Phylogenetic studies of larval digenean trematodes from freshwater snails and fish species in the proximity of Tshwane metropolitan, South Africa

Potential Hybridization of Fasciola hepatica and F. gigantica in Africa-A Scoping Review

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 co-occurrence 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.

Occurrence of Fasciola (Digenea: Fasciolidae) Species in Livestock, Wildlife and Humans, and the Geographical Distribution of Their Intermediate Hosts in South Africa—A Scoping Review

This review was conducted to provide an update on the status of the occurrence of Fasciola species in livestock, wildlife and humans, and the geographical distribution of snail intermediate host (IH) species in South Africa. The literature search was conducted on four electronic databases using the Boolean operators in combination with predetermined search terms for thematic analysis. Results showed that Fasciola species have been reported in six out of nine provinces of South Africa in the last six decades (1960–2021), with both F. hepatica and F. gigantica infecting vertebrate hosts and F. hepatica and Fasciola spp infecting humans. Results also showed that most studies relied on morphological identification of eggs and flukes without molecular confirmation, which might have led to the misidentification of specimens, especially when immature. Fasciola hepatica has been documented in Limpopo, Mpumalanga, and KwaZulu-Natal provinces. The occurrences of Galba truncatula as the probable snail IH for F. hepatica in the three provinces has been documented while Pseudosuccinea columella has only been documented in Mpumalanga and KwaZulu-Natal provinces. The occurrence of F. gigantica to date has been reported in Mpumalanga and KwaZulu-Natal provinces, with overlapping distribution with F. hepatica. Radix natalensis, the main IH of F. gigantica has been documented in all the three provinces, while the two alien Radix species (R. auricularia and R. rubiginosa) were documented in KwaZulu-Natal province and have been implicated elsewhere with the transmission of F. gigantica. The presence of Fasciola spp eggs and antibodies in humans were documented in the Eastern Cape and the Western Cape provinces, where both P. columella and G. truncatula are known to be present. The prevalence of Fasciola spp infection in livestock ranged from 9.1 to 37.67 %, with an estimated annual financial loss ranging from R44930.26-129901 in cattle production in the Eastern Cape province of South Africa. This review reaffirms the scarcity of information on the occurrence and burden of fasciolosis in South Africa, and further highlights the importance of future research covering all provinces of the country and assessing the public health significance of the disease in resource-poor livestock communities in the areas where the parasite is endemic.

Diversity of Trichobilharzia in New Zealand with a new species and a redescription, and their likely contribution to cercarial dermatitis

In response to annual outbreaks of human cercarial dermatitis (HCD) in Lake Wanaka, New Zealand, ducks and snails were collected and screened for avian schistosomes. During the survey from 2009 to 2017, four species of Trichobilharzia were recovered. Specimens were examined both morphologically and genetically. Trichobilharzia querquedulae, a species known from four continents, was found in the visceral veins of the duck Spatula rhynchotis but the snail host remains unknown. Cercaria longicauda [i.e. Trichobilharzia longicauda (Macfarlane, 1944) Davis, 2006], considered the major aetiological agent of HCD in Lake Wanaka, was discovered, and redescribed from adults in the visceral veins of the duck Aythya novaeseelandiae and cercariae from the snail Austropeplea tomentosa. Recovered from the nasal mucosa of Ay. novaeseelandiae is a new species of Trichobilharzia that was also found to cycle naturally through Au. tomentosa. Cercariae of a fourth species of Trichobilharzia were found in Au. tomentosa but the species remains unidentified.

First Description of the Metacercaria of Nematostrigea serpens serpens (Nitzsch, 1819) (Trematoda, Strigeidae) and Phylogenetic Affiliation of Nematostrigea vietnamiensis Zhokhov & Mishina, 2011

BACKGROUND

The genus Nematostrigea comprises trematodes parasitising in fish-eating birds of Europe, Africa, and North America. Their life cycle is unknown.

PURPOSE

To provide the first description of metacercariae of Nematostrigea serpens serpens, a nominative subspecies of the type species of Nematostrigea, and to record metacercaria of Nematostrigea vietnamiensis, with molecular data.

METHODS

Encysted metacercariae of N. serpens serpens and N. vietnamiensis were collected from fish in Russia and Vietnam, respectively, and were processed, identified, and documented using standard morphological techniques. The 28S rRNA gene of metacercariae of both species and the cox1 gene of metacercariae an earlier studied adult of N. serpens serpens were sequenced and used for phylogenetic analysis.

RESULTS

Metacercaria of N. serpens serpens have a spatulate body with a foliate forebody and a short hindbody, two long lateral rectilinear pseudosuckers, and the holdfast organ with bifurcated anterior and entire posterior external lobes. The analysis of the cox1and 28S rRNA gene sequences unequivocally showed the conspecificity of metacercariae and adult stage of N. serpens serpens. Based on the 28S rRNA gene sequence-based phylogenetic analysis, the genus Nematostrigea is a sister taxon to the group of strigeid genera Cotylurus + Ichthyocotylurus. Morphological and phylogenetic data demonstrated that N. vietnamiensis does not belong to the genus Nematostrigea and is possibly be affiliated with the crassiphialine trematodes.

CONCLUSION

This is the first record of metacercariae of N. serpens serpens. N. vietnamiensis, renamed Prodiplostomulum vietnamiense comb. nov., must be moved to the crassiphialine 'Prodiplostomulum'-type metacercariae group.

Trematode diversity reflecting the community structure of Danish freshwater systems: molecular clues

Background

Digenean trematodes are parasitic platyhelminths that use several hosts in their life cycles and are thereby embedded in various ecosystems affected by local environmental conditions. Their presence in a habitat will reflect the presence of different host species and, as such, they can serve as ecological indicators. Only limited information on the occurrence of trematodes and their link to other trophic levels in the Danish freshwater ecosystems is currently available.Therefore, the main aim of the present study was to increase our knowledge in this field.

Methods

Snails were sampled from 21 freshwater lakes in Denmark, following which shedding procedures were performed, cercariae were recoved and the released parasites were identified using molecular tools (PCR and sequencing).

Results

A total of 5657 snail hosts belonging to ten species were identified, revealing a highly diverse parasite fauna comprising 22 trematode species. The overall trematode prevalence was 12.6%, but large variations occurred between host species. The snail host Lymnaea stagnalis showed the highest prevalence and also exhibited the highest diversity, accounting for 47.6% of the species richness.

Conclusions

This survey contributes updated information on parasite–host relations and compatibility and may assist in describing the ecological structure of the investigated Danish freshwater ecosystems.

Exposing the Barcoding Void: An Integrative Approach to Study Snail-Borne Parasites in a One Health Context

Trematodes are snail-borne parasites of major zoonotic importance that infect millions of people and animals worldwide and frequently hybridize with closely related species. Therefore, it is desirable to study trematodiases in a One Health framework, where human and animal trematodes are considered equally important. It is within this framework that we set out to study the snail and trematode communities in four artificial lakes and an abattoir in Zimbabwe. Trematode infections in snails were detected through multiplex PCR protocols. Subsequently, we identified snails by sequencing a partial mitochondrial cytochrome c oxidase subunit I (COI) fragment, and trematodes (adults from the abattoir and larval stages detected in snails) using COI and nuclear rDNA markers. Of the 1,674 collected snails, 699 were molecularly analyzed, in which we identified 12 snail and 19 trematode species. Additionally, three parasite species were sampled from the abattoir. Merely four trematode species were identified to species level through COI-based barcoding. Moreover, identification of members of the superfamilies Opisthorchioidea and Plagiorchioidea required a phylogenetic inference using the highly conserved 18S rDNA marker, as no related COI reference sequences were present in public databases. These barcoding challenges demonstrate a severe barcoding void in the available databases, which can be attributed to the neglected status of trematodiases. Adding to this, many available sequences cannot be used as different studies use different markers. To fill this gap, more studies on African trematodes, using a standardized COI barcoding region, are desperately needed.