EXPERIMENTS ON THE TRANSMISSION OF SURRA
BY THE TICK ORNITHODOROS THOLOZANI LABOULBENE AND MEGNIN
By S. K. SEN, Imperial Veterinary Research Institute, Mukteswar
(Received for publication on 15 October 1946)
I N a paper published in 1922,* Cross and Patel, in the Punjab, brought forward some evidence
to show that, under experimental conditions, surra was capable of being transmitted through
the agency of Ornithodoros tholozani Laboulbene and Megnin†, a tick of fairly common occurrence in
that province. They further observed that these ticks transmitted the disease to healthy rabbits
67, 83 and 101 days after feeding on a surra-infected animal, but that they proved non-infective
when tested one minute to 46 days after their infective feed. In fact that the ticks required at least
an interval of 46 days to become infective for healthy animals led them to postulate the occurrence
of a cyclical development of the trypanosome within this invertebrate host, on the analogy of what
is known to occur in certain other forms of protozoan infection. In a later communication, however,
Cross and Abdulla Khan [1923] stated that 'these ticks were found capable of spreading the disease
to a healthy animal 17 days and one month after feeding on an infected animal', whilst Kahan Singh
[1925] fixed the maximum limit at the 212th day. It is noteworthy that this last worker also reported
having obtained positive results when the ticks were fed by the 'interrupted method', and further-
more, these results appeared to him to point to the conclusion that 'not less than 10 ticks of this
species are capable of transmitting the disease.'
On the other hand, a series of experiments carried out by Yorke and Macfie [1924], by means of
infected O. tholozani tick forwarded to Liverpool by Cross from India, yielded results of an entirely
negative order. It occurred to these workers that a possible explanation for the failure of these ticks
to infect was the fact that, immediately after the infecting feed, they were subjected to relatively
low temperature during transit from India to England in the month of December. In order to exa-
mine this question, they obtained a second supply of ticks that had been fed on a heavily infected
dog on 23 July, 1923. These ticks, which were received by them on 24 August, were allowed to feed
on a rabbit at frequent intervals, but no infection resulted. In commenting on these results, the
authors remark: 'We have no explanation for these negative results, but the subject is one of such
practical importance as to demand re-investigation.'
The experiments described in this paper were undertaken with a view to further pursuing the
question and more particularly with the object of obtaining any indication as to the occurrence of
a cyclical development of the surra trypanosome in O. tholozani, a supply of these ticks having been
obtained through the courtesy of the Principal of the Punjab Veterinary College, Lahore.
For providing the infective feeds, guinea-pigs were used showing trypanosomes at the rate of
12 to 40 per field. A total of 502 ticks were thus infected and they were later placed in seven groups,
as shown below, in accordance with the date on which they were fed and the temperature at which
they were maintained.
Group I. 26 August 22 ticks fed on a guinea-pig showing trypanosomes at the rate of 12 per
field.
Ticks were kept at room temperature (about 20ºC.).
Group II. 27 August 56 ticks fed on a guinea-pig showing trypanosomes at the rate of 15 to
20 per field.
Ticks were kept at room temperature (about 20ºC.).
Group III. 27 August 56 ticks fed as above, but kept in incubator at 25ºC.
Group IV. 1 September About 49 ticks fed on a guinea-pig showing trypanosomes at the rate
of 20 per field.
Ticks were kept at room temperature (about 20º C).
Group V. 1 September About 48 ticks fed as above, but kept in incubator at 25ºC.
Group VI. 2 September About 137 ticks fed on a guinea-pig showing trypanosomes at the
rate of 40 per field.
Ticks were kept at room temperature (about 20ºC.).
* Paper read at the Jubilee Session of the Indian Science Congress held in Calcutta. January 1938. Revised and
re-written.
† This tick has also been known by the names of O. crossi Brumpt and O. papillipes Birula, whilst, in a recent paper
(Ann. Parasit. Hum. Com. 1946, 21, 74-88), Desportes and Campana have designated it O. tholozani Var.crossi.
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