Spillover, hybridization, and persistence in schistosome transmission dynamics at the human-animal interface.

Zoonotic spillover and hybridization of parasites are major emerging public and veterinary health concerns at the interface of infectious disease biology, evolution, and control. Schistosomiasis is a neglected tropical disease of global importance caused by parasites of the Schistosoma genus, and the Schistosoma spp. system within Africa represents a key example of a system where spillover of animal parasites into human populations has enabled formation of hybrids. Combining model-based approaches and analyses of parasitological, molecular, and epidemiological data from northern Senegal, a region with a high prevalence of schistosome hybrids, we aimed to unravel the transmission dynamics of this complex multihost, multiparasite system. Using Bayesian methods and by estimating the basic reproduction number (R0 ), we evaluate the frequency of zoonotic spillover of Schistosoma bovis from livestock and the potential for onward transmission of hybrid S. bovis × S. haematobium offspring within human populations. We estimate R0 of hybrid schistosomes to be greater than the critical threshold of one (1.76; 95% CI 1.59 to 1.99), demonstrating the potential for hybridization to facilitate spread and establishment of schistosomiasis beyond its original geographical boundaries. We estimate R0 for S. bovis to be greater than one in cattle (1.43; 95% CI 1.24 to 1.85) but not in other ruminants, confirming cattle as the primary zoonotic reservoir. Through longitudinal simulations, we also show that where S. bovis and S. haematobium are coendemic (in livestock and humans respectively), the relative importance of zoonotic transmission is predicted to increase as the disease in humans nears elimination.

Recovery of Schistosoma haematobium ovum from Labeo rohita: first report from Pakistan.

Schistosomiasis, also known as bilharzia, is a parasitic disease caused by trematodes from the genus Schistosoma that can infect humans and animals. S. mansoni, S. japonicum, and S. mekongi all causes intestinal schistosomiasis except S. haematobium that causes urinary schistosomiasis. It is only specie which effects urinary system, it can affect liver, heart, lungs also but very rarely. Schistosoma haematobium is endemic to over 50 countries in Africa and the Middle East and Western Asia and may be fatal in HIV positive people. A number of reports from the African countries like Nigeria have been reported. A few cases are reported but in Pakistan it has never been reported before in native people. It is first time reported in Pakistan in the intestine of Rahu (Labeo rohita). The purpose of this study is to elaborate the approach of zoonotic agent by various other routes including the commonly available fish.

Hamster Weight Patterns Predict the Intensity and Course of Schistosoma haematobium Infection.

Although Syrian golden hamsters are widely used as hosts for experimental infection by Schistosoma haematobium , surprisingly little is known about the course of infection and associated intensity (as defined by measures of parasite burden). As such, we sought to define inexpensive, simple, noninvasive, and accurate methods for assessing and predicting the severity of disease in S. haematobium -infected hamsters in order to prevent premature hamster sacrifice and unexpected morbidity and mortality. Through monitoring the weight and behavior of infected hamsters, we determined that the weight-loss patterns of infected hamsters are highly correlated with commonly used measures of the severity of infection (i.e., numbers of eggs passed in the stool, worm burdens, and total egg yields). In contrast, we found no significant correlation between hamster weight-loss patterns and egg yields from liver and intestinal tissues. Our findings suggest that a more complex relationship exists among worm burden, fecundity, and egg passage in the feces than previously appreciated. Regardless, our data may be useful for workers seeking to optimize harvests of S. haematobium eggs and worms from infected hamsters for downstream applications.

Bulinus nyassanus is an intermediate host for Schistosoma haematobium in Lake Malawi.

At Cape Maclear on the Nankumba Peninsula, close to the southern end of Lake Malawi, Schistosoma haematobium is highly prevalent in the local people and many tourists become infected with this parasite each year. A 'Bilharzia Control Programme' was initiated in this area in August 1998, as a development collaboration between the Government of Malawi, the Danish Agency for Development Assistance (Danida), and the Danish Bilharziasis Laboratory. Although Bulinus globosus is a known host for S. haematobium, B. nyassanus has not previously been incriminated as an intermediate host. However, schistosome-infected B. nyassanus were discovered in surveys to identify transmission sites on the peninsula. Experimental infections of wild-caught B. nyassanus with S. haematobium proved successful and S. haematobium eggs were found in hamsters experimentally exposed to cercariae retrieved from schistosome-infected, field-collected B. nyassanus. These are remarkable observations since, although there are very few reports of diploid members of this species group being experimentally infected with S. haematobium, B. nyassanus is a diploid member (2n = 36) of the truncatus/tropicus group. Bulinus nyassanus is probably responsible for transmission in Lake Malawi, along rather exposed shorelines, devoid of aquatic macrophytes, with a substrate of sand or gravel.

Natural infection with schistosomes of the Schistosoma haematobium group in a dog in Zambia.

Post-mortem examination of an adult male Jack Russell dog from Zambia revealed that it was heavily infected with schistosomes. The dog had been admitted, with a history of retching, 4 days before its death. At necropsy, the liver was found to be enlarged, with multiple pin-point yellowish-white foci scattered diffusely throughout the organ. Multiple pin-point recent and old haemorrhages were seen on the mucosal surface of the gastrointestinal tract, particularly in the stomach and proximal duodenum. Large numbers of schistosome worm pairs and eggs were found in all mesenteric, gastric and hepatic veins. Histological examination of the intestines, mesenteric lymph nodes, liver, spleen, pancreas, stomach and lungs revealed numerous strongly fibrotic, encapsulated, epithelioid-giant cell granulomata containing dead, degenerating and viable eggs. A few examples of the Splendore-Hoeppli phenomenon were also detected. The eggs collected at necropsy had a terminal spine and an average length and breadth of 187.6+/-14.1 microm and 57. 3+/-4.1 microm, respectively. DNA analysis of female worms indicated that the schistosomes were either Schistosoma haematobium or a hybrid of Schistosoma mattheei and S. haematobium.

Selection of susceptible lines of Biomphalaria alexandrina and Bulinus truncatus snails to S.mansoni and S.haematobium infection.

Selection of progenies from infected B.alexandrina and B.truncatus snails resulted in higher infection rates. This observation was consistent when the source of micardia were from either infected human or hamsters. Infection rate of B.alexandrina increased up to 88.2% while B.truncatus did not. Compatibility between the parasites and their intermediate hosts were also studied.

The epidemiology of human and animal schistosomiasis in the Senegal River Basin.

The results of four field surveys in Senegal are reported. 1. A snail survey in various parts of the Senegal River Basin, including the Senegal River, temporary rain-fed pools, swamps, irrigation canals and drains, ricefields and Lac de Guier was carried out. Three species of snails were commonly found: Bulinus guernei was the most common, occurring in permanent habitats, Bulinus senegalensis occurring in laterite pools in the eastern part of the Middle Valley, and also in the ricefields of Guédé Chantier and Lampsar; B. forskalii was found in small numbers in Lac de Guier and Richard Toll. Three B. guernei were found to be naturally infected with S. bovis. Neither B. jousseaumei, B. globosus nor B. umbilicatus were found in our surveys. 2. A survey for urinary schistosomiasis was carried out in 100 villages (walo, near the Senegal River) and 11 villages (diéré, away from the river) by delivering questionnaires in schools and by direct examinations of haematuria samples. The prevalence of haematuria varied between 0 and 33%. Generally, walos showed low rates of haematuria with the exception of Lampsar and Guédé Chantier, and diérés showed higher rates of haematuria. 3. Examination of 400 cattle at the abattoir St. Louis, revealed a prevalence of 80% of schistosome infection. Two species were present, S. bovis and less commonly S. curassoni. Sometimes high worm burdens were seen, but lesions appeared to be minimal because of high ratio of male to female worms. 4. Examinations of 5722 sheep and 1752 goats in the abattoir, Dakar revealed an overall prevalence of 2.1%. Of the infected animals, 97.3% were infected with S. curassoni and 2.7% with S. curasonni and S. bovis. Laboratory snail infection experiments showed that S. curassoni is marginally compatible with B. senegalensis, but incompatible with B. guernei.