Fatal toxoplasmosis in brown hares (Lepus europaeus): possible reasons of their high susceptibility to the infection

Brown hares (Lepus europaeus) trapped in the countryside and domestic rabbi ts were experimentally infected with Toxoplasma gondii (K7 strain) oocysts. Hares (n = 12) were divided into groups of 4 and infected with 10, 10(3) a nd 10(5) oocysts. Rabbits (n = 12) were infected in the same way. The exper imentally infected animals were monitored for 33 days after infection (p.i. ). Most of the infected hares demonstrated behavioural changes, and all of them died between 8 and 19 days p.i. Three of the rabbits demonstrated only clinical changes related to the concurrent pasteurellosis. The typical pat hological finding in the hares we,re haemorrhagic enteritis, enlargement an d hyperaemia of mesenteric lymph nodes, splenomegaly and multiple miliary n ecrotic lesions in the parenchyma of the liver and other organs. Pathologic al changes in the rabbits were less pronounced than in the hares. In rabbit brains, tissue cysts of the T: gondii were found. The incidence of ir: gon dii antibodies both in the hares and the rabbits was first ascertained on d ay 7 p.i. On day 12 p.i., antibodies were already found in all the animals infected. Antibody titres in indirect fluorescence antibody test (IFAT) usi ng the anti-rabbit conjugate wt:re markedly higher in rabbits than in hares . In all hares, T. gondii was isolated post mortem from the liver, brain, s pleen, kidney, lung, heart and skeletal muscles. Although I: gondii was als o isolated in all rabbits, it was not always isolated in all their organs. In all hares, parasitemia was demonstrated on days 7 and 12 p.i. The percen tage of rabbits with detected parasitemia was lower. In hares, a decrease i n the numbers of leukocytes during the infection was observed. No such decr ease was observed in the rabbits. The lymphocyte activity after the stimula tion with non-specific mitogens showed significant differences between the hares and the rabbits even before the infection. After the infection, the h ares infected with 10(3) and 10(5) doses and in rabbits infected with a 10( 5) dose showed a decrease of lymphocyte activity. Rabbits infected with a 1 0(3) dose showed an increase of the lymphocyte activity. While in hares tox oplasmosis was an acute and fatal disease, the infection in rabbits had sub clinical manifestations only and easily passed to a latent stage. The diffe rent courses of toxoplasmosis in the hare and the rabbit may be due to the differences in the natural sensitivity of the two species to the I: gondii infection or a negative impact of stress to the immune status of hares. (C) 2000 Elsevier Science B.V. All rights reserved.