|
Besnoitiosis: Introduction |  |
| Besnoitiosis is a protozoan disease of the skin, subcutis, blood vessels, mucous membranes, and other tissues. |
| Etiology and Transmission: |
| The causal agent of the cutaneous disease is
Besnoitia
besnoiti
in cattle and
B
bennetti
in horses and burros.
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 antelope; an unidentified
Besnoitia
sp
has been found in goats in Iran, New Zealand, and Kenya. Wildlife in Australia and blue duiker, impala, and blue wildebeest in Africa have been affected.
B
besnoiti
has been reported from southern Europe, Africa, Asia, and South America, but it has not been reported in cattle in North America.
B
bennetti
has been reported from Africa, southern France, Mexico, and in 2 imported burros in the USA. |
| These
Toxoplasma
-like organisms multiply in endothelial, histiocytic, and other cells and produce characteristic large, thick-walled cysts filled with bradyzoites. |
| Experimental cyclic transmission with intestinal sexual stages in a definitive host—the cat—has been reported for
B
besnoiti
,
B
wallacei
, and
B
darlingi
. Transmission of
B
besnoiti
from cattle to cats has not been substantiated by subsequent studies. Biting flies (eg, tsetse) or ticks may transmit
B
besnoiti
mechanically from chronically infected cattle; some
Besnoitia
spp
can be transmitted artificially to suitable hosts by needle inoculation of tissues that contain cysts. Contamination of water or feed by infected cat feces are other possible routes of transmission. Individual isolates appear to be fairly specific for intermediate hosts. |
|  |
| Clinical Findings: |
| Infected cattle often show no clinical signs other than a few cysts in the scleral conjunctiva. Illness begins with fever followed by warm, painful swellings ventrally (anasarca). Swollen lymph nodes, diarrhea, inappetence, 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. |
| A diagnostic finding is the appearance of cysts in the scleral conjunctiva and nasal mucosa. Diagnosis can also be made by finding crescent-shaped bradyzoites in skin scrapings, biopsy, or conjunctival scrapings. |
| 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. |
| |
| Prevention and Treatment: |
|
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 and lower market value, and damage to the hide. |
| In some countries, cattle are immunized with a live, tissue-culture-adapted vaccine. Affected animals should be isolated and treated symptomatically. Reduction of biting insects and ticks also may reduce transmission. In limited studies of
B
besnoiti
in rabbits, both antimony and sulfanilamide complex prevented cyst development. Oxytetracycline also may have some therapeutic value if given early in the course of the disease. |
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