Ticks, ticks, and more ticks
The Deer Task Force is charged with advising the Town Council on ways to dramatically reduce or eliminate deer on Block Island in order to reduce the incidence of Lyme Disease and other tick-borne disease.
At the meeting on September 7, Chair Sue Hagedorn presented the DTF with a report she received from researchers Dr. Danielle Tufts of the University of
Pittsburgh and Dr. Maria Diuk-Wasser of Columbia University, who have been studying Block Island’s ticks for ten years. The researchers have specifically been studying two tick species native to North America, the lone star tick and the rabbit tick. Both ticks are expanding their ranges in the United States and have come to Block Island, though both species are currently much less common on the island than the deer tick, also known as the blacklegged tick. The blacklegged tick is the usual suspect in cases of Lyme disease on the island.
The lone star tick has been steadily increasing in numbers, however, on Block Island and elsewhere. Researchers in New Jersey report the lone star tick is becoming the dominant tick in their area, surpassing the number of blacklegged ticks within a few years. On Block Island, the researchers recovered one lone star tick in 2010, and 1,330 in 2019. Most of the lone star ticks discovered in 2019 were larvae, rather than nymphs or adults. In 2020 and 2021 the researchers were hampered by Covid and budget constraints and only came to Block Island once in 2020 and three times in 2021. In normal years, the researchers collect samples each week from May to August.
Ticks were collected for the study by dragging a corduroy cloth along the ground at the edge of dense vegetation and stopping every 10 meters to remove the attached ticks. Additionally, biweekly small mammal trapping occurred, and birds were sampled using mist netting techniques.
As the lone star tick does not carry Lyme disease, it is sometimes viewed as less harmful than the blacklegged tick. But lone star ticks have come to be associated with several human diseases including tularemia, ehrlichiosis, Heartland virus disease, red meat allergy, and southern tick-associated rash illness or STARI (which presents a Lyme-like rash). Dr. Goudarz Molaei reported in the New England Journal of Medicine that “symptoms of STARI and early Lyme disease are similar, and STARI may be misdiagnosed as Lyme disease in areas with both lone star ticks and blacklegged ticks.”
Lone star ticks are larger and are also considered more aggressive than the blacklegged tick, due to their “indiscriminate biting habits.”
While studying these two tick species, both native to the United States, the researchers discovered two non-native species of tick on Block Island: the
red sheep tick, and the Asian longhorned tick. The red sheep tick is native to Europe, eastern Asia, and Africa. According to Drs. Tufts and Diuk-Wasser,
this is the “first documented discovery of the red sheep tick collected from the environment in the western hemisphere.” The Asian longhorned tick is native to East Asia and this is the first time it has been observed in Rhode Island.
The researchers found red sheep tick larvae on both bird and mammal hosts, although both tick species prefer mammals. Only two Asian longhorned ticks were observed during the study, one in 2018 and another in 2019. The research team encountered many more red sheep ticks, however. Red sheep ticks were found almost every year during the ten-year study, more than six individual adults were discovered during that time, and individual ticks in different life stages were encountered, leading the researchers to conclude that the species is “established” on Block Island. Dr. Tufts told The Times that she believes the ticks are “feeding on deer, as we have not found them on any of the other animals we have sampled (mice and birds).” While larvae and nymphs feed on ground nesting birds, adults prefer large mammals such as deer.
According to the U.S. Department of Agriculture, the red sheep tick transmits a variety of diseases to cattle, horses, dogs, and sheep. They also transmit several diseases to humans, including tick paralysis, tick-borne encephalitis virus, Tribec virus, Bhanja virus, Crimean-Congo hemorrhagic fever virus,
Coxiella burnetti, and Francisella tularensis.
Asian longhorn ticks were found by researchers to be carriers of, but were not carriers of Lyme disease.