Pleuro-Pneumonia of Cattle. 16 J 



Veterinary service, it became necessary for the Department of 

 Agriculture to modify and relax the usual method of dealing 

 with outbreaks of contagious pleuro-pneumonia. It is a signifi- 

 cant fact, that during that war period, the disease became more 

 prevalent throughout Victoria than it had been for many years. 



As far as Victoria is concerned, the difficulties of control and 

 eradication are enormously increased by the border traffic in 

 animals from neighbouring States, and the impossibility of recog- 

 nising, by clinical examination alone, the presence of carriers of 

 latent infection. 



The records obtained over a number of years in Victoria show 

 the large percentage of outbreaks of the disease, which owe their 

 origin to the unsuspected introduction of a carrier of the infec- 

 tion into a healthy herd. The diagnosis and destruction of these 

 so-called "recovered animals/' carriers of a potential infection, 

 which readily becomes actual when they come in contact with 

 susceptible animals, is therefore a matter of prime importance 

 in successfully eradicating the disease from any particular State. 



In certain European countries, notably Great Britain, and in 

 the U.S.A., the disease has been eradicated by adopting the pro- 

 cedure of wholesale slaughter of all the animals concerned in 

 each and every outbreak. This procedure, whilst economically 

 justifiable in those countries with our present knowledge of the 

 disease, is at the same time unscientific and costly, since it neces- 

 sitates the destruction of a very large number of healthy cattle 

 in order to attain its object. 



The difficulties of adopting such a course of stamping out the 

 disease in Australia at the present day are obvious, owing to the- 

 large area over which the disease has spread, the scattered nature 

 of the outbreaks, the number of cattle, the slaughter of which 

 would be involved in such stamping out process, the enormous 

 cost of compensating the owners of the slaughtered animals, and 

 also owing to the existence of the disease on stations situated 

 in the more remote parts of Australia, where it would be im- 

 possible to muster all the cattle on the particular property at any 

 one time. 



The variable incubation period, which may be anything from* 

 10 to 30 days, and the fact that an animal affected with the 

 disease, but not showing recognisable clinical signs of such in- 

 fection, may be an actual infective agent, renders the task of" 

 localising outbreaks exceedingly difficult. The role played in the 

 dissemination of the disease by so-called " recovered am'mals/ r ' 



12 



