White-footed mice: tick burdens and role in the epizootiology of Potomac horse fever in Maryland.

The study investigates the role of white-footed mice in the spread of Potomac horse fever, by analyzing the presence of ticks and specific antibodies in their systems. The results indicate that these mice do not serve as a reservoir for the disease-causing agent, suggesting that ticks do not acquire it from feeding on these mice.

Sample Collection and Testing

• The researchers performed the study on 110 white-footed mice that they captured from horse farms in south-central Maryland.
• Once captured, the team examined the mice for ticks and conducted tests on them to look for the presence of specific antibodies to Ehrlichia risticii, the bacteria that causes Potomac horse fever.
• This was performed to understand whether these mice serve as a host for the disease and help in its spread.

Tick Infestation

• The study found that the white-footed mice were consistently infested with immature American dog ticks (also known as Dermacentor variabilis).
• The prevalence of these ticks in the mice population was particularly high, scoring as much as an 80% infestation rate in certain months.

Absence of Ehrlichia risticii

• When it came to testing for antibodies to Ehrlichia risticii, all 97 mice samples showed negative results.
• This suggested that the white-footed mice do not carry E. risticii and therefore are not reservoirs for Potomac horse fever.

Implications for Tick Feeding

• Based on these findings, the researchers proposed that immature American dog ticks do not acquire E. risticii when feeding on the white-footed mice.
• This challenges the previously assumed role of these mice in spreading Potomac horse fever.