In 2017, a New Jersey farmer discovered a significant number of ticks that were only on his sheep. Neither the sheep nor its owner had traveled from the farm or had come in contact with other livestock. Experts are scrambling to learn more about this latest invasive species. This tick has caused significant economic losses in Australia, New Zealand and China. As of July 2024, this pest has spread to 20 U.S. states and the District of Columbia.
Females can lay thousands of eggs without mating
Smaller than native ticks, the Asian longhorned tick (ALHT), Haemaphysalis longicornis, can be identified by the shapes of specific mouthparts, which require magnification, and by its lack of visible markings. Rosalie Ierardi, DVM at the veterinary medical diagnostic laboratory at the University of Missouri, says, “The ticks cannot be identified by their legs, which have no distinctive features relative to native ticks. Several native ticks have markings visible to the naked eye.”
Females make up the majority of ALHT populations, which replicate by parthenogenesis, like some aphids. Females can lay hundreds, if not thousands, of fertilized eggs without assistance from a male, which is very unusual in ticks. Researchers have only discovered a handful of males.
Ierardi says, “You need only one female to establish a new population. She’s capable of reproduction by herself, making these ticks adaptable and able to spread easily with this reproductive strategy.”
The ALHT also feeds on a wide variety of hosts. Humans have found them on their arms and legs. However, it seems to prefer wildlife and livestock for blood meals. It can potentially be found on all warm-blooded wildlife. This tick often travels on cattle, deer, dogs and birds. This pest has been discovered on migratory finches and Canada geese.
ALHTs are now in isolated pockets of Missouri, rather than contiguous counties; experts need more information to better understand their true populations in the state. Ierardi reports they climb grass or other plant stalks, then extend their long front legs, sniffing for a host with sense organs on the tips of their legs. Then, they attach to a passing mammal or bird.
“We only find this tick when we look for it,” Ierardi says. “Ticks may be in other [Missouri] counties. We haven’t found them yet. Because of staffing and funding, only so many folks are looking for ticks.”
The ALHT carries theileria, a disease caused by the protozoa Theileria orientalis, genotype Ikeda, that lives in the tick. Theileria orientalis Ikeda infects and destroys the red blood cells in cattle, other mammals and birds, causing anemia. “To our current knowledge, Theileria orientalis Ikeda doesn’t affect animals other than cattle and closely related cud-chewing animals,” Ierardi explains. “Asymptomatic infections have been reported in sheep. There are no reports of this organism causing infections in birds.”
In cattle, anemia leads to jaundice and production losses, such as weight loss or failure to gain, and lost pregnancies. “It looks like less than 5 percent of infected cows will become seriously ill,” Ierardi concludes. “Ninety percent of infected cattle will be clinically asymptomatic, displaying no symptoms. When it is recognized, it may have infected a number of cattle in the herd.”
Watch for theileria, which looks like anaplasmosis
Rosslyn Biggs, DVM, beef cattle specialist with Oklahoma State University’s Extension and College of Veterinary Medicine, says, “For many producers familiar with anaplasmosis, theileria caused by Theileria orientalis Ikeda looks similar. If a producer or herd veterinarian thinks it’s anaplasmosis and animals don’t respond to typically [prescribed] oxytetracycline, that could indicate we’re dealing with theileria, not anaplasmosis. The veterinarian will make an official diagnosis with a blood test.”
The ALHT must live on three different hosts during its life. “It spends 90 percent of its life cycle off of cattle,” Biggs explains. “The larvae, commonly called seed ticks, feed on smaller animals, such as mice and other rodents. During the nymph and adult stages of the life cycle, they will move to larger [mammals] like cattle. We can also see the tick on other species commonly around cattle operations, such as horses, sheep, goats and dogs. Once a tick enters a geographic area, we could potentially see large numbers of these ticks in two to three weeks.”
Although the tick and theileria, the disease it causes, are in the eastern U.S., it will likely make its way west. “First, we want to implement tick control,” Biggs recommends. “Consider pasture management, which is very challenging. It’s not as practical to spray pastures as it might be to treat a yard for cats or dogs. Try to keep pastures mowed. Controlled burns can help eliminate ticks.
“I don’t want to scare anyone at this point,” Biggs argues. “[In states where we haven’t had the tick or theileria], we need to be aware the Asian longhorned tick is a possibility. The tick can carry other blood-borne diseases. We must be vigilant by monitoring our cattle regularly and practicing tick control and pasture management where it is practical. If we suspect we may be dealing with an Asian longhorned tick, and potentially theileria Ikeda, we need veterinarian involvement. Make sure to build those veterinarian relationships well in advance of having a problem to discuss what measures ranchers need to take.”
If a producer finds an unusual tick, Biggs recommends collecting it and placing it in a jar with rubbing alcohol, also known as isopropyl alcohol. Contact the herd veterinarian, who can tell producers how to submit it to the state diagnostic lab or other research facility.
“This discussion is not to strike fear in any of our producers but to bring awareness to them. Be vigilant. Currently, no product is labeled to treat the disease theileria. Prevention and tick control are the best actions to take now.”
Check cattle often and isolate newly purchased cattle
Sonja Swiger, PhD, an entomologist with Texas A&M AgriLife Extension, says, “Asian longhorned ticks aren’t easy to identify. Producers should check cattle more often than they have in the past. If you see a tick that looks different, reach out to your extension agent or local veterinarian. They will pass it to your state animal health authority for identification.”
Pour-on products or sprays and insecticide eartags control this invasive species, which is great news. Swiger reports that producers who practice excellent fly management have fewer flies and ticks. “Not every pour-on works because there is always the resistance issue. Currently, we aren’t finding resistance with Asian longhorned ticks.”
Because these ticks are moving westward, Swiger recommends producers know where their new cattle come from before they receive them. “Quarantine newly purchased animals, keeping them separate from the original herd,” Swiger advises. “Inspect new animals and allow time to treat them to ensure they aren’t carrying a tick load. You have to scratch the animals and check crevices to find these small ticks. They like to congregate in the ears; that doesn’t mean that’s the only place they’ll be.”
People traveling with horses and dogs should be vigilant, especially in livestock arenas or when hiking with dogs in wooded areas. Scientists across the U.S. are studying this pest to learn more about its life cycle and the diseases it can spread to wildlife, ruminants and birds. Stay in touch with your extension agent and veterinarian to learn if your area has an occurrence of Asian longhorned ticks.
