54
Previous observers have pointed out, that if "Surra" is contagious, it is
not so in the ordinary sense of the word. Evans* found no evidence to show
that the disease is either contagious or infectious in the ordinary sense." Steele †
noted "that the evidence which we have to hand about the mule disease, is
strongly opposed to the theory of its communicability by contagion ; no conta-
gious influence can be traced in its manner of spreading, among mules in one
stable, or working together."
The chief arguments that can be brought in favour of the contagious nature
or otherwise of the disease may be here noted :—
(i.) When one horse is attacked with Surra, it often happens that other cases
follow in succession in the same stable, or in the same district.—Numerous instances
of this kind are forthcoming, of which one of the most important is Evan's statis-
tics with regard to the 4th Panjab Cavalry horses, when a total of 272 animals
died in three years 1878—1880, numbers varying from 14 to 47 being attacked
about the same time at several stations. Again at Tonghoo in 1884-85, one
hundred and eighty-two mules were attacked between September and the follow-
ing January. And in the case of the Bombay Tramway Company, fourteen
animals developed Surra in 1888 out of a total stud of 739 horses, and forty-
seven in 1889.
But on the other hand in 1890, only one case occurred in the same stud ; too
much importance however must not be laid on such examples, for such cases
can be readily explicable on the supposition that the disease has a local origin.
(ii.) In some instances cases have followed one another, so as to favour the
idea that the disease has been communicated by one horse to another.—Is the
prevalence of Surra in direct proportion to the degree of intercourse between
the healthy and the sick animals ?
We have abundant evidence to prov3 to the contrary. Evans ‡ states " that
seventy-seven horses of the 3rd Panjab Cavalry becoming affected with Surra
at Jutta, from which they all died at Edwardesabad, did not communicate the
disease to others." Gunn § found at Kohat, " that the grass-cutters' ponies
stood in the same lines as the other animals, but no mule belonging to the
mountain battery, nor horse from the Panjab Cavalry became ill of the disease.' 7
Again in the Bombay Tramway outbreaks, with one exception, when several
animals became affected, which had been located on the north-side of the stables ;
the animals attacked with Surra were not found to be in close proximity to each
other, but to have been dotted about over the large area which the stables cover ;
and in most instances were far apart, and surrounded by healthy animals, which
remained free from the disease.
(iii.) Animals brought from localities where the disease is unknown are at-
tacked on being taken to districts where the disease is endemic.—On several
occasions it has happened, that Australian horses belonging to the Tramway
Company, under one year in this country, have been the first animals during
the year to be attacked with Surra, so that contagion is out of the question in
those cases.
(iv.) That animals are occasionally found suffering from this disease in dis-
tricts not known previously to be in fected localities.—Althoughcases may occasionally
be found in a part of the country where it is not endemic, and where the conditions
are not favourable for its development, it will generally be found on inquiry, that
such cases can be traced to the fact, that the animals affected have been recently
imported from places where it is endemic (see Case No. X); and also one may
mention the outbreak in 1S85 which occurred amongst transport animals, which
had been collected from low-lying districts below the Ghats, &c, and brought
to Poona where the disease is not endemic ; but when these cases succumbed, no
fresh cases occurred in the station.
(v.) There are no records to be found as to Surra having been imported by
suffering animals into localities before exempt from it, and the disease from that
time forward becoming endemic.
* Evans, page 63.
†
Steele, page 37, para. 17.
‡ Evans, page 62-63.
§ Gunn, loc cit.