By Alan C. Graham, State Entomologist, Vermont Agency of Agriculture, Food & Markets
The blacklegged tick or deer tick may transmit Lyme disease and other tick-borne diseases in Vermont. Thirty years ago the tick was not found in the state, but now it is commonly found in many areas. Along with increased numbers of blacklegged ticks, we are also finding an increase in the number of reported cases of Lyme disease. Currently Vermont, New Hampshire, and Maine are among the states with the highest per capita rate of Lyme disease.
There are 13 tick species in Vermont. Most species are difficult to find, but the blacklegged tick, Ixodes scapularis, is now found in every county in the state. It was originally described by Thomas Say in 1821, when it was typically found in the southeastern part of the United States. In the 1980s this tick started becoming more abundant in New England. This discovery was so unusual that one researcher at Harvard, Andrew Spielman, originally reported it as a new species.
The blacklegged tick has a 2-year lifecycle. Eggs hatch in June and July into a tick larva. This life stage is unusual in that it has 6 legs, compared with the usual 8 legs found in adult ticks. The larva looks for a small rodent host on which to feed, and then drops off to molt in September. This is a process in which the larva sheds its skin and becomes a nymph with 8 legs. Nymphs winter over from October to April and are safe in the leaf litter under snow cover, protected from extreme temperatures. In April, May, or June, nymphs look for another rodent host and feed. They drop off in September and molt to become an adult. Any time during the fall and winter when the temperature is above 50 F, adult ticks may be found “questing” for a large animal host. The deer is a preferred host, but humans, dogs, and other mammals may be selected.
In 2015 the Vermont Agency of Agriculture surveyed in 7 counties to look for blacklegged ticks and 3 tick-borne pathogens: Lyme disease (Borrelia burgdorferi), Anaplasmosis (Anaplasma phagocytophilum), and Babesiosis (Babesia microti). Most of the ticks collected were blacklegged ticks. Dog ticks, Dermacentor variabilis, may occasionally show up during the warmer months of the year. Of the 659 blacklegged ticks tested by the Vermont Agency of Agriculture laboratory in Burlington, 58% carried Lyme disease. Another 10% had the bacteria Anaplasma, and 1 site in Bennington had 5 ticks with Babesia (0.8%), a disease not previously found in either ticks or humans in Vermont. Two pathogens were found in 56 ticks (8.5%), and 1 tick had all 3 pathogens. The survey did not look at blacklegged nymphs. The highest rate of Lyme disease transmission in Vermont is in July when the nymphs are active. They are small and easy to miss when doing a body inspection. You may not even notice that you have been bitten.
For those of us who work outside, this finding means that we need to change our behavior. It is important to do tick checks on ourselves, our children, and our pets. The Vermont Department of Health recommends that we use a tick repellant, one recommended by the CDC. Ticks attached to a human for more than 36 hours may transmit disease. Clothing treated with the pesticide Permethrin is recommended for hunters and loggers who are especially at risk for ticks and tick-borne diseases. There are few other tick management options at this point. Some possible options include reducing deer numbers on islands in Maine, mouse and deer stations baited with a pesticide, pesticide treatment on the ground, and landscape modifications. The use of Guinea fowl to control ticks has been popular, but scientific studies have not found these birds to be effective. Ticks do not do well in dry environments. Cutting grass and opening up forest edges can be helpful. Hope for the future may focus on biological controls that would reduce the population of this species.
For more information see:
Tick Management Handbook CAES: http://www.ct.gov/caes/lib/caes/documents/publications/bulletins/b1010.pdf