Almost half of deer ticks carry Lyme disease: New study

Blacklegged/deer tick

The blacklegged ticks, Ixodes pacificus (depicted here), and I. scapularis, are known vectors for the zoonotic spirochetal bacteria, Borrelia burgdorferi, which is the pathogen responsible for causing Lyme disease. The ticks, inoculated with the bacterium when they bite infected mice, squirrels and other small animals, subsequently pass the pathogens to their human victims when they obtain a blood meal. Here, you are looking at a dorsal view of a female I. pacificus hard tick. (Courtesy of CDC/ James Gathany; William L. Nicholson, Ph.D.)

Nearly half of more than 2,000 deer ticks collected last year for a new study in Connecticut were infected with Lyme disease.

Of 2,068 deer ticks tested at the Center for Vector Biology and Zoonotic Diseases at the Connecticut Agricultural Experiment Station in New Haven, Connecticut, 46 percent carry the Lyme disease pathogen Borrelia burgdorferi.

About 13 percent also carried the human disease-causing pathogen Babesia microti, which causes babesia, a life-threatening infection of the red blood cells in humans.

Researchers found that 9 percent of the adult ticks carried Anaplasma phagocytophilum, which causes anaplasmosis, which is marked by fever, headache, chills and muscle aches; 2 percent carried Borrelia miyamotoi, which cause hard tick relapsing fever, bacterial infection that can cause recurring bouts of fever, headache, muscle and joint aches and nausea; and 1 percent carried Powassan virus, which can cause Powassan encephalitis, which produces symptoms of fever, headache, vomiting and weakness, and can lead to encephalitis) meningitis.

The ticks were gathered in the first year of a new federally funded Connecticut-wide surveillance program for ticks and associated tick-borne diseases.

More than 2,500 ticks were collected throughout spring, summer and fall 2019 from 40 publicly accessible locations in all eight Connecticut counties and screened for five different human disease-causing pathogens.

Deer ticks, also known as black-legged ticks, were the most collected species, at 2,068 adult ticks, followed by American dog tick, at 437; lone star tick, at 3; and Asian longhorned tick, at 2.

All adult female and nymphal deer ticks were tested at CAES for the presence of the five different disease-causing pathogens.

About 15 percent of the nymphs carried Lyme disease, 6 percent carried babesiosis, 5 percent carried anaplasmosis and 2 percent carried hard tick relapsing fever.

The survey was funded by a one-year grant issued from the Centers for Disease Control and Prevention through the Connecticut Department of Public Health and has potential to continue into a multi-year effort to document tick and pathogen abundances statewide to inform the public so appropriate precautions are taken when spending time outdoors.



So, similarly to CDC 2-tiered testing, “heads you win, tails you lose.” 

A while back I posted the following information about nationwide tick testing results:

Our current research shows that 60% of tick tested are infected with at least one disease causing organism, 38% are co-infected with two or more, 15% carry three or more, and 5% of the ticks tested carry four or more.

The percentage of Wisconsin ticks being infected, as of 2017:

On average, about 22 percent of deer tick nymphs in Wisconsin have been found to be infected with Borrelia burgdorferi. The infection rate for adults is about twice as high, around 40-45 percent. In some locations, though, researchers have found infection rates as high as 75 percent of the tick population.

The number of deer ticks in specific areas of Wisconsin can vary widely by area, by landscape, and by forest type. Researchers have not found any relationship with the numbers of white-footed mice or white-tailed deer in any given areas.

Russell Labs states the following:

In 2019, we documented established populations of the deer tick in every Wisconsin County except for Dodge and Winnebago. In those two counties, we found a very low number. Any forested locations could be a source of deer ticks and Lyme Disease.

Waukesha, Dane, and Sauk counties have the highest reported rates of Lyme disease in Wisconsin:

Please remember, this is only covers Lyme disease statistics. Wisconsin is home to many other diseases spread by ticks and we are a hot spot for Powassan Virus.
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