Species composition and diversity of freshwater snails and land snails at the swampy areas and streams edges in the urban zone of Douala, Cameroon

Fascioliasis and bilharzia occur in the Littoral region of Cameroon. Recent reports indicate a high prevalence of bilharzia in school-age children in the locality of Njombé-Penja, close to the city of Douala. This infectious disease may spread in the near future to the city of Douala, especially if the localities at risk are visited by infected people, who defecate or urinate in streams or swamps as is the habit of populations in populous zones of the city and where environmental cleanliness is not respected. It is known that several molluscs are intermediate hosts of the infectious agents of this pathology but little is known about the snail’s community structure at the coastal zone of the country. The present study aimed to establish a baseline of information on the distribution of snails in the urban environments of the Douala coastal Littoral-zone, as a first step in evaluating the status and the occurrence level of snails known as intermediate hosts of schistosomiasis and distomatosis agents. Seventy-three sample units where inspected from July to November 2020 in eight quarters of the Douala city, using 49 non-contiguous transects 5x40 m² each along streams and 24 non-contiguous quadrates 10x10 m² each around swamps. A total of 4,068 snail’s shelter belonged to 9 families: 3(33.3%) and 6 (66.7%) families for land and freshwater snails respectively. Specimens belonged to 14 genera [6 (42.9%) and 8 (57.1%) genera for land and freshwater snails respectively], and 30 species [14 (46.7%) and 16 (53.3%) species for land and freshwater snails respectively]. Land snails were most diverse [E(Sn=151) = 14 ± 0 species] than freshwater snails [E(Sn=151) = 11 ± 1 species]. Economically important species were highly represented in land snails (30.3%) and lowly represented in freshwater snails (6.1%). Between land snails Achatina and Archachatina (invasive pests for agriculture) were highly recorded in Bépanda-Sic-Cacao, Makepé-Missoké and PK10-Plateau quarters while between freshwater snails known as obligate intermediate hosts for fascioliasis and bilharzia agents, Lymnaea was recorded in Bépanda-Sic-Cacao, Nkomba and Mbanga-Pongo quarters while Biomphalaria occurred exclusively in PK10-Plateau quarter. The community exhibited low evenness, low species richness, low species diversity and low dominance by a few species. The theoretical lognormal model fitted the species abundance distributions and species exhibited a positive association (Schluter’s ratio VR = 6.69, statistic W = 53.49, df = 8, p<0.001 for land snails; VR = 2.27, W = 18.18, df = 8, p = 0.020 for freshwater snails; VR = 4.17, W = 33.42, p<0.001 for the pooled data). Low dominance by a few species indicated that study sites were slightly influenced by interspecific competition and/or disturbance by human activities.

First Record of Trichobilharzia physellae (Talbot, 1936) in Europe, a Possible Causative Agent of Cercarial Dermatitis

Several species of avian schistosomes are known to cause dermatitis in humans worldwide. In Europe, this applies above all to species of the genus Trichobilharzia. For Austria, a lot of data are available on cercarial dermatitis and on the occurrence of Trichobilharzia, yet species identification of trematodes in most cases is doubtful due to the challenging morphological determination of cercariae. During a survey of trematodes in freshwater snails, we were able to detect a species in the snail Physella acuta (Draparnaud, 1805) hitherto unknown for Austria, Trichobilharzia physellae; this is also the first time this species has been reported in Europe. Species identification was performed by integrative taxonomy combining morphological investigations with molecular genetic analyses. The results show a very close relationship between the parasite found in Austria and North American specimens (similarity found in CO1 ≥99.57%). Therefore, a recent introduction of T. physellae into Europe can be assumed.