364
Equine Encephalomyelitis in India
symptoms in individual cases must, apparently, depend on a study of dege-
neration of ganglionic centres, and their residual neuronal capacity associated
with impulse transference along the neuronal pathways.
The question as to whether carriers exist in this disease is one of much
importance and has occasioned considerable perplexity in the minds of army
authorities in India. That question seems, at least, to have been answered.
The proof is indirect, it must be admitted, but the contention that carriers
exist is the only reasonable explanation of the genesis of certain outbreaks
that have been observed. The history of the three recovered cases which
relapsed at Jullundur is a further support of this contention. The virus was
recovered from the brain tissue eighteen months after apparent recovery.
One question that cannot be answered is, what is the potential danger
of such cases in an equine population ? No effectual answer can be supplied
at the moment, since all attempts to explain the mysterious spread of the
disease during the course of an outbreak have proved unavailing. Attempts
were made to transmit the disease to susceptible horses (Jullundur, 1936)
by the inoculation of blood from horses showing the earliest symptoms of the
disease, with negative results. It would appear at first sight, therefore,
that insect vectors can play little part in the dissemination of the disease.
Recent American work shows, however, that the virus is present in the blood
in the prodormal, prefebrile phase of the infection, and that certain species
of Aedes can be responsible for the spread of the disease. This aspect of the
problem is one that has not, as yet been studied in India and is one, obviously,
that demands further investigation. The writer believes, however, although
the evidence may be circumstantial, that infection is air borne, as in the case
of the equine influenza virus. One of the earliest symptoms in the disease,
and one that is frequently overlooked, is a mild, watery discharge from the
nose. The nasal pharyngeal atrium is one that is well established in certain
neurotropic diseases of the human subject and the extreme susceptibility of
small rodents to intranasal insufflation, in conjunction with observed clinical
facts, points to a probability of this being the method of spread during the
course of an outbreak.
Whatever the method of spread of the virus, there appear to be deter-
mining or controlling factors which, during the course of an outbreak, operate
conjointly with the virus. The waves of infection noted appear to be governed,
in some obscure fashion, by external (climatic) and possibly metabolic factors.
There can be little doubt of the truth of that observation and in this direction,
rather than in an immediate solution of the vagaries of the virus, much im-
portant work remains to be done.
" The circumstances under which infection occurs appear to depend
upon the presence of favouring environmental conditions, the nature of which
is unknown ". (Edelman, quoted by Hutyra and Marek).
The somewhat equivocal results obtained in transmission experiments
in rabbits are comparable with the results recorded by American and French
workers. Meyer [ 1932 ] explains these apparent discrepancies by saying
" it is sometimes impossible to find the virus in the central nervous system,
as the results either of unequal distribution or of autolysis." Lesions in the
brain are, in the Indian form of equine encephalomyelitis, certainly of irregular