Besnoitiosis

Previous authors: R D BIGALKE AND L PROZESKY

Current authors:
W U BASSO - Senior Research and Teaching Associate, Head of the Veterinary Parasitology Diagnostic Section, Dipl. EVPC, EBVS® European Veterinary Specialist in Parasitology, Institute of Parasitology, Vetsuisse Faculty, University of Bern, Bern, 3012, Switzerland

GENERAL INTRODUCTION: COCCIDIA

Introduction

Besnoitiosis is a disease of domestic and wild animals caused by several species within the genus Besnoitia (Protozoa, Apicomplexa, Sarcocystidae). To date, 10 Besnoitia spp. have been named: B. besnoiti, B. bennetti, B. caprae, B. tarandi, B. jellisoni, B. akodoni, B. darlingi, B. wallacei, B. oryctofelisi and B. neotomofelis, with particular host ranges.^{31, 32, 33, 35, 36, 100.} (Table 1). Among these, Besnoitia spp. affecting ungulates: B. besnoiti (cattle and other bovids) B. caprae (goats), B. tarandi (reindeer) and B. bennetti (equids) have the greatest significance, as they are responsible for economically important diseases in some regions worldwide.

Bovine besnoitiosis is a relatively common disease of cattle in Africa and in some countries in Europe and Asia. It is caused by B. besnoiti, a protozoan parasite described in 1912 by Besnoit and Robin in a chronically infected cow in France.⁹ Severe, mild and inapparent forms of the infection may occur in cattle. The severe form is characterized by an acute stage with fever and oedema, as well as orchitis in bulls, which is followed by a chronic stage with thickening, hardening and folding of the skin, alopecia, hyperkeratosis, and severe loss of bodily condition. Nevertheless, in most animals, the infection remains clinically inapparent.

Although cattle may die from the disease during the acute (“anasarca”) or chronic (“scleroderma”) stages, the mortality rate is generally low. Of more importance are the debility, the possible sterility of bulls (which is usually permanent if the animal has shown frank clinical signs) and the down-grading of carcasses in abattoirs, due to trimming, or even the condemnation of carcasses resulting from the presence of cysts in the fasciae and intermuscular connective tissues.

Caprine besnoitiosis, caused by B. caprae, was also recognized as being economically important in goats, mainly in Kenya and Iran, where the disease is characterized by scleroderma, alopecia and the presence of large numbers of cysts in sites similar to those observed in cattle.^{19, 20, 81}

Equine besnoitiosis is caused by B. bennetti. The first records of this disease were from France⁵⁷ and Sudan.⁸  In South Africa, clinical B. bennetti infections were recorded in horses and donkeys, and subclinical infections in mules and zebras (Equus burchelli)^{11, 83, 93} Clinical B. bennetti infection was also reported in donkeys in the US.³¹ Recently, antibodies against Besnoitia spp. infections were detected in 16 (2.9 per cent) horses, 13 (15.3 per cent) donkeys and 22 (26.5 per cent) mules in a serosurvey in Spain using ELISA for screening and western blot as confirmatory test. However, parasite isolation and/or molecular techniques are still needed to determine which Besnoitia spp. might be present in Spanish equids.⁵⁴

Bovine besnoitiosis is a much more common disease than caprine or equine besnoitiosis and has therefore been studied more comprehensively. Bovine besnoitiosis will thus form the basis of the descriptions in this chapter and be compared to the disease in goats and equids where appropriate.

Aetiology and life cycle

Bovine besnoitiosis is caused by Besnoitia besnoiti. It is classified together with the closely related protozoan parasites Toxoplasma, Neospora and Sarcocystis within the group of the cyst-forming coccidia, in the taxon Apicomplexa, family Sarcocystidae.^{29, 67, 85}

It is suspected that B. besnoiti, like other cyst-forming coccidia, has an indirect life cycle with a carnivore as a definitive host, and domestic and wild bovids (e.g. antelopes) playing the role of intermediate hosts. However, the life cycle of B. besnoiti needs further elucidation and a definitive host, which sheds oocysts after ingestion of infected tissues, could not be conclusively identified so far.^{5, 27, 84}

The domestic cat is the definitive host of four of the ten described Besnoitia spp. (i.e. B. darlingi, B. wallacei, B. oryctofelisi and B. neotomofelis.^{32, 36, 41, 100} (Table 1). Based on a single report from the former Soviet Union,⁸² domestic (Felis catus) and wild cats (Felis libyca) were first assumed to also serve as definitive hosts for B. besnoiti, but this fact could not be confirmed in later experiments feeding cats with skin and/or tissues from infected cows containing abundant B. besnoiti cysts.^{5, 27, 84}

Carnivores that have been tested and could not be confirmed as definitive hosts of B. besnoiti so far include 13 species of mammals (domestic dog, domestic cat, serval (Leptailurus serval), jungle cat (Felis chaus), caracal (Caracal caracal), small spotted genet (Genetta genetta), marsh mongoose (Herpestes palludinosus), lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), banded mongoose (Mungos mungo), black-backed jackal (Canis mesomelas), cape fox (Vulpes chama),  two species of carnivorous birds (marabou stork [Leptoptilos crumeniferus] and white-backed vulture [Pseudogyps africanus], and six species of snakes.^{5, 27, 84} Unfortunately, oocysts shed by some of the experimentally inoculated...