Attempted Ehrlichia risticii transmission with Dermacentor variabilis (Acari: Ixodidae).

The research article discusses an experiment of attempting transmission of Ehrlichia risticii, a disease causing bacteria in horses, using larvae of Dermacentor variabilis ticks and Balb/C mice. The study found that despite the ticks feeding on infected mice, there was no transmission of the bacteria to uninfected mice.

Experiment Design and Procedures

• The researchers utilized 327 larval Dermacentor variabilis ticks, also known as the American dog tick.
• These ticks were fed on Balb/C mice that had previously been inoculated with Ehrlichia risticii, a bacteria that is the causal agent of Potomac horse fever or equine monocytic ehrlichiosis.
• All mice used in the study displayed clinical signs of E. risticii infection at the time the ticks were feeding on them.
• The ticks were allowed to molt and the resulting nymphs (a later stage in the lifecycle of a tick) were then put on other, uninfected mice to feed on them.

Results and Findings

• No clinical signs of E. risticii infection were observed in the second group of mice that were fed upon by the nymphal ticks. This indicates that the ticks did not pass on the infection to the mice despite having taken their blood meal from already infected mice.
• The mice remained seronegative for E. risticii for 6 weeks after the feeding took place. Being seronegative means no antibodies were formed against the bacteria indicating that the mice were indeed not infected.

Implications and Conclusion

• This research suggests that despite feeding on infected hosts, Dermacentor variabilis larvae may not be effective in transmitting Ehrlichia risticii. Further research may be required to confirm these findings and to explore other potential vectors for E. risticii.