96 ■ Journal of Agriculture. [10 Feb., 1910. 



TICK FEVER IX FOWLS. 



A. A. Broivn, M.B., B.S., hupcctor of Foods for Export. 



A disease that is the cause of considerable mortality in fowls, and con- 

 sequently of great losses to poultry breeders, prevails over a large extent 

 of Australia. It would be difficult to estimate the losses annually inflicted 

 on the poultry industry in the Commonwealth by the depredations occa- 

 sioned by the fowl tick {Argas americanus) that is the primary factor in 

 the dissemination of the infective agent. The infective agent is a micro- 

 organism which lielongs to the protozoa, or lowest division of the animal 

 kingdom. It is harboured in the bodies of Argasides or fowl ticks, and 

 the ticks bv biting fowls introduce it into their bodies. 



Female. Male. 



Dorsal aspect. Ventral aspect. Ventral aspect. Dorsal aspect. 



(Two and three-quarter times natural si?.e.) 



FOWL TICK. {Argas americanus.) 



Tick fever is a disease of the blood in which haemolysis, or destruction 

 of the red blood corpuscles, is a characteristic feature, and this haemolysis 

 is produced by the vital activities of the micro-parasite. 



Fowl tick does not mature on the bodies of horses, cattle, sheep, pigs, 

 dogs, ducks, or geese, although ticks may occasionally perhaps be observed 

 on them. The special micro-organism prevailing in the Argas americanus 

 that causes the fever in fowls has not, moreover, ever yet been detected in 

 the blood of any animal or bird in the orders mentioned. 



Ticks attack birds belonging to the pigeon and fowl tribes and \oung 

 ticks attach themselves to their bodies, and there they may remain until 

 they undergo certain transformations incidental to their development. 



There is as yet no direct e\idence to prove that chickens hatched from 

 the eggs of fowls that had suffered, and yet recovered from tick fever, are 

 hereditarily immune. Young chickens in the infested areas are probably 

 often attacked and inoculated by ticks so that by the time they have reached 

 the adult stage of exi.stence, provided they have survived the inoculations, 

 they have acquired immunit\ to the specific micro-organisms. Ticks are 

 the carriers of the infection, but all ticks may not contain the specific 

 organism in their bodies. Ticks can be kept in receptacles that admit air 

 without food for twelve months without losing their vitality. 



The micro-jjarasite, the I'iro plasma gallincc, which is the actual cause 

 of the fever in fowls suffering from tick fever, is a particularly small motile 

 organism belonging to the animal kingdom. The organisms exist both in 

 the blood-cells (intra-corpuscular forms) and in the blood serum (extra- 

 corpu.scular forms). The extra-corpuscular forms are far more numerous 

 and larger than the intra-corpuscular forms. In preparations made froirj 

 the blood of the heart and large vessels only a few organisms are at any 

 time detectible, but in preparations made from the blood of capilliaries of 



