Chorioptes bovis — chorioptic mange

The mange mite Chorioptes occurs on cattle and other domestic animals and wildlife around the world, including in Canada.  Probably each host species has its own species, sub-species or strain of the mite, and successful transfer of the mites from one host species to another happens very rarely.  The life cycle is entirely on the host, although adult Chorioptes, and perhaps other life cycle stages, can survive off the host, likely for several days, and perhaps several weeks, given supportive environmental conditions.  During feeding Chorioptes do not penetrate the skin but feed on skin debris.  Lesions are most common around the tail head region, although in dairy cattle they also occur around the coronary bands.  Chorioptes is not known to be zoonotic.

Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Acari
Order: Astigmata (Sarcoptiformes)

As well as the Order Astigmata, the Subclass Acari consists of the Order Ixodida containing the hard ticks (Family Ixodidae) and soft ticks (Family Argasidae), and several other Orders (Mesostigmata, Prostigmata and Orbatidae) containing the parasitic and free-living mites. Other members of the Order Astigmata of importance in veterinary medicine include Otodectes, Psoroptes and Sarcoptes.

In Canada, Chorioptes mites are found on cattle, horses and occasionally sheep. There is uncertainty if the mites on these various hosts are members of a single species, or whether each type of host has its own species. Even if they are all the same, transmission between host species seems not to be significant.

Adult Chorioptes bovis measure approximately 200-300 μm in length and can just be seen with the naked eye on a microscope slide, but not on the animal. Chorioptes bovis are surface mites and in the adult stage they have four pairs of long legs that extend past the body margin, and at the tip of some of the legs is a short, un-jointed pedicel (pretarsus) supporting a terminal "sucker".

Chorioptes bovis occurs on cattle in many parts of the world, including Canada. The mite is especially common on animals that are closely confined during the winter, for example dairy cows.

Chorioptic Mange in Sheep

Chorioptes mites have been recovered occasionally from sheep in Canada. Lesions are most common on the lower limbs and feet, and sometimes occur on the scrotum, which may lead to temporary infertility.

Chorioptic Mange in Goats

 

Characteristics of Chorioptes in goats are as for sheep, except that apparently scrotal infestations have been less commonly observed.

The entire life cycle of C. bovis occurs on the host. The mites live on the skin surface, where adult females lay eggs, which hatch to release a six-legged larva, which develops to the adult stage. The life cycle can be completed in a few weeks.

Life Cycle: Chorioptes bovis

Transmission of C. bovis is direct animal-to-animal or sometimes by fomites such as fences, scratching posts and grooming equipment. Experimental evidence indicates that adult C. bovis can survive for several weeks away from the host, but mite numbers decrease very rapidly during the first couple of weeks. There is circumstantial evidence that Chorioptes mites can survive in bedding for at least several days.

Cattle with very small numbers of mites may be normal, and clinical signs typical of mange are more common in the winter, particularly in confined animals. Unlike Psoroptes bovis, C. bovis does not penetrate the skin during feeding, but lives instead on skin debris. The activities of C. bovis on the skin surface can cause severe pruritus, with alopecia, oozing, crusting and sometimes ulcers. In cattle, Chorioptes most often affects the tail head region. In dairy cattle, it may also cause lesions around the coronary bands and in severe cases this can interfere with milk production.

History and clinical signs can be very helpful, but recovery of adult mites, or even fragments, and microscopic examination, confirms the diagnosis. The pedicels on the legs (short and un-jointed for Chorioptes) are the basis for differentiation from Psoroptes.

There are several endectocide products approved in Canada that are effective for chorioptic mange in cattle: eprinomectin (EPRINEX), doramectin (DECTOMAX), ivermectin (VARIOUS) and moxidectin (CYDECTIN). Only the topical (pour-on) preparations are effective for Chorioptes.  When using these products, it is essential to take note of milk withdrawal and slaughter delay requirements, if any.

Additional information on the products mentioned is available from the Compendium of Veterinary Products (Twelfth Edition, 2011), or from the manufacturers.

Effective control of Chorioptes bovis and chorioptic mange depends on the rapid isolation and treatment of infested animals, together with treatment of all contacts and, where possible, adjusting management practices to minimize transmission. This may include leaving areas housing infested animals empty for several weeks.  Laboratory work, together with anecdotal evidence from the field, suggest that under favourable Chorioptes mites can survive and remain infective in the environment for days and perhaps for weeks.

Human infestations with C. bovis have not been reported.