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Possible Existence of Fowl Paralysis
and Dalling [1932] have suggested ' lymphomatosis ', the difference lying in
the fact that the former term suggests that the nerves are always affected
whereas in practice it is known that certain cases occur affecting the ovary
or other organs without involving the nerves. It is more correct to use these
terms instead of fowl paralysis which is an indefinite term and which should
therefore be discarded as we have done in the case of ' roup ' in favour of fowl
pox.
ETIOLOGY
The cause of this disease is not definitely known but there is some evidence
that the disease is due to a filterable virus and is of a hereditary nature but
secondary factors appear necessary to help such a latent condition flare -up.
This explains why transmission experiments carried out in America by Pappen-
heimer and his associates [1929] and in England by Warrack and Dalling
[1932] by inoculating young birds with a saline suspension of affected spleen
were not cent per cent successful. The disease was reproduced only in 25 per
cent of the inoculated birds. Seager [1933] has collected experimental evidence
to show that the etiological agent of this disease is a virus which may provoke
a cellular hyperplasia of tumour-like proportions in the nervous system and
various visceral organs particularly the ovary. He has also recorded
that lymphoid cellular lesions of the iris are frequent, lymphocytosis in the
blood is usually present in active cases and the various secondary factors help
to precipitate the invasion of the tissues by the virus. Blakemore and Dalling
[1939] have produced evidence to show that fowl paralysis is an infectious
disease and the infecting agent is probably filterable. A series of passage
experiments with liver emulsions in groups of young chicks was carried out,
and it was shown that the infecting agent increased in virulence and caused
illness and death among chicks within 1 to 4 weeks. They have further
stated that previous failures to transmit the disease may be due to the sus-
ceptibility of the strain of fowls employed, the degree of virulence of the in-
fecting agent, the stage of the disease at which tissues are selected for trans-
mission work, and the type of tissue selected.
The research work carried out at the Poultry Pathological Research
Laboratory, Goring, Reading, under the Poultry Disease Investigation Fund
(Bulletin No. 1 and 2—Fowl Paralysis) shows that the secondary factors can
be described under the following three headings :—
1. Parasites.—The disease can undoubtedly occur without the presence
of parasites like coccidia and round or flat worms but in the majority of cases
one or more of these parasites are present in abnormal numbers. In the same
manner as leg muscles become paralysed in this disease through affection of
nerves so the intestinal tract can also become disorganized and it is not un-
reasonable to presume that such a process will foster the development of an
intestinal parasitosis. The increase in intestinal parasites with the consequent
formation and absorption of their toxins causes a further reduction in general
vitality and greater leg paralysis. Thus a vicious circle is produced.
2. Nutrition.—The lymphocyte-like tumour cells which infiltrate the
nervous and other tissues in this disease require, like the normal body cells,
a growth-promoting stimulus (vitamins) and growth building material
(proteins) for multiplication to form a mass, colony or group of cells.