Schistosoma japonicum infection in the pig as a model for human schistosomiasis japonica

Valuable information on human schistosomiasis japonica has been provided using primates and experimental rodent hosts. However, major drawbacks such as high costs and ethical concerns for the primate models and large biological deviations for the rodent models have led to the search for more appropriate models. Recent data on the pig indicate that this natural host for Schistosoma japonicum might be a realistic alternative. As only very few research groups have investigated the S. japonicum/pig model, the present review mainly deals with the experimental methods and the major host/parasite findings obtained from the authors own research group. With emphasis on a critical evaluation of the work, the results are compared to the scarce information existing on human schistosomiasis japonica. Like in humans, S. japonicum establishes mainly in the large intestinal veins, with high faecal egg counts during the acute phase of infection, which varies greatly within and between days. Concomitant resistance is another shared feature, but studies in pigs have indicated that the phenomenon is more complex than generally thought. Clinical signs as eosinophilia and diarrhoea with mucus and blood in the acute phase of infection and hepatomegaly, increased portal diameter, periportal fibrosis and ascites in chronic infections are common findings in both humans and pigs. Low protein diet aggravates the disease in pigs by increasing the establishment rates, the faecal egg excretion and the morbidity. A 100% cure rate is achieved when treating S. japonicum infected pigs with praziquantel at 40 mg/kg, and 4 weeks post treatment pigs remain resistant to reinfection. Lastly, human congenital S. japonicum infection has been confirmed in pigs but the implications of such infections for the pathogenesis of schistosomiasis japonica remain to be investigated.