A multidisciplinary analysis led by Santiago Mas-Coma, emeritus full professor of Parasitology at the University of Valencia (UV) and published in Clinical Microbiology Reviews, reveals the strategies of two trematodes (Fasciola hepatica and F. gigantica) to expand globally from the Neolithic. These parasites cause fascioliasis, an emerging zoonotic disease, which can cause death in humans, especially during infancy, and causes great losses in its natural reservoir, livestock. With this analysis, the molecular and genetic characteristics of the causal agents and the characteristics of this disease in each area are understood.
The World Health Organisation (WHO) highlights that fascioliasis is the cause of underdevelopment and includes it on its list of priority neglected diseases. It is the only food fluke that has a worldwide distribution, with many different transmission patterns and in which humans are infected through the consumption of fresh aquaculture vegetables and natural drinking water carrying the infectious larval stage released by the vector snails.
According to the study, in which María Adela Valero and María Dolores Bargues, professors of Parasitology at the Faculty of Pharmacy of the University of Valencia also participate, both species derive from the fasciolide that infects hippos by speciation in wild ruminants. Thus, Fasciola gigantica originated in southeastern Africa thirteen and a half million years ago, while F. hepatica appeared in temperate areas and cold mountainous foothills of Near Eastern Asia between 6 and 4 million years ago.
To determine the expansion strategies of Fasciola, the latest studies of palaeontology, palaeoclimatology, palaeobiogeography (geographic distribution of organisms from the past by their fossils), archaeology and history, and the connections between fasciolids, snails, reservoir mammals and humans everywhere, in field studies carried out on expeditions of the authors to endemic countries on all continents.
Thus, F. gigantica initially spread with wild African ruminants along the East African Rift and the Levant Mediterranean corridor to Near East Asia. The two fasciolids coexisted in the past and took advantage of animal domestication in the Fertile Crescent of Mesopotamia between 12,000 and 10,000 years ago. Through human-guided movements of domesticated ruminants, equines, and camelids, they subsequently spread throughout the Old World, and then also the Americas and Oceania as they were passively transported with animals on ships over the last 500 years. “This explains the foundational effect that is evident in the molecular studies carried out everywhere”, notes Mas-Coma in this regard.
By continents
In Europe, there were three tracks of western expansion through Cyprus and Aegean islands first; of the Strait of the Dardanelles in second; and the other from the North Caucasus with the Yamnaya herdsmen.
In Asia, three other routes of eastern expansion allowed the fasciolids to further use the Silk Road from Iran and Uzbekistan to the eastern tip of China; the southern Great Trunk Route from Afghanistan and India to present-day Bangladesh; and thirdly the Tea and Horse Route in southern China to Nepal and eastern India and then Southeast Asia. Land connections of the Maritime Silk Road from Egypt through the Arabian Sea and Indian Ocean and beyond to the Pacific also contributed to such Asian expansion.
In Africa, F. hepatica was introduced via the Arabian Peninsula and the Horn of Africa, and F. gigantica took advantage of the ancient civilisations of Nubia and Ancient Egypt to spread west across the Sahara, and pastoralists Bantu to reach South Africa.
In the Americas, F. hepatica was introduced by Spanish colonisers to North America, Central America, and the Caribbean. In South America, this fasciolid was introduced from the Pacific coast and then spread eastward to the Atlantic coast through the transport of minerals and goods by pack animals.
In Oceania, F. hepatica was introduced from Germany and quickly colonised Tasmania and New Zealand.
Article: Mas-Coma S., Valero M. A., Bargues M. D. Human and Animal Fascioliasis: Origins and Worldwide Evolving Scenario. Clin Microbiol Rev (2022), Ahead of print: 96 pp., 56 figures, 626 references. Doi: https://journals.asm.org/doi/10.1128/cmr.00088-19.
