MICRO-PARASITES 237 



wild birds suffer from tuberculosis. In the U.S.A. it has been recorded 

 from sparrow, crows, cow-birds, pheasants, the sparrow-hawk and 

 barn-owl. In Britain the disease is most frequently met with in gregari- 

 ous birds such as starlings, rooks, sea-gulls and wood-pigeons. This is 

 scarcely surprising, since avian tuberculosis is passed from bird to bird 

 by contact, or by the accidental ingestion of freshly contaminated 

 faeces or the exudate from the lungs. In the case of barnyard fowl, which 

 are also liable to contract the illness, old birds are more susceptible than 

 young birds. The disease is initiated by way of the digestive tract, not 

 the lungs, and ulcerative lesions can form in the liver, spleen, intestines, 

 bone marrow, ovaries, lungs, air-sacs and in fact most tissues. There is 

 no rise in temperature but a characteristic symptom is the gradual 

 wasting away of the body, associated with extreme exhaustion. Affected 

 birds may die within a few months or may survive for several 

 years. 



Another well-known group of bacteria which attack both birds and 

 mammals is the genus Salmonella (family Bacteriaceae), the causative 

 agent of typhoid and paratyphoid fever in man, and puUorum disease 

 and fowl typhoid in birds. These bacteria are primarily intestinal 

 parasites. They are rod-shaped motile organisms with numbers of 

 flagella distributed indiscriminately over the surface of the cell. All are 

 Gram negative, that is to say, they do not retain Gram's stain if de- 

 colorised by ethyl alcohol or acetone. 



Birds are particularly susceptible to Salmonella and no less than 

 forty species have been described from the fowl in the U.S.A. alone. A 

 few are host-specific, but many attack a wide range of warm-blooded 

 animals. Pullorum disease {S. pullorum) has been recorded from several 

 wild birds including the bullfinch, chaffinch, goldfinch and certain 

 pigeons. Sparrows, quail, pheasants and bitterns are also susceptible 

 to experimental infection. This is by far the most important disease of 

 birds which is transmitted via the tgg. On poultry farms large numbers 

 of chicks may be infected by contact with contaminated excreta or the 

 down in incubators, or by contaminated food or water in brooders. 

 Nevertheless the chief vehicle of infection is certainly the ^gg. In 

 virulent epidemics the death rate of affected chicks may reach 90 per 

 cent, or more and pullorum disease has been the cause of huge losses to 

 the poultry industry. Various other bacteria of the paratyphoid group 

 have been isolated from wild birds ranging from teal to siskins. Duck 

 eggs are a recognised source of Salmonella food poisoning in man. 



