The Intergovernmental Panel on Climate Change (IPCC, 2007) reports an increasing trend in mean surface air temperature in Southeast Asia over the past several decades, with a 0.1–0.3 °C increase per decade recorded between 1951 and 2000. As mentioned earlier, all trematodes have check details complex life cycles and use snails as their first intermediate hosts. Asexual
multiplication of the trematodes in snails produces a large number of infective cercariae. The cercarial production rate in snails is fundamental for overall parasite transmission success and this process is relatively temperature dependent, in that an increase in temperature is coupled with an increase in cercarial output (Lo and Lee, 1996, Umadevi and Madhavi, 1997 and Mouritsen, 2002). Temperature-mediated changes in cercarial output also vary among trematode species, from small reductions to 200-fold increases
in response to a 10 °C rise in temperature (Poulin, 2006). In addition, geographical latitude may also affect the production of cercariae by snails. Within the latitude range of 20–55°, trematodes from lower latitudes showed more pronounced temperature-driven increases in cercarial output than those from higher latitudes. The net outcome of increasing temperature will be a greater number of cercarial infective stages in aquatic Selleckchem Akt inhibitor habitats. A few reports have mentioned the effects of climate and environment changes on O. viverrini and C. sinensis emergence, albeit indirectly ( Sithithaworn and Haswell-Elkins, 2003 and Andrews et al., 2008). By the nature of their life cycle, it is possible that climate change in SE Asia, including intense rainfall and flooding and warmer temperatures, may enhance liver fluke abundance and transmission. Schistosomiasis is caused by infection with species of found the blood-fluke Schistosoma. The life-cycle includes a single intermediate host, a freshwater snail, which for the endemic Chinese and Southeast Asian Schistosoma, is always of the family Pomatiopsidae. Three Schistosoma species are recognized as infecting humans in Southeast Asia, namely S. japonicum, S. malayensis and S. mekongi.
Phylogenetically all three species belong to the Schistosoma sinensium clade ( Attwood et al., 2008), so named because of the basal (ancestral) position of S. sinensium in the clade comprising these four Schistosoma species and S. ovuncatum. S. sinensium and its sister taxon S. ovuncatum are both transmitted by snails of the Triculinae and both are exclusively parasites of rodents; these two characters are regarded as plesiomorphic (ancestral) in Asian Schistosoma (see Davis, 1992 and Attwood et al., 2002). These taxa have also been referred to as the “Schistosoma japonicum-group” because all have a minutely spined egg as first described for S. japonicum (see Rollinson and Southgate, 1987). Schistosoma japonicum is often described as a “true zoonosis” ( Ross et al., 1997, Gan et al.