364 Acarology 



found in the skin follicles. The adult male or immature female emerges 

 within four to six days after 'the egg hatches. The male, which is rare, 

 is found in a short burrow where it remains for a brief period, since 

 it spends a considerable time on the skin surface searching for unfer- 

 tilized females. Although the unfertilized female makes a small bur- 

 row it stays in it for only a day or so. Mating probably takes place on 

 the skin. The cycle from egg to ovigerous female takes from ten to 

 fourteen days. Less than 10 per cent of the eggs give rise to adults. 

 Movement or burrowing usually follows egg deposition. 



The mites cause severe itching which keeps the patient awake at 

 night. Itching is associated directly with burrowing; each time the mites 

 irritated the skin or caused itching they were found to be moving on. 

 There is a characteristic rash, due both to the mite and to scratching. 

 Erythematous patches and follicular papules appear in areas under the 

 arms, around the waist, on the wrists, between the legs, on the thighs, 

 and on the ankles. Most of the skin symptoms are due to secondary 

 infections which follow scabies. It is believed that the first case of 

 scabies causes no itching. After a month or so, when the rash appears 

 in the area of the burrows, the itching begins since the patient has now 

 become sensitized to the mite. Once having had scabies and acquiring 

 another infection, the area around the burrow becomes inflamed within 

 a few hours. A sensitized person begins to scratch immediately and 

 often is able to dislodge the Sarcoptes and automatically stops the in- 

 fection, whereas in the nonsensitized person the infection builds up 

 over a period of about a month before the patient is aware of harbor- 

 ing the mites. 



Scabies is common in the history of man and appears to come in 

 waves. Sensitization forms a so-called immunity and the mites can be 

 located easily and dislodged. The next group of people have not been 

 infected and are not sensitized and the mite population builds up as 

 in diseases. The real causes of the rise and fall may not yet be known. 

 The highest incidence is in winter when people sleep together to keep 

 warm and there is less washing. Scabies is not acquired through ordi- 

 nary social contacts but through sleeping in the same bed with an 

 infected person. 



Secondary infections due to scratching are often more serious than 

 the actual scabies. Reaction to different sulfur compounds used to con- 

 trol the mite may also set up a serious skin condition. 



Sarcoptes mange of the dog is caused by Sarcoptes scabiei var. canis. 

 It is to be found on any part of the animal but usually first on the head. 



