STATE HYG-IENE 615 



EPIZOOTIC HEAET-WATEE. 



This South African disease, for which there is no other 

 name than the above, affects cattle, sheep, and goats. It 

 is limited to certain areas of Cape Colony and the Trans- 

 vaal, preferring, like ' horse- sickness,' low-lying and warm 

 pastures. 



It is an inoculable disease but not contagious ; the 

 organism has never been seen, but Eobertson has filtered 

 it from virulent blood* so that it should come within the 

 limit of visibility. 



The disease is transmitted by a tick known as the Bont- 

 tick {Amhlyomma habrceum) either in the nymph or adult 

 stage, but the virus does not pass from the female into the 

 egg. Wherever the particular infected tick is found the 

 disease is perpetuated, but excepting in heart-water districts 

 the same tick is harmless. 



As the bont-tick can only live at certain altitudes and 

 among bushes, the confinement of the disease to certain 

 localities, and its disappearance where altitude fails to give 

 the needful warmth, are easily explained. 



The incubation period in natural infection is from eight 

 to ten days though it may vary from five to fifteen. Cattle, 

 sheep, and goats, placed on affected pastures soon succumb, 

 but animals reared on such pastures have an immunity. 

 Hence the common sheep and goat of the country lives and 

 thrives in parts absolutely fatal to high-class stock. 



Eobertson and Lounsbury have pointed out the re- 

 markable immunity possessed by Persian sheep to the 

 disease. Crosses between the Persian and South African 

 breeds produce an animal which can live and thrive on 

 virulent heart-water pastures, where all other sheep and 

 goats die.t 



The preventive measures are to move animals at once 

 from infected pastures to higher ground, and to keep them 



* Eeport of Chief Veterinary Surgeon, Cape Colony, 1903. 

 t Agricultural Journal Ga^e of Good Hope, August, 1904. 



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