Catarrhal Fever of Sheep — Blue-tongue or Bbkziekte. 517 



CATARRHAL FEVER OF SHEEP— BLUE-TONGUE 

 OR BEKZIEKTE. 



By R. W. Dixon, M.R.C.V.S., Senior Veterinary Officer, Cape. 



This is a specific disease which affects sheep over a large area of 

 South Africa. It is characterized by high fever, a catarrhal inflam- 

 mstory condition of the mucous membranes of the mouth, lips, tongue, 

 upper air passage, and intestines, very often accompanied with 

 inflammation of the laminre of the feet and coronary band, followed 

 in some cases by suppuration and shedding of the hoof and also 

 shedding of the fleece. The lips, cheeks, and tongue become greatly 

 swollen, the latter assuming a purple colour from discoloration of 

 the lining membrane, hence the term applied to this disease: " blue- 

 tongtce." 



Originating Cause. 



Blue-tongue is not a contagious disease (affected sheep have been 

 kept in intimate contact with healthy susceptible sheep with no ill 

 effects), but is readily communicable by inoculation with a small dose 

 of blood taken from an aft'ected animal, either subcutaneously or 

 intravenously, and is due to a micro-organism. So far, all attempts 

 to find the organism, both by microscopical and bacteriological 

 means, have failed. It has been found that the blood of a sick sheep 

 when passed through a Berkefeld filter retains its virulence. All 

 visible micro-organisms would be unable to pass through such a filter, 

 consequently the conclusion is formed that the organism of this 

 disease must be so small as to be non-visible under the highest power 

 of our microscopes. 



The disease is very much more prevalent in some years than in 

 others. In very dry seasons it is much less prevalent and is mainly 

 confined to the low-lying districts, whereas in seasons in which there 

 has been an abundance of rain it prevails over a large area of the 

 country. Under warm and moist conditions, the disease may appear 

 as early as December or even November, but February to April 

 are the months in which we find it most general. It is veiy rarely 

 met with in mountain veld, being usually confined to the valleys and 

 plains, but it is the local elevation which gives the protection, not as 

 elevation above sea-level, but as compared with the surrounding 

 country. If sheep are kraaled before sunset on the top of high, 

 elevated portions of the farm, or placed in proper sheds during the 

 night, this malady can be prevented. Further, if a flock of sheep, 

 in which the disease is prevalent, is dipped in some sheep dips, 

 esjecially the carbolic or tar derivative dips, the spread of this 

 disease can be arrested. 



It has long been suspected that the disease is contracted and 

 sjiead under natural conditions by the agency of flying insects, 

 probably mosquitoes. We have no positive proof of this yet, but the 

 negative evidence produced is so strong as to justify these suspicions. 



