NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
13
In connection with their work on El debab (trypano-
somiasis of camels in North Africa), Drs. E. and E. Sergent
found that in Algeria it was rarely found on camels. In
Mohand, however, it was not only found in hundreds on
all our camels, but it showed a marked preference for biting
the camel rather than the horse.
This was so pronounced that if a horse was taken into
the proximity of a camel nearly all the flies worrying
the horse would join those already on the camel; the
probable reason is that the camel is an easier prey, for
the panniculus is less developed and the tail is of no use for
switching off flies excepting in the groin; when it is
swarming on him, his only defence is by muscular exertion
with head and feet or by rolling, and he soon tires of
this and eventually lies prostrate on his side, blowing
and occasionally kicking feebly, and, like the horse,
his temperature rises considerably from the exertion and
irritation.
Sand-flies.—Bite most in the late afternoon and evening.
In very wet weather they sometimes covered the sides and
belly of our horses and camels and gave rise to intense
subsequent irritation.
Camels show this by rubbing against trees. It was impos-
sible to tell whether sand-flies usually gorge themselves on
one victim or not.
Mosquitoes.—Bite horses, cattle and buffaloes.
The common species in Mohand were Anopheles,
Culex and Stegomyia. Anopheles and Culex bite chiefly
by night and have a preference for the legs of the horse
and the belly of the camel, although they will bite almost
anywhere; a drop of blood is often left near the bite, but
this is not from the puncture but comes from the anus of
the gorged mosquito. Mosquitoes are difficult to see at
work on animals and are easily missed. When in large
numbers, they give rise to some uneasiness on the part of
the animal attacked.
Stegomyia bites in the day time and has a marked
preference for the ears and brisket of the horse. Males are
found hovering about these situations too, but, of course, only
the females bite. Stegomyia was always scanty in number
14
and is therefore unlikely to have any specific action in
spreading surra.
Mosquitoes generally gorge themselves on one animal
and do not move from one animal to another much during
the meal.
DOES TRANSMISSION OF SURRA IN NATURAL OUTBREAKS
DEPEND UPON SOME CYCLE OF DEVELOPMENT OF
THE TRYPANOSOME IN THE BODY OF ONE
GENUS OR SPECIES OF BITING-FLY ?
If so, that fly must have been present in fair numbers
at least in Mohand in July and August; it must also have
a seasonal occurrence corresponding on the whole with
that of surra (i.e., it must be far more prevalent in the
rains than in May and June), and it must freely bite horses,
camels and cattle since all these animals frequently get surra.
The biting diptera fulfilling these conditions are
Tabanus, Hæmatopota, Stomoxys, mosquitoes and sand-flies.
On the Kathgodam-Naini Tal Road in 1907, Mr. Cross
and I found that fresh cases of surra in ponies were
occurring in the absence of Tabanus, Hæmatopota and sand-
flies (Journal of Tropical Veterinary Science, Vol. III,
pp. 163 and 4); it would seem therefore that there can be
nothing specific about these three genera. On the other
hand, a good deal of circumstantial evidence was collected in
favour of mosquitoes being involved in the natural trans-
mission of surra; and Stomoxys was also under suspicion.
At Mohand, therefore, a good deal of time was spent
in the examination of the gut and contents of the gut of
mosquitoes at different intervals after they had fed on a surra
patient; the object being to search for any change in the
form of the trypanosome suggesting the beginning of a cycle
of development.
The appearances of the organism in the mosquito,
however, did not differ from those in Tabanus and other
flies similarly treated. Some of the specimens were checked
by the Imperial Bacteriologist.
No change was observed in the trypanosome, excepting
those attributable to degeneration ; and this applies to all
the genera of biting-flies examined.
15
I have more reliance, however, on the result of the
following transmission experiments as evidence against a
cycle of development of the trypanosome in the mosquito.
In these experiments mosquitoes were caught at night biting
camels and horses which had trypanosomes in their blood at
the time ; they were then kept in captivity and the survivors
fed on healthy guinea-pigs or white rats after two days and
thereafter every two days as long as the mosquitoes could be
kept alive. The guinea-pigs and rats were kept in separate
cages proof against the entry of any biting-fly (except sand-
flies, which, however, were never found to enter the cages).
Controls were kept under similar conditions.
The blood of the guinea-pigs and rats was daily examined
during the experiment and also for 50 days following the
last bite if the animal lived that length of time (which it did
except where otherwise stated). The mosquitoes were fed in
tubes placed against the shaved damped skin of the guinea-pig
or rat ; this method, though very laborious, has the advantage
over others that each bite can be fully vouched for in every
case, and therefore the negative results are of some value.
Experiment II.—Between the 13th July and 13th
August, 33 mosquitoes thus obtained and treated were fed on
a guinea-pig (No. 2), after an interval of 2 or 2½ days. Result
negative. The 33 mosquitoes consisted of 17 Anopheles, 6
Stegomyia and 10 Culex (and other) mosquitoes.
Experiment III.—Between the 16th August and 8th
September, 25 mosquitoes thus obtained and treated were
fed on a guinea-pig (No. 9) after an interval of 2 to 2½ days.
Result negative. The 25 mosquitoes consisted of 13 Ano-
pheles and 12 Culex (or other) mosquitoes. One Anopheles
in addition was fed in error after an interval of 8 days.
Experiment IV.—Between 17th July and 26th August
a guinea-pig (No. 3) was bitten on 34 different occasions by
mosquitoes thus obtained and treated, after the following
intervals of time, viz. :—
Anopheles
Culex
Stegomyia
... 4 to 8 days inclusive ... 20 bites.
10 days
...
1 bite.
... 4 „
...
1 „
... 4 to 8 days inclusive ... 6 bites.
10 to 16 „
„
...
6 „
34 bites.
Result negative.
16
Experiment V.—Between 29th August and 16th Sep-
tember a white rat (No. 11) was bitten on 17 different occa-
sions by mosquitoes thus obtained and treated after the
following intervals of time, viz.:—
Anopheles
Culex
... 3 to 9 days
11 to 13 „
... 4 to 6 „
8 to 10 „
... 9 bites.
... 2 „
... 4 „
... 2 „
17 bites.
Result negative.
SUMMARY OF THE ABOVE FOUR EXPERIMENTS.
At 2 to 2½ days, 30 Anopheles and 28 other mosquitoes
failed to transmit.
At 3 to 6 days, animals bitten 25 times by Anopheles
and 9 times by other mosquitoes remained healthy.
At 7 to 10 days, animals bitten 5 times by Anopheles
and 6 times by other mosquitoes remained healthy.
At 11 to 13 days, animals bitten twice by Anopheles
remained healthy.
At 11 to 16 days, animal bitten 4 times by Stegomyia
remained healthy.
The following experiment was carried out under similar
conditions except that the mosquitoes were originally caught
when biting horses or camels suffering from surra, but not
showing trypanosomes in the blood at the time of capture :—
Experiment VI.—Between 26th July and 5th August a
guinea-pig (No. 7) was bitten on 15 occasions by mosquitoes
so obtained after the following intervals :—
2, 3 & 4 days
6 & 8 „
10 & 12 „
...
...
...
...
...
...
5 anopheles and 3 culex.
4 anopheles.
3 „
Result negative, but guinea-pig died as a result of an
injury on 17th August, never having shown trypanosomes.
I therefore obtained no further evidence in support of
the mosquito as a surra transmitter depending on any cycle
of development, but a good deal against it.
Stomoxys had to be considered also in this connection.
Its disappearance at Kathgodam in 1907 coincided with the
cessation of the outbreak of surra, but it was found at
every stage of the tonga line, although the surra outbreak
was practically confined to two stages.
PLATE IV.
11—13. TABANUS FOUND IN MOHAND.
17
Microscopic examination of the gut and gut-contents
proved negative as regards developmental forms.
The following transmission experiments were carried
out with the object of ascertaining whether the trypanosome
undergoes any special development in the body of Stomoxys.
(The experiments were carried out and protected exactly as
in the case of the mosquito experiments, the flies being-
caught feeding on surra horses or surra camels with
trypanosomes in their blood at the time.)
Experiment VII.—Between 12th July and 1st September
a white rat (No. 2) was bitten by 30 Stomoxys (thus obtained
and treated) after an interval of 42 to 48 hours. Result
negative.
Experiment VIII.—Between
14th July and 11th
September a white rat (No. 3) was bitten by 15 Stomoxys
(thus obtained and treated) after an interval of 3 to 4 days.
Result negative.
Experiment IX.—Between 16th July and 13th Septem-
ber a white rat (No. 4) was subjected to 33 bites by Stomoxys
(thus obtained and treated) after intervals of 5 to 21 days.
The number of individual flies used was 10, and they
fed every 2 days on this rat from the 5th or 6th day follow-
ing capture until they died. Result negative.
The number of bites at different intervals is shown
below :—
5 to 8 days
9 or 10 „
11 to 12 „
12 to 21 „
...
...
...
...
...
...
...
...
17 bites.
6 „
4 „
8 „
35 bites.
I therefore obtained no evidence in support of the
fly as a surra transmitter depending on any cycle of devel-
opment, but a good deal against it.
MECHANICAL TRANSMISSION OF SURRA BY BITING-FLIES.
Tabanus has been proved by many observers to be
capable of conveying trypanosomiasis from one animal to
another, but it was absent during the latter part of the
Kathgodam outbreak, and further it has been proved capable
18
of conveying T. brucei (E. and E. Sergent). Etudes sur les
trypanosomiasis de Berberie en 1905 (Annals Inst. Pasteur,
August 1906), and T. equiperdum (Laveran and Mesnil
Trypanosomes and trypanosomiases. English translation,
1907, p. 219), although observations have hitherto indicated
that transmission in natural outbreaks of Nagana and Dourine
is not by the agency of Tabanus.
I therefore carried out experiments with all the 5 genera
of biting-flies which fulfilled the necessary conditions as
regards seasonal occurrence, to try and ascertain how many
of them are capable of withdrawing trypanosomes of surra
from one animal and depositing them into the tissues of
another by biting both animals within a short space of time.
Strictly speaking, the flies used for such experiments
should be bred in captivity, because in dealing with wild flies
there is a possibility of their having bitten a surra animal
some days before capture, and if a positive result subsequent-
ly occurs by its bite, it does not absolutely prove that trans-
mission was not by a cycle of development in the fly.
In the case of Stomoxys, however, our experiments are
to a great extent controlled by experiments VII, VIII and
IX ; and in the case of Tabanus and Hæmatopota, by the
Kathgodam outbreak which continued in their absence,
indicating that there can be nothing specific about their power
to transmit.
In the circumstances we could not under-
take the laboratory breeding of flies and had to catch them
wild.
All the small animals used were examined and protected
against chance infection as in the experiments already quoted
(II to IX), and the flies were made to bite in glass tubes
held over the skin of the animals under experiment; each
bite can therefore be vouched for. The flies were first
allowed to bite and suck a little blood from animals showing
trypanosomes in their blood at the time (excepting where it
is otherwise stated); they were then conveyed as quickly as
possible to the healthy animal and allowed to gorge them-
selves on it. Every fly was only used once. When the
trypanosome was subsequently found in the blood of an experi-
mental animal, care was taken to see that its morphology
was that of T. evansi. In the negative cases excepting
19
where it is otherwise stated, daily examinations of the blood
of the animal under experiment were continued for 50 days
from the last bite.
First, it was necessary to prove that the local species of
Tabanus were capable of acting as mechanical agents.
Experiment X.—With the local Tabanus (of Mohand).
The flies were caught wild and biting on a surra camel,
and were immediately transferred to a healthy white rat
(No. 1), which they bit in from ½ to 3 minutes. Four flies
were used as follows :—
9th July ...
11th „ ...
16th „ ...
One Tabanus ...
One „ ...
Two „ ...
Approximate number of tryps. in camel's
blood at the time. (Zeiss D, ocular 4, tube in.)
None.
6 to 8 in a field.
20 in field.
The four flies used were of two different species which
are not yet identified.
Result positive, trypanosomes first appearing in the
rat's blood on 21st July ; rat died on the 6th August.
The following experiments (XI and XII) were done
with Hæmatopota.
Experiment XI.—With a large species of Hæmatopota
(hitherto undescribed, Mr. Howlett the Entomologist says).
Ten flies were used and were transferred from surra
animals to a healthy guinea-pig (No. 5) as under—
Date.
22nd July
...
...
1st August ... ...
2nd
„
...
6th
„
...
...
Number
of flies
used.
6
1
1
2
Animal on which fly was
first fed.
Camel ... ...
White
rat
...
...
„ ... ...
Pony ... ...
Approximate number of
tryps. in the blood of the
animal at the time.
25 in field.
Swarming.
„
15 in field.
Result positive, trypanosomes first appearing on 15th
August. Guinea-pig died on 14th September (duration 20
days).
This is, I believe, the first time that trypanosomiasis has
been conveyed experimentally by Hæmatopota.
Experiment XII.—With a small species of Hæmatopota
(hitherto undescribed according to Mr. Howlett), known
locally as "andhimakhi " or " blind fly."
20
Eight flies were used and transferred from a surra camel
to a healthy guinea-pig (No. 4), thus :—
22nd July
23rd „
... 6 flies
... 2 „
the camel having on both days 25 to 30 trypanosomes
in field. Result negative.
The following three experiments (XIII, XIV and XV)
were done with Stomoxys calcitrans; the results were
negative in two, and positive in one experiment:—
Experiment XIII.—Between 29th July and 5th August
15 Stomoxys were used, being transferred from a white rat
with surra to a healthy guinea-pig (No. 8).
The white rat's blood was swarming with trypanosomes
at the time of each bite. Result negative.
Experiment XIV.—Ten
Stomoxys were transferred
from surra animals to a healthy white rat (No. 7) as
under:—
Date.
13th August ... ...
14th to 20th August ...
Number
of flies.
1
9
Animal on which fly was
Camel ... ...
White rat
...
Approximate number of
tryps. in the blood of the
animal at the time.
Over 50 in field.
Numerous or swarming.
Result negative.
Experiment XV.—Ten flies were used and transferred
from a white rat with surra to a healthy white rat (No. 9)
as under :—
20th August ... ...
22nd
„
...
...
2lst & 23rd August ...
1
2
7
Stomoxys ... ...
„ ... ...
„ ... ...
No. of tryps. in blood of
surra rat at time.
30 in field.
25
Over 50 in field.
Result positive, trypanosomes appearing first on the 1st
September. Rat died 5th October, duration of the disease
being 35 days, which is most unusual in that animal.
The following two experiments were done with mos-
quitoes, although their habits render it unlikely that they
21
would act as simple mechanical agents in natural circum-
stances. Both experiments were negative : —
Experiment XVI.—With mosquitoes. Six Stegomyia
were used and transferred from surra animals to a healthy
guinea-pig (No. 6) as under :—
Date.
3rd July ...
26th do. ...
27th do. ...
Number
of mos-
quitoes.
1
3
2
Animal on
which 1st fed.
Camel ...
Pony ...
Do. ...
Tryps. in animal's blood
at the time.
30 in field.
15 do.
8 do.
Result negative.
Experiment XVII.—With
mosquitoes (Anopheles and
Culex).
Ten Anopheles and two Culex were used and transferred
from surra animals to a healthy white rat (No. 5) as
under :—
Date.
August 6th ...
„ 7th ...
„ 10th ...
„ 10th ...
„ 11th ...
„ 11th ...
„ 12th ...
„ 14th ...
„ 17th ..
„ 22nd ...
Number of mosquitoes
used.
1 Anopheles ...
1
Do. ...
1
Do. ...
1 Culex ..
1
Do. ...
1 Anopheles ...
2
Do. ...
2
Do. ...
1
Do. ...
1
Do. ...
Animal first bitten.
White rat ...
Guinea-pig ...
Pony ...
Do. ...
Camel ...
Do. ...
Do. ...
White rat ...
Do. ...
Do. ...
Tryps. in animal's blood
at time.
Over 50 in field.
15
5
„ ...
5 „
20
20
Over 50
40 „
Over 50
„ 26
„
Result negative.
The following experiment with sand-flies was done of
necessity under different conditions from the above :—
Experiment XVIII.—With sand-flies. On six evenings
when sand-flies were swarming on our camels and ponies, a
large number were caught in a jar from animals showing
very many trypanosomes in their blood at the time. A white
mouse (No. 1) was put in the jar with some of its hair shaved
off and many of the sand-flies bit it, although no estimate can
be given of the number. This mouse died 14 days after
the last exposure, but not of surra, and the blood did not
show trypanosomes at any time. Result negative.
22
The ease with which a positive result was obtained in
the Tabanus experiment (in which the animal providing the
infection was a camel) is noteworthy. Hæmatopota (the
large variety) also seems to act with ease as a mechanical
transmitter. With regard to Stomoxys, it will be noticed
that at least 25 flies (those used in experiments XIII and
XIV), biting under what appear to be more favourable
conditions than usually occur in the natural state (the animals
on which they took their first feed having very many
trypanosomes in their blood at the time ; and the flies being
transferred as quickly as possible and at a favourable stage of
the feed) may fail to transmit the disease ; but the Stomoxys
can transmit surra. The natural conclusion is that, a
Tabanus has far more power of transmission than a Stomoxys.
In Mohand, however, in the surra season of 1908
matters are balanced somewhat by the fact that there were
quite 500 Stomoxys to every one Tabanus; and large Hæma¬
topota was about twice as numerous as Tabanus.
It may be here noticed that although Stomoxys shows
less ability to carry the disease mechanically than Tabanus,
its powers compare favourably with those of the tse-tse fly,
to carry T. gambiense according to the experiments of
Dutton and Todd (Annals of Tropical Medicine and Parasit-
ology, Vol. 1, pp. 204-6).
Mosquitoes and sand-flies show no tendency to trans-
mit mechanically either by habit or by their properties
(ascertained in experiments XVI, XVII and XVIII).
Lice were not experimented with ; in camels they are
chiefly winter parasites and are got rid of at the spring clip-
ping ; but as plenty of " reservoirs of infection " are usually
present, they must be suspected as possible, though very
occasional, transmitters of the disease in the camel. Accord-
ing to Neumann (Parasites of Domesticated Animals, 2nd
edition, p. 58), lice only quit their host "accidentally ;" there
is, however, plenty of opportunity of " accidental " change of
host of the camel louse.
The powers of Lyperosia are not known as mechanical
surra transmitters; they were in very few numbers at
Mohand, but at Ganjyal, Khushab tehsil, a very dry place,
and one which all evidence shows not to be surra zone,
23
they were swarming on 14th October. So that circum-
stantial evidence points to their share in mechanical trans-
mission as being very insignificant, if any.
I consider it well established, therefore, that Tabanus is
the most dangerous transmitting fly; and that Hæmatopota
(large species) is also dangerous. I believe too that Stomoxys
is involved in a considerable degree in the transmission of
surra, and it will be specially considered.
There is, of course, no difficulty about the source of infec-
tion. I do not think that surra camels are as dangerous
to horses as they are to other camels, because I have
found that the Tabanus and Stomoxys much prefer the camel
and are not likely to leave him after a partial feed for a
horse ; it is also a fact that in the case of many of the roads
through the foot-hills where some of the worst horse-out-
breaks occur, such as that from Kathgodam to Naini Tal,
camels are taken off the road and out of the district by their
owners from about 20th May until October. Oxen (and per-
haps buffaloes) are, therefore, chiefly to blame for acting as
reservoirs of infection for horses ; out of 4 apparently healthy
bulls working on the Naini Tal Road in 1907 by inoculation
experiments, one was found to have surra, and out of 51
carefully selected Indian cattle in 1906 at least 17 contained
T. evansi (Report of Chief of Bureau of Animal Industry for
1907, U. S. A., Department of Agriculture, pp. 22 and 27).
COMPARATIVE PRACTICAL IMPORTANCE OF STOMOXYS AS A
SURRA TRANSMITTER.
According to my observations, Stomoxys is a more
generally distributed fly than Tabanus, probably as it is less
dependent upon a water-supply. In the rains and autumn it
is the commonest biting-fly by far at every stage on the
Kathgodam and Naini Tal Road and on the Saharanpur to
Dehra Dun Road. Kahan Singh, 2nd Veterinary Assistant,
of this office, found it at every stage of the road march from
Saharanpur to Jullunder (about 175 miles) in September.
I have found it also in the Lahore Veterinary College on
27th September; in Rakh Pabbi, Gujrat district, on 30th
September; and at Kharian, Gujrat district, on 14th October.
Its general distribution is therefore an argument against its
24
being the first cause of an outbreak in horses, for surra in
horses is not so generally distributed.
In my opinion
it is unlikely to act that way because the powers of the
fly to transmit are never great, and as cattle usually have
the trypanosomes so scanty in the blood or apparently absent
from it, the chance of the fly transmitting from ox to
horse are reduced to zero. But the case is quite different
when, by Tabanus, surra is already started amongst a stud of
horses from an ox. Trypanosomes are often numerous in the
horse with surra, and Stomoxys is numerous and is often dis-
lodged during a feed on these animals and seeks a new victim.
The transmission is rendered easier since horses are
often standing close together in lines, or working in double
harness in tongas. In these circumstances (i.e., surra
already started amongst a stud of horses), the Stomoxys is
probably an active agent helping in the spread of the disease.
The explanation therefore of the difficulty that, although
in the 1907 Kathgodam outbreak it was found at every
stage on the road, but surra only at Kathgodam and Bojia-
ghat, seems to depend upon the foregoing facts. Local
opinion insisted that Tabanus, when present, was confined to
these two stages, and no doubt they may have been responsible
for the occurrence of the outbreak (i.e., bringing the try-
panosomes from the ox) and after they had disappeared,
Stomoxys was only able to carry on the outbreak amongst
the ponies in the stages in which surra was already rife. The
close of the outbreak corresponded with the disappearance of
the latter.
I think, that in camels it may also be an agent for
the spread of surra, although of much less importance
than Tabanus.
A Stomoxys, as I have said, more often finishes his
feed on one camel than on one horse.
Late in the surra season at Mohand I exposed a newly
purchased healthy pony with the surra ponies to its bites
for about an hour a day on 20 days with negative result; but
as Tabanus was then still present, the exposure could only
be made at times and places where biting-flies of all kinds
were not very numerous, and I do not attach any importance
to the negative result of the experiment,
PLATE V.
A to D. HÆMATOPOTA FOUND IN MOHAND.
E. CHRYSOPS FOUND IN MOHAND.