Schistosoma japonicum in the pig: a new technique for estimation of intestinal tissue egg counts.

This study introduced a new method for estimating intestinal tissue Schistosoma japonicum egg counts, based on scraping of the mucosal layer of different sections of the intestines. Twenty-eight Danish Landrace/Yorkshire/Duroc crossbred pigs were divided into 3 groups of 15, 5 and 8 pigs, respectively. Pigs were fed either a high- or low- protein diet and were infected by an intra-muscular or per-oral route of infection with doses of either 1,000, 1,500 or 3,000 S. japonicum cercariae. The pigs were killed 9-11 weeks post infection. For all 28 pigs the intestines were divided into 3 sections: cecum, colon and rectum and the entire mucosa was scraped off the serosa of each section and homogenized. Subsequently, samples corresponding to 5 g homogenised mucosal tissue were digested and egg counts were determined and correlated to liver egg counts. In order to compare the relative distribution of eggs in the mucosa and the serosa, small intestinal wall subsamples formerly taken from each section from a subgroup of 5 pigs were homogenized and egg counts determined for both the mucosa and serosa. The number of eggs were significantly higher in the mucosa than in the serosa. Egg counts estimated from digestion of mucosa subsamples either over or underestimated egg counts based on scrapings of the entire mucosa when compared, reflecting the very patchy distribution of S. japonicum eggs in the intestinal wall. Correlating liver egg counts with the number of eggs based on scrapings from the entire mucosa from cecum, colon and rectum, respectively, significant correlations were found for 2 out of 3 groups of pigs. The present study revealed that estimating intestinal tissue egg counts based on scrapings of the entire mucosa is a reliable and convenient approach, nicely supporting the liver tissue digestion approach. In addition, a reduction of the processing time of intestinal tissue in general was achieved due to the very simple scraping technique.

The population dynamics of cercariae of Schistosoma japonicum in Oncomelania hupensis.

The population dynamics and production of cercariae of Schistosoma japonicum in Oncomelania hupensis are reported. The experiments covered the whole life span of positive snails and different intervals of cercariae shedding. The results indicated that two patterns of the dynamics of cercariae shedding had been found in the life span of positive snails. The first was a long-time interval (4-7 days) and progressive decline pattern. The cercariae shedding of positive snails lasted 18-19 weeks in males and for 32-33 weeks (once a week). The second was a short-time interval (1-3 days) and continued release pattern. The cercariae shedding of positive snails lasted for 20-36 days (every day shedding). Shedding cercariae stimulate cercariae development.

Susceptibility of Oncomelania hupensis subspecies to infection with geographic strains of Schistosoma japonicum.

Subspecies of Oncomelania hupensis were exposed to infection with zoophilic and anthropophilic strains of Schistosoma japonicum. The snails were Philippine O. h. quadrasi from the islands of Bohol, Leyte and Mindanao, O. h. formosana from Changhua and Ilan, and O. h. chiui from Taiwan, O. h. hupensis from China, O. h. nosophora from Japan and O. h. lindoensis from Indonesia. Anthropophilic strains of S. japonicum were from Bohol and Leyte in the Philippines, China, Japan and Indonesia. The zoophilic strains were from Changhua and Ilan, Taiwan. All geographic strains of the parasite developed exceptionally well and produced cercariae in 32-50% of O. h. chiui and 5-43% of the natural snail hosts. Development in other subspecies of snails with geographic strains of the parasite were variable. Only a few O. h. formosana (Changhua) could be infected with the parasites from other geographic areas and only one O. h. quadrasi each from Mindanao became infected with the Bohol and Changhua strains of S. japonicum.

Further studies on the susceptibility of new Taiwan foci of Oncomelania hupensis to geographic strains of Schistosoma japonicum.

Two known colonies of O.h chiui in Alilao and of O.h. formosana in Changhua and four new foci of snails in Nantou, Chiayi, Hualien and Taitung on Taiwan were exposed each to 5 miracidia of Changhua Zoophilic strain and Chinese, Philippine and Indonesian anthropopilic or human strains of S. Japonicum. The results showed that all four new foci demonstrated various degrees of susceptibility to this parasite. Infectivity of Chinese strain of S. japonicum in 4 new foci of snails is reported for the first time. Changhua race of O. hupensis was also found slightly susceptible to Chinese strain of the parasite. The average infection rate to both zoophilic and human strains of S. japonicum was 39.0%, 14.5%, 10.8% and 9.8% for Taitung, Chiayi, Hualien and Nantou snails respectively. Susceptible snails now been found in 7 counties and if by chance human pathogenic strains of the parasite were accidentally introduced into Taiwan, a public health problem could possibly develop.