TRANSMISSION OF RANIKHET DISEASE OF FOWLS
By J. A. IDNANI and C. SEETHARAMAN, Indian Veterinary Research Institute, Mukteswar-Kumaon
(Received for publication on 6 May 1947)
A LTHOUGH an efficient prophylactic vaccine has now been evolved for use in the field, much
can be done apart from this to control the disease in unvaccinated areas by means that can
easily be employed by poultry farmers. The experiments described in this paper were designed to
examine some aspects of this control.
Various views and experimental data on the dissemination of Ranikhet disease under natural
or artificial conditions are recorded in the literature on the subject. Outbreaks of the disease occur
mostly on the introduction into healthy flocks of newly purchased birds which are either diseased
or are in the incubation period or have just recovered, and the dissemination of virus is brought about
by infected exudates and excreta. Outbreaks in flocks with no history of contact infection are
attributed to the dissemination of the virus by such mechanical carriers as crows, pigeons, vultures
and other wild birds, but there is as yet no proof of this nor has the virus been isolated from any
such carriers. The possibility of its transmission by fowl ticks (Argas persicus) has been investigated
by Komarov [1940] with negative results. We have observed that lice from an infected bird on
being transferred to a healthy one did not transmit the. disease. Thus the digestive and respiratory
tracts appear to be the usual routes of infection.
Extensive studies have been made on the bionomics of the causal agent in countries where the
disease occurs. Virus suspension, on which most of the experimental work has been done, at ice
temperature retains its viability for several months and this explains the wide incidence of the disease
during the cold season. However, the virus is very fragile and is readily affected by a warm at-
mospheric temperature and by sunlight. At 50ºC. to 55ºC. the virus is rendered inert by 30 minutes'
exposure and killed by direct sunlight in one hour. In garden soil or in stagnant water at room
temperature (temperature not given) it became non-infective in four days [Farinas, 1930]. In con-
taminated brooders Dobson [1939] was able to recover the virus for a period of seven weeks. In the
light of these data a vigilant breeder can achieve considerable success in mitigating losses. The
secretions, excretions and tissues of affected fowls are all infective, providing wide scope for dissemi-
nation. Doyle [1927] demonstrated that the disease is readily produced by a light application over
the mouth and pharynx with a swab of cotton wool soaked with mouth exudate of an affected bird.
Even small quantities of the virus set up the disease by intravenous, subcutaneous and intraperi-
toneal inoculations, as well as by scarification and instillation into the eye or into the respiratory
tract [Stover, 1942] of susceptible birds. Under natural conditions, apart from direct contact— a
term which is somewhat meaningless—ingestion of infected material is reported to be the most
common method of transmitting the disease [Farinas, 1930].
EXPERIMENTS ON INGESTION
Virus in pills or capsules. Fresh spleens from two fowls, which died of Ranikhet disease were
made into a paste and weighed into 0.5 gm. quantities. Such weighed quantity was made into a
dough with wheat flour and formed into pills with particular care that the surface of the pill should
not be contaminated. Similar quantities of tissue were enclosed in gelatin capsules. Four birds
were given pills and four gelatin capsules, each receiving one pill or one capsule, which passed through
the gullet into the crop. The birds were then kept isolated from one another for 8-10 days but no
reaction ensued and all were later proved to be susceptible. The experiment was repeated on four
fowls, 0.5 gm. infected spleen in dough pills being given to each bird. They too reacted to inocula-
tion of virulent virus fifteen days later.
Virus mixed with grain. Five fowls were given with their grain ration pieces of fresh infected
spleen. The feeding was individual and each fowl got 0.5 gm. spleen tissue after which some more
uncontaminated grain was given. The minced spleen was well mixed with grain (crushed maize,
crushed barley, bran) and was not wetted with water before it was fed. The birds remained unaffect-
ed; eight days later they reacted to test virus and died of Ranikhet disease.
167
E