The Asian longhorn tick (ALHT), native to eastern Asia, was first found in the U.S. in 2017. In less than a decade, ALHT populations are thriving. Established populations cover the East Coast from New York to Georgia, and all the way west to Missouri. And the disease-causing pathogen Theileria orientalis that they can carry also continues to spread.

Even though the ALHT wasn’t officially recognized in Iowa until 2025, Grant Dewell suspects that the pest showed up earlier but hadn’t reached population levels where it was easily identifiable. Dewell is an associate professor of veterinary diagnostics and production animal medicine at Iowa State University (ISU).

Dewell and his colleague Matt Brewer, an associate professor of veterinary pathology at ISU, said the ISU Veterinary Diagnostic Lab has confirmed cases of T. orientalis in at least four Iowa beef herds.

T. orientalis is a blood-borne parasite that can be transmitted to wild and domestic animals. In cattle, it causes a disease called bovine theileriosis. Signs of infection include weakness, fever, reluctance to walk, loss of appetite, difficulty breathing, reduced milk production, foamy nasal discharge and abortion.

According to Brewer, T. orientalis has been present in the U.S. for a few decades, but disease transmission was relatively rare since a less pathogenic strain of the parasite was present. A more pathogenic strain of it was first discovered in Virginia in 2017.

“Now that we have the tick here, then the movement of this parasite is going to be a lot easier,” Dewell said.

The ALHT prefers to feed on hoofed animals, but it is opportunistic and will take a blood meal from any host. The ticks are often transported via birds and white-tailed deer. Another successful strategy of the ALHT is that individual females can lay eggs without mating, essentially cloning themselves to create the next generation.

“One reason why we see these massive numbers is that we have a tick that is able to reproduce on its own,” said Dewell.

There are four life stages of the ALHT: egg, larva, nymph and adult. Larvae, nymphs and adults take one blood meal as they transition to the next life stage. After each successful blood meal, the tick releases from its host, molts and then begins to look for its next host. It is during the blood meals of nymphs and adults that T. orientalis can be transferred to a host such as a steer.

Groups that may be particularly susceptible to disease from bovine theileriosis include young animals, naïve animals that have been introduced from regions without exposure to T. orientalis, bulls during breeding season and late-gestation cows.

Naïve animals are most susceptible. “This results in sort of a sudden acute disease or possibly none at all, typically followed by periods of stability. We expect that probably we’re going to see some morbidity and potentially mortality associated with this disease, but we expect that once it becomes endemic, we should have a relatively stable situation,” said Brewer.

Currently, there are no approved drug treatments for T. orientalis; therefore, all management and control efforts must be focused on controlling the ALHT. The ALHT prefers a humid environment, so Dewell and Brewer suggested one helpful practice may be burning pastures in spring to kill overwintered larvae. If burning is not an option, mowing any woody areas around pastures can help reduce ALHT populations.

“It doesn’t stop a bird or white-tailed deer from moving in, but the ticks aren’t going to move past it on their own,” said Dewell.

The pair recommended using a pour-on, pyrethroid-based product on cattle prior to spring turnout. (Be sure to read manufacturers’ labels for proper application.) When tick numbers increase and to obtain better skin penetration, pivot to using an organophosphate carried in diesel fuel applied to a back rubber. Consider a macrocyclic lactone such as ivermectin when tick numbers become excessive; however, ticks usually have to bite to be affected by this medication.

At this time, ALHT is not thought to pose a threat to human health in North America. It has not yet been demonstrated that the ALHT is capable of transmitting human pathogens in the U.S. For example, while AHLT has been found to obtain the bacteria that cause Lyme disease, it appears to be an inadequate host and loses the pathogen when the tick molts to another life stage.