Introduction to the Symposium on Echinococcosis

China is one of the world’s most highly endemic countries for the cestode zoonosisechinococcosis. In the northwest of the country, both Echinococcus granulosus and E.multilocularis are transmitted between domestic livestock or wildlife hosts respectively, over vast and relatively remote regions. Traditional pastoralist communities of Tibetan, Kazakh and Mongol ethnic minorities appear to be most at risk of human cystic echinococcosis or alveolar echinococcosis, as are also Han Chinese that reside in the endemic Prefectures. This mini-review summarizes the situation of parasite transmission in animal hosts in China and focuses on the epidemiology of human disease in those regions where in-depth studies have been undertaken. however, clear evidence for active transmission of E.granulosus within these latter countries has not been confirmed (WHO/OIE, 2001). E.granulosus and CE are also currently endemic in Australia, and formerly throughout New Zealand prior to the end of the National Hydatid Control Program (1959-1989) in that country (Gemmell and Roberts, 1998). The distribution of the fox tapeworm E.multilocularis and human AE is much more restricted over its known range in Asia. Clear evidence for sustained transmission is available only for northeastern Russia, north and west China, and northern Japan; largely unconfirmed reports of human AE cases have also been made in Pakistan, India, Afghanistan, Kazahkstan, Kyrgystan, Uzbekistan, and Mongolia (WHO/OIE, 2001; PSCraig and P Torgerson, unpublished observations). As in other regions of the world, it is very difficult to determine or even estimate the total numbers of human CE and AE cases in Asia. This is because of the long asymptomatic period (usually >5 years), the difficulty in diagnosis, poor record keeping, failure of patients to seek medical attention for a chronic condition, and also poor access to medical facilities especially for remote communities. Nevertheless, it is clear that for the Asian region the greatest numbers of both CE or AE cases occur in China and eastern Russia (Wen and Yang, 1997; WHO/OIE, 2001; Bessonov, 2002). It also appears, however, that human CE has re-emerged since the early 1990s as a significant public health problem in parts of Central Asia including Kazahkstan and Kyrgystan (Torgerson et al, 2002). Furthermore, human AE disease is an emerging or newly recognized public health problem in remote Tibetan communities in areas of Qinghai and Sichuan Provinces of China (Qiu et al, 1999; Schantz et al, 2003). Human CE and AE are typically chronic cystic mass/lesion infections of the liver, and these helminthic Correspondence: Philip Craig, Cestode Zoonoses Research Group, Bioscience Research Institute and School of Environment and Life Sciences, University of Salford, Salford, Greater Manchester, M54WT, UK. E-mail: [email protected] INTRODUCTION Echinococcosis refers to infection of humans or animals with the larval cystic (metacestode) or adult stages (tapeworm) of any of the currently recognized 4 tapeworm species belonging to the genus Echinococcus (Family: Taeniidae, Order: Cyclophyllidea). Hydatidosis is the traditional term for human or animal infection with the larval cystic stage. Echinococcus granulosus causes cystic echinococcosis (CE) in humans, and E.multilocularis is the cause of human alveolar echinococcosis (AE). Both CE and AE are potentially highly pathogenic following a variable period of chronic incubation or lesion growth (Craig, 2003; McManus et al, 2003).The two other species in the genus, E.vogeli and E.oligarthrus occur only in Central and South America and may cause polycystic echinococcosis in humans though infections are very rare (D’Alessandro, 1997). Only two Echinococcus species are currently considered to occur in Asia ie E.granulosus and E.multilocularis. The species E.granulosus has the greatest geographical distribution in the Region and this parasite infects humans and animals in eastern Russia, Mongolia, all the five Central Asian Republics (Turkmenistan, Uzbekistan, Kazakhstan, Kyrgystan, and Tadjikistan), China (including Tibet), India, Pakistan, Afghanistan, Bangladesh, Sri Lanka, Nepal, and Bhutan. Sporadic human cases of cystic echinococcosis have also been reported in Thailand, Vietnam, Cambodia, Lao PDR, Malaysia, Indonesia, the Philippines, North and South Korea, and Japan,