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Ectoparasites - Psoroptes

Psoroptes equi, P. ovis, P.cuniculi: Scab mite. Only P.cuniculi is reported in New Zealand.

General Description: The oval body of the psoroptic scabies mite is 0.6 mm. long with 8 long legs. The mouth parts are elongated, adapted for piercing the skin to suck lymph. Pretarsi are present.

Life Cycle: Mite life cycle stages are described in the overview. Psoroptes mites puncture the skin to suck lymph fluid. All stages of the life cycle occur around the edges of the oozing lesions. Generation time is 1.5 to 3 weeks, even in winter on heavily coated horses. Psoroptes mites can survive off the host for 2 to 3 weeks.

Location: The Psoroptes mite prefers areas of thick hair, ears, mane and tail but untreated infections will spread over the entire body surface of the animal.

Geographical Distribution: Psoroptes equi is found only in England, whereas P. ovis occurs on horses, cattle, and sheep in many parts of the world. P.cuniculi is found in New Zealand.

Significance: Psoroptic mange is not common. Heavy infestation causes severe debilitation.

Effect on Host: Bites of these lymph-sucking mites cause inflammatory lesions that ooze fluid which dries to form crusts. The infection is known as psoroptic mange. The bare scabby areas produced are unsuitable for the mites, which migrate to surrounding healthy skin, potentially spreading tissue damage over the entire body. Psoroptic mange causes horses to itch and scratch, which can cause hair loss and skin trauma. Severe mite infestations cause anorexia, emaciation, and anaemia.

Diagnostic Information: Mites can be identified in skin scrapings taken from the edges of active lesions.

Control: Treatment of infested animals is important to arrest the spread of the skin lesions and to prevent contamination of the environment and other livestock. Currently, organophosphate compounds are used. The heaviest infestations generally occur in late winter and early spring, when the host animals carry denser hair coats, tend to huddle in groups for warmth, and may be confined to restricted, more crowded quarters than during other seasons. In the latter case, treating the animals´ environment is important in the control of Psoroptes infestations. During the summer, "latent" infestations are common. In a latent infestation, small dry lesions may exist for months on protected body areas before the infested animals show typical clinical symptoms.

Psoroptes image
Psoroptes– adult female nymph, and larvae

       

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