Ticks are hitching a free ride to the US from different parts of the world, raising concerns among scientists. In a recent study, researchers reported the introduction of seven exotic tick species to Connecticut, U.S., by travelers between 2019 and 2023. The identified ticks were natives of Germany, Guatemala, Costa Rica, Poland, Scotland, Tanzania, and Belize.
Rising international travel and animal trade are introducing exotic tick species into the US, creating the troubling possibility that both the ticks and the pathogens they carry establish a permanent foothold in the country. Setting up surveillance programs that include tick species identification and pathogen screening can help protect human and veterinary health, according to the researchers.
An estimate by the Centers for Disease Control (CDC) suggests that approximately 476,000 people may be diagnosed and treated for Lyme disease each year in the United States. The disease is caused by bacteria transmitted to humans through infected tick bites, especially those of the blacklegged tick, also known as the deer tick, found in the northeastern, mid-Atlantic, and north-central United States. The symptoms can range from a simple rash to joint pain and serious neurological problems. Bites from the lone star tick can give rise to the Alpha-gal syndrome (AGS) in which people develop an allergy to alpha-gal, a sugar found in red meat. While in most cases the allergic symptoms are limited to vomiting and diarrhea, in some cases the reaction can escalate to anaphylactic shock.
The list of recognized tick-borne pathogens has significantly grown over the last two decades. At the same time, more than 140 nonnative tick species have entered the U.S. in the past 50 years, some of which, like the longhorned tick (Haemaphysalis longicornis), have rapidly proliferated and established thriving populations across multiple states.
An increase in tick population elevates the number of possible human-tick encounters, thus increasing the chances of being exposed to disease-causing pathogens. Accurate identification of ticks is a crucial step in assessing the risk of acquiring a specific tick-borne disease. The team received ticks removed from travelers returning to Connecticut from across the globe. They examined each tick under a dissecting microscope to identify its species based on taxonomic markers and noted potential pathogens. Unfamiliar specimens underwent DNA analysis, which confirmed their species and screened them for pathogens.
Out of the seven ticks identified, two Amblyomma mixtum nymphs (one from Guatemala and one from Costa Rica) tested positive for Rickettsia amblyommatis. While the medical significance of R. amblyommatis remains uncertain, some cases of Rocky Mountain spotted fever are caused by a pathogen belonging to the same group of bacteria. The findings highlight the risk of invasive ticks and their pathogens spreading to new areas of the US.
The researchers emphasized the need to provide clinicians and public health officials with information about various tick species, including how to distinguish between native and non-native ones. Public awareness programs that provide travelers with advisories, such as avoiding tick exposure by staying alert to their surroundings and checking for possible bites, can also help prevent the importation of these potential vectors into the US.
