Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/29/2004
Publication Date: 8/1/2005
Citation: Elsheikha, H.M., Mackenzie, C.D., Rosenthal, B.M., Marteniuk, J.V., Steficek, B., Windsor, S., Saeed, M.A., Mansfield, L.S. 2005. A natural infection of miniature donkeys with the sarcoccoidal protozoa besnoitia bennetti. Journal of Parasitology.91(4):877-881. Interpretive Summary: Parasite species of the genus Besnoitia form visible, white nodules in the muscles, connective tissue, and various organs of herbivorous hosts. Macroscopic cysts, which can attain sizes large enough to be readily seen and felt, can cause livestock carcasses to be condemned. The clinical spectrum can range from inapparent infection to severe disease, resulting in weight loss, depression, systemic problems, often complicated by bacterial superinfection. The health consequences of human infection with parasites of this genus has yet to be defined, although concern is raised by the serious public health risk posed by Toxoplasma gondii, a related coccidian parasite. Here, a rare outbreak of Besnoitia bennetti is described in donkeys. Parasites ascribed to this species have been recognized in various equids. This manuscript provides a careful account of the clinical, epidemiological, morphological, and genetic characteristics of the parasites implicated in this outbreak. ARS's contribution includes the first genetic characterization of this parasite, which may aid future diagnostic efforts and which should also provide a means to determine what carnivore may expose equids to risk of such infection.
Technical Abstract: Besnoitiosis is an uncommonly detected protozoal infection of a wide range of species, including equids. Fourteen miniature donkeys (Equus asinus) in a herd of 38 animals resident in a mid-Michigan farm presented with clinical signs of besnoitiosis. These animals showed different intensities of an essentially similar clinically picture, which included cysts (¿pearls¿) in the ocular sclera, the sub-mucosa of the inner lip, and the eyelids and external nares of some animals. Focal areas of rough lichenified skin with raised small dermal nodules were present on the head, the base of the ears, the shoulders and in the inner aspects of the hind limbs as well as the perineal and perivulvar regions. These lesions did not appear to be pruritic. Examination by light and ultrastructural microscopy of isolated scleral cysts and skin biopsies showed the presence of protozoal organisms consistent in morphology with that of Besnoitia bennetti bradyzoites. The common histopathological change seen was the presence of many 100-200 um diameter, thick walled, Besnoitia cysts together with a chronic cellular response. Minor peri-vascular cellular accumulations of plasma cells, lymphocytes and scattered eosinophils were present around some vessels. Degenerating cysts, when present, were involved in granulomatous cellular responses and were most common in the animal undergoing treatment with trimethoprim and sulphamethoxazole (1.0mg/Kg and 20mg/Kg daily for 42 day); this treatment resulted in a some clinical improvement. Although this infection has been reported infrequently in equids in Africa as well as in the USA, this is the first report of a significant outbreak in a herd of donkeys. Besnoitiosis should therefore be considered more often in the differential diagnosis of cutaneous nodular diseases in the donkey. The presence of the distinct ocular signs (scleral pearls) together with the buccal sub-mucosal cysts and the nodular dermal lesions appear to be strong and consistent clinical indicators of the presence of this infection.