The Asian longhorned tick (ALHT) poses a serious threat to cattle health. ALHTs carry Theileria, which is a protozoan parasite that infects red and white blood cells. It can lead to anemia and, in some cases, death.
In the U.S., ALHT was first detected in New Jersey in 2017. Since then, it has spread to more than 20 states. With the recent discovery of ALHT in southeast Iowa, the Iowa Cattlemen’s Association hosted a webinar lead by Cassandra Olds, Kansas State University Extension entomologist, who explained the tick and pathogen background, its potential impacts, best practices for prevention, as well as caring and treatment strategies.
“This was always a when, not an if,” Olds explains. “You did absolutely nothing wrong. If you have the tick or the pathogen, this was an inevitable thing.”
What We Know about ALHT and Theileria
Biologically, the ALHT is a three-host tick, meaning each life stage — larva, nymph and adult — feeds on a different host. Olds says unlike other tick species, it can reproduce asexually, with all adult ticks being females capable of laying eggs without mating. This characteristic allows for rapid population growth, as a single tick can potentially establish an entire population.
Once an animal is infected with Theileria, it becomes a chronic carrier for life, with the potential to relapse during high-stress periods. The pathogen replicates in red blood cells, causing anemia and a range of symptoms including loss of appetite, weight loss, fever and respiratory issues.
Olds says while the first year of exposure can be challenging, long-term production impacts are typically minimal. The key is to approach the situation with knowledge, preparedness and a calm, strategic mindset.
She stresses that just because a cow herd does not have the symptoms doesn’t mean it doesn’t have Theileria. It just means that if an animal was infected, it didn’t develop the disease.
She reports mortality rates due to Theileria range from 5% to 20%. With the highest mortality when pathogen is first introduced — the outbreak. An animal can have a relapse of disease, often during high stress or immune compromising events.
She explains the high-risk animals are young (under 6 months), pregnant animals, stressed animals and any naïve animal moving into an area with previous outbreaks.
Best Practices for Prevention
Olds notes the pathogen can spread through tick bites and through shared veterinary needles. She says her team is currently researching the role of biting flies in transmission.
She stresses the importance of maintaining animal health and reducing stress to prevent disease outbreaks.
“Keep animals happy and healthy. Stress does weird things to immune responses,” she adds.
According to Olds these strategies can help control AHLT:
- Burning pastures
- Keeping grass short
- Careful use of insecticides
- Pasture rotation
- Ear tags and pour-ons
Real-World Experience
Veterinarians John Currin and Austin Williams share their firsthand experiences with ALHT and Theileria.
Currin serves as associate professor and production management medicine with the VA-MD College of Veterinary Medicine at Virginia Tech. He says in his area more than 90% of the herds are infected and many don’t know they’re infected.
“The tick epidemiology is — I’ll use a scientific term — weird,” he says.
He explains as the disease became endemic in Virginia, its clinical presentation changed. While it initially affected adult pregnant cows, it now more commonly impacts 2-month-old calves in spring calving herds.
“There is no in utero spread of this organism, so every calf starts naïve,” Currin says.
Approximately 80% of calves in infected herds become positive by 3 months of age, though most do not show severe clinical signs.
He adds contrary to initial concerns the Theileria appears to have minimal impact on cattle in a feedlot. Currin says research found no significant differences in weight gain between negative and positive cattle.
He stresses the primary concern is for cow-calf operations bringing naive animals into infected areas.
Currin shares these key points about Theileria:
- 99% of herds will experience minimal problems
- Most infected animals show no significant clinical signs
- The disease primarily causes anemia
- There’s no direct treatment available
- Positive tests are now almost meaningless in endemic areas
Williams serves producers in northwest Arkansas and southwest Missouri.
“I think it’s been here longer than we recognize and it’s more widespread than what we realize it too,” he says. “I would say some states have it that don’t know they have it.”
In Williams’ area he has seen the tick infestation become widespread. The key challenges he’s witnessed is the difficulty of managing the tick population and the potential for secondary health issues in infected cattle.
He recommends individual herd management strategies, including regular checks, treatment plans and potentially moving infected herds to different pastures.
Treatment Strategies
There are currently no labeled treatments for the disease or a definitive cure. Typically, treatment focuses on secondary issues and providing basic care.
Avoid mass injecting ivermectin, as it can cause resistance and harm beneficial insects like dung beetles.
“Please don’t just mass inject everybody with ivermectin because you’re worried about the Asian longhorned tick,” Olds says.
Vaccine Developed
Medgene has developed a tick vaccine that is designed to work on multiple tick species, including ALHT. Veterinarians can purchase directly from Medgene. The vaccine requires two initial doses, followed by yearly booster shots.
Williams says he’s had clients use the vaccine this year, and he’s hopeful about the vaccine’s potential and is waiting for more research from the University of Arkansas to provide concrete data on its effectiveness.
Gary Bosch, Medgene executive vice president, says animals should be vaccinated before they encounter ticks.
“In the Southern U.S. where ticks are a year-round problem, early vaccination is especially crucial because the Asian longhorned tick can overwhelm an animal very quickly,” he says.
Industry Impacts
Olds says the goal is to achieve “endemic stability” — when most animals are exposed early and develop lifelong immunity with minimal disease symptoms.
She emphasizes the need to remove the stigma associated with the tick or pathogen presence, noting that infection is an inevitable part of agricultural reality. Producers should focus on proactive testing, management and community support.
To prepare for and to deal with Theileria, Olds recommends producers:
- Establish a good relationship with a veterinarian
- Conduct regular herd testing
- Maintain low-stress environments
- Implement careful tick control measures
- Share information and support each other as a community
Her final advice is to be vigilant but not panicked.
“Producers should view the Asian longhorned tick as a manageable challenge rather than a catastrophic threat,” she summarizes. “By working together, maintaining animal health and implementing smart management strategies, the agricultural community can effectively navigate this emerging issue.”
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