The Biology of the Goat
Mites
Mites belong to the Arachnoidea class which includes spiders and ticks. Like spiders, mites have 4 pair of legs. Mites are usually microscopic in size and their body and legs are covered with long hairs.Goats can be host to three different types of mites. Psoroptes and Chorioptes mites are non-burrowing. Sarcoptic mites burrow into the skin.
At the end of the legs of all three types are thin structures called pedicles which have a sucker at the end. The appearance of these pedicles is used to identify the type of mite. The pedicles of the Psoroptes type of mite are long and jointed. Sarcoptic mites also have long pedicles but they are not jointed. The pedicles of Chorioptic mites are short.
Psoroptes mites
Infections of Psoroptes mites, called mange or scab mites usually starts on the shoulders, back or the tail area since they prefer areas that are well covered by hair. Later in the course of infection they can spread to any other part of the body. Psoroptes cuniculi mites prefer to live inside the ears. This is a very contagious mite and is considered to be reportable in Cattle and sheep in some states of the US.Psoroptes mites do not burrow into the skin. These mites have piercing mouth parts that they use to puncture the skin and to suck lymph. This stimulates an immune reaction by the host. The area will swell and serous fluid will seep to the surface creating a crust and scabs. The hair or wool will fall out or the goat or sheep will pull it out when biting at the very itchy lesions.
The Psoroptes mites do not prefer to live on the bare crusty patches so they will migrate to the edges extending the infection outward. Skin scrapings to identify this mite needs to be made at the edges of the crusty lesions. Long standing infections can cause weight loss. These mites are most active in the autumn and winter. Psoroptes mites are identified by their long, segmented pedicles.
Life cycle
The life cycle of P. ovis which infects sheep is typical of most Psoroptes mites. The female lays eggs at the edges of crusty lesions. If laid close to the skin they hatch in 1 to 3 days. If the eggs are separated from the skin they take longer to hatch or may die.Larvae feed for several days after hatching then molt to a nymph stage. These nymphs will molt in another 3 to 4 days into young females or males. Usually about twice as many females than males form. Mating takes place shortly after the molt and lasts only for 1 day or less. The female mite will molt again about 2 days later then will begin laying eggs in another day. This whole cycle takes only 9 days after she first hatched from the egg. The female will live for 30 to 40 days, laying about 5 eggs every day.
Chorioptes mites
This type of mite commonly called a mange mite, causes tail or foot mange It does not burrow into the skin. Chorioptes mites are not species specific. Different species of this genus can be found on cattle, sheep and goats and the different species can interbreed with each other. Although the species that usually infect goats is called Chorioptes caprae, it is probably the same as the species that infects, sheep and cattle. Chorioptic mites can be identified by their very short, unjointed pedicles.Infections of Chorioptes caprae the species that infects goats usually begins on the lower legs, later spreading to the hindquarters. Infections cause itching, and crust and scab formation. The life cycle is very similar to Psorptes mites, but is completed in about 3 weeks.
Sarcoptes mites
This type of mange mite burrows into the skin often spending the entire life cycle within burrows. Sarcoptes scabei is the species that infects most mammals. An infection begins in hairless regions or regions of short hair usually on the face or ears. Sarcoptes mites have long unsegmented pedicles.Life cycle
The female Sarcoptes scabei burrows into the skin, and lays 40 to 50 eggs, 4 to 5 a day, in the tunnels. The eggs hatch in 3 to 5 days producing six-legged larva. The larva leave the breeding tunnels and wander on the skin or remain in the breeding tunnels and develop to the nymph stage. Those that reach the surface may die, or they can make shallow pockets in the skin tissue to feed and molt to several nymph stages which can also wander on the surface and make new pockets or extend the molting tunnels. Adult males and females form about 17 days after the eggs were first laid.The female remains in her moulting pocket until fertilized by a male then extends it into a breeding tunnel, or returns to the skin surface to create a new tunnel and then begins laying eggs. Mature females do not live much longer than a month. Wandering larvae, nymphs and fertilized females spread the infection on the host and to other hosts. They cannot survive off the host for more than a few days.
As they pierce the skin to feed on lymph fluid and skin cells they cause a great deal of irritation, itching, and scratching which worsens the condition. Crusts form on the skin and then the skin becomes thickened and wrinkled and the hair falls out. Lesions in the skin begin to develop in just a few days after infection, but the intense itching typical of Sarcoptic mite infection does not begin for a month or so later. The fecal pellets of the mite are responsible for the host inflammatory response.
These mites prefer areas where there isn't much hair such as the face of goats and ears although in long standing infections the mites can spread to all parts of the body.
The signs include bare skin, which is thick and wrinkled and covered in dry crusts. Early in the infection small raised red bumps and fresh exudate can be seen. To identify these mites in the microscope deep scrapings of skin must be made down to the point of drawing blood. It still might be difficult to find live mites in the burrows.