[Biological and parasitic variations in horses infested and reinfested by Trichinella spiralis]

Seven mares were infected with 20,000 Trichinella spiralis larvae; 2 of them were reinfected 22 wk later with the same amount of larvae. The course of infection in horses was assessed by serology (ELISA), biochemistry (aldolase activity), parasitology and histopathology. In each animal, infection was followed by a significant rise in specific antibody titers culminating at 5-10 wk post-infection (pi) and decreasing thereafter. Reinfection was followed by a slight rise in antibody levels. Aldolase activity increased during the first infection, but was not modified by reinfection. The parasite burden was maximum 20 wk pi (24-145 larvae/g according to localisation) and was very low at 52 wk pi (0.4-5 larvae/g). Compared to mares infected only once, the number of parasites in the reinfected animals was similar 28 wk pi but much lower 40 wk pi. Moreover, 6 wk post-reinfection, the larvae were surrounded by a large inflammatory granuloma which could have been caused by larvae from the reinfection batch. These experiments confirm the susceptibility of horses to Trichinella spiralis and the rapid disappearance of specific antibodies which prevents usual serological methods from being used in the diagnosis of infected animals. Reinfection could help the horse to eliminate the larvae more rapidly.