Infection of aquatic insects with trematode metacercariae carrying Ehrlichia risticii, the cause of potomac horse fever

Joon Seok Chae, Nicola Pusterla, Eileen Johnson, Elfriede Derock, Sharon P. Lawler, John E Madigan

Research output: Contribution to journalArticle

31 Scopus citations


We provide evidence of Ehrlichia risticii Holland, the agent of Potomac horse fever, in trematode stages found in aquatic insects collected from a pasture stream in northern California, using nested polymerase chain reaction (PCR) amplification and sequence analyses of the 16S rRNA, 51 kDa major antigen and groEL heat shock protein genes. E. risticii was detected in metacercariae found in the immatures and adults of the following insects: caddisflies (Trichoptera), mayflies (Ephemeroptera), damselflies (Odonata, Zygoptera), dragonflies (Odonata, Anisoptera), and stoneflies (Plecoptera). The prevalence of E. risticii was 31.9% (n = 454 individuals) in aquatic insects (13 of 17 species were positive). Prevalence within orders was as follows: 43.5% (n = 207) in caddisflies, 15.2% (n = 92) in mayflies, 13.9% (n = 115) in damselflies, 10.0% (n = 10) in dragonflies, and 80.0% (n = 30) in stoneflies. This study demonstrates a broad intermediate host range for trematodes that act as vector for E. risticii. Insects are likely to play an important role in the epidemiology of this disease.

Original languageEnglish (US)
Pages (from-to)619-625
Number of pages7
JournalJournal of Medical Entomology
Issue number4
StatePublished - Jul 2000



  • Aquatic insect host
  • Ehrlichia risticii
  • Potomac horse fever
  • Trematode vector

ASJC Scopus subject areas

  • Insect Science
  • veterinary(all)

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