength of the
population—and ‘may exercise in the long run a more harmful effect upon the
public health than even the most severe epidemic’ [12, p. 418].
Recent exercises in the mathematical epidemiology of malaria have amended
and enlarged on Macdonald’s analysis with a variety of modelling techniques
[13]. A simulation of the dynamics of transmission of malaria in association with
variation in weather, the Liverpool Malaria Model, designed by Hoshen & Morse
[14], has lately been updated by Morse and co-workers [15].
From field studies throughout India on which Macdonald built his theory
of equilibrium of transmission, with the rate of enlarged spleens and later
parasitaemia in a given population taken as the index of malarial infection,
variation between stable–endemic and unstable–epidemic types of malaria
was localized to specific regions of the Indian subcontinent—a remarkable
achievement of the Malaria Survey of India within 6 years of its establishment in
1920 (figure 1).
Phil. Trans. R. Soc. A (2012)
Phil. Trans. R. Soc. A (2012)
transmission regular,
by vector Anopheles
of frequent
man-biting habit,
moderate longevity,
at temperature
>15◦ C, favouring
rapid completion of
extrinsic plasmodial
cycle, all altitudes,
latitudes
I stable
II unstable transmission irregular,
with gross
variations, by
vector Anopheles of
relatively infrequent
man-biting habit,
short-lived, at low
altitudes only
determining causes
type
very high:
anophelism
without
malaria also
found
variation, lowmoderate,
may be high
very low: ≤0.025
man-bites per
night
relatively high: 1 to
≥10 man-bites
per night
Anopheles density
required to maintain
transmission
endemicity
regularity of
transmission
likely to ensure
stable immunity
with local
variations.
Experience of
malaria and
resistance
throughout
population,
except youngest
children
very variable:
significant
proportion of
population not
immune, no
resistance to
upswing in
transmission in
unstable
conditions
very marked: mean value of
transmission
moderate-low, seasonal
epidemics exaggerated,
endemicity exacerbated by
increase in favourable
breeding conditions.
Major regional epidemics,
invasion of previous
non-malarial areas
where/when climatic
factor(s) favour vector
longevity, breeding over
large areas
very marked response to
variations in
temperature, low
humidity, other
unfavourable vector
breeding conditions.
Virtual cessation of
transmission in some
years. Seasonal, severe
epidemics: abrupt
onset at relatively high
temperatures; rapid
cessation as
temperatures fall
immunity of
population
slight, seasonal: mean value
of amount of transmission
high, with seasonal and
local variations. Virtual
cessation of transmission
rare. Epidemics unlikely
fluctuations in
incidence
slight: complete
termination of
transmission unlikely
despite conditions
unfavourable to
breeding or prolonged
adult survival
(temperature <15◦ C,
low rainfall, low
humidity)
seasonal changes: effect
on transmission
Table 1. Epidemiological types of malaria, according to Macdonald’s theory of equilibrium [11].
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Indian rivers, monsoon and malaria
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E. Whitcombe
70°
80°
90°
Punjab:
malaria epidemic–
hyperepidemic
a
30°
30°
b
c
Sindh:
focal epidemic malaria
Bengal:
Maleria endemic–
endemicmalaria
hyperendemic
20°
20°
70°
80°
90°
Figure 1. Epidemiological types of malaria prevalent in Punjab, Sindh and Bengal. From
Christophers & Sinton [16].
The association of these contrasting epidemiological types of malaria and the
great river basins of northern India is apparent. In the northeast (NE), humid
subtropical region of the subcontinent of south Asia, the western part of the
Bengal foreland basin (the oldest, least active region of the inland delta of the
Ganges–Brahmaputra system) has a history of stable–endemic, stable malaria,
with hyperendemic foci. The death rate was constant, but small, associated with
a constantly high spleen rate and a relatively low birth rate [12]. Immunity
levels were consistently moderate to high. The semi-arid region of the Indus
foreland basin to the northwest (NW), characterized by recent, dramatic river
shift particularly in its eastern part, has a history of unstable–epidemic malaria,
with hyperepidemic foci. The death rate was high, but for short periods only,
with a ‘remarkable freedom from mortality during inter-epidemic periods’ [12].
In the Indo-Gangetic river systems, a dynamic equilibrium between relative
stability and instability is adjusted and readjusted by phases of progradation
and aggradation, at rates of greater or lesser activity according to the balance
of forces—fluvial and, at the coastal deltas, tidal processes, on a seasonal,
interannual and interdecadal scale, complicated by the anomalies of the Asia
monsoon cycle and constrained by tectonic movements. The systems arose in
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Indian rivers, monsoon and malaria
high
High
pressure
dry
dry
NE phase
transitional phase
Dec
Jan
Nov
Oct
Feb
Sept
Mar
Aug
April
July
SW phase
June
thermal
Low
low
pressure
pressure
May
transitional phase
wet
2000 km
Figure 2. The Asia monsoon cycle. From data in Pithawala [18] and Kump et al. [19].
the Himalaya–southern Tibet with the progressive collision of the Indian and
Eurasian plates during the Tertiary. The convergence of the plates, together
with gravitational spreading, unleashed forces that uplifted the Himalayan ranges
and east Asian plateaux—movements that continue at the present day. In the
Himalayan–south Tibetan drainage basin, the action of eroding forces towards
the head of the rivers is counteracted by northward migration of rivers north
of the rising Himalaya [17]. In their passage south, the forerunners of the IndoGangetic system have cut great gorges in the south Tibetan plateau and in the
foothills through which they debouch, abruptly into the plains of the northern
subcontinent, to form vast, braided fans of inland and coastal deltas. Delta
building continues, in phases of greater or lesser activity and forcefulness of
fluvial and tidal processes, subject below to tectonic movements and above to
the vagaries of the monsoon (figure 2; table 2).
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E. Whitcombe
Table 2. History of the Asia monsoon system [20,21].
chronology (Ma)
events
9–8
aridity in Asian interior increases
onset of Asian, East African monsoons
ca 5
intensification of Asian monsoon
3.6–2.6
intensification of East Asian NE and SW monsoons continues
dust transport to North Pacific Ocean increases
ca 2.6
increased variability in monsoons: continued strengthening of East Asian
NE monsoon, weakening of Asian and East Asian SW monsoons
The modern Asia monsoon system is a complex, cyclical weather system
in dynamic equilibrium, varying with regular or irregular regularity about
a relatively stable norm to unstable anomaly in wind speed and direction,
barometric pressure, precipitation, temperature and relative humidity, over years,
decades, centuries and aeons [21–25]. But ‘the defining variability of a monsoon
system is its seasonal character’ [26, p. 203]. The strongly defined seasonal cycle
marks out the Asian monsoon system from others with their weaker annual cycles
[27]. The NE monsoon of the Asian cycle, in the NE and NW of the Indian
subcontinent, a relatively low-grade wind bringing gentle patchy precipitation,
associated with mild temperatures, is in evidence at the turn of the calendar year
and dies away through March into a transitional phase, abruptly interrupted,
during May–June, by the onset, commonly tumultuous, of the southwest (SW)
monsoon winds, in an east to NW progression, the date of regular onset varying
according to location. The SW monsoon provides up to ca 80 per cent of
the annual discharge of the Indo-Gangetic rivers, augmented by snow-melt.
In September, the SW winds are exhausted and come gradually to cessation.
A transitional phase follows, to the close of the year. Within the cycle, there is
much intraseasonal variability—in onset and duration of monsoon wind, between
weak and strong spells, in amount and distribution of precipitation, in coincident
temperatures and in relative humidity [23,26].
2. Bengal: the Ganges–Brahmaputra river system
The dynamic equilibrium of the Bengal delta (figure 3; table 3) is most evident
where it is least stable, at its margins—south, in the tidal delta of the Bengal
coast; north, where the mountain torrents emerge from the gorges into the plains.
In the tidal delta, as Hunter, Statistical Officer to the Government of Bengal
observed in the course of his field surveys of Bengal (and every district in British
India) for the Imperial Gazetteer [32, p. 20]:
An eternal war goes on between the rivers and the sea, the former struggling to find a
vent for their columns of water and silt, the latter repelling them with its sand-laden
currents.
From the Early Holocene, the shoreline has lost ground to the rivers and
retreated south over some 80 kyr, with marked acceleration in pace between
80 and 6 kyr, to its present position (figure 3). The sluggish end-streams of the
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Indian rivers, monsoon and malaria
88°
89°
91°
90°
Jamuna
Bhagirathi
24°
Gange
24°
s
Pa
dm
a
moribund delta
hnnaa
Megg h
M
active
delta
23°
23°
mature delta
tidal delta
22°
Hu
gli
22°
subaqueous
delta
of
Bay
present shoreline
palaeo-shoreline 6000 yr BP
palaeo-shoreline 80 000 yr BP
90°
gal
Ben
40 km
Figure 3. Bengal basin. Delta zones and palaeo-shorelines. From data in Lindsay et al. [28], Kuehl
et al. [29] and Geological Survey of India [30].
Ganges now debouch into the NW reach of the Bay of Bengal. The deposition of
their sediment load varies with their rate of discharge by an order of magnitude
corresponding to the seasonal variation in precipitation of NE and SW monsoons.
Fluvial processes are here counteracted by the eroding forces of tides with
a diurnal variation of 1.9 m range, compounded by a periodic variation at
14–15 day intervals, stirred alternately by the clockwise and anti-clockwise gyre
of the monsoon wind systems and funnelled 8 km or more into the estuary
and the network of tidal creeks, relicts of the old Ganges in its migration
east–northeast [33].
Phil. Trans. R. Soc. A (2012)
Early Cretaceous
Cretaceous–Early Eocene
Early Eocene–Mid-Miocene
Mid-Miocene–Holocene
Early Pleistocene
Early Holocene
Mid-Holocene
>126 Ma
126–49.5 Ma
Phil. Trans. R. Soc. A (2012)
49.5–10.5 Ma
10.5 Ma–present
1.5 Ma
11–7 ka
7 ka
<7 ka
7.5–6 ka
150 years
<5 ka
<3 ka
transitional delta
modern delta
proto-delta
initial
stage in delta
formation
fragmentation of Gondwanaland: delta formation begins from slow
sedimentation at Indian plate margin, northward drift of Indian plate,
colliding with Eurasian plate: great increase in rate of sedimentation
deposition of carbonate–clastic associations:
early, in high-latitude, restricted marine environment
later, in low-latitude, open marine equatorial environment
formation of deep-sea fan from increased sediment load
major eustatic fall in sea-level, resulting in erosion of earlier
depositions—modern delta formation begins
sea-level high; small deltas form around inner boundary of basin; with
successive falls in sea-level, deep dissection of delta sediments
upper delta plain: accretion of major fluvial and flood basin sequences
delta depositional sequences largely aggradational
depositional sequences mostly progradational; alluvial sands widely
distributed across coastal plains
progradation most prominent in western delta, where Ganges system
discharging
eastern delta: Brahmaputra shifts eastward, into Sylhet basin, depositing
most load inland, not delta front
Brahmaputra shifts to westward, coastal depositions revived
In Brahmaputra, further cycle of east–west shift, main Ganges course
shifts eastward. Subaerial depositions extend to modern coastline
east delta: progradation of coastline begins
Brahmaputra shifts to modern, western, course
events
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by 6–5 ka
geological era
age
Table 3. History of the Ganges–Brahmaputra river system, Bengal delta. Sources: Lindsay et al. [28], Kuehl et al. [29] and Goodbred & Kuehl [31].
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Indian rivers, monsoon and malaria
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The NW shoreline of the Bay is distinguished by a series of tidal lakes where,
as Hunter observed, ‘the strong monsoon and violent currents which sweep from
the south during eight months of the year have thrown up ridges of sand’ [32].
The largest of these, Chilka Lake, a pear-shaped ‘inland sea’ at the southern
extremity of the Mahanadi delta of Orissa, measured over 70 km long in Hunter’s
time, with a surface area varying from a minimum of 891 km2 during the eight dry
months to a maximum of 1165 km2 in the rains. The lake was joined to the sea
by a narrow neck much silted up since 1780, when the opening in the bar—more
than 1.5 km wide—had had to be crossed in boats. Forty years later, the neck was
‘choked up’ and an artificial mouth had had to be cut, which was now silting up
[32, p. 23]. Hunter observed how the seasonal variation in the dominance of tidal
as against fluvial forces was reflected in the composition of lake water [32, p. 20]:
The narrow tidal stream which rushes through [the neck, now a few hundred metres broad]
is speedily lost in the wide interior expanse and produces a difference never more than 1.2 m
between high and low tide and at times barely 0.45 m, while the tide outside rises and falls
1.5 m. It suffices to keep the lake distinctly salt during the dry months, December to June.
But once the rains have set in, the rivers come pouring down upon [the lake’s] northern
extremity, the sea-water is gradually pushed out and the Chilka passes through various
stages of brackishness into a freshwater lake
The subtropical tidal deltas of the northern Bay of Bengal, as exemplified today
in the World Heritage Site of the Sunderbans, are swamp–creek–lake ecosystems.
Their predominant vegetation, forests of mangrove, harbour a wide variety of
fauna, not least arthropods, and flora. Mangrove is adapted to the hydrodynamic
circumstances peculiar to estuaries. Its swamps are aquatic at high tide, terrestrial
at low and subject to discontinuous flow given the wide diurnal and seasonal
variation in tidal and fluvial volumes. Trees and roots act as a brake on tidal
and fluvial forces and by creating eddies, enforce non-laminar flow. Mangrove is
halophilic and adapted to seasonal variation in the saline concentration of creek
and lake water [34, pp. 27–42].
The youngest, most active and unstable sector of the lower Bengal delta inland
from the coast lies to the east, at the apex of the Bay of Bengal, where the
Meghna, carrying a combined sediment load of Ganges and Brahmaputra south
from their confluence, enters the Indian Ocean. In the NE monsoon season, the
Meghna’s sediment load at a discharge rate of ca 10 000 m3 s−1 is easily kept at
bay by the tides. During the SW monsoon, when the Meghna increases 10-fold
or more, a freshwater layer 50–100 m in thickness displaces the sea water in the
north of the Bay [28,29,35].
At the northern margins of the Bengal basin, rivers rising from the eastern
Himalaya, still uplifting since the Asia–Eurasia collision of the Cretaceous, pour
through steep gorges in the foothills to fan out at the sudden, drastic change
in gradient on meeting the plains in great, unstable deltas, their courses shifting
direction within the constraints of terraces thrown up by tectonic forces. One such
is the Kosi river, one of the great Ganges tributaries to the NW of the basin, in
modern Bihar. Draining a catchment of some 61 869 km2 , the Kosi is braided
throughout the 209 km of its course. Its fan, ca 154 × 147 km in maximum width,
slopes from 0.89 m km−1 at the apex of the cone to 0.06 m km−1 at its base [36,
p. 291]. Its discharge may vary by ±50 per cent, from 0.006 to 0.024 m3 s−1 from
NE to SW monsoons, with an average annual sediment load of 118 000 000 m3 ,
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E. Whitcombe
ranging in content from boulders towards the apex of the fan to coarse pebble and
shingle over the base, the more coarse sediment contributing to relatively rapid
rates of aggradation [29]. The recent history of the Kosi fan is exceptionally well
documented. A series of observations from Rennell’s survey of 1731 to the present
day shows a shift of 113 km 50◦ to the west in some 250 years [37,38].
The Kosi’s stepwise migration to the west is less likely to reflect sudden,
cataclysmic events, earthquakes and floods but rather ‘stochastic and autocyclic’
shifts [38], irregular ‘oscillations’ by the sediment-laden river, which from time
to time is forced out of its course and migrates laterally, overwhelming smaller
streams in its path to leave a succession of dead and dying rivers in its wake.
The history of delta building in the great plains of the western Bengal basin
is written in the intricate networks of obsolete and obsolescent channels: ‘like
fossils’, the geologist James Fergusson observed in his survey of the Bengal delta
in the mid-nineteenth century. The shallow pools and streams of these remnants
of river shift have been transformed into wetlands, bogs and lakes and refreshed
seasonally, but irregularly, by the monsoon [38,39].
The onset of NE monsoon sea-winds was first felt in February–March. This
winter–spring precipitation, ‘less regular and lighter’ than elsewhere in northern
India, continued through April. The transitional phase, in May, was brief
[1, p. 600]. From the first or second week of June, the SW monsoon
current ‘pours into the funnel-shaped opening occupied by the delta, then
turns westward and passes up the Ganges Valley towards the Punjab. The
Bengal basin is thus the recipient of most of the moisture it carries’. The
SW monsoon phase ended in late ‘autumn’ rains, in October, initiating
a turbulent transitional phase when winds over Lower Bengal—the delta—
were ‘conflicting and variable and calms (alternating with storms) at their
maximum frequency’. From the end of October and November, the NW
wind current of Upper India combined with NE winds of north Bengal in
a continuous stream over the Bengal basin, heralding the next NE monsoon
phase. Temperatures were generally more equable in humid, subtropical
Bengal than in the semi-arid NW. From a mean of 66◦ F (19◦ C) in
January, there was a gradual rise to a mean of 85–90◦ F (29–32◦ C) in
April, with a further, slight increase in May. Temperatures decreased through
the SW monsoon phase from June. Regions where the rains were most
copious, such as Bengal, were the coolest. By early October, as the rains
ceased, mean temperature was a near-uniform mean at 81–82◦ F (27–28◦ C)
[1, pp. 584–585]. Humidity, higher in every season in the tidal than in the
inland delta, varied in relation to the prevailing winds. During the driest months,
humidity increased, more so in the east than the west, and decreased from
the onset of the SW monsoon in June, more so in the west than the east
[1, p. 597].
The defective drainage of mature, and more especially moribund, regions of
the western–central Bengal delta, the oldest, least active sectors, was highlighted
annually, during and after the SW monsoon. These regions correspond, on
the malaria map (figure 1), to stable–endemic areas, where malaria of varying
intensity was ‘practically never absent . . . largely a reflex of a multiplicity of
natural features of the country . . . rainwater collections, streams and rivers,
swamps, ponds, lakes’ [16]. The spleen rate was rarely above 50 per cent,
maximum, largely confined to young children, with a ‘relatively low rate in
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Indian rivers, monsoon and malaria
2227
resident adults who have had considerable immunity to malaria and suffer
little from its effects’, in contrast to the high incidence among—non-immune—
immigrants to the region. The map shows extensive areas of high- and hyperendemicity in the deltaic plains within the endemic tracts and ‘apparently
associated with secular changes affecting the physiographic conditions’ favouring
transmission of malaria: ‘decayed rivers’. Smaller such foci were found where oldestablished malaria was slowly enhanced in intensity over years. Hyperendemic
foci were also associated with forested hills to the north, jungle and terai, boulderstrewn marsh at 305–900 m in altitude at the debouchement of foothill streams
[16]. In marked contrast to the western deltaic plains, malaria in the eastern,
active delta was markedly lower in both incidence and prevalence, particularly
in the tidal delta, which had not lost its mangrove forests [40–42]. The stripping
of mangrove from much southern reaches of the old delta from the eighteenth
century [39] may well have contributed to a rise in endemic malaria. In these
stable–endemic areas, epidemics were rare [16].
The association of malarious fever and its seasonality with physiographic
conditions peculiar to the old inland delta of the western Bengal basin—the lie of
the land and the effect of the SW monsoon—was well recognized by the Sanitary
(public health) Commissioners of Bengal through the later nineteenth century.
Observations abound in their annual reports as to how the districts of the old
delta constituted ‘a vast alluvial plain intersected by six large rivers, numerous
smaller channels and by a labyrinth-like network of forsaken river-beds and old
rivers in every stage of decay and effacement. . . . The regularity of the slope
of the country is broken up by the tangle of rivers and river-beds that cross
and recross one another and obstruct the natural lines of surface drainage. . ..
The high mortality in October, November and December is undoubtedly due to
malarial fever caused [sic] by the marshy and waterlogged state of the country
after the rains. . .worst in dense jungles and along drying-up river-beds, converted
in the monsoon to a series of still pools’ [43]. Jessore district, in the heartland
of endemic–hyperendemic malaria, was typical of the moribund delta—‘seamed
with the beds of extinct rivers, with a languid vitality during the rains and in
dry weather a chain of foetid swamps’ [44, appendix III].
Ross’ and Manson’s experimental confirmation of the mosquito–malaria
hypothesis in 1897–1900 was matched before long by field observations. After the
(annual, June–August) Ganges floods, the Sanitary Commissioner commented in
his report for 1904 that there were ‘large collections of stagnant water [freshened
by the recent rains] . . . and as these became breeding places for anopheles, so
malarious fever became rife during the latter months of the year’ [45].
Over the next four decades, officers of the Indian Medical Service and, from
1920, of the Malaria Survey of India compiled a mass of field and experimental
observations on the transmission of malaria, unique in the annals of epidemiology,
identifying Anopheles, their habits and habitats, specific to the several regions of
the subcontinent (table 4).
The work of control by the distribution of quinine from local dispensaries and
post offices, which had begun in the nineteenth century, was stepped up. But
tens of thousands of doses distributed per annum for a population of upwards of
some 70 000 000 had little impact on annual mortality. Experiments in prevention
by spraying kerosene on breeding pools were sporadic and confined to occasional
villages. Throughout the 1930s, the death rate from malarious fevers continued to
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E. Whitcombe
Table 4. Bengal basin. Distribution of Anopheles species identified by mid-twentieth century [46].
epidemiological
type of malaria
stable–endemic,
hyperendemic where
vector population
density high
region
vector
breeding: site,
seasonality
inland, mature,
A. philippinensis river relicts—pools,
moribund delta
streams, swamps, clear
water, in sunlight
SE coastal deltas
A. sundaicus
SE coastal plains
A. aconitus
A. annularis
north, NE hills
A. minimus
lagoons formed by silting
of river mouths,
especially where
mangrove cleared
swamps, ponds, creeks,
river-beds, where cattle
abundant
still water with floating
vegetation active at
12◦ C. Increased
longevity in autumn
clear, slowly moving
water with grassy
edges, death point
40◦ C
adult feeding
habit
chiefly domestic,
anthropophilic
anthropophilic >
zoophilic
zoophilic >
anthropophilic
zoophilic,
anthropophilic
zoophilic,
anthropophilic
dominate registered annual mortality: at an average for 1937–1940, for example,
of 15‰. ‘The total loss . . . inflicted on this province annually by this devastating
scourge is colossal’ [47, p. 67].
3. Punjab: the upper Indus
From its debouchement at the Salt Range—the northwestern foothills of the
Himalaya—the Indus river flows for some 1600 km through the semi-arid plains of
Indian and Pakistan Punjab and Pakistan Sindh to its exit into the Arabian Sea
southeast of Karachi. It drains a foreland basin of 970 000 km2 —the world’s 12th
largest, and forms the seventh largest known coastal delta of some 30 000 km2 . Its
annual sediment load, deposited in the sea over aeons, some 60 per cent of it by the
SW monsoon flood, has formed the gigantic Indus Deep-sea Fan, in its volume of
ca 5 000 000 km3 second only to the Bengal (Ganges–Brahmaputra) Fan [48,49]
(see table 5). An integral part of an Indo-Gangetic river system following the
collision of the Indian and Eurasian plates before 126 Ma, the Indus is thought to
have separated from the Ganges, which subsequently expanded eastward. The
Indus, and its main tributaries, migrated west. The impetus may have been
a strengthening in the SW monsoon from ca 5 Ma, increasing erosion in the
Himalaya, bringing down a greater load of coarse sediments from increased erosion
in the western Himalaya [48,52]. As the sediment-laden rivers of the western
Indo-Gangetic system burst from the steep gorges in the Himalayan foothills
into the low-gradient foreland basin, they overwhelmed old courses of the inland
delta to form new streams successively to the west [50,51,53]—events similar
to sequential river shift in the Bengal basin, as described above, to fetch up in
their present course, further gross westward movement being forestalled by the
mountain ranges rising northward from the SW.
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Table 5. History of the Indus river system. Sources: Inam et al. [48], Clift & Blusztajn [50] and
Schroder [51].
age
geological era
events
>126 Ma
Early Cretaceous
75 Ma
57–37.5 Ma
Late Cenozoic
Eocene
24.5–5 Ma
Miocene–Pliocene
<5 Ma
<20 ka
Pleistocene
fragmentation of Gondwanaland: northward drift of
Indian plate, colliding with Eurasian plate
palaeo-Indus north, west of present location
parallel, west-flowing streams south and north
(palaeo-Indus) of Himalaya
continued uplift of Himalaya, Suleiman
Range—corresponding flexion of Indian plate,
formation of Indus foreland basin
ca 18 Ma: diversion of upper Indus south, through
Himalaya close to Nanga Parbat massif, into
foreland basin and east, into Ganges
separation of Indus, Ganges
last glacial maximum
expansion of Ganges basin
contraction of Indus basin
westward migration of major Indus tributaries
main depositional lobe of Indus (coastal) delta
formed: westward shift in main channel
in westward shift, obsolete–obsolescent channels
abandoned by main streams, forming riverains
shift of upper and lower Indus to west constrained
by uplifting western ranges running north from
Karachi
The westward migration of the Indus (figure 4) has been the object of close
attention from the early nineteenth century, when British Indian surveyors
and administrators, learned in Sanskrit and with a bent for history, began to
explore the abandoned riverains (jhils in the vernacular: obsolescent–obsolete
river channels in Punjab, turned to ponds during monsoon) of the Indus
basin for evidence of the ‘lost river Saraswati’ of Vedic times, the Ghaagar–
Hakra–Nara Nadi river systems and the Indus (Harappan) civilization itself
and subsequent settlements, successively abandoned and now identified from
archaeological remains [54,56–58].
With a resurgence of interest in the Indus civilization since the late twentieth
century, professional exploration of the obsolete–obsolescent foreland basin has
intensified, equipped with remote-sensing imagery and the latest geophysical and
geochemical techniques [51,53,59–61]. As yet, there is no consensus on the exact
courses taken by former Indus channels.
The annual monsoon cycle in Punjab was distinguished by its volatility. The
NE monsoon, from December to March–April, was more regular and ‘copious’—at
a mean monthly precipitation of ca 0.5–1.3 inches (13–33 mm)—than in the south
and east Gangetic valley. A transitional phase followed, through April–May and
into early June, marked by ‘scanty and uncertain rainfall from occasional thunderstorms’. Rainfall in the SW monsoon, from mid–late June to September, was in
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(a)
100 km
(b)
100 km
Figure 4. The Indus foreland basin. Westward river shift, plotted from historical documents and
archaeological remains. (a) 2000 BC; (b) AD 1940 (based on Wilhelmy [54]). For a critique of
Wilhelmy’s reconstructions in the light of LANDSAT imagery, see Ghose et al. [55]. Dashed lines
in panel (b) represent abandoned channels.
inverse proportion to distance from the coast—‘much lighter than elsewhere in
India except in Sind . . . ’ [1, pp. 568, 600–602]. Even submontane Rawalpindi
registered a total precipitation for the season of 17.2 inches (437 mm), while the
total average fall at Multan, on the south-central plains, was 5 inches (127 mm)
from June to October.
The south west wind is not . . . here a rain-bearing current. It probably comes as much from
the desert as the sea, and passing in its course over the heated arid plains that surround
the lower course of the Indus, the increase of its temperature counteracts any tendency to
precipitation which may be induced by the upward diffusion of its vapour . . . [It] appears
that during the SW monsoon the winds perform a kind of cyclonic circulation in the Punjab,
converging from the plains to the south and east
There was a similarly marked annual variation in mean temperature, from
55◦ F (13◦ C) in January, when Punjab was ‘the seat of greatest cold’, to a sharp
rise in March–April to 95◦ F (35◦ C) and upwards. In the SW monsoon, Punjab
became ‘the seat of the highest temperature’, at means of over 90◦ F (32◦ C)
[1, pp. 586–588]. Humidity in the Punjab plains was at a minimum in May–June
and at a maximum in December.
Dry winds were characteristic of Punjab’s weather, and drought frequent. In
an examination of anomalies in annual precipitation in Punjab from 1845 to 1878
Blanford showed a complementarity between NE and SW monsoons. In 12 years
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of the series, the NE rains were excessive and SW deficient; in 13 years, the
converse was recorded; in 3 years, both NE and SW monsoons were excessive;
in 6 years, both were deficient. Further, in years of dry land winds and deficient
rainfall during the SW monsoon, an unusually heavy snowfall was recorded in
the NW Himalaya. From this, Blanford suggested that ‘the varying extent and
thickness of the Himalayan snows exercise a great and prolonged influence on the
climatic conditions and weather of the plains of North-Western India’ [62, p. 3]. A
recent assessment by Fasullo [63] of Blanford’s hypothesis with satellite imagery
suggests that the association of Eurasian snow cover and the intensity of the
monsoon is complicated by the El Niño Southern Oscillation (ENSO). Northern
India showed the closest association between rainfall and snow cover, vindicating
Blanford.
The distinctive topographical features of the eastern Indus basin were well
recognized in official records of the Government of Punjab. These vast, semiarid plains, low in gradient and apparently featureless, were distinguished, on
closer inspection, by ‘great riverains’ lying slightly below the surrounding country,
which had been deserted by rivers migrating to the west. Soils were composed
mostly of fine silt sediments, laced with salts—especially CaCO3 , deposited in
concretions known locally as kankar in the desiccation of summer, which formed
an indurated layer a few feet below the surface. The riverains were peculiarly
liable to flood from mid-June to early September, during the SW monsoon. On
its cessation, surface pools formed by rainfall gradually dried out, ‘as much by
evaporation as by absorption’, where kankar layers prevented downward drainage
[64]. The SW monsoon gradually weakened in its progression northwestwards,
with the heaviest precipitation at the eastern extremity of the Indus basin and in
the submontane tracts to the north, and the least, even in a strong monsoon, in
the west.
In the malaria map (figure 1), the epidemic tracts in the NW region are roughly
co-extensive with the foreland basin of the Indus (Punjab), the upper Ganges
basin (Northwestern Provinces, from 1901 United Provinces of Agra and Oudh)
and the arid desert of Rajputana to the west. Christophers & Sinton [16] describe
the prevalence of malaria in this area as ‘markedly seasonal’, being enhanced
somewhat in early summer (March–April), followed by a lull on account of
widespread desiccation, with a marked increase in early autumn (late September),
following the cessation of the SW monsoon.
Within these tracts of unstable–epidemic malaria, the map shows a dense belt
stretching from the centre and east of the Indus basin on to the upper Gangetic
plain, roughly co-extensive with the obsolete–obsolescent Indus riverains. This
belt represents ‘fulminant malaria . . . vast cyclical disturbances peculiar to this
region’ manifested in a great, pandemic exaggeration of the normal autumnal
rise in prevalence, at ca 8 year intervals and mostly in years when the SW
monsoon was unusually heavy. An area of at least 25 000 km2 was affected, with
death rates of 40‰ or more [2,64,65]. Spleen rates among the population of this
‘hyperepidemic’ belt were characteristically low, ca 10 per cent before epidemics,
rising to 80–90% in their aftermath, to fall gradually back to the usual low level
over the following 5 or so years. Endemicity, and hence immunity, was low [16].
The vast areas of the eastern and central riverains afflicted with epidemic malaria,
particularly in its fulminant form after an exceptionally heavy SW monsoon, made
Punjab ‘the unhealthiest province in India’ [66].
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Table 6. Indus basin delta, Punjab–Sindh. Distribution of Anopheles species identified in the
twentieth century [46].
epidemiological
type of malaria
region
vector
breeding: site, seasonality
adult feeding
habit
unstable–epidemic,
with ‘fulminant’,
autumnal,
hyperepidemic
foci
NW India: Indus A. culicifacies
foreland basin
chief malaria vector of NW
indifferent:
India, largely rural, breeds
zoophilic–
in winter in sluggish
anthropophilic
streams, river-bed pools,
freshwater sheets, irrigation
channels, particularly
associated with extensive
flooding, hibernates in larval
stage, adults common from
May 1 to end December
unstable–epidemic
NW India: Indus A. stephensi
foreland basin
centralA. fuliginosus
submontane
sunlit pools, stream beds,
marshes, hardy, long-lived
breeds December–January,
found throughout year
epidemic
anthropophilic >
zoophilic
The seasonality of malarious fevers in Punjab and their association with
riverains and heavy SW monsoons had long been recognized by the Sanitary
Commissioner’s department. A review of fever mortality from 1869 to 1876
showed a sudden, steep increase in the monthly death rate from fever—mostly
of the kind called ‘malarious’—through October to December, chiefly in areas
of poor natural drainage with additional ‘accidental obstruction’ [67, pp. 33–34].
Rainfall was ‘invariably excessive every third year’ and associated with maximum
prevalence and fatality from epidemic fever ‘in low-lying tracts where drainage is
obstructed’ [67, pp. 33–34]. In east Punjab, ‘vast jhils’ formed in the abandoned
channels of the Indus in the wake of a heavy SW monsoon in 1887 and the fever
death rate rose: in 1887, to over 25‰ [68, p. 33].
From early in the twentieth century, the chief Anopheles species associated
with epidemic malaria in the Punjab were readily identified—A. culicifacies chief
among them, infesting the central and eastern riverain tract (table 6).
The highest mortality from malarious fevers was recorded in years of excessive
SW monsoon preceded by deficient precipitation in the NE phase. With the
expansion of breeding grounds in the waterlogged riverains under the heavy
summer rains, the Anopheles population exploded, with consequent increase in
transmission of plasmodium. Drought in the preceding winter and spring also
contributed, indirectly, to increased transmission by changing the biting habit
of the female Anopheles. A. culicifacies, the predominant species in Punjab,
was zoophilic and would only turn to man ‘as an alternative to starvation’
[11, pp. 820–821; 69, p. 882]. In rural Punjab, such zoophilic Anopheles would
feed preferentially on cattle. The death of cattle in vast numbers from drought
obliged Anopheles to feed off humans [70].
The melancholy record continued in the twentieth century. Localized epidemics
of malaria were recorded in districts marked by riverains and visited by
heavy rainfall and floods. A. culicifacies was regularly identified as the agent
[65, pp. 12–14; 71, p. 11; 72, p. 19; 73, p. 1].
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Within the regions of the Indus basin characterized by epidemic malaria, there
were exceptions to the general rule of low endemicity, pockets where spleen rates
were persistently high, and immunity in adults relatively rare. These pockets
were ‘more associated with old defective [irrigation] systems, where leakage and
waterlogging are a feature’—perennial seepage and pooling in terrain and climate
geared to episodic, seasonal waterlogging [64]. Whether the large-scale canal
systems for perennial irrigation introduced by the British Government of India
were responsible for an aggravation of malaria, if so, how much, and how to
rectify it, were questions repeatedly debated by Government throughout the
nineteenth and early twentieth century [74]. The western Jumna Canal, the first
large-scale system in British India, was a strict realignment-cum-reconstruction
by British Indian military engineers in the early nineteenth century of an old
Moghul irrigation channel meandering through low-gradient plains just to the
west of Delhi. Defective drainage along the lower reaches of the canal and the
‘liability of the inhabitants to miasmatic fever’ were the subject of an extensive
enquiry in 1847: the three-man committee travelled 1400 miles in a few months,
visited more than 300 villages and clinically examined more than 12 000 villagers
of all ages. From the findings, Surgeon-Major Dempster devised the spleen rate
(which served as index of malarial infection until replaced by blood sampling for
parasitaemia early in the twentieth century). The committee concluded that in
tracts of stiff, retentive soils, swamps bordered on the canal, from seepage and/or
the canal embankments’ obstruction to natural drainage. The district of Karnal
was especially remarkable for insalubrity [75].
From the 1850s to 1885, various drainage schemes were implemented,
culminating in realignment in 1885, with little change in the annual mortality
from fever in the low-lying districts [76, pp. 250–252]. In dry years, the death
rate from malarious fever in Punjab fell, except in Karnal district. With an
abnormally heavy SW monsoon, it was the worst in the Province—endemicity
complicated by fulminant epidemic [65,77,78]. Intensive epidemiological studies
of the Karnal district in the 1930s by the Malaria Survey of India showed why: the
swamps were favoured breeding places of the chief malaria vectors of the Punjab,
A. culicifacies, A. stephensi and A. fuliginosus [77,78].
The great canal systems pioneered in the late nineteenth and early twentieth
centuries to reclaim and colonize the uplands of the western Indus basin had a
better record, largely because the natural drainage was by no means defective
[12]. But where perennial canals, their distributaries and the embankments of
roads and railways cut across obsolete and obsolescent riverains of the central
and eastern basin, perennial swamps arose and, with them, malarious fever settled
into endemicity [76, pp. 254–255].
4. Sindh: the lower Indus
South of the foreland basin, the Indus narrowed in a relatively steep-sided channel
to emerge near Sukker, to spread over alluvial plains with a fall of a mere 55 m
in 402 km into a huge delta. Most of its old channels east of the main stream
were abandoned by the main stream of the Indus in its shifts to the west: ‘the
whole surface is furrowed and cross-furrowed by the beds of ancient river channels
which have left their meanders’, shrinking to a string of dhands or salt lakes. On
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the eastern boundary, one old channel, the eastern Nara, meandered southwards
[79]. The climate was, and remains, harsh—the epitome of monsoon instability.
In field surveys of the 1920s and 1930s, rainfall was described as ‘scanty and
precarious’, average annual precipitation ranging from 73 mm at Sukker, at the
apex of the southern, inland Indus delta, to 179 mm towards its base, with wild
interannual variation; summer temperatures of at least 45◦ C and a seasonal mean
humidity of 41 per cent. Sindh was the driest and hottest of British India’s
provinces [18,48,79,80].
Throughout most of its moribund delta, the bed of the main Indus stream
is higher than the surrounding country. The subsoil water rises at the time of
every inundation, assisted, in the traditional, rich, rice-growing tracts of the delta
closest to the main stream, by flooding from seasonal, inundation canals.
Sindh was visited periodically by unstable epidemics, as in 1897, 1906, 1916–
1917 and 1929, with a high death rate generally through the population,
most likely from a coincidence of unusual rainfall and flooding [81–83]. Stable,
hyperendemic pockets were recognized, chiefly in the rice-growing tract of
Larkana on the west bank of the lower Indus, distinguished by a moderate
death rate and high immunity. Elsewhere, ‘the amount of endemic malaria
according as local conditions were favourable or unfavourable for the breeding
of malaria-carrying mosquitoes . . . Thus villages situated on the banks of “dead”
rivers (e.g. the Sind Dhoro, a former bed of the Indus) were invariably highly
malarious’ [80,81].
In 1932, the Lloyd Barrage at Sukker with its canal system, the penultimate
great irrigation enterprise of the British Indian Government, began operation.
In 1927, before the Barrage’s construction, Government had launched the Sind
Malaria Inquiry. In an exemplary series of field surveys, from May 1928 to
May 1935, Gordon Covell and Subedar J. D. Baily surveyed selected areas
in all talukas (district subdivisions) that came under the command of the
scheme, before and after its coming into operation, together with certain tracts
outside, for comparison. Establishing the incidence and prevalence of malaria
as above, prior to the scheme’s operation, they revisited each area after it
opened in 1932, to assess its effects. They concluded that, in many places,
the incidence of malaria had increased: in the areas most affected by the
epidemic of 1929, the spleen rate had fallen below its level immediately after
the epidemic—the usual finding, as earlier, in Punjab—but was still much higher
than in the 10 year period between epidemics observed before the barrage
was opened.
The higher incidence, and prevalence, of endemic malaria was to be attributed
to ‘conditions favouring malaria transmission produced by the operation of the
Barrage Scheme’—familiar from long experience in northern India: a rise in
subsoil water level; actual or threatened waterlogging; seepage from some new
canals; the ‘cutting-off of sections of old canals, thus forming prolific Anopheles
breeding grounds; a 40 mile lake had formed above the Barrage, and the subsoil
water level had risen along it; rice cultivation had expanded in the areas outside
the scheme, under irrigation with water from the lake and remodelled canals—a
wretched catalogue of the adverse effects of irrigation and especially overirrigation by inundation in the presence of defective drainage, largely determined
by geomorphology, and a highly unstable climate, so familiar from the NE Indus
basin [80,84].
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Recommendations for rectifying a root cause of intensified malaria transmission
by the provision of efficient drainage would not be implemented—or could not,
given the simple impediment of low gradient. The options for treatment, strongly
recommended by Covell [84], were wretchedly inadequate.
It was fitting that, in 1952, the year Macdonald published his theory
of equilibrium, an India-wide programme for the eradication of malaria by
eliminating vector populations with dichlorodiphenyltrichloroethane (DDT) was
under way, with considerable initial success. The interruption of the programme
in the late 1950s has led to a revival of malaria, albeit not with its former
ferocity. Our understanding of transmission and transmissibility, while vastly
more sophisticated in recent years, with the introduction of complex probabilistic
analysis and stochastic modelling, is still far from complete.
5. Conclusions
The use of historical records in reconstructing the recent past of the Earth, its
geomorphological processes and the variations of its climates is often frustrated
by the limitations of elderly data. For the Indian subcontinent, it is a different
matter. Through the later nineteenth century, to the mid-twentieth century,
officers of the British Government of India—engineers, surveyors, geologists,
meteorologists, zoologists, botanists, physicians—explored the subcontinent’s
landscape, its mountains, rivers, flora, fauna, its populations, the history of their
habitations, their occupations and their diseases, with inexhaustible curiosity,
great skill in observation and methods of surface recording and a remarkable
command of the language of analysis, verbal and mathematical.
The great Indo-Gangetic river systems of northern India, the site of continuous
habitation over many millennia, were a constant focus of scientific enquiry by
the Imperial Government. From its records, unsurpassed in their consistency
and accuracy over the better part of a century, an extraordinary river history
can be reconstructed—extraordinary in its events, given the dynamic nature of
fluvial processes forming these great deltas and the variability of the monsoon
weather system to which they were subject, and in the conditions of their
environment, which favoured vector-borne disease, principally malaria. With such
a history to hand, present-day problems of rivers and their environment may be
better understood.
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