Identification of Trematode Cercariae Carrying Neorickettsia risticii in Freshwater Stream Snails

Abstract

We provide evidence of Neorickettsia (Ehrlichia) risticii Holland, the agent of Potomac horse fever, in trematode larval stages found in aquatic snails and insects collected from a stream in Korea, using nested polymerase chain reaction (PCR) and sequence analysis of the 16S rRNA gene fragment amplified from several cercaria species. It was observed that of 423 (13.1%) of 3,219 snails infected with cercariae, 77 (20.8% of the 371) were infected with N. risticii. Five families of trematode cercariae, Schistosomatidae, Echimostomatidae, Heterophyidae, Microphallidae, and Acanthocopidae were identified morphologically within Semisulcospira libertina, Radix auricularia coreana, and S. gottschei snails. Echinostoma cinetorchis, E. hortense, and Metagonimus sp. were identified based on both the cercarial morphology as well as by phylogenetic analysis of the amplified 18S rRNA gene sequences. Adult aquatic insects were also collected from the same sites and were sorted into five species, Ischnura asiatica in Coenagrionidae and Calopteryx japonica, Sympetrum darwinianum, Symptrum eroticum, and Symptrum parvulum in Calopterygoidae. One thousand and two hundred eighty five metacercariae (classified into groups A through F) were isolated from 310 adult aquatic insects, and the average number of metacercariae per aquatic insect was 4.1. However, there was no amplification of N. risticii from these metacercariae.

Transmission rates of the bacterial endosymbiont, Neorickettsia risticii, during the asexual reproduction phase of its digenean host, Plagiorchis elegans, within naturally infected lymnaeid snails

“…However, as a result of combined molecular and experimental approaches it was demonstrated to be associated with digeneans [14-18]. Since then, N. risticii was detected in representatives of several digenean families, e. g., Lecithodendriidae, Plagiorchiidae, Microphallidae, Macroderoididae, and Echinostomatidae [7,17-25]. Although the digenean hosts of N. risticii have diverse life cycles that utilize various groups of invertebrates and even vertebrate intermediate hosts, it has been shown that amphibiotic insects such as mayflies and caddisflies play a particularly important role in the epizootology of Potomac horse fever [20,22,26].…”

Comparison of 18S ribosomal RNA gene sequences of Eurytrema coelmaticum and Eurytrema pancreaticum

“…Previous studies on E. coelmaticum and E. pancreaticum were greatly focused on their morphology, life history, main organs and their functions, and epidemic investigation (Vykhrestyuk and Yarygina 1982;Pinheiro and Amato 1995;Dorny et al 1996. However, no molecular data on E. coelmaticum and E. pancreaticum are available at present, and their relationship is not determined based on molecular data, which have successfully been used in the analysis of phylogeny and in the identification of trematodes (Attwood et al 2002;Park et al 2003;Olson et al 2003). Until recently, only three partial 18S rRNA sequences of three genera, Brachylecithum, Lyperosomum, and Dicrocoelium, are available and two of them have been used in molecular phylogenetic analyses (Olson et al 2003).…”

An Ecotype of Neorickettsia risticii Causing Potomac Horse Fever in Canada

“…of trematodes, and Myotis yumanensis bats and tree swallows (Hirundo rustica and Tachycineta bicolor) were also reported to be infected with N. risticii (10). In addition, N. risticii DNA fragments have been detected in various other digenean trematodes having life cycles typical of freshwater/terrestrial ecosystems (11,12). However, due to limited molecular analysis, the relatedness of these Neorickettsia organisms to N. risticii strains infecting horses, and whether they can infect horses and cause PHF, is unknown.…”