Cercarial dermatitis in the UK: a long established history

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.

A report of Bilharziella polonica cercariae in Knowsley Safari, Prescot, United Kingdom, with notes on other trematodes implicated in human cercarial dermatitis

As part of surveillance of snail-borne trematodiasis in Knowsley Safari (KS), Prescot, United Kingdom, a collection was made in July 2021 of various planorbid (n = 173) and lymnaeid (n = 218) snails. These were taken from 15 purposely selected freshwater habitats. In the laboratory emergent trematode cercariae, often from single snails, were identified by morphology with a sub-set, of those most accessible, later characterized by cytochrome oxidase subunit 1 (cox1) DNA barcoding. Two schistosomatid cercariae were of special note in the context of human cercarial dermatitis (HCD), Bilharziella polonica emergent from Planorbarius corneus and Trichobilharzia spp. emergent from Ampullacaena balthica. The former schistosomatid was last reported in the United Kingdom over 50 years ago. From cox1 analyses, the latter likely consisted of two taxa, Trichobilharzia anseri, a first report in the United Kingdom, and a hitherto unnamed genetic lineage having some affiliation with Trichobilharzia longicauda. The chronobiology of emergent cercariae from P. corneus was assessed, with the vertical swimming rate of B. polonica measured. We provide a brief risk appraisal of HCD for public activities typically undertaken within KS educational and recreational programmes.

Characterization of microRNAs from Orientobilharzia turkestanicum, a neglected blood fluke of human and animal health significance

The neglected blood flukes Orientobilharzia spp. belonging to the Platyhelminthes, infect animals in a number of countries of the world, and cause cercarial dermatitis in humans, as well as significant diseases and even death in economically-important animals. MicroRNAs (miRNAs) are now considered to be a key mechanism of gene regulation. Herein, we investigated the global miRNA expression profile of adult O. turkestanicum using next-generation sequencing technology and real-time quantitative PCR, to gain further information on the role of these molecules in host invasion and the parasitic lifestyle of this species. A total of 13.48 million high quality reads were obtained out of 13.78 million raw sequencing reads, with 828 expressed miRNAs identified. Phylogenetic analysis showed that the miRNAs of O. turkestanicum were still rapidly evolving and there was a “directed mutation” pattern compared with that of other species. Target mRNAs were successfully predicted to 518 miRNAs. These targets included energy metabolism, transcription initiation factors, signal transduction, growth factor receptors. miRNAs targeting egg proteins, including major egg antigen p40, and heat shock proteins were also found. Enrichment analysis indicated enrichment for mRNAs involved in catalytic, binding, transcription regulators and translation regulators. The present study represented the first large-scale characterization of O. turkestanicum miRNAs, which provides novel resources for better understanding the complex biology of this zoonotic parasite, which, in turn, has implications for the effective control of the disease it causes.