vol.
19•s
HER.q.•.•,
BirdMala';-ia
[25
1928. "Noteson BandingTernsat Chatham,Mass.,for 1928." Bull. N. E.
B. B. A., Vol. IV, No. 4, October,1928,pp. 125-132.
1929. "Noteson BandingTernsat Chatham,Mass.,for 1929." B•dl. N. E.
B. B. A., Vol. V, No. 4• October, 1929 pp. 144-148.
1930. "Further Banding Notes from Tern Island, Mass." Bird-Banding,
Vol. I, No. 4, October, 1930, pp. 181-184.
1932. "Report of Tern Bandingon CapeCodDuring 1932." Bird-Banding,
Vol. III, No. 2, April, 1932,pp. 63-65.
17ORBUSH,
E. $.
1925. Birds of Massachusettsand Other New England States, Vol I, pp. 105126.
BIRD MALARIA
AND MOSQUITO CONTROL
By CAR•-TONM. HERMAn'
Department
of ProtozoSlogy
Johns
Hopkins
University
School
of Hygiene
and Public Health
THE purposeof this paperis to point out that a large percentage
of birds in nature are infected with a mosquito-bornemalaria, and
that this fact presentsa phaseof a problemof wild-lifemanagement
that has been overlookedalmostentirely.
OCCURRENCE OF •)LASMODIUM IN NORTH AMERICAN BIRDS
The causativeagent of malaria in birds was discoveredin 1885,
only five years after it was first recognizedin man. Although
malaria parasiteshave beenreportedfrom many speciesof birds
throughoutthe world, very little is as yet knownof their prevalence
amongthe avifaunaor the effectson the avian population.
In its broadestsense,malaria, whichoriginallymeant "bad air",
may today be interpretedas applyingto the diseases
causedby the
blood-inhabitingprotozoaof the family Plasmodid•e. At least
three generaof Plasmodid•e
have beenreportedfrom birds:Le•cowtozoSn, Hezmoproteus,and PIasmodium. All these forms live
within red blood cells. Only one genus--PIasmodium--is
kno•vn
to occurin man. There has beenmuch experimentalinvestigaiion
on the PIasmodiumof bird•swhich has had direct bearingon the
humanmalady. Mosquitotransmission
wasfirst workedout with
birds in India by Ross in 1898. Most of the recent advancesin
drug treatmeht of malaria have been tested first in the laboratory
on canaries. Studies of avian PIasmodium,however, have been
mainly with laboratorybirds and have not addedgreatly to our
knowledgeof the conditionsin the wild bird hosts.
Mos• protozoSlogists
recognizeonly three valid speciesof Plasmodiumas occurringin man. However, as hasbeenshownrecently
by Manwell (1935),thereare at leasteightvalid species
prevalent
I Contribution No. 30, Austin Ornithological ResearchStation.
Read at the 55th annualmeetingof the-AmericanOrnithologists
,Unionat Charleston,South
Carolina, November, 1937,
26]
,
'-
HERMAN,
BirdMalaria
- Bird-Banding
J•.nuary
in birds from North America alone,and severalother specieshave
beenisolatedelsewhere. More than thirty of our North American
speciesof birds have been observedto harbor at least one of these
speciesof Plasmodium. No doubt, further study will reveal a more
widespreadprevalence among our avifauna, with perhaps even
addedspeciesof the parasite.
In order to understandthe importanceof Plasmodiuminfections
in our wild birds it is necessaryto know somethingof the prevalence.
within a single speciesof bird. Although our knowledgeis still
quite limited, recent studies on a few of our birds present some
tangible facts. Most studieshave been basedmerely on the examination of a single blood-smearfrom a bird. Very little value can
be attachedto sucha methodif it is to be interpretedas a picture
of the total prevalence of infection. Mostly from studies with
canaries, it has been learned that when a bird becomesinfected it
is usuallya xveekor two before parasitesare in the bloodin sufficient'
numbers to be found on examination of the blood film, and in one
case-.-Plaswodiumpolare--the incubation period may be several
months. With most of the speciesthe acute infectionlasts but a
few days, and •vithin a short period the parasitesare so few in
number in the blood of the infected bird as to be rarely seen by
.examinationof a blood-smear. Relapsesare known to occur in
experimentally infected canaries, but we have no knowledge of
their frequencein the natural infectionsof the wild birds. Thus it
is that Plasmodium speciescan be diagnosedby routine bloodsmearsonly during a short period of the bird's life. However, by
injecting some of the blood from a wild bird into a malaria-free
canary, the canary will usually develop an acute initial infection
which'caneasilybe demonstratedif periodi'csmearsare made every
few days. This procedure was tested by Manwell and Herman
(1935) with a seriesof birds captured in the vicinity of Syracuse,
New York. The most outstandingof the resultsobtainedwas with
a series of twenty-nine Song Sparrows"(Melospiza m. melodia).
Only six were diagnosedfrom blood-smears,but injections into
canariesdisclosedseventeen--wellover fifty per cent•to be infected
with at least one species.of malaria. This method of procedure
givesa closerapproximationof the true prevalenceof Plasmodium.
During the summer of 1936, blood-smearswere made from 193
Eastern Red-wings(Agelaiusp. ph•e•iceus)at the Austin Ornithological ResearchStation on Cape Cod. Of this number, only seven
were diagnosed with Plasmodium (Herman, 1938). During the
summerof 1937bloodfrom forty-eightRed-wingswassubinoc•ulated
into canaries. Plasmodiumwas subsequentlydiagnosedin at least
twenty-nineof thesecanaries--thusdemonstratinga prevalenceof'
well over sixty percent in the Red-wings.
The prevalenceof malaria in the Eastern Robin (Turdus m. migratomus)is even more striking. As early as 1904, Novy and MacNeal
ix
1938
I-IER3•fAN,
Bird Malaria
[27
reported Plasmodiumto be common in Robil•s in Ann Arbor,
Michigan. All the adult Robinsexaminedin the laboratoryof
Dr. R. I). l•Ianwell at SyracuseUniversity within the past few
years (at least thirteen birds) have been infected'with at least one
speciesof Plasmodium,and the few adult Robins that have been
studiedby the author at the Austin Station (sevenbirds) alsohave
been infected.
EFFECT ON THE BIRDS
The high prevalenceof this diseasein our wild birds having been
determined,the next questionwhichpresentsitselfis the detrimental
effects of the diseaseon the health of the individual. Although
fatalities from malaria frequently occur in humans,death is often
causedby complicationsor secondaryinvaders, particularly
pneumonia. Relapsesalsofrequently occurafter surgicaloperation
or after a shock or strain of any description. Whether or not an
analogouscondition prevails in birds is not khown. It is known,
however,that pneumoniais a commoncauseof death with birds
kept in captivity.- It has never been determined whether PlasmoJ•u• infectionsin any group of birds is responsiblefor great
losses,suchas O'Roke (1934) has shownto be the casewith
½y•ozo6•in young ducks. Nevertheless,so many of the red blood
cellsof the bird are destroyedby the parasitesthat the health of
the individualmust be impairedconsiderably
and the resistanceof
the bird thusmarkedlylowered. It mustbe emphasized
that small
birds,whenthey becomeweak from illness,are easilycapturedby
predators. Also, if birds are dyingof malaria in natureit wouldbe
unlikely that they would be found by man. Except in severe
epidemics,deadbirds would be hiddenfrom the sightof man and
would be quickly devouredby carrionanimals. In the caseof the
infectionsobserved
in the Red-wingsexaminedduringthe pasttwo
summersat the Austin Station only one bird has been under observation while it had a heavy acute infection obtained in nature.
This bird did not seemto be sufferingany noticeableill effects,and
the only indicationof the diseasewasthe greatnumberof parasites
to be seenin its blood-smear. However,canariesinoculatedwith
the Red-wings'blooddemonstrated
a very highmortality during
the acute stages of the infection--more than half the infected
canariessuccumbedto the disease. Two speciesof
were.diagnosed,
P. circumfiexum
and1:). cathemerium.
The former
species
is about'twiceasabundantand apparentlymorepathogenic.
All casesobserved
in the blood-smears
fromthe Red-wings
wereP.
circumfiexum.PIasmodiumcathemerium
was diagnosedonly by
injectioninto canaries. It may be that the Red-wingshave a
greaterimmunity to the one species,but further studiesand researchwill be necessaryto determineto what extent the diseasein
wild birds parallelsthe conditionsin the human ailment.
28]
HgR•N,BirdMalaria
Bird-Banding
z.... ry
TRANSMISSION
The Plasmodid•e are transmitted from one host to another by
blood-suckinginsects. The parasites develop within the insect,
and the stageswhich are infective to the vertebrate host become
concentratedin the salivary glands. During the processof sucking
blood theseinsectsinject saliva containingthe parasitesand thus
transmit the infection into the blood-stream. Certain groups of
insectshave been found to be responsiblefor the transmission
of
specificparasites,and it hasbeendemonstrated
that undernormal
laboratoryconditionsthe parasiteswill reachmaturity--so as to be
infectiveto new hosts--onlyin particular insects. Thus it hasbeen
found that Hcemoproteu.s
is transmitted 'by louse-flies(Hippoboscid•e),Leucocytozo6n
is transferredfrom one animal to anotherby
black flies (Simulid•e), and the vector of the genusPlasmodium--.
as is well known--is the mosquito. Curiously enough,the malaria
of man is transmitted by a differentgroupof mosquitoes
from those
responsiblefor the transferenceof Plasmodiumin birds. The
malaria of humans is transmitted by anophelinemosquitoes,while
the culic{negroup have been shown to be the vectorsof the bird
disease.It is a simplematter for an experienced
personto tell these
two groupsof mosquitoesapart. iViost malaria studieshave been
done with those mosquitoesimplicated in human malaria, but
several investigatorshave determined some of the speciesof
quitoescapableof transmittingbird malaria. In fact, as previously
stated, mosquitotransmissionof malaria was discoveredwith birds
even beforeit was known to be the meansof contractingthe disease
in humans.
Different speciesof culicinemosquitoestransmit differentspecies
of bird malaria. The most commonvector is Culexpipiens,which
hasbeenshownto be capableof transmitting three of the commonest
speciesof bird plasmodiain the United Star.es. This mosquitois
often popularlyreferredto as the "house"mosquito,and it breeds
in the temperate regionsthroughout the world. It can be found
ßbreedingin swamps,but becomesparticularly abundant in rainbarrels or other standing water about human habitations. During
the past summer it has been found to transmit readily one of the
species(P. cathemerium)obtained from the Red-wing, as well as
the same speciesof malaria obtained from a Cowbird (J]lolothrus
a. ater). However, this speciesof mosquitois immune to Plasmodium circumfiexum,the speciesfound to be most prevalent in the
adult Red-wingsat the Austin Station.
The only speciesof mosquitowhich has thus far beenfound to
be capable of transmitting the Plasmodiumcircumfiexumof the
Red-wing is 'Theobaldia•nelaneura. Very little is known of the
habits of this mosquito. Matheson (1929) states that it occursin
the eastern United States from the Gulf of Mexico to Canada, and
that it is rare and local. It breedsin permanentwater in swamps,
and on CapeCodhasbeenfoundto be mostabundantin a wooded
1938
vo•.
•x
' HERMAN,Bird Malaria
[29
swamp in the poolsof water under the roots of the trees. Several
attempts to transmit P. kathemeriumwith this mosquito have
been unsuccessful,
and as yet it has not been tested on any of the
other speciesof plasmodia. One other speciesof Theobaldia(T.
morsitans)occursin North America, but.this specieshas not been
tested as a possiblevector of bird malaria.
Anotherspecies
of mosquito
I havefoundto be capable•f transmitting Plasmodiumcathemerium
from the Cowbirdsand Red-wings
is Aedes sollicitans. This is the common salt-marsh mosquito. It
breeds in the salt marshes along the Atlantic and Gulf coasts.
However, Huff (1927) experimentedwith this mosquitoas a possible
vector of severalspeciesof malaria obtainedfrom English Sparrows
(Passerdomesticus)
and found it immune to a strain of this species
of malaria. This demonstratesthat mosquitoesare specific as
transmitters not only for particular speciesof bird malaria, but
possiblyalsofor certainstrainsof the samespecies,or perhapsthat
there is an immunological
differencein mosquitoes
collectedfrom
different
localities.
Severalother of the more commonculicinemosquitoeshave been
shownexperimentallyto be capableof transmitting variousspecies
of bird plasmodia,but no positivereports have been publishedon
the vectorsof someof the more recently discoveredspecies.
CONTROL •IEASURES
For many years conservationistsand ornithologistshave been
opposedto many of the mosquito-controlprojects, particularly
those involving drainage,as being detrimental to wild life. It has
been felt that
these conservationists
have not been aware of the
prevalence of malaria in birds and therefore have not seen this side
of the problem. It would be utterly impossibleto control the
malaria of birds by any other method but the eradication of the
vectors. In the caseof Plasmodium,this would mean mosquitocontrol. With the exceptionof certainmethodsof Paris greendusting, proiectsfor the controlof the mosquitoesresponsible
for the
transmission of human malaria often serve to rid the environs of
many of the culicinespeciesas well. Severalof the speciesresponsible for the transmissionof bird malaria, though not locally implicated as vectorsof any human disease,are neverthelesslooked
upon as pests becauseof the discomfort they bring to the human
race and are thereforecontrolledalong with the anophelinespecies.
In a recent editorial in Bird-Lore (1935) mosquito control in
isolatedregionsaway from the vicinity of settlementsis condemned
as an unnecessarywaste of funds as well as detrimental to the wild
life of the area. Often,locally,in regionswhere.humanmalariais
no longer endemic,mosquito-control
projectsare taken to task by
conservationists
as beingunnecessary
and servingonly to upsetthe
ecologyof the wild life, especiallythe birds. It must be agreed,at
the start, that thereare not, by any means,sufficientdata to prove
30]
Bird-Banding
HERMAN,
BirdMalaria
J.... ry
the value of mosquito-control to the reduction of bird malaria.
However, the admirable resultsin the reduction of human suffering'
from malaria by these control measuresshould serve as an excellent
exampleas to what might be donefor the birds. We cannot expect
to obtain funds for mosquito-controlas a means of reducing the
prevalenceof bird malaria. However, it is indeed fortunate that
the control measures for the pests of the human race often also
serveto reducethe numbers
of mosquitoes
whichfeedon the birds,
even specieswhich do not feed on ma•.
Control of mosquito-borneavian malaria is, at present,not an
urgent measure. The speciesof birdsthus far found to be commonly
infected with Plasmodium sp. are, for the most part, among the
most abundantof the Passeriformes.However, evenmore devastating in its effectson our bird populationthan diseasehas been the
encroachment
of human
civilization.
One
of the
chief
factors
resultingin the reductionof the avian populationof North Americk
has beendrainage. An admirablereviewof this subjectis being
distributed by the National Association of Audubon Societies'
(Vogt, 1937).
Where drainage is being employed as a control measure and is
proving injurious to the bird population it may often be that other
methods of control could be utilized. Quite frequently drainage
methodsare resortedto as the easiestand least expensiveapproach
as well as the most permanent meansof control.. Stocking ponds
with certain larvivorous fish, changing the acidity of the water,
fluctuation of the water-level, and other methods have at times
provedto be adequatecontrolmeasures. In suchcases,where other
methods are feasible, funds should be diverted to methods of
mosquito-controlwhich are not detrimental to wild life.
The previously-mentionededitorial in Bird-Lore also condemns
the policies which allow one group to undertake large drainage
projects while another group is creating large •bodies of water.
However, we must not lose sight of the fact that impounding of
water, performed under proper supervision and with biological
foresight,can createmuchbetter habitatsfor wild birds than might
exist in many naturally occurring marshes or swamps, and can
control mosquito-breedingas well. An excellent example is the
Souris River project in North Dakota, where over an extended area
flood-controland maintenanceof breeding and feeding areas for
the birds can be regulatedand maintainedunder all conditionsof
weather. It is such projectsas this that may be expectedto maintain our bird population. Methods of mosquito control can be
incorporatedin these projects and thus the prevalenceof avian
Plasmodium can be lowered.
..•. . : . -.. .
' SUMMARY
ANDCONCLUSIONS
Malariais a common
infection
in birds. Threegeneraoccurin
the red blood cells of the avifauna. Plasmodium,the genuswhich
'alsocausesthe malaria of humans, is very widespread.among the
avian species,and}at leastin some.s•ecies
of birds,its prevalenc•
is well over fifty percent. While Plasmodiuminfectionsprobablydo
not causea high mortality in the birds, the diseasetends greatly
.tolowertheresistance
of aninfected
individual
andthusmakeit
vulnerable to death from other diseases or natural enemies.
As in the human disease, Plasmodium infections of birds are
transmittedby mosquitoes.The mosquitoeswhich transmit avian
malariaThe
sites.
differ
mosquitoes
from those
which
which
transmit
are theone
vectors
species
of the
of avian
human
malaria
pard,
may differ from thosewhich transmit another species. A mosquito
which servesas a vector of arian malaria in one locality may elsewhere prove immune to a different strain of the same speciesof
parasite. Some of the mosquitoeswhich transmit avian malaria
are amongthe most abundant pestsof mankind; othersmay never
attack
man.
While it is true that the harm done by certhin anti-mosquito
projects(drainage)far overbalancesthe advantages
ßto be gained
by reducingthe Plasmodiuminfectionsof birds, it is advisablethat
methods of mosquito-controlwhich would not interfere with wild
life but whichwouldreduceboth anophelineand culicinemosquitoes
should be substituted.
Research to devise further suitable methods
of reducingmosquitopopulationand decreasingavian malaria as
well as the diseaseof man, without upsettingwild-life habitats, is
much needed.
BIBLIOGRAPHY
Bird-Lore
1935--Vol. 37, p. 127.
Herman, C.M.
•ß
'
1938--Th•
relatNe
'incidence
ofblood
protozoa
insome
birds
fromCape
Cod
Trans.Amer.Micr.Soc.(In press).
'
........
Huff, Clay G.
1927--Studies
on the infectivityof plasmodia
of birdsfor mosquitoes,
with
specialreferenceto the problem of immunity in the mosquito. Amer.
Jour.Hyg.7: 706-734.
..
Manwell, R. D.
1035--How many speciesof arian malaria parasitesare there? Amer. Jour.
Trop. Med. 15: 265-283.
Manwell,
R. D. andHerman,C. M.
1935--The occurrence
of the arian realariesin nature. Amer.Jour.Trop. Med.
Matheson,R. 1929•A Handbook of the Mosquitoesof North America. Thomas.
Novy, F. G. and MacNeal, W. J.
1904--Trypanosomesand bird malaria. Amer. Med. 8: 932-934.
O'Roke,E. C.
1934•Amalaria-like
disease
ofducks
caused
byLeucocytozoon
anatis.
Wickware.
Univ.Mich.
Sch.
Forest.
Publ.
No.4.
1037--Thirst
onthe'land,
apleaforwater
conservation.for
thel•enefit
ofman
Vogt,W
andwildlife. Nat.Assoc.
Audubon
Soc.
Cir.32. 32pp.