The Connecticut Agricultural Experiment Station (CAES) has reported the first evidence of the invasive longhorned tick, Haemaphysalis longicornis, being infected with Ehrlichia chaffeensis in the United States. This discovery was published in the Emerging Infectious Diseases journal and is based on collaborative research by CAES and USDA scientists.
Since its initial appearance in the U.S. in August 2017, the longhorned tick has spread to at least 21 states, mainly in the east and northeast, including Connecticut, as well as the District of Columbia. Native to eastern Asia, this tick thrives in warm, humid environments and is also found in Australia, New Zealand, and several Pacific Islands. It reproduces parthenogenetically and feeds without restriction.
Ehrlichia chaffeensis is a Gram-negative bacterium primarily transmitted by the lone star tick (Amblyomma americanum). It infects monocytes and causes human monocytic ehrlichiosis (HME), which can lead to severe symptoms if untreated. There is no vaccine for ehrlichiosis; prevention involves avoiding tick bites on humans and pets.
Between 2001 and 2019, HME cases rose from 142 to 2,093. In Connecticut alone, cases increased from two between 2008-2018 to 28 between 2019-2023. Dr. Goudarz Molaei of CAES highlighted that “the first fully engorged human-parasitizing longhorned tick specimen was recorded by the CAES in 2018 from Fairfield, Connecticut.” Since then, these ticks have expanded into various counties.
The longhorned tick poses risks to both domestic animals and wildlife due to its ability to feed on a wide range of hosts. While it has been collected from over 40 mammalian and bird species in the U.S., its frequency of infesting humans remains uncertain. The tick can carry pathogens causing diseases like Lyme disease and anaplasmosis; however, its role in spreading these diseases is still unclear.
Dr. Molaei emphasized that “a rigorous program in mitigating risks should include expanded tick surveillance programs” among other measures. Public awareness about invasive ticks and emerging illnesses is crucial for health safety.
Further information about CAES’s Tick Testing Laboratory and related topics can be accessed through various online resources provided by health organizations.
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