ORIGINAL ARTICLES
EXPERIMENTS ON THE TRANSMISSION OF ANTHRAX THROUGH FLIES
By S. K. SEN and F. C. MINETT, Imperial Veterinary Research Institute,
Mukteswar-Kumaun
(Received for publication on 6 April, 1944)
(With Plate XII
THE experiments described in this paper were
carried out at Mukteswar (alt. 7,500 ft.) between
May and October, 1941-43. The daily maximum
temperature range during this period was 68°-80°
F. in May-June, 64°-72°F. in July-September and
64°-69° F. in October. Goats were used as experi-
mental animals, since they are cheaper and more
susceptible than cattle to experimental inocula-
tion. The anthrax culture used was highly
virulent for goats and gave typical rough colonies
on agar. The species of insects tested were
Stomoxys calcitrans, Musca domestica, Calliphora
erythrocephala and, in one instance, Sarcophaga
sp. In the earlier experiments, Tabanids (mainly
Tabanus orientis) were employed, but, as none of
these hill species would readily bite in captivity,
the experiments were discontinued shortly after
their commencement, with a view to resuming
them in the plains where several species of Tabanids
with better biting propensities were known to
occur. It is hoped to report later on some of
these plains species.
Although Tabanids are believed to be more
commonly involved in the spread of anthrax
[Mitzmain, 1914; Kehoe, 1917; Frey, 1919;
Morris, 1920; Nieschulz, 1928,; Olsufev and Leler,
1935; Kraneveld and Djaenoedin, 1940], several
workers have also incriminated S. Calcitrans as a
transmitting agent. Thus, Mitzmain [1914]
succeeded in transmitting anthrax from a guinea-
pig to other guinea-pigs through the bites of S.
calcitrans by the interrupted method of feeding,
the flies being fed on the donor from 2½ hours to a
few minutes before its death. Schuberg and
Kuhn [cited by Schuberg and Böing, 1914] report
having successfully transmitted anthrax to guinea-
pigs and mice through S. calcitrans, while Schu-
berg and Böing [1914], after failing with one goat,
transmitted the disease to one out of three sheep
through the same species of fly. They point out
that biting flies may be a much more important
factor in transmission in some lands, e.g. N. and S.
America, than in others, e.g. Great Britain and
Germany. Hetsch [1915] likewise considers S.
calcitrans to be the 'most dangerous carrier of
anthrax', being able to carry the infection for
about two hours and over a distance of not less
than 1¾ miles. Morris [1919], working with
guinea-pigs, found S. calcitrans capable of trans-
mitting anthrax mechanically from opened car-
buncular swellings of animals suffering from
anthrax. He considers the fly may sometimes
play this role in nature. He [1918] also records
having obtained positive results by using the allied
species, Lyperosia (Haematobia) irritans. Flies
of this species were fed for one minute on guinea-
pigs, previously inoculated subcutaneously with
anthrax spores, and then on healthy ones from
one to three minutes, the feeding being done
through wire-gauze fixed on the top of a wooden
box in which the flies were confined. The greatest
proportion of successful transmissions was obtain-
ed when the infected animal was bitten a short
time before its death. Also, an immediate trans-
fer of flies from the infected to healthy animal
appeared to be necessary for positive results.
Morris refers to the bacilli carried on the proboscis
of the fly producing, as a rule, the external or
carbuncular form of anthrax. It is noteworthy
that, according to him, the disease is not ' usually '
spread through the excreta of infected insects and
that L. irritans. would not feed satisfactorily on
anthra carcases. In contrast with the positive
result obtained by Morris with L. irritans,
Nieschulz [1928] records having failed to transmit
anthrax through the bites of L. exigua.
As regards M. domestica, this species has been
shown by Morris [1919] to be capable of carrying
anthrax bacilli from anthrax-infected flesh and
so contaminating wounds on healthy guinea-pigs.
Nieschulz [1928] used M. inferior and obtained
positive results with guinea-pigs in one out of six
experiments.
The possibility of Calliphorids being concerned
in the spread of anthrax has been mentioned by a
number of workers. Dunn [1918] refers to the
common phenomenon of swarms of screw-worm
flies (Chrysomyia macellaria) being attracted to
blood-stained exudation from the mouths and
nostrils of anthrax carcases, and he, therefore,
considers it probable that some of these flies
would infect any animal they might visit shortly
afterwards, provided it has some unhealed skin
abrasion. Osins' kii [1938] refers to the habit of
Lucilia and Sarcophaga of sucking fluids from
carcases, e.g. of rabbits dead of anthrax. He
describes experiments in which Calliphora
and Lucilia flies were placed on agar, after they
had sucked the juices from anthrax meat. In
such cases, anthrax bacilli were found to be
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