Experimental infection with Besnoitia besnoiti tachyzoites in calves and young bulls

Bovine besnoitiosis is considered as a re-emergent disease in Europe. No treatments or vaccines are available for disease control. Therefore, the development of animal models of infection is urgently needed. The aim of the present study was to develop an experimental model of B. besnoiti infection in cattle. Two experimental infections were realized. In experiment A, 12 Holstein Friesian 3-month old male calves were inoculated intravenously with either 3 different doses of tachyzoites (G1: 108 ; G2: 107 ; G3: 106 ) or with PBS (G4). In experiment B, 6 young bulls (14 months of age) were inoculated with the infection dose that showed the best results in experiment A (106 tachyzoites). In both experiments, temperature and clinical signs compatible with acute and chronic besnoitiosis were monitored daily and blood samples were collected regularly for antibody and parasitemia detection. The experiment A was followed up to 70 days post-infection (pi), whilst the experiment B lasted 115 days pi. At the end of the trials, animals were euthanized and tissues from skin, eyes, respiratory and reproductive tracts among others, were collected for lesions and parasite detection. Clinical signs compatible with acute phase, such as lymphadenopathy and fever were observed in both calves (from 12 hours pi until 7 days pi) and young bulls (from 6 days pi until 9 days pi). Parasitemia was detected sporadically in calves from G1 on days 4 (n=2) and 7 dpi (n=3); and in G2 on 7 dpi (n=1). However, no clinical signs characteristic of the chronic stage of the disease, such as tissue cysts, were detected. All infected animals seroconverted around 16-19 days pi and antibody levels remained high until the end of the trials. In calves, parasite-DNA was detected in conjunctiva, ocular sclera, epididymis, as well as skin of scrotum and carpal zone (n=10, 6 of which belonged to calves inoculated with 106 tachyzoites). However, in young bulls only 2 tissues (pampiniform plexus and testicular paren