11
2ndly, at Dera Ismail Khan the local transport camels are always kept
together, and at Dera Ismail Khan tabanidae abound; surra amongst the
camels at Dera Ismail Khan is very common, but if the spread of surra is by
direct transmission it is difficult to believe that a single camel could escape.
Srdly, we have the the same conditions prevailing at Bannu as at Dera
Ismail Khan, and here again we find only a certain percentage of camels
infected.
4thly, in certain parts of Bikaner surra is common, though tabanidse
are absent.
If the spread of the surra is by direct transmission by tabanidae it is
difficult to explain why more camels are not infected ; but if a life cycle of the
trypanosome takes place in blood-sucking insects and only a small percentage
of these become infective, then we have an explanation of why the disease is
not spread more rapidly. Investigators on sleeping sickness agree that very
seldom, if ever, does transmission take place by direct transmission, that there
is a life cycle in the fly and that only 2 5 per 1,000 flies become infective.
In connection with the spread of surra it is an extraordinary fact that
although so many cases of surra occur amongst camels at Dera Ismail Khan
and Bannu no case of surra amongst mules and ponies (though kept only a
very short distance away from the camels) have been reported. Although
surra is prevalent amongst the grantee camel corps camels, from inquiries
that I have made, surra amongst the horses is unknown in the colony.
At Sargodha and Mona remount depots there have been no outbreaks
of surra, in spite of the fact that there are many cases of surra amongst camels
in these districts.
The same remark applies to Rawalpindi; surra is common amongst the
51st silladar camel corps and tabanidae are very common about Rawalpindi,
especially numerous in Topi park, yet no outbreak of surra has been reported
amongst mules or horses. I found cases of surra amongst camels working
on Murree road last year, though as far as could be ascertained there was no
case of surra amongst the ponies on this road.
Although it is known that tabanidae prefer the camel to the pony,
it is quite common to find tabanidae biting the mules at Dera Ismail Khan
and Bannu and the ponies on the Murree road, and it seems incredible to think
that at Dera Ismail Khan and Bannu where camels (amongst which I found
surra cases) are so close to the mules that tabanidae do not go from one
animal to the other. That trypanosomisis can be conveyed from the camel to
the pony I have proved by inoculation ; moreover a few years ago at Sohawa
a horse kept near surra camels developed the disease from them. "Why the
disease is not spread from the camels to the mules at Dora Ismail Khan and
Bannu and why no outbreaks have occurred amongst the horses of the Chenab
colony, Shahpur district or the army remount depots, I am unable to ex-
plain, but because up to the present no outbreaks of surra have occurred it
does not necessarily follow that such will always be the case. To my mind it
is most important to determine—
(1) the exact method of spread of surra whether by mosquitoes,
ticks, tabanidae etc.,
(2) why in a district where camels are infected with surra, ponies
escape, and
(3) why low lying marshy ground is favourable for the spread of
surra ;
(It cannot be explained by the prsence by tabanidae as tabanidae
are found on high dry ground provided there is a stream of
water.)
(4) why the greater the rainfall during the rainy season the heavier
the mortality from surra.