The Lyme disease-causing vector, blacklegged ticks, are now in all US states and in half of all US counties according to a report recently published in the Journal of Medical Entomology, Science reports.
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Lyme disease is an acute inflammatory disease characterized by a rash with joint swelling and fever, caused by bacteria carried by the bite of a deer tick the Borrelia bacteria, carried by blacklegged ticks. Researchers say the ticks causing Lyme disease have now expanded to half all the counties in the US, raising concerns for public health.
To this extent, the number of people coming down with Lyme disease tripled within the past 20 years in the US, with nearly 300,000 people affected yearly in the US alone.
The disease can be cured with effective antibiotics if properly diagnosed early, but when not diagnosed or treated early, it could result in joint stiffness, brain damage, and nerve pain among other serious infections.
There are predominantly two species in the US – the blacklegged tick (Ixodes scapularis) and the rare western blacklegged tick (Ixodes pacificus).
Researchers from the US Centers for Disease Control and Prevention (CDC), led by Rebecca Eisen, scoured reports published from 1996 to the present to obtain the geographical areas where the ticks can be seen.
Their study revealed that the ticks are now in 45.7% of US counties, as against the 30% there were in 1998. The blacklegged species dominate 37 states and the western species take up 6 states.
“Since the late 1990s, the number of counties in the northeastern United States that are considered high-risk for Lyme disease has increased by more than 320%,” Eisen says. “The tick is now established in areas where it was absent 20 years ago.”
Nearly 95% of most Lyme disease incidents are reported in 14 states in the northeast and upper Midwest, even though the chances of people contracting the disease is not equal in all counties.
The PLOS ONE journal carried a report published in 2015 where Isis Arsnoe, a parasitologist from Michigan State University reported that blacklegged ticks in the north and south of the US behave differently. Little ticks in the north are more active in seeking a bite – questing, while those in the south tend to stay more in their leaf litter.
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"Questing behavior is a key factor affecting the risk of tick bites,” Arsnoe said. "Ticks that stay buried in the leaves are not likely to have an opportunity to bite passing humans—and unless they bite they cannot transmit disease.”