Global distribution of zoonotic digenetic trematodes: a scoping review

Abstract

Background: Digenetic trematodes, including blood flukes, intestinal flukes, liver flukes, lung flukes, and pancreatic flukes, are highly diverse and distributed widely. They affect at least 200 million people worldwide, so better understanding of their global distribution and prevalence are crucial for controlling and preventing human trematodiosis. Hence, this scoping review aims to conduct a comprehensive investigation on the spatio-temporal distribution and epidemiology of some important zoonotic digenetic trematodes.

Methods: We conducted a scoping review by searching PubMed, Web of Science, Google Scholar, China National Knowledge Infrastructure, and Wanfang databases for articles, reviews, and case reports of zoonotic digenetic trematodes, without any restrictions on the year of publication. We followed the inclusion and exclusion criteria to identify relevant studies. And relevant information of the identified studies were collected and summarized.

Results: We identified a total of 470 articles that met the inclusion criteria and were included in the review finally. Our analysis revealed the prevalence and global distribution of species in Schistosoma, Echinostoma, Isthmiophora, Echinochasmus, Paragonimus, Opisthorchiidae, Fasciolidae, Heterophyidae, and Eurytrema. Although some flukes are distributed worldwide, developing countries in Asia and Africa are still the most prevalent areas. Furthermore, there were some overlaps between the distribution of zoonotic digenetic trematodes from the same genus, and the prevalence of some zoonotic digenetic trematodes was not entirely consistent with their global distribution. The temporal disparities in zoonotic digenetic trematodes may attribute to the environmental changes. The gaps in our knowledge of the epidemiology and control of zoonotic digenetic trematodes indicate the need for large cohort studies in most countries.

Conclusions: This review provides important insights into the prevalence and global distribution of some zoonotic digenetic trematodes, firstly reveals spatio-temporal disparities in these digenetic trematodes. Countries with higher prevalence rate could be potential sources of transmitting diseases to other areas and are threat for possible outbreaks in the future. Therefore, continued global efforts to control and prevent human trematodiosis, and more international collaborations are necessary in the future.

Keywords: Digenetic trematode; Epidemiology; Spatio-temporal distribution.

Fig. 1

Life cycle of digenetic trematode. a Dioecism. The representative genus Schistosoma undergoes two stages in its life cycle, an asexual stage in snails and a sexual stage in mammals. Eggs are discharged into the water through feces (Schistosoma japonicum and Schistosoma mansoni) or urine (Schistosoma haematobium). Under appropriate conditions, the eggs hatch and release miracidia, which penetrate snail intermediate hosts. In snails, miracidia successfully complete sporocyst generations and produce the infective cercariae, which penetrate the skin of mammalian hosts (definitive hosts) and become schistosomulae. The schistosomulae migrate to lungs via venous circulation, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when mature. Finally, adult worms copulate and reside in the mesenteric venules (Schistosoma japonicum and Schistosoma mansoni) or urinary bladder (Schistosoma haematobium). b Hermaphrodite. The representative genus Clonorchis and Paragonimus undergoes two stages in the life cycle, an asexual stage in snails and a sexual stage in mammals. Eggs in the feces (Clonorchis & Paragonimus) or sputum (Paragonimus) are discharged into water. Under appropriate conditions, the eggs hatch and release miracidia, which penetrate snail intermediate hosts. In snails, miracidia go through several developmental stages (sporocysts, rediae, and cercariae). The cercariae penetrate the flesh of raw fish or crabs, where they encyst as metacercariae. Mammalian hosts (definitive hosts) become infected by ingesting metacercariae on contaminated vegetables or in raw fish and crabs (foodborne trematodes). Finally, metacercariae developed into adult worm in lung (Paragonimus) and bile duct (Clonorchis). These figures are created with BioRender.com

Fig. 2

Flow diagram presenting the search process, including inclusion and exclusion criteria for articles screen

Fig. 3

Total number of the research articles searching through PubMed, Web of Science, Google Scholar, CNKI and Wanfang databases