RATE OF REINFECTION BY OPISTHORCHIS-VIVERRINI IN AN ENDEMIC NORTHEAST THAI COMMUNITY AFTER CHEMOTHERAPY

Patterns of re-infection by the human liver fluke, Opisthorchis viverrini, were studied over a period of 1 year after chemotherapy in a community in Northeast Thailand. Praziquantel (40 mg per kg body weight) was administered to 808 subjects; 88.4% of those examined after 2 weeks had negative stools. Within 1 year of treatment, however, 87.7% of the cured subjects who were re-examined had become re-infected, and 51.5% had infections of at least moderate intensity (1 epmg of faeces), in comparison with 72% of the same group before treatment. Those with high pre-treatment intensities of infection tended to have heavier intensities of re-infection, indicating that some people are predisposed to heavy infections. The rate of re-infection of those with heavy pre-treatment intensity of infection was about twice that of those who were negative or had only light infection before treatment. The rate of re-infection was markedly higher than concurrently and previously measured natural incidences of infection. These findings suggest that chemotherapy would have to be applied several times a year in order to control opisthorchiasis, and that it might be most cost-effective to preferentially treat heavily infected individuals.