Chipmunks and Granulocytic Anaplasmosis: A Vector Disease

Data collected on small mammals show that the prevalence of infection varies considerably between species, ranging from 7.1% in greater shrews to 64.7% in eastern chipmunks. By comparison, the infection affected 31.1% of white-footed mice.

“Our statistical analyzes confirmed that chipmunks were three times more infected than mice, even taking into account the presence of nymphs feeding on the animal,” underlines Raphaëlle Audet-Legault.

The study also found that males were twice as likely to be infected as females across all taxa. “They get bitten more because they are more exploratory,” mentions the researcher. This behavior exposes them more to ticks in their environment.

Chipmunks also carried 39.6% of the nymphs taken from all small mammals, despite their low representation in the captures, probably because they “are heavily bitten by ticks, being very active in nature,” specifies the researcher.

In addition to the prevalence of infection, the team measured the actual capacity of small mammals to transmit the bacteria to ticks. The results showed that 60% of infected chipmunks transmitted the infection to at least one feeding larva, compared to 57.9% for mice. Even more telling, infected chipmunks transmitted the bacteria to an average of 52.9% of the larvae feeding on them, compared to 36.8% for mice.

Several factors explain this “efficiency”. “We suspect that their immune response is different,” indicates Raphaëlle Audet-Legault. When they are infected, it could last several weeks and then they would have more opportunities to infect more ticks.”

The lifespan of chipmunks, which can reach up to eight years in some cases compared to less than a year for mice, also gives them more opportunities to contaminate ticks throughout their existence.

“In the future, it would be interesting to precisely measure the duration of the infectious period of chipmunks for ticks, with a view to designing effective preventive strategies by applying the One Health approach, which recognizes the interdependence of human, animal and environmental health,” observes Raphaëlle Audet-Legault.

Protect yourself from ticks and granulocytic anaplasmosis

Transmission of the bacteria Anaplasma phagocytophilum to humans is not carried out directly by small mammals, but by the infected tick. The symptoms of anaplasmosis are similar to those of the flu: fever, weakness, headache, muscle pain. Unlike Lyme disease, it does not cause erythema migrans, that characteristic red spot on the skin. The bacteria can also be transmitted a little more quickly than that responsible for Lyme disease.

“To avoid tick bites, you must stay on the trails, wear long clothes, put your stockings over your pants, wear DEET-based mosquito repellent,” recommends Raphaëlle Audet-Legault. After any outdoor activity, it is essential to inspect yourself thoroughly. The nymphs measure 1.5 to 2 mm and are particularly active in spring, when people begin to be outdoors and may be less cautious.

There is less risk of infection if the tick is removed within 24 hours of the bite. However, this time window remains short and vigilance remains essential.