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

Abstract

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.

Experimental model in rats for study on transmission dynamics and evaluation of Clonorchis sinensis infection immunologically, morphologically, and pathologically

“…Nine rats were successfully found with one adult worm in extrahepatic bile duct and with pathological changes (infection rate was 90%, data not published). The infection rate will be higher for human beings than rats, for rats were known to highly resist C. sinensis during reinfection (Sohn et al 2006;Zhang et al 2008); whereas, human develops immunotolerance to C. sinensis. Up to now, little was reported about the least infection dose of pathogens.…”

Changing Patterns of Serum and Bile Antibodies in Re-infected Rats with Clonorchis sinensis

“…This finding suggests that previous infection affords poor protection against reinfection or super-infection in humans. However, rats are known to develop near-complete resistance to re-infection or superinfection by C. sinensis [7,8]. Although the mechanism of resistance to re-infection is unknown, it has been suggested to involve an immune-related host response [8,9].…”

“…However, rats are known to develop near-complete resistance to re-infection or superinfection by C. sinensis [7,8]. Although the mechanism of resistance to re-infection is unknown, it has been suggested to involve an immune-related host response [8,9]. It was observed that rats immunized with crude antigens of C. sinensis had high serum IgG levels but exhibited no protection against infection [10].…”

“…Nude and immunosuppressed rats lose resistance to C. sinensis but splenectomized rats do not. Furthermore, immunization of rats with C. sinensis antigens induces no resistance to re-infection [8]. There have been several vaccine trials using DNA vaccines that encode fatty acid-binding or a cysteine proteinase and a tegument protein vaccine, although these vaccines were found to provide only partial protection [11][12][13].…”

“…There have been several vaccine trials using DNA vaccines that encode fatty acid-binding or a cysteine proteinase and a tegument protein vaccine, although these vaccines were found to provide only partial protection [11][12][13]. These findings suggest that the resistance of rats to re-infection by C. sinensis is linked mainly to local immune responses in the bile duct [8].…”