72
Conjunctivitis of Sheep and Goats in India
the incidence of the affection was so insignificant as to occasion no comment by the local Veterinary
Officers and it would certainly have passed unnoticed had we not been particularly on the look out
for it. Nor have we encountered the affection in the many hundreds of goats used in experimental
work at the Institute over the last four years.
In our limited investigation into the ætiology of conjunctivitis and keratitis of sheep and goats
in Bihar, we arrived at the conclusion that the condition had much in common with the similar disease
described in these animals by Coles [1931], and that the cause was R. conjunctivæ. It is true that the
disease we investigated was clinically similar to that described by Coles, and that R. conjunctivae
was identified in one of the sheep from Bihar and in several cases of the same disease in goats occur-
ring at an army depot in 1945, but we are now by no means convinced of the ætiological relationship
of these organisms. There are two main reasons for our doubt. Organisms which cannot be different-
tiated from R. conjunctivæ on morphological characters and staining affinities have been demon-
strated within the conjunctival cells of every goat and sheep and of the few bovines that we have
examined, and, with one exception, the eyes of all the animals selected for examination were per-
fectly healthy. We have no doubt that, if we extended our examination, the finding would be
practically universal. In the second place we failed to infect the conjunctival membrane of normal
sheep with ocular discharge from a frank case of conjunctivitis in a sheep from Bihar in which R.
conjunctivæ was identified within the conjunctival cells. This experience confirmed the work of
the field workers in Bihar and is contrary to the experience of workers in other countries on rickett-
sial conjunctivitis in small ruminants. One possible explanation of our experience is that the infec-
tion is really ubiquitous and latent in the sheep and goats that we have worked with, even if there
are no apparent sub-clinical lesions.
Abdussalam [1944] found rickettsiæ similar to R. conjunctivæ within the conjunctival cells of a
buffalo affected with conjunctivitis, but makes no comment on the examination of healthy eyes of
the same animal species. He also records that, on examination of the eyes 24 of Malvi
goats, chronic trachoma-like lesions were found in every case and rickettsiæ identified within the
conjunctival cells, although there was no outward appearance of eye affection such as keratitis. He
considers that these animals had suffered from a more acute form of the disease in their kidhood, and
that in the adult this had reached a stage of chronicity. No systematic examination, however, of
kids in the area was undertaken. It is also noteworthy that no transmission experiments with materi-
als from the Malvi goats could be carried out, as ' unaffected goats could not be made available '. It
is not quite clear from this statement whether all the goats in the area were affected with specific
conjunctivitis, or simply whether R. conjunctivæ infection could be determined within the conjunc-
tival cells of these goats. If the latter, it agrees with our own observations. In the eyes of the
normal goats and sheep which we examined, and in which we found rickettsiæ conforming in type to
R. conjunctivæ, we have seen no signs of persistent and chronic trachoma-like lesions. According
to information received, sub-clinical trachoma is a prevalent affection among the Indian population,
and, even in apparently normal eyes, can be detected by slit-lamp examination of the vessels of the
limbus. It may well be that a more careful examination of the eyes of goats and sheep on these lines
would give a more accurate interpretation of the finding of R. conjunctivæ, within the conjunctival
epithelium of these animals though, on naked eye examination, there is no evident abnormality.
It may well be that the latency of the animal disease is similar to what has been observed in the
human population. In this connection, it seems worth emphasising the statement of Beveridge
[1942] that, although it has not been possible to prove the ætiological role of R. conjunctivæ in con-
tagious conjunctivitis of goats and sheep, there is strong justification for accepting it as a working
hypothesis. If, however, this position be accepted in respect of frank clinical cases of the disease
in which the organism can be identified, what interpretation can be vouchsafed for the identification
of the parasite in cases where no clinical disease exists?
There is one last point. Contagious conjunctivitis of sheep and goats has been described as a
superficial infection, and yet, although little work seems to have done on the essential pathology
of the condition, there is some evidence that the deeper structures of the eye may be involved. Thus,
Coles [1931] describes lesions of irido-cyclitis. It is not clear whether this lesion is considered a direct