Itch mite (Psorergates ovis) is a microscopic mite that lives in the skin. In heavy infestations it may cause skin disease and fleece damage from itching. It is limited to sheep, usually as a subclinical infestation.
Widespread use of macrocyclic lactone drenches like ivermectin have greatly reduced the incidence of itch mites and the condition is now rare. In addition, itch mite populations build more slowly than lice and the mite does not prefer hot, humid conditions or exposure to sunlight in short wool.
It causes scratching, biting and fleece damage in heavy infestations. It should be suspected when lice or grass seeds are not found.
Laboratory confirmation requires skin scrapings collected using a scalpel blade dipped in paraffin oil. A skin biopsy submitted in buffered formalin may assist in differential diagnosis.
Macrocyclic lactones such as ivermectin are highly effective.
Specific preventative measures beyond the occasional use of macrocyclic lactone drenches are usually unnecessary.