NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
380 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, IV.
Edwards [1928] encountered outbreaks of surra among buffaloes maintained for
serum production at Muktesar and by the systematic examination of the blood of
infected animals, he found that in these trypanosomes persisted for some months,
relapsing in relatively small numbers in the blood stream at relatively prolonged
intervals. Many of the naturally infected stock, therefore, appeared to be on the
road to spontaneous recovery, which process in these animals is characterised by the
recurrence of trypanosomes being progressively lessened and spaced by longer
intervals. It is true that during such a period in the progress of recovery from
trypanosomiasis in bovines or buffaloes a concomittant attack of rinderpest is cap-
able of accentuating a relapse of the trypanosomes.
From these observations of Edwards it is clear that the trypanosomes may be
made to relapse during the early phases of spontaneous recovery in cattle, but in
the light of the observations of Lingard, Schien, Cross and Patel and our own, it
seems that it is not possible to cause these trypanosomes to relapse in the later
phases of recovery, thus resuscitation of trypanosomes in cattle seems possible only
in the earlier phases of spontaneous recovery, unlike what happens in piroplasmosis,
in which disease the majority of the animals are known to remain in a state of
premunition, perhaps for life.
Lingard [1906], discussing the periodical outbreaks of surra in ponies in Bhu-
giaghat, one of the stages on the road from Kathgodam to Nainital brewery, says,
" In some cases the disease no doubt may be first disseminated through flies carry-
ing bovine or buffalo blood to the equines on the road; but this will not account
for the first case of surra always appearing at one particular stable (Bhugiaghat) for
the horses ran up 8 miles and continuously met bullock carts and military bullock
trains one way or the other." He also remarks that when the old stable at Bhugia-
ghat was abandoned in favour of a new one, half a mile down the road, surra ceased
to break out until the old stable was again occupied some time later.
Holmes [1908] writing on the outbreak of surra in Bhugiaghat said that surra
broke out each time at this halting place alone, and not at the others, although near
each halting place there existed a camping ground for bullock carts, etc. In the
Bhugiaghat stable the first case of surra appeared when tabanus flies were becoming
scarce.
Leese [1908], who was deputed to investigate the outbreak at Bhugiaghat, said
that he injected the blood of four apparently healthy bovines into experimental
animals and found one among them infective to experimental animals. He, therefore,
opined that the probable reservoirs of surra were cattle.
The observations of these three workers suggest that though cattle and biting
flies, believed to be the necessary factors to initiate an outbreak of surra in horses,
OBSERVATIONS ON TRYPANOSOMES OF CATTLE IN SOUTH INDIA
381
were present in every stable on the tonga line on the road between Kathgodam and
Nainital, yet surra appeared year after year at the Bhugiaghat stable only.
Another interesting feature was the subsidence of surra when the ponies were
removed to a new stable at Bhugiaghat not far away from the old one, though the
common factors necessary were present there too. Thus if cattle were the reservoirs
in that area, surra should have appeared in other stables as well, and it is suggested
that since cattle are liable to infection of surra, the finding of one infective bullock
by Leese in the locality, during an outbreak, does not form a logical basis to con-
clude that cattle were the reservoirs from which originated the outbreak among the
horses at Bhugiaghat, and at that place alone.
In trying to settle the question whether biting flies were chiefly responsible for
the spread of surra, Leese [1909] chose Mohand, a locality well known as a surra
zone where plenty of ponies died of surra, when a tonga service existed there. The
condition of Mohand in connection with surra is best described in his own words.
" The traffic in the rainy season has been insufficient for years because of the
construction of a railway to Dehra Dun; the tonga service has been abandoned now
for about eight years, and the bullock cart traffic in the surra season is very small
indeed. The only equine traffic is a drove or two daily of pack animals. Only the
older inhabitants of Mohand know anything about surra, and although about ten
ponies are kept by the villagers and are constantly in contact with the milch cows
and buffaloes of the village, no losses now occur in the rains. This is interesting
that owing to the scarcity of " reservoirs of infection" (i.e., cattle and buffaloes
working through Mohand) the danger to local animals has been largely removed."
" Camels always leave this road from about the 15th May to October; none are
kept in the neighbourhood between these dates."
" The country consists of first class jungle full of game, but the latter evidently
do not act as reservoirs of infection to domesticated animals."
" I had a temporary stable put up a quarter of a mile from the village,
The disease did not occur in the village and the outbreak was confined to our
stable."
Mohand village in Mohand Pass evidently has always been used as a halting
place to bullock cart and pack-ponies traffic, and the conditions as regards the
prevalence of biting flies and the existence of domesticated animals of the village
have been constant factors. Surra broke out constantly among the ponies in the
tonga service till the latter was terminated some years previously and from what
Leese says it would appear that surra did not exist in the village at the time of his
visit. If cattle and buffaloes were the reservoirs, then there should have been
enough of them to initiate the outbreaks of surra among ponies of the tonga service
382 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, IV.
and also to infect other healthy cattle at that time in the presence of biting flies
there. In other words, there should have been a few bovines there as surra reser-
voirs, and these few should have naturally acted as so many foci, in the presence of
the biting flies, from which the next generation of cattle or the new arrivals could
be infected to become reservoirs of surra in their turn from one surra season to
another. But it would appear from the observations of Leese that there were no
reservoirs of surra at the time of his visit and no losses occurred among the village
ponies. Even if cattle and buffaloes working through the village were limited, yet
at least one among these might have been expected to have become a reservoir of
surra, and one is as good as many, in the spread of the disease when so many biting
flies prevailed there during the surra season. This scarcity of reservoirs, observed
by Leese, casts a doubt on the theory of cattle being the reservoirs of surra from
one surra season to another, since Mohand appears to have been an ideal place for
the formation of such reservoirs in working or milch cattle.
Leese [1909] admits that in cattle the trypanosomes of surra are scanty in their
blood or apparently absent from it, thus reducing the chances of mechanical trans-
mission practically to nothing and this has been proved experimentally by Cross and
Patel [1922] who found that if the number of trypanosomes in the blood of an
animal was less than five per field mechanical transmission through the agency of
biting flies was not possible.
Leese created in Mohand a limited outbreak of surra in his experimental
animals which were kept only two furlongs away from the village from June to
the end of September, and he admitted that some of the village cattle strayed near
the camp in spite of which the village ponies remained healthy though these mixed
freely with the cattle. This he thought was due to the cattle remaining healthy,—
an unlikely thing in the vicinity of a focus of surra and during the full swing of the
fly season.
Fraser and Simmonds [1909] working in the Federated Malay States, an endemic
area of surra, found that the blood of cattle whose temperature remained normal
after an attack of surra, was non-infective to other experimental animals. They
also found that surra in bovine did not confer immunity after recovery. From this
finding the present authors deduce that recovered bovines are not in a state of
" Premunition," a condition which should be present if cattle and buffaloes do act
as reservoirs of surra.
In the fly belts of Africa, cattle appear to be in a state of premunition, as
regards T. congolense and the like, because a cyclical development of these trypano-
somes is known to occur in the tse-tse flies, the bites of which help to induce such a
condition in cattle making them carriers of the disease. The conditions in India
OBSERVATIONS ON TRYPANOSOMES OF CATTLE IN SOUTH INDIA
383
are however not parellel and do not help us to derive at a conclusion on the point
at issue, as regards T. evansi and its reservoir, particularly in view of our present
limited knowledge of the " mechanical " vector concerned.
Sowerby [1911] conducted two series of experiments in Bombay to find out
latent trypanosomiasis in buffaloes. He injected into guinea pigs one c.c. of blood
from apparently healthy buffaloes slaughtered in Bandra. The first series of
experiments were conducted in the 3rd week of April 1908 when he injected the
blood of five buffaloes into guinea pigs, one of which developed trypanosomiasis in
the middle of June, almost two months after the primary inoculation which appears
to be an unusually long incubation period. In the second series, conducted from
11th May to the 16th July 1911, he injected the blood of 44 buffaloes into as many
guinea pigs among which three developed trypanosomiasis with an incubation period
ranging from 3 to 4 weeks. These experiments no doubt proved the possibility of
buffaloes acting as reservoirs of surra, but it would appear that Sowerby had not
satisfied himself that the buffaloes whose blood proved infective were not actually
suffering from the disease at the time. In this connection, it is of interest to quote
Lingard [1906] who observed that the first case of equine surra appeared in Bombay
a few weeks after the onset of the monsoon (June and July) although sporadic cases
occasionally occurred prior to that date in some portions of the province and it is
suggested that Sowerby's buffaloes may have been in the early phases of spontane-
ous recovery after a natural attack of surra and may not have been actual
reservoirs.
Gaiger in April 1911, conducted a few experiments to find out if cattle in the
Pubjab acted as reservoirs of surra. He selected eight emaciated cattle from
which he drew blood and injected it into rabbits. One among these developed
surra after an incubation period of 9 days. This experiment suggests the possibility
of latent trypanosomiasis in cattle, but it appears that Gaiger did not satisfy
himself that that positive bovine was not in contact with surra camels which are
common in that Province.
From the above discussion it appears that, though some workers have shown
the possibility of bovines and buffaloes having latent trypanosomiasis, there is no
evidence to prove that their condition remains unchanged from one surra season to
another. In countries where camels abound, cattle may get infected from them
and this fact is liable to vitiate the results of experiments.
It is well known that cattle are refractory to surra, comparatively speaking,
and that a large majority of them recover spontaneously but in these animals
trypanosomes may be found for a few months, after which they appear to become
negative to animal inoculation. Hence in the light of the experimental evidence of
384 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, IV.
the workers quoted above and of this laboratory, a doubt arises if cattle really act
as agents in carrying trypanosomes of surra in their tissues from one surra season to
the next.
Some workers claim to have discovered in bovines and buffaloes the so-called
reservoirs of surra by infecting laboratory animals with a syringeful of blood which
happened to be negative under the microscope at the time of testing. But this can-
not be taken as proved for the reasons already stated. In nature a biting fly will
carry on its proboscis, only a minute fraction of a drop of infective blood, and in
that quantity a comparatively large number of trypanosomes must, as proved by
Cross and Patel [1922], be present for successful infection. In the blood of cattle that
have recovered there are very few trypanosomes, or none at all, and it seems doubt-
ful if they could carry the disease over from one surra season to another. The question
of the number of flies which feed on a bullock with latent trypanosomiasis and
immediately feeding on a healthy animal has also to be considered. This may be
dealt with by quoting Gaiger [ 1911 ] who drew a few drops of blood of a camel bet-
ween paroxysms and injected into horses with negative results.
The present authors therefore agree with Montgomery [ 1908 ] that bovines are
less dangerous than camels as foci of infection and much less important as store-
houses and wish to add that more experimental evidence is needed to class them as
reservoirs of surra to bridge over the period from one surra season to another.
There is no evidence to show that game animals in India are not reservoirs of surra
and work in this direction appears to be required.
MECHANICAL TRANSMISSION BY TABANUS.
In Northern India, and in some other parts of the world, a few workers have
shown that it is possible to mechanically transmit surra from one animal to another
through the agency of certain blood sucking flies. From the literature available on
this subject, it appears that there is hardly any statement made by one worker,
regarding the power in mechanical transmission of any one fly, which is not contra-
dicted by another with experimental evidence. In spite of so much conflicting
experimental evidence, the power of the Tabanidae to act as mechanical carriers or
transmitters is considered to be well established by many workers, particularly by
Leese, who spent some time in India on this problem. In his remarks on the out-
break of surra in Bhugiaghat stable in 1907, Leese [ 1908 ] said that the disease
was discovered at a time when tabanus was certainly absent. He found that cessa-
tion of the outbreak corresponded with the diminution in the number of stomoxys
and also with the diminution in the number of blood marks caused by some ' unde-
termined ' fly, which evidently bit all classes of animals and made no particular
OBSERVATIONS ON TRYPANOSOMES OF CATTLE IN SOUTH INDIA.
385
choice of animals to feed on. Holmes [ 1908 ] says that there are grounds for
concluding that stomoxys could not have been the sole agent in the transmission of
the disease, because stomoxys attacked the healthy horses working in contact with
diseased ones during the day and nothing happened.
Leese [ 1909 ] said that the general distribution of Stomoxys is an argument
against its being the first cause of an outbreak in horses, because surra in horses
is not so generally distributed. In his opinion, stomoxys is unlikely to act that way
and as cattle usually have the trypanosomes so scanty in the blood or apparently
absent from it, the chances of this fly transmitting surra from an ox to a horse are
reduced to zero. The same author [ Leese 1912 ] says tabanus also has a very
wide distribution though not to the same extent as stomoxys. Hence what has
been said about stomoxys applies equally well to tabanus flies in relation to their
distribution and outbreaks of surra. Leese himself has said that surra does not
appear in horses in every fly zone. It would appear therefore that the abundance
and distribution of tabanus flies have no exact bearing on these outbreaks.
Leese has observed the spread of surra in camels or in horses in the absence of
tabanus but in the presence of other biting flies, yet he appears to hold that tabanus
flies are the most dangerous though adequate arguments are wanting to prove
this.
Pease [ 1884 ] in his report on surra stated that in the Bombay Tramway
outbreak, the animals attacked with surra were not in close proximity to each other,
but were dotted over the large area which the stables covered and were surrounded
by healthy animals, which remained free and he concluded that animals suffering
from the disease were not a source of danger to healthy animals.
Holmes [ 1906 ] said that in Muktesar Laboratory during the surra season,
numerous green coloured tabanidae infested the stables and were seen to feed on
infected ponies for a time till disturbed and immediately fed on healthy ones, kept
in the same loose box. He observed this for three years running and no spontane-
ous case of surra occurred. He further said that the theory of such biting flies
mechanically transmitting the disease in cases of natural infection looked less
probable and less worthy of consideration from a practical standpoint.
Allen [ 1930 ] has reported on the outbreak of equine surra in Mona Remount
Depot in December when there were no tabanus flies present there. He failed to
secure even a single specimen of tabanus during the course of the outbreak although
a careful search was made for them daily. He quotes a mass of literature which
indicates that the observations made on the common species of tabanidae definitely
show that the seasonal abundance of these flies varies within wide limits according
to the species, and the localities in which they appear. Hence it seems that the
386 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, IV.
generalisation that tabanidae are the main factor in the transmission of surra and
more especially the cause of the first case in an outbreak is inadmissible. There
have been more unsuccessful experiments in transmission of surra with biting flies
in a laboratory than successful ones, but none, excepting Cross and Patel [ 1922 ],
seems to have explained the cause of the failures. At any rate successful transmis-
sion does not explain how the first case occurred in an outbreak especially in South
India where the admitted reservoir, the camel, does not exist. The question there-
fore arises why tabanus flies alone are to be looked upon as the most important ones
concerned and not other biting flies. It has been proved by various workers that
no cyclical development of T. evansi takes place in the tabanus, stomoxys, haema-
topota, etc., and it has been shown that even in the absence of these flies outbreaks
of surra are encountered.
Patton [ 1909 ] described crithidia tabani in the gut contents of some of the
tabanus flies caught by him. He doubted the existence of any connection between
these crithidia with any hæmoflagellates and opined that new flies got infected with
the post-flagellate stages passed in faeces on places where they rested. While work-
ing in Mesopotamia he found similar crithidia in hundred per cent. of Tabanus glaber
during an outbreak of surra in camels in one of the camps. He observed that these
gad flies fed on the dromoderies and in so doing they ejected a dark fluid from their
alimentary tracts, sometimes pure blood, on to the skin and hair of the animals.
This fluid he examined and found to contain crithidia and their post-flagellate stages.
The dromoderies were noticed to drive away the gad flies by licking the areas where
they were bitten and at each of such acts the material infected their lips. It there-
fore occurred to him that the trypanosomes found in the dromaderies may be but a
stage of the crithidia parasitic in the flies and that when these crithidia, etc., came
in contact with the mucous membrane of the mouth, they penetrated it and entered
the blood stream, to assume the trypanosome form. With this in view he applied
to the mucous membrane of the mouth of two young camels the gut contents of the
tabanus, but he lost touch with these experimental animals owing to change in camp
and the results are not known.
In 1931 one of us (M. A. Rao) had an opportunity of visiting Kaveripakam,
Ranipet, etc., where outbreaks of surra among ponies had been observed periodi-
cally for some years. A few cases of surra appeared in ponies in February 1931, and
it was possible to visit the area in the month of May, when it was found that there
were a very large number of tabanus flies present. Kaveripakam in particular was
full of these flies and within sixty minutes over 65 T. striatus, 5 T. ditaeneatus,
2 T. virgo, a few lyperosia and stomoxys were collected. Most of the T. striatus were
caught on the trunks of trees near which ponies and cattle were tethered. The
people here have no stables for their ponies and these are kept in the open under the
OBSERVATIONS ON TRYPANOSOMES OF CATTLE IN SOUTH INDIA
387
shade of trees. Some of the tabanus and the other flies were caught on the bodies
of animals in the act of feeding. Of these gad flies thirty-five were dissected and
ten of them possessed crithidia and their post-flagellate form in their gut contents.
An emulsion of these was injected into a white rat subcutaneously and brought to
the College Laboratory, Madras, via Ranipet where twelve more T. striatus were
caught in the cattle sheds of the market. The other two species of Tabanus, lype-
rosia and stomoxys were found free from any flagellates in their intestinal contents.
The remaining tabanus flies were divided into two batches and each batch was put
in a wide mouthed bottle and applied to a dog and a calf for six days consecutively.
The majority of these did not feed and the mortality rate being high, they all died
out in six days. Those that fed on the dog and calf passed faeces or even blood
through the alimentary canal on the bodies of those two animals which they licked
after the withdrawal of the flies. The rat and these two animals were under obser-
vation for over two months and did not develop surra.
Kaveripakam was again visited in July of the same year and though the flies
were scarce at the time, over 88 T. striatus were caught while feeding on bullocks
and ponies. The blood of these animals (8 pairs of bullocks and six ponies) was
found to be negative for trypanosomes. These flies were brought to the College
Laboratory in a cage covered with netting. 25 flies were dissected and only four
were found infected with crithidia. Two white rats were injected with one c. c.
of the emulsion which contained an average of three crithidia per field under the
microscope and the result was negative. A few flies were allowed to feed on a
white rat which was kept under observation for 23 days with negative results. One
bull calf was injected subcutaneously with 2 c. c. of the emulsion of the gut contents
containing on an average of six crithidia per field under the microscope and another
calf was injected intravenously with the same quantity of the emulsion. These
calves were under observation for a month and they did not develop surra. The
blood of these calves was examined under the microscope periodically for T. evansi
and at the same time cultures of the blood were made to find if T. theileri could
be obtained but results were negative to develop it.
Our observations on the crithidia parasitic in the gut of tabanus show that
they are usually present only in the alimentary tracts of those gad flies that have
fed on blood. Patton [1909] has observed that a large percentage of female
tabanus which he caught and dissected had not fed on blood and yet their eggs
were mature and that they had some other food was indicated by the presence of a
yellowish fluid containing yeast-like cells, vegetables fibres, bacteria and gregarine
cysts. In his observations on flies, which did not feed on blood, he was not able to
find the parasitic crithidia. This supports our finding that blood is essential
for the development of these crithidia from whatever source they may have been