Fasciola hepatica and lymnaeid snails occurring at very high altitude in South America

Abstract

Fascioliasis due to the digenean species Fasciola hepatica has recently proved to be an important public health problem, with human cases reported in countries of the five continents, including severe symptoms and pathology, with singular epidemiological characteristics, and presenting human endemic areas ranging from hypo- to hyperendemic. One of the singular epidemiological characteristics of human fascioliasis is the link of the hyperendemic areas to very high altitude regions, at least in South America. The Northern Bolivian Altiplano, located at very high altitude (3800-4100 m), presents the highest prevalences and intensities of human fascioliasis known. Sequences of the internal transcribed spacers ITS-1 and ITS-2 of the nuclear ribosomal DNA of Altiplanic Fasciola hepatica and the intermediate snail host Lymnaea truncatula suggest that both were recently introduced from Europe. Studies were undertaken to understand how the liver fluke and its lymnaeid snail host adapted to the extreme environmental conditions of the high altitude and succeeded in giving rise to high infection rates. In experimental infections of Altiplanic lymnaeids carried out with liver fluke isolates from Altiplanic sheep and cattle, the following aspects were studied: miracidium development inside the egg, infectivity of miracidia, prepatent period, shedding period, chronobiology of cercarial emergence, number of cercariae shed by individual snails, survival of molluscs at the beginning of the shedding process, survival of infected snails after the end of the shedding period and longevity of shedding and non-shedding snails. When comparing the development characteristics of European F. hepatica and L. truncatula, a longer cercarial shedding period and a higher cercarial production were observed, both aspects related to a greater survival capacity of the infected lymnaeid snails from the Altiplano. These differences would appear to favour transmission and may be interpreted as strategies associated with adaptation to high altitude conditions.

Epidemiological studies onFasciola hepaticain Gafsa oases (South West of Tunisia)

“…This old disease has a great power of expansion in view of the large colonisation capacities of its fasciolid causal agents as well as the freshwater lymnaeid snail vector species (Mas-Coma et al, 2001). Recent reports indicate that fasciolasis is a reemerging highly pathogenic human infection whose epidemiological picture has changed in recent years (Moghaddam et al, 2004).…”

Fasciola hepatica Infection in an Indigenous Community of the Peruvian Jungle

“…13 Previous reports have shown adaptation of the parasite to very high altitudes, different snail species, and wild animal reservoirs. 6,14,15 Fasciola has not been previously described in animals in the Madre de Dios area. However, potential Fasciola natural hosts exist in Manu National Park and are in contact with Yomibato population.…”

“…5 The snails actually live longer and produce large numbers of cercariae at higher altitudes, which increases transmission. 6 In fact, it is estimated that half of the subjects infected with F. hepatica worldwide live in the Andes of South America. 7 In Peru, cases have been described in 17 out of 24 regions, all of which are located at high altitude.…”

The first record of Galba cubensis (L. Pfeiffer, 1839) (Mollusca: Gastropoda: Lymnaeidae) from open fields of Europe

“…G. truncatula is the main fascioliasis vector in Europe, Asia, and Africa (barGueS et al 2011). According to MaS-coMa et al (2001) it was introduced from Europe to South America, but in the opinion of correa et al (2010: p. 6) G. truncatula "represents a branch of an American clade that reached the Old World".…”