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

The research article provides an in-depth investigation into aquatic insects carrying E. risticii, the bacterium causing Potomac horse fever, through infection by trematode stages. The study was conducted in a pasture stream in northern California, and the presence of the bacterium was validated through different gene analyses.

Methodology for detection of E. risticii

• The research utilized nested polymerase chain reaction (PCR), an amplification process used to make multiple copies of a specific DNA segment, to detect the presence of E. risticii in the trematode stages of the aquatic insects.
• For further validation, sequence analyses of the 16S rRNA, 51 kDa major antigen, and groEL heat shock protein genes were conducted. These genes were chosen due to their distinctive structures in E. risticii bacterium, thus assisting in its accurate identification.

Detection of E. risticii in various aquatic insects

• The bacterium was detected in metacercariae, a developmental stage of certain parasites including trematodes, found in both the immature and adult stages of various aquatic insects.
• The aquatic insects that were found to be carriers included caddisflies, mayflies, damselflies, dragonflies, and stoneflies – making these an intermediate host range for the said trematodes acting as vectors for E. risticii.

Prevalence of E. risticii in aquatic insects

• The overall prevalence of E. risticii in the examined aquatic insects was 31.9% (with 454 individuals tested), and 13 out of the 17 species were found to be positive.
• Among different insect orders, the prevalence of E. risticii varied, with caddisflies at 43.5% (in 207 individuals), mayflies at 15.2% (92 individuals), damselflies at 13.9% (115 individuals), dragonflies at 10.0% (10 individuals), and stoneflies at the highest, 80.0% (30 individuals).
• These numbers demonstrate the ability of E. risticii to survive and possibly propagate in a broad range of insect hosts, indicating their potential role in the lifecycle and spread of this bacterium.

Implications on Disease Epidemiology

• The study suggests that the aquatic insect hosts might play a significant role in the epidemiology of Potomac horse fever.
• This information is crucial for formulating disease control strategies, like vector management, thus minimizing the instances of Potomac horse fever, which can be devastating to equine populations.