Introduction: The prevalence of Francisella tularensis in Minnesota ticks is unknown. Ticks collected at seven sites were tested to determine the infection prevalence of F. tularensis in Dermacentor variabilis in Minnesota.
Materials and Methods: Ticks were collected from two properties at an epizootic site and at five long-term tick research sites. Ticks were pooled by species, sex, date, and site with a maximum of 10 ticks per pool. Ticks were bisected and homogenized; DNA from supernatant was extracted and tested by real-time PCR (RT-PCR). Twice, additional ticks were collected for bacterial culture and isolation of F. tularensis. Proportion of positive pools and minimum infection rate (MIR) were calculated.
Results: A total of 3527 ticks were tested for F. tularensis including 1601 male D. variabilis and 1926 female D. variabilis. Across all sites, 128 (34%) of 378 pools were RT-PCR positive for F. tularensis. Of 128 positive pools, F. tularensis from 96 (75%) was identified as type A; F. tularensis from 32 pools was unable to be subtyped. The overall MIR was 3.6%. The MIR was significantly lower at the epizootic site compared with Morrison County 1 (3.9% vs. 7.2%; p = 0.02) but did not differ between the epizootic site and Pine County 1 (3.9% vs. 2.1%; p = 0.49). Within the epizootic site, the MIR was significantly higher at Washington County 2 compared with the adjacent property (5.7% vs. 2.3%; p < 0.001). F. tularensis was cultured from 6 (15%) of 40 pools.
Conclusions: F. tularensis was found in ticks at a majority of sites tested. The MIR of F. tularensis in D. variabilis ticks in Minnesota varied geographically. Our findings support the hypothesis that D. variabilis plays an important role in the natural history of tularemia in Minnesota. Further ecologic studies are needed to fully understand the importance of tick species in the maintenance and transmission of F. tularensis in Minnesota.
The Dermacentor variabilis tick is a hard bodied tick, also known as the American Dog tick or Wood tick and is widely known. It transmits Rocky Mountain spotted fever (RMSF) and tularemia to humans as well as canine tick paralysis to dogs. http://edis.ifas.ufl.edu/in781
Dorsal view of American dog ticks, Dermacentor variabilis (Say), with male on left, and female on right. Credit: J.F. Butler, University of Florida
It was been suggested that adult ticks move to the edge of the roads and trails in an attempt to find a host, or “quest.” Some have hypothesized that because many animals typically follow trails, they leave an odor that attracts these ticks causing them to move toward and quest alongside trails in attempts to find a host (Mcnemee et al. 2003).
More on Tularemia: https://madisonarealymesupportgroup.com/2016/10/25/of-rabbits-and-men/
Normally thought of as inhabiting areas east of the Rocky Mountains, the Wood tick is obviously defying entomology maps and traipsing all over – from Minnesota to Missouri, California, and most probably everywhere in-between.
I remember hearing Timothy Lepore, MD, FACS, surgeon at Nantucket Cottage Hospital, at a Lyme conference. He explained that Tularemia is also a disease of those who work with the land such as landscapers and farmers, as well as those who get bit by a tick. There are cases reported in every state but Hawaii, and many other wild and domestic animals can be infected. The highest rates of infection are in Arkansas. Please see this link for more details but know that this is a bioweaponized pathogen: https://madisonarealymesupportgroup.com/2016/10/25/of-rabbits-and-men/ The WHO estimates that an aerosol dispersal of 50 kg of F. tularensis over an area with 5 million people would result in 25,000 incapacitating casualties including 19,000 deaths.
Transmission: Transmission can occur through the skin or mucous membranes when handling infected animals as well as through tick bite, contact with fluids from infected deer flies, mosquitoes or ticks, handling or eating undercooked rabbit, drinking contaminated water, inhaling dust from contaminated soil, and handling contaminated pelts or paws of animals. It can also be inhaled from infected hay, grain, or soil. Dr. Lepore had patients who contracted it from their pet dog who shook rain water on them after chewing on a dead rabbit, as well as from folks eating road kill, a person who held sick animals, and a gentleman who slept with his pet bunny.
Another reminder – don’t sleep with pets!
The fact that 35% of Minnesotan ticks are infected with Tularemia is concerning. Spread the word.