Strain complex of Schistosoma japonicum in the mainland of China.

The present paper deals with studies on the characteristics of Schistosoma japonicum isolated from five localities in the mainland of China. The following items were observed and compared including morphometric data, susceptibility of six mammalian hosts, prepatent period, compatibility between larvae and snail hosts, size of hepatic granuloma produced by eggs, immunoreactions in experimental animals, sensitivity to praziquantel, SDS-PAGE protein pattern and its antigenicity analysis, DNA hybridization and genetic variation and differentiation by analysis with multilocus enzyme electrophoresis. By means of these multidisciplinary methods, from morphological to molecular level, the following conclusions may be drawn from our results. The evidence indicates firstly that S. japonicum in the mainland of China comprises a strain complex with several components of geographically distributed strains. At least four distinct strains exist, ie Yunnan, Guangxi, Sichuan and Anhui-Hubei. Characteristics of each strain are distinct and the results of these studies lead to discussion on the problem of the intraspecific and interstrain differentiation of S. japonicum in the mainland of China.

Sensitivity of different isolates of Schistosoma japonicum from China to praziquantel.

Groups of C57BL inbred mice infected with each of the 4 different isolates, (Anhui, Hubei, Sichuan and Yunnan) of Schistosoma japonicum from the mainland of China were treated with praziquantel (PZQ) and the parasiticidal effects were compared. Worm reduction rate was recorded to assess systematically the sensitivity of 4 different isolates to PZQ in the mouse. Three dosage-levels of PZQ, ie 150, 230 and 310 mg/kg body weight in single doses were used. The worm development rates of control groups infected with schistosomes from Anhui, Hubei, Sichuan and Yunnan were 75.5, 81.8, 81.5, and 83.0%, respectively. At the dosage-level of 150 mg/kg, the worm reduction rates for the 4 different isolates were 36.0, 33.9, 25.5 and 35.6%, respectively. At the dosage-level of 230 mg/kg, the rates were 47.1, 46.0, 38.1 and 47.7%, while at the dosage-level of 310 mg/kg, they were 59.3, 58.6, 50.8 and 61.7%, respectively. The results indicated that the worm reduction rate of the Sichuan isolate was lower than that of the other three isolates, however, the differences were not statistically significant, suggesting that schistosomes of Anhui, Hubei, Sichuan and Yunnan isolates bear resemblance in drug response.

Parasitological and histopathological studies on rhesus monkeys infected with Chinese mainland strain of Schistosoma japonicum.

Fifteen rhesus monkeys were infected by cutaneous exposure each with 200 or 300 cercariae of Schistosoma japonicum. The dynamic distribution of schistosomula in the skin showed that 77-90% of them were found in the connective tissue, while 10-23% migrated in the hair follicles and sebaceous glands at different time intervals after cercarial penetration. Dead schistosomula recovered from the skin varied from 8.7% to 28.7%. The average rate of adult worm recovery was 74.4% and 61.3% in the 6th and 15th weeks of infection, thereafter the rate decreased to 32.3% and 9.0% in the 19th and 42nd weeks, respectively. The mean length of mature pair-worms was 13.2 +/- 2.3 mm in male and 18.0 +/- 1.9 mm in female 6 weeks of worm age. Afterwards the body length of females and their sexual gland diminished markedly. The mean prepatent period was 35.0 +/- 0.6 days. The average size of mature eggs in the feces was 86.6 +/- 5.4 x 64.3 +/- 3.6 microns, and the peak of eggs passage in the feces occurred between 7th and 15th weeks after infection, later on the number of eggs markedly decreased. Skin reaction to the primary infection was slight. The pathological changes observed in liver were chiefly cellular infiltration of portal spaces and the lesions produced by egg granulomas. The mean volume of single-egg granulomas of the productive stage in liver was 22.7 +/- 10.5 mm3 x 10(-3). The most intensive damages in the gastro-intestinal tract were observed in the large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of different isolates of Schistosoma japonicum from China in the final hosts.

The present paper deals with the susceptibility of common laboratory animals, such as mouse, rat, hamster, jird, rabbit and rhesus monkey, to infection with different isolates of Schistosoma japonicum in the mainland of China under laboratory conditions. With the exception of the rat, all the animals under study were permissive hosts for different isolates though their worm recovery rates varied. The mean body length of pair-worms of the Yunnan isolate was considerably smaller than that of the Anhui, Hubei, Guangxi and Sichuan isolates, and the percentage of male specimens with 7 testes in the Yunnan isolate was also significantly less than that in the other 4 isolates. Judging from the egg index (width/length x 100), the eggs of the Sichuan isolate were broad and short in shape, giving a high index; those of Guangxi and Hubei isolates were oblong, giving the lowest index; the other two isolates from Yunnan and Anhui, lay between these two extremes. The mean prepatent periods were longer in mice, hamsters and rhesus monkeys infected with Yunnan and Guangxi isolates, than those with Sichuan isolate. A dendrogram of the 5 isolates of S. japonicum was constructed on the basis of similarity coefficients by means of fuzzy cluster analysis on the biological characters mentioned above. Our results provide evidence of the existence of different strains of S. japonicum in the mainland of China as shown by comparative studies of their characteristics in the final hosts.

Compatibility between Oncomelania hupensis and different isolates of Schistosoma japonicum in China.

Oncomelania hupensis from six localities were used for infection with different isolates of Schistosoma japonicum in the mainland of China, ie Anhui in the east, Hubei in the center, Guangxi in the south, Sichuan in the West, Yunnan in the southwest and Fujian in the southeast. Snails from Anhui and Hubei were readily infected with the local isolate of S. japonicum and cross infection also took place readily between the snails and the schistosomes from these two places. Snails from Sichuan and Yunnan were refractory to infection with schistosome isolates from Hubei and Anhui, but the isolates from Sichuan and Yunnan were able to develop in snails from Hubei and Anhui. Though the Guangxi isolate developed readily in both Anhui and Guangxi snails, the average precercarial period in the former was significantly longer than in the latter. None of the other snails from Sichuan, Yunnan and Fujian became infected. On the other hand, snails from Guangxi infected with Anhui parasites also had a longer precercarial period than that in Anhui snails. Snails from Fujian were readily infected with the isolates from Anhui and Yunnan. The present results suggest that there might be different geographic strains of S. japonicum and their Oncomelania snail hosts in the mainland of China.