Introduction

Bovine besnoitiosis/bovine elephantiasis/bovine anasarque is a protozoal disease of cattle. Besnoitia besnoiti infections cause economic losses to cattle owners in endemic areas due to mortality, loss of condition, low market value and temporary or permanent sterility. Besnoitia besnoiti is a coccidian parasite endemic in many tropical and subtropical areas where it causes both acute and chronic bovine besnoitiosis leading to significant economic constraint to commercial cattle production. Cattle regardless of breed, sex and age are affected, although clinical disease occurs rarely in calves less than 6 months of age. The first recorded cases of bovine besnoitiosis were described in southern France by Besnoit and Robin (1912). Recently, besnoitiosis has been recognized as an emerging disease in European countries such as France, Portugal, Spain, Germany and Italy (Gottstein et al., 2009) and there is evidence of an increased number of cases and geographic expansion of the disease based on epidemiological data. The occurrence of the disease is usually sporadic, and only a small proportion of infected animals develop clinical disease. In the acute stage of disease, parasitic tachyzoites invade blood vessels of the skin, subcutaneous tissues, fascia and testes causing widespread vasculitis and thrombosis. The result is a severe generalized reaction which is accompanied by oedema of the skin and acute orchitis. During the chronic stage, large numbers of tissue microcysts containing bradyzoites are formed. The most striking features of this stage are thickening, wrinkling and hair loss of the skin, accompanied by anorexia and severe weight loss. Male sterility or impaired fertility is a common sequele in breeding bulls, and is one of the most negative aspects of the disease in animals that survive the acute and chronic stages of infection (Sekoni et al., 1992; Cortes et al., 2005). Although mortality rate is low, a significant proportion of affected animals suffer loss of productivity and bulls are frequently rendered permanently infertile. The complete life cycle of the parasite remains unknown, although seasonal presentation of the disease (mainly in summer and in beef cattle while they are on pastures) suggests an important role for horizontal transmission by either direct contact, through natural mating or through mechanical transmission by blood-suckling arthropods (Castillo et al., 2009). At present, bovine besnoitiosis has not been reported to infect humans.

Manifestation and Effects

Typical clinical cases of bovine besnoitiosis appear in two distinct sequential stages: the acute anasarca stage, which is mainly associated with proliferation of endozoites in blood vessels, and the chronic scleroderma stage, which is mainly associated with cyst formation. The severity of the disease may vary between mild and severe and even death of seriously affected animals. Many infected animals remain asymptomatic and the only sign of the disease is the presence of cysts in the sclera and conjunctiva and/or the vulval area in cows. Initially the infection is characterised by hyperthermia and non-specific clinical signs, such as depression, swelling of superficial lymph nodes and loss of weight. Simultaneously, tachyzoites invade endothelia of blood vessels and subsequently oedema appears as a consequence of vascular damage. Oedema in joints causes pain during movement and may progress to permanent posterior lameness. This phase of the infection is known as the acute anasarca stage, and it is followed by chronic scleroderma stage. Very characteristic, macroscopically visible tissue cysts develop inside cells of the subcutaneous connective tissue and may be visualized by clinical inspection in the sclera and conjunctiva and vulval regions. With the disappearance of oedema, a progressive thickening, folding or wrinkling of the skin, alopecia, hyperkeratosis (known as elephant skin) are noticed, with the eventual shedding of epidermis. Sterility in males is caused by a necrotizing orchitis. Death may occur in both the anasarca and scleroderma stages of the disease, regardless of the sex of the animal. Animals may be culled after severe deterioration of body condition and loss of commercial value.

Diagnosis and Control

A number of diagnostic tests such as cytology, histopathology (Bigalke, 1968) , serology (Cortes et al., 2006; Fernandez-Garcia et al., 2009; Alvarez-Garcia et al., 2009;) and PCR testing (Cortes et al., 2007) are available for the diagnosis of the disease. During the first weeks of infection, acutely infected animals may be difficult to be accurately diagnosed clinically due to non-specific signs. The characteristic clinical signs appear with the development of tissue cysts during the chronic stage, when the clinical inspection is very useful to detect affected animals. Skin biopsies to confirm the existence of tissue cysts, examining the sample by trichinelloscopy plates and histopathology are good methods to confirm the disease. Serological tests (ELISA and Western blot) could be useful tools to detect asymptomatic/sub-clinical cattle. There are not any effective drugs or vaccines available to control the disease although a live-attenuated vaccine has been used in certain parts of the world (Basson et al., 1970). In South Africa, in an extensive field trial on farms where the disease was severe, Bigalke et al (1974) found that 100% of the cattle were protected from the clinical form of the disease over an observation period of 1 to 4 years when inoculated with a blue wildebeest strain of B. besnoiti vaccine. However, reliable diagnosis together with herd-management measures to avoid that non-infected herds acquire the infection due to trade with infected animals are the only available measures for control of the disease in most of the countries.

References

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