In an article published in the Journal of Entomology, authors looked at the incidence of blacklegged ticks across counties in the US and compared the number in 2015 with those previously reported in 1998. According to the authors, there is a 44.7% increase in the number of counties with ticks in 2015 over the number reported in 1998. The majority of the changes occurred in the Northeastern and North Central United States. This study is important because it shows the migration of the ticks causing a number of illnesses. Tick vigilance is becoming increasingly important even in areas where none were thought to exist. To look at this information by county, see the journal article. The graph, taken from the article shows the difference in time periods and the migration of the ticks.
The information on Lyme disease presented on this web site has been reviewed and approved by one or more members of our Medical Leadership Board.
A multitude of environmental and human factors has created a near “perfect storm” over the past 20 years leading to a population explosion of ticks throughout North America.
There are two families of ticks found in the United States: Ixodidae (hard ticks) and Argasidae (soft ticks). Of the 700 species of hard ticks and 200 species of soft ticks found throughout the world, only a few are known to bite and transmit disease to humans.
Hard ticks and soft ticks have different life cycles, growing larger and changing their appearance at each stage.
Hard ticks (Ixodidae) begin as an egg that is laid by an adult female tick. Once the egg hatches a larva emerges that must then find and feed on a small mammal or bird (host). After feeding it drops to the ground from the host and goes through a molting process, emerging as a nymph.
Nymphal hard ticks then seek larger hosts, and after feeding drop off and molt into adults. The life cycle of hard ticks lasts one to two years depending on the species. The bite of a hard tick is generally painless, with a feeding process lasting several hours, to days, even weeks.
Soft ticks (Argasidae), like hard ticks begin as an egg, hatch into a larva, feed and then molt into a nymph. Nymphal soft ticks may go through as many as seven phases as nymphs, requiring a blood meal at each stage.
Soft ticks’ life cycle lasts from months to years depending on the species. The bite is typically painless and only lasts 15-30 minutes, making it harder to detect.
While both hard and soft adult ticks are easiest to identify, it is important to note that nymphal ticks are equally capable of transmitting disease. In some areas the nymphal tick infection rate is actually higher than the adult tick infection rate.
The following is a list of ticks found in the United States that are known to bite and transmit disease to humans:
See link above.