Do Asian longhorned ticks bite humans?

The Asian longhorned tick (Haemaphysalis longicornis) has attracted a lot of media and research attention in recent years. It is an invasive species of tick that was brought to the United States in or before the early 2010s, and has spread to more than a dozen U.S. states since that time. Federal and states agencies closely monitor reports of H. longicornis sightings and extensive field collection is conducted when this tick is thought to have appeared in a new locale.

Do Asian longhorned ticks bite humans?

Yes, though we humans don’t seem to be their first choice (so far). Although the first “official” report through government and public health channels was released in 2019, TickReport passive surveillance had already identified three separate H. longicornis ticks that bit humans in 2017. H. longicornis bites on humans and pets have increased in that time, though people may have gotten a break in 2023 because of a rainy summer or other factors (see figure for annual submissions to TickReport for testing). Still, it’s reassuring that even in a big year of TickReport users being bitten by H. longicornis ticks as we saw in 2022, those bites represent a fraction of 1% of the human-biting ticks we tested that year. Familiar species like the deer tick (Ixodes scapularis), American dog tick (Dermacentor variabilis), and Lone star tick (Amblyomma americanum) are by far the most common human-biting ticks across the U.S..

H. longicornis ticks submitted to TickReport year over year, and the host they were reported as biting.

Although these ticks will certainly bite humans and pets when given the opportunity, they are most often reported on wildlife and livestock. They are aggressive feeders and large animals like cattle can host more than a thousand feeding ticks at a time! Heavy infestations can slow animal growth and can even kill weakened animals because of the sheer volume of blood that many ticks can drain from their host.

Do Asian longhorned tick bites spread disease?

Asian longhorned ticks are capable of transmitting a wide range of bacterial, viral, and protozoan pathogens, including some that are already found in North America or are closely related to North American pathogen species.

The good news so far is that these ticks haven’t seemed to acquire these pathogens in great numbers in the U.S.. None of the H. longicornis ticks we have received and tested in our lab have tested positive for any of the two dozen pathogens we target, and other researchers in state and federal agencies have similarly not detected pathogens in Asian longhorned ticks in the U.S.. As their range continues to expand and they interact with a broader range of reservoir hosts, it is certainly possible that surveillance will begin to see patterns of infection emerge.

Ignored surveillance data: an editorial soapbox

Public health narratives of the emergence of H. longicornis and its early interactions with humans tell a familiar story of passive surveillance data from TickReport testing not reaching the right audience, or not being considered as valid as those data that come through government-sponsored channels.

Both the first reported identification of the tick species on U.S. soil and the first reported bite of a person were incorrect by at least two years. The USDA confirmed the presence of the tick in 2017, but an engorged nymph was sent to TickReport in 2015. The first human bite was officially recorded in June 2018, but TickReport testing had already confirmed three human bites between May and August of 2017.

Nationwide surveillance of ticks and the pathogens they carry already exists, and that surveillance data is made available to the public in real time on our statistics page at no charge. Public health officials need to make use of this resource. TickReport testing identifies the expansion and migration of tick and pathogen ranges well beyond the territories established by surveillance projects that haven’t asked the right questions yet. Bourbon virus and Heartland virus discoveries in New York were triggered by TickReport submissions, as was the presence of Ehrlichia muris eauclairensis in Massachusetts. Tick testing serves both individual risk assessment and public health knowledge, but until public health researchers consistently make better use of the surveillance data we’ve curated through TickReport testing since 2006, education and research will lag years behind changes in tick risks.