Factors in the resistance of rats to re-infection and super-infection by Clonorchis sinensis.

Rats develop resistance to re-infection by Clonorchis sinensis while humans do not. We investigated factors involved in the development of resistance to re-infection and super-infection in rats. Sprague-Dawley rats were infected by C. sinensis metacercariae and treated with praziquantel, then re-infected after immune modulation. The rats were also subjected to super-imposed infection after primary infection. Resistance to re-infection was observed by lowered rates of worm recovery after various durations from treatment; 1% at 5days and 24.4% at 11months vs 56.2% in the control. Similar significant resistance was observed in the super-infected rats after 3weeks of primary infection. The re-infected or super-infected worms grew very slowly and remained immature. Resistance disappeared in immune-suppressed and nude rats but not in splenectomized rats. Immunization with antigens of C. sinensis produced no resistance. Local tissue reaction and immune response in the infected bile duct may play an important role in the resistance, although the crowding effect may also be implicated in resistance in super-infected rats.

Sexual development of Taenia solium in hamsters from rodent-derived cysticerci.

In order to determine whether Taenia solium can be maintained in the laboratory using rodents as definitive hosts, six nude rats, 20 immunosuppressed Mongolian gerbils and 20 immunosuppressed Syrian hamsters were each inoculated through a stomach tube with three cysticerci recovered from SCID mice. No adult worms of T. solium were found in the intestinal tract of any of these 46 rodents. In addition, five immunosuppressed Syrian hamsters were fed with the same number of cysticerci enclosed in rodent muscles from SCID mice. Two of these hamsters were found to be infected 40 days post-infection, each harbouring a sexually developed worm in the intestinal tract. Although no eggs were produced, prepatent infections may be possible if a longer time was allowed for worm development. Moreover, the maintenance of the life cycle of T. solium in the laboratory using the rodent model can be established.

Survival of Onchocerca volvulus in nodules implanted in immunodeficient rodents.

Onchocerca volvulus is an obligate human parasite, and its study has been difficult due to an inability to maintain it outside the human host. We report the successful transplantation of onchocercomata containing living adult O. volvulus worms into immunodeficient C.B.-17.scid/scid (scid) mice or athymic rnu/rnu (nude) rats. Living, motile worms containing viable microfilariae were present in onchocercomata recovered from scid mice or nude rats for up to 20 wk, establishing a novel animal model for future investigation of O. volvulus.