Potential hybridization of Fasciola hepatica and F. gigantica in Africa

Abstract

The occurrence of Fasciola gigantica and F. hepatica in Africa is well documented; however, unlike in Asia, there is a paucity of information on the existence of hybrids or parthenogenetic species on the continent. Nonetheless, these hybrid species may have beneficial characteristics, such as increased host range and pathogenicity. This study provides evidence of the potential existence of Fasciola hybrids in Africa. A literature search of articles published between 1980 and 2022 was conducted in PubMed, Google Scholar, and Science Direct using a combination of search terms and Boolean operators. Fasciola species were documented in 26 African countries with F. hepatica being restricted to 12 countries, whilst F. gigantica occurred in 24 countries, identified based on morphological features of adult Fasciola specimens or eggs and molecular techniques. The cooccurrence of both species was reported in 11 countries. However, the occurrence of potential Fasciola hybrids was only confirmed in Egypt and Chad but is suspected in South Africa and Zimbabwe. These were identified based on liver fluke morphometrics, assessment of the sperms in the seminal vesicle, and molecular techniques. The occurrence of intermediate host snails Galba truncatula and Radix natalensis was reported in Ethiopia, Egypt, South Africa, Tanzania, and Uganda, where F. hepatica and F. gigantica co-occurrences were reported. The invasive Pseudosuccinea columella snails naturally infected with F. gigantica were documented in South Africa and Egypt. In Zimbabwe, P. columella was infected with a presumed parthenogenetic Fasciola. This suggests that the invasive species might also be contributing to the overlapping distributions of the two Fasciola species since it can transmit both species. Notwithstanding the limited studies in Africa, the potential existence of Fasciola hybrids in Africa is real and might mimic scenarios in Asia, where parthenogenetic Fasciola exist in most Asian countries. In South Africa, aspermic F. hepatica and Fasciola sp. have been reported already, and Fasciola hybrids have been reported? in Chad and Egypt. Thus, the authors recommend future surveys using molecular markers recommended to identify Fasciola spp. and their snail intermediate hosts to demarcate areas of overlapping distribution where Fasciola hybrids and/or parthenogenetic Fasciola may occur. Further studies should also be conducted to determine the presence and role of P. columella in the transmission of Fasciola spp. in these geographical overlaps to help prevent parasite spillbacks.