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42
Studies on the field population of mosquitoes and the incidence of
malaria in Kasaragod
Suresh Mohan Ghosh* and P.V. Mini
Department of Zoology, Government College Kasaragod,
Vidyanagar (PO), Pin 671123. E mail: [email protected]
Abstract
Field surveys carried out on the population of mosquitoes of Kasaragod during the year
2010-2011 revealed high population of mosquitoes during the months of April, May,
June, July and August .The population was comparatively low during the month of
October, November and December. The data also showed that the population of Culex
mosquito is comparatively higher in Kasaragod District. Anophilus sp. was rare. The
Culex reported from our study is the vector of filariasis which is very common in the
coastal areas of Kasaragod. The incidence of Malaria has reduced considerably in
Kasaragod and there was a steep decline in malaria during the last ten years.
Introduction
Malaria is a mosquito-borne infectious disease caused by a eukaryotic protist of the
genus Plasmodium. It is widespread in tropical and subtropical regions, including parts
of America, Asia and Africa. Each year, there are approximately 350-500 million cases
of malaria, killing between one to three million people, the majority of whom are young
children of sub Saharan Africa. 90% of malaria related deaths occur in sub Saharan
Africa.
The most important disease causing mosquitoes of India belong to the genera of
Anopheles,culex,Aedes.Mansonia,
Haemogogus,
Sabithes
and
Psorophora
(Manimegalai, 2010). In India Anopheles, Culex, Aedes, Mansonia are reported to be
important carriers of diseases like Malaria,Filariasis Japanese encephalitis,Dengue fever
and Dengue haemorrhagic fever (Williams, 2000).The genus Plasmodium includes the
malarial organisms of man, other mammals and vertebrates. These parasites possess a
life cycle with an alternation of generation accompanied by an alternation of hosts.
Asexual cycle occurs in vertebrates and gamatogony and sporogony occur in blood
sucking invertebrates. Five species of the Plasmodium parasites can infect human. The
most serious form of the disease is caused by Plasmodium falciparum. Malaria caused
by P.vivax, P.ovale, P.malariae causes milder disease in humans that is not generally
fatal. P.knowlesi, is a zoonosis that causes malaria in macaques but can also infect
human.
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Mosquito vectors and the Palsmodium life cycle
The life cycle of Plasmodium vivax is digenetic involving two hosts. Its life cycle is
completed both by asexual and sexual phases. Asexual phase is completed in man by
schizogony and sexual phase of its life cycle is completed in female Anopheles
mosquito by gametogony, syngamy and sporogony.
Knight and Stone (1977) have reported more than 3100 species of mosquitoes belonging
34 genera. The parasite’s primary (definitive) hosts and transmission vectors are female
mosquitoes of the genus Anopheles, while humans and other vertebrates are secondary
hosts. Anophilus species reported include A.stephensi, A.fulviatilis, A.culicifacies, A
minimus etc.
Materials and Methods
Field collection of mosquitoes
Adult of mosquitoes that rests on the walls during 7 p.m to 9 p.m. were collected for one
year (2010 June to 2011 May) from eight houses using nets. Mosquitoes collected were
brought to laboratory for final identification.
Tiger mosquitoes which are active during day time were observed and collected between
9.30 to 10.30 am. Their numbers were noted and tabulated.
A survey was also conducted in Kasaragod about the incidence of malaria during the
past thirteen years. This was done by visiting District Government Hospital, Kasaragod
and reports of malarial infection during the past thirteen years were collected.
Results and Discussion
Survey showed that during the study year the population of mosquitoes were high during
the months of April, May, June, July and August and low during the month of October,
November and December (Table.1). This correlates with high incidence of malaria
during these months. The data also showed that the population of Culex mosquito is
comparatively higher in Kasaragod District from the months of April to September .The
Culex reported from our study is the vector of filariasis which is very common in the
coastal areas of Kasaragod. The population of all species of Mosquitoes were low during
the month of December (Fig.1)
The incidence of malarial infection in Kasaragod was very high during the year 1998
with 1675 reported cases of malaria. In 2009 there were only 71 reported cases (Table
2).
GCK Science Letters
.Table 1. Population of Mosquito in Kasaragod district.
Month
June
July
August
September
October
November
December
January
February
March
April
May
Total
Types of Mosquito and their relative number
Aedes
Others
Culex sp.
sp.(Tiger
(Mansoni and
mosquito)
others )
156
78
98
139
53
84
138
44
77
108
40
63
95
36
38
98
35
49
30
25
16
85
43
54
77
30
45
75
42
41
128
53
64
133
85
73
1262
564
702
Figure 1. Population of different species of mosquitoes during the year 2010-2011
44
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Table 2: The incidence of malarial infection during the past thirteen years in kasaragod
Plasmodium
Vivax
728
1185
402
275
208
449
335
380
404
223
164
107
62
YEAR
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
P.falciparum
121
158
25
24
34
51
59
63
56
58
46
11
0
Mixed
infection
13
332
79
6
30
80
60
80
69
40
33
19
9
1400
1200
1000
Plasmodium Vivax
800
P.falciparum
600
Mixed infection
400
200
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
0
Figure 2. Incidence of Malaria in Kasaragod
In Kasaragod highest incidence of malaria occurred in1998 .Since then the incidence of
the disease reduced considerably. (Figure. 2).
Culex sp. is the main species of mosquito recorded from Kasaragod. Its population is
maximum from June to September and minimum during December. Alten et al. (1977)
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recorded highest number of mosquitoes during summer and autumn and less number
during winter. However Manimegala (2010) got highest peak of mosquito population
during the month of January to March and October to December which according her
was due to the Monsoon pattern of Coimbatore. According to Bhat (1975) and
Renapurkar (2001) Culex occur in all climatic zones of India from forest to desert zones
and the altitude does not affect its distribution. Because of the development of modern
medicines and treatment facilities, spread of malaria is fast decreasing day by day.
Mosquito control
Efforts to eradicate malaria by eliminating mosquitoes have been successful in some
areas. Malaria was once common in the United States and southern Europe, but vector
control programs, in conjunction with the monitoring and treatment of infected humans
eliminated it from those regions. In some areas, the draining of wetland breeding
grounds and better sanitation were adequate. Malaria was eliminated from the northern
parts of the USA in the early 20th century by such methods, and the use of the pesticide
DDT eliminated it from the South by 1951.
In 1950s and 1960s, there was a major public health effort to eradicate malaria
worldwide by selectively targeting mosquitoes in areas where malaria was rampant.
However, these efforts have so far failed to eradicate malaria in many parts of the
developing world—the problem is most prevalent in Africa (Trager and Jensen, 1976)
Malaria transmission can be reduced by preventing mosquito bites by the distribution of
inexpensive mosquito nets and insect repellents, or by mosquito-control measures such
as spraying insecticides inside houses and draining standing water where mosquitoes lay
their eggs.
Sterile insect technique is emerging as a potential mosquito control method. Progress
towards transgenic, or genetically modified, insects suggest that wild mosquito
populations could be made malaria –resistant. Researchers at Imperial College London
created the world’s first transgenic malaria mosquito, with the first plasmodium –
resistant species announced by a team at Case Western Reserve University in Ohio in
2002. Successful replacement of current populations with a new genetically modified
population, relies upon a drive mechanism, such as transposable elements to allow for
non-Mendelian inheritance of the gene of interest
Acknowledgements
The authors are thankful to the Principal Govt. College Kasaragod for the facilities
provided. The help and support rendered by the authorities of District hospital
Kasaragod is also duly acknowledged
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