Two economically important species of mites infest dairy cattle in the Northeast. One species, Chorioptes bovis, lives on the animals’ skin and hair. Infestation by these mites results in a condition known as chorioptic mange, or barn itch. Chorioptic mange is generally characterized by dermatitis, hair loss, and scabbiness in small areas around the feet, legs, and tail head. The skin underneath the affected areas becomes swollen and inflamed. Infestations by this mite are usually localized, although in some cases the lesions can spread to cause a more generalized dermatitis resembling sarcoptic mange.
Chorioptic mange mites live on the surface of the host animal’s skin and feed on lymph as well as dead cells and other debris. Development from egg to adult mite is completed in about 2 weeks. Mite populations usually are very low in the summer months, and symptoms of infestation typically disappear during this time. Populations increase again in the fall, with the most severe problems occurring in winter. High levels of chorioptic mange in dairy herds can reduce milk production.
Sarcoptic mange is a condition caused by another, smaller species of mite, Sarcoptes scabiei. The skin lesions arising from infestation by these mites are so severe that sarcoptic mange is handled as a quarantinable disease.
Unlike lice and Chorioptes mites, the microscopic sarcoptic mange mites burrow deeply into the skin, laying eggs inside the burrows. The eggs hatch into the larval stage. The larval mites then leave the burrows, move up to the skin surface, and begin forming new burrows in healthy skin tissue. Development from egg to adult is completed in about 2 weeks. The lesions resulting from infestations by these mites are a consequence of the reaction of the animals’ immune system to the mites’ presence. Because of the intensity of the animals’ immunological response, it takes only a small number of mites to produce widespread lesions and generalized dermatitis. Animals show remarkable variation in the extent to which they react to the infestation, however. It is not uncommon to have healthy-looking animals in stanchions next to animals with lesions over much of their bodies.
Mange lesions often first appear around the tail, anus, thighs, udder, legs, and feet. The first sign of infestation usually is hair loss from the animals’ rubbing as they try to relieve the itching. As the infestation progresses, the lesions become larger and bloody or moist, followed by the formation of thick, crusty scabs. If left untreated, the lesions may eventually cover the animal’s body. When this happens, the entire hide may take on a thick, wrinkled appearance.
Sarcoptic mange mites are nearly invisible to the naked eye. In addition, mange is only one of several conditions resulting in somewhat similar symptoms. The only way to diagnose mange accurately is by having skin scrapings taken by a veterinarian or other trained professional. Scrapings are made with a scalpel by abrading rather deeply into the skin. The scrapings are then brought back to the laboratory and examined under a microscope for the presence of mites and for species determination.
Mange mites, like lice, are permanent external parasites that do not survive away from the host for very long. The best way to minimize the risk of introducing the mites into a herd is to be cautious when buying or boarding new animals. Avoid any animals that show visible skin lesions or that appear to be abnormally itchy or agitated. As an extra precaution, it is wise to segregate all newly purchased animals from the rest of the herd for several weeks and keep them under observation. A veterinarian should be called in if any of the animals show signs of unusual itchiness.
Several pesticides used for controlling cattle lice also are effective against chorioptic mange mites. These are shown in Table 4. Because of the severity of sarcoptic mange, it is regarded from a regulatory standpoint as a reportable disease. Therefore, the threshold for placing a herd under quarantine is the discovery of a single mite on one animal.
Once a herd has been placed under quarantine, animals may not be moved off the farm except for slaughter. Every animal in the herd must then be treated with high-pressure hydraulic spray equipment by certified pesticide applicators under the supervision of a state veterinarian. Either two or three treatments must be made, depending on the choice of insecticide used, with treatments spaced 7 to 10 days apart. Quarantine is lifted when post-treatment skin scrapings demonstrate the infestation has been eradicated. Because high-pressure spray equipment is necessary to ensure penetration by the spray into the skin, "home remedies" applied with low to moderate pressure gear of the type owned by many dairy producers are never successful.