Overview of Besnoitiosis

The most significant condition in domestic animals is that of cattle, in which B besnoiti causes economic loss through reduced milk production, infertility and sterility, skin lesions, and increased mortality; similar effects are likely with B caprae in goats in Africa, southern Europe, and New Zealand. Recent studies indicate that infection is being detected more commonly in cattle in Europe (ie, Spain, Portugal, Italy, Germany, Switzerland, Hungary, and Greece). B bennetti has been reported to be present in donkeys in Africa, southern France, Mexico, and in a number of locations in the USA. B bennetti is also found in horses, especially, but not only, those living in the tropics. B jellisoni and B wallacei have been described from rodents; B tarandi from reindeer or caribou; B darlingi from lizards, opossums, and snakes; and B sauriana from lizards. Viscerotropic strains of B besnoiti have been isolated from African antelopes; and serologic evidence of infection was detected in red and roe deer. Wildlife in Australia and blue duiker, impala, and blue wildebeest in Africa have been affected; to date it has not been reported in cattle in North America. A recent addition to these species and their hosts is B oryctofelisi in Argentinian rabbits.

It is thought that these parasites may have both definitive and intermediate hosts, and although the cat is often named as the likely candidate for the role of definitive host, this has not yet been clearly defined for most Besnoitia sp. Various animals, usually rodents or small mammals, such as woodrats and opossums, have been suggested as intermediate hosts.

These Toxoplasma/Neospora-like organisms multiply in endothelial, macrophage, and other cells and produce characteristic large, thick-walled cysts filled with bradyzoites. These, along with the oocyte stage in cats and the tachyzoite stage in other animals, are the infectious forms.

The true route(s) of transmission remains unclear despite many experimental and epidemiologic attempts. Experimental cyclic transmission with intestinal sexual stages in a definitive host—the cat—has been reported for B besnoiti, B wallacei, and B darlingi, and experimental transmission using genetically modified mice and tissue culture has been achieved with B oryctofelisi. Transmission of B besnoiti from cattle to cats has not been substantiated by subsequent studies. The suggestion that biting insects may transmit B besnoiti mechanically remains a possibility but has not been substantiated; Besnoitia spp can be transmitted artificially to suitable hosts by needle inoculation of tissues that contain cysts. Water or feed contaminated by infected cat feces are other possible routes of transmission.

Infected cattle often show no clinical signs other than a few cysts in the scleral conjunctiva or a localized, scaly, papular dermal change. Illness begins with fever followed by warm, painful swellings ventrally (anasarca). Swollen lymph nodes, diarrhea, anorexia, photophobia, rhinitis, and orchitis also are seen. Anasarca gives way to sclerodermatitis. The skin becomes hard, thick, and wrinkled and develops cracks that allow secondary bacterial infection and myiasis to develop; movement is painful. There is loss of hair and epidermis. In addition to the skin lesions, there may be focal, disseminated myositis, keratitis, periostitis, endostitis, lymphadenitis, pneumonia, periorchitis, orchitis, epididymitis, arteritis, and perineuritis. Severely affected animals become emaciated. Although mortality is low, convalescence is slow in severe cases. Severely affected bulls can become permanently sterile. Affected animals remain carriers for life. The disease in goats is similar to that in cattle. In horses, the clinical signs are similar but tend to be less severe or invasive. Infected donkeys, which are most commonly young (<2 yr old), also present with similar signs and symptoms, which are often more severe than those seen in horses.

The appearance of cysts in the scleral conjunctiva and nasal mucosa are useful diagnostic indicators. Parasitologic diagnosis is made by finding the crescent-shaped bradyzoites in biopsies or skin/conjunctival scrapings.

B besnoiti infections are economically important to cattle owners in endemic areas because of mortality (although usually <10%), sterility (which may be temporary or permanent), loss of condition, lower market value, and damage to the hide.

Although the route of transmission remains unclear, cattle are usually isolated and protected from biting insects and ticks to reduce transmission, and then treated symptomatically. In some countries, cattle are immunized with a live, tissue culture–adapted vaccine. Chemotherapy remains very limited and only minimally effective. Both antimony and sulfanilamide complex prevented cyst development by B besnoiti in rabbits, and oxytetracycline may have some therapeutic value if given early in the disease course. Clindamycin has been used to treat cats, but this has no positive effect on the stages present in other animals. Ponazuril has been found to be generally ineffective in infected donkeys.