42 



Diagnosis and treatment — In man, the diagnosis of a simple case 

 is readily made by finding the galleries with the female at the end, 

 but there is often secondary infection, due to scratching. Treatment 

 consists in preparatory warm bath, or for cleaning off scales, incrusta- 

 tions, etc., and softening of the skin and then in applying a sulphur 

 ointment. 



Psoroptes communis ovis, mite of common sheep scab, the most 

 prevalent and most injurious malady of sheep. May begin attacks 

 in almost any part of body but usually in parts covered by wool; 

 wool falls out, scabs are formed, and finally the skin becomes more 

 or less bare, parchment like, greatly thickened, furrowed and bleed- 

 ing in the cracks. 



Description — One of the larger mites, males 500-600/^ x 340-370/^, 

 female 670-740/* x 450-460/a, quite easily seen with naked eye. 

 Rostrum or beak elongated, conical. Ambulatory suckers on long, 

 3-jointed pedicle, on first three pairs of legs in the male, and on first, 

 second, and fourth legs of the female. Male with copulatory suckers 

 and abdominal prolongations. 



Life history — Female lays 15-24 eggs on the skin, or fastened to 

 the wool near the skin. In three or four days the six-legged larva 

 hatches and three or four days later molt to form nymphs which pair, 

 molt twice more and begin to lay eggs. Gerlach estimates fifteen 

 days as an average for a generation and that under ideal conditions 

 a single pair of mites may produce 1,500,000 individuals in three 

 months. 



Methods of control — Preventive and curative. Exceedingly con- 

 tagious and penalties for shipment of diseased sheep are heavy. 

 Contagion may be direct, by contact of sheep with one another or 

 indirect, from fences, posts, etc. or from places where infested sheep 

 have been "bedded" down. Hence, if pastures, corrals, or sheds 

 become infested leave them vacant for at least four weeks before 

 using for clean sheep. Curative treatment, some external application 

 which will kill the parasites. Various dips used. For details see 

 Bureau of Animal Industry Bui. 21 "Sheep Scab, its Nature and 

 Treatment", or more recent publications of the Bureau. 



