Skip to content

Home > Themes > Ecology of Cestode transmission

Ecology of Cestode transmission

Cestode zoonoses (Echinococcoses , Taeniases, Cysticercoses) are neglected zoonotic diseases which are highly endemic in western China, Central Asia and Europe. On the Tibetan Plateau ecosystem uniquely 3 species of the parasite Echinococcus are endemic in wildlife and/or domestic mammals, with E. granulosus and E. multilocularis causing a serious public health problem of cystic (CE) and alveolar (AE) echinococcosis amongst Tibetan pastoralists. E. shiquicus has also been described in Tibetan wildlife populations but host specificity and zoonotic potential are unknown. In Western China, E. granulosus and E. multilocularis are sympatric.

Dogs scavenging on a sheep carcass at Sary Mogol, 3000 m alt., Alay Valley, Kyrgyzstan

Human cysticercosis is caused by the development of Taenia solium cysticerci in human tissues. Cysticercosis mainly affects the health and livelihoods of subsistence farmers in developing countries of Asia (but also Africa and Latin America) as it can lead to epilepsy and death in humans, reduces the market value of pigs and makes pork unsafe to eat.

The life-cycle of those diseases ranges from merely sylvatic to merely domestic and offers unique opportunities to understand how anthropogenic human disturbance of ecosystems leads to transmission re-enforcement, sustained stability or to extinction in various conditions. For instance, a striking feature of the transmission ecology of E. multilocularis in China is the diversity of hosts that contribute to the parasite cycle (see e.g. Giraudoux et al. 2013).

On the Tibetan plateau grassland management and overgrazing influence intermediate host species populations and the sheer size of the area could be a major contributing factor to sustaining transmission in the region. In Southern Gansu and Southern Ningxia the processes of deforestation have temporarily provided optimal habitat for key reservoir intermediate hosts of E. multilocularis, resulting in high transmission and human disease, however currently the parasite may be extinct locally.

Yak herd on the Tibetan plateau, 4200 m alt., Siqhu, Sichuan, China

Faced with this pattern of potentially transient transmission in a diversity of communities the question of the dispersal potential of the parasite arises. The reforestation program currently active across much of Western China has the potential to give rise to a massive increase in habitat favourable to suitable intermediate hosts and emergence or re-emergence of the zoonosis alveolar echinococcosis in many areas. This potential epidemic could be mitigated by both natural and human-induced parasite dispersal mechanisms including fox migration and the sale of infected dogs originating from stable endemic foci on the Tibetan plateau. However, currently the degree of genetic exchange between discrete transmission foci is unknown and it is expected that genetic techniques could provide crucial information regarding this important question.

Tibetan grand-mother and her grand-children patting a dog. This behaviour is at high risk regarding Echinococcus transmission since villages and their surroundings are largely contaminated by dog faeces

Our research aims at developing methods for those studies integrating host ecology, epidemiology and spatial modelling and can find application to other diseases or/and areas. This is currently the case for Echinoccocus studies extended to pastoral communities of Kyrgyzstan, and Taeniases/Cysticercosis in Tibetan farmer communities in Sichuan, China, and in Bali, Indonesia, where host ecology and spatial modelling approaches developed in our network help to better understand transmission patterns and processes.

See also: Mountain Ecosystem Management in the LTER site Jurassian Arc