Haemaphysalis longicornis: A tick of considerable veterinary importance, now established in North America

Haemaphysalis longicornis, the “Asian longhorned tick” (ALT), is native to eastern Asia and has spread to Australia, New Zealand, and several Pacific islands, where it is a threat to the health and welfare of wild and domestic animals (1,2). This tick is now established in the United States. Large numbers of all active life stages were collected from sheep, humans, and vegetation on a ranch in Hunterdon County, New Jersey, in October 2017 (3). From April to September 2018, numerous ALTs were collected from vegetation, domestic animals, wildlife, and humans in 8 additional States (4). Retrospective examination of tick collections revealed that populations were present in New Jersey as early as 2013 (5). Fortunately, this tick has not been detected in Canada; this was confirmed through re-examination of Haemaphysalis species held in the Canadian National Collection, Ottawa (Wayne Knee, Canadian National Collection of Insects, Arachnids and Nematodes, personal communication, 2018).

Life history and biological traits of ALT promote its continued range expansion. Asian longhorned ticks are 3-host ticks, with larvae, nymphs, and adults feeding on separate individuals of a wide range of wild and domestic species (6), including birds, domestic animals, livestock, and humans. Once introduced into suitable habitats, ALT populations can build rapidly, partly because the strain introduced into the United States is parthenogenic (3). Preliminary analyses of the potential geographic range in North America, based upon habitat suitability and the environmental requirements of H. longicornis in New Zealand (2), indicate a potential for ALTs to establish in parts of Quebec, Ontario, and Manitoba (7). Although these early models are imperfect, they serve as a warning that parts of Canada likely meet minimum criteria to support ALT populations.

Incursion and establishment of ALT populations in Canada represent risks to animal health/welfare because this species has been associated with several pathogens, including Theileria orientalis and 2 Anaplasma species (3,8). These ticks are also significant pests that can occur in large numbers; heavy infestations can lead to exsanguination (1). To date, pathogens have not been detected in ALTs collected in the United States; however, there is concern that this species may play a role in transmission of endemic tick-associated pathogens such as Anaplasma, Babesia, and Theileria species.

Early detection will be critical to implementation of suitable mitigation measures for minimizing risks associated with H. longicornis. Asian longhorned ticks are readily distinguished from species that commonly infest domestic animals and livestock in Canada, including the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and the blacklegged tick (Ixodes scapularis) (9). However, ALTs are difficult to differentiate morphologically from the 2 endemic Haemaphysalis species in Canada, particularly the larval and nymphal stages (6,9). Molecular methods may be required to confirm species identity (3). Endemic Haemaphysalis species typically occur on rabbits or birds, so the presence of Haemaphysalis ticks on other animals should raise suspicion, particularly when they occur in large numbers. To facilitate accurate tick identification, please contact your local/regional tick surveillance program or one of the authors, if you detect ticks on animals that are atypical or that you suspect may be ALTs.