Immunity to coccidiosis after treatment with toltrazuril

Some characteristics of immune sera after toltrazuril treatment which may b e involved in the enhancement of immunity are as follows. Firstly, toltrazu ril acts against all intracellular parasite stages from I to 168 h post-inf ection: intracellular schizonts of generations I, II and III and also intra cellular gamonts. These damaged stages remain in the host cell for a prolon ged time, during which they act as antigens which can be recognised by the immune system. Secondly, immune sera during therapeutic treatment with tolt razuril show a high antibody titre of 1:100 and 1:250 in IFAT after challen ge. In the immunoblot, these sera show a strong reaction with low molecular protein fragments between 14 and 20 kDa. Toltrazuril does not interfere wi th the process of parasite protein recognition by the immune system during infection. Thirdly, there is a tendency for a higher IgG response after tre atment with toltrazuril. Fourthly, a higher antibody titre in IFAT, immunob lot and ELISA correlates with a higher reduction in oocyst excretion, lesio n scoring and increased weight gains in toltrazuril-treated animals.