Tick watch accelerates

American agriculture has a new enemy that’s posing massive headaches for livestock owners in the eastern half of the country. The Asian longhorn tick is swarming pastures and spreading sickness to cattle as far west as Oklahoma.

This tiny, unique animal’s most alarming trait is its ability to reproduce asexually. A single female can clone herself to lay up to 2,000 eggs without a mate, triggering massive, sudden tick infestations, said Tara Felix, PhD, Extension beef cattle specialist at Penn State University.

“A single tick can start a new population,” Felix said. “They’re nearly 100% female, so virtually all ticks can lay eggs, resulting in massive population explosions.”

Cattle infested with Asian longhorned ticks (Haemaphysalis longicornis) can literally be attacked inside and out. Hundreds or thousands of ticks can attach to and feed through the hide of a cow—typically congregating in the ears, groin, and tailhead. In high numbers, the blood loss alone can be fatal to the animal.

The ticks can also transmit a protozoan parasite, Theileria orientalis (Ikeda genotype) into a cow’s bloodstream. The parasite destroys red blood cells, resulting in bovine infectious anemia. The visible clinical signs of theileriosis are fever, lethargy, reduced appetite, weakness, and occasional abortions.

The native range of this tick species includes eastern China, Japan, the Russian Far East, and Korea. It has spread to Australia, New Zealand, and several island nations in the western Pacific Region.

In 2017, this tick was found in the U.S. on a sheep farm in New Jersey. It may have been in the country as early as 2010 but was undetected.

Symptoms mimic bovine anaplasmosis, but a crucial distinction is that theileriosis frequently affects calves and young stock under two years old, whereas anaplasmosis rarely does.

Members of the National Cattlemen’s Beef Association (NCBA) have been keeping close watch on the spread of the Asian longhorned tick for several years. The organization recently ramped up pressure on U.S. Congress and USDA to provide research funding for specific Asian longhorned tick control measures and expand surveillance of the tick and its diseases.

Missouri Cattlemen’s Association president Anita Vanderwert recognizes that the tick has been costly to cattle producers. She’s backing NCBA’s push to get help for this growing national animal health concern.

“We need to find a way to control this disease and protect our herds against bovine theileriosis,” Vanderwert said. “We’ve got to get on top of this.”

She says the USDA’s Animal Health and Plant Inspection Service needs more money to find a solution for the problem.

“This tick species is of great concern, but producers can protect their herd through frequent inspection and by reporting sightings to their veterinarian,” said Kathy Simmons, DVM, NCBA’s chief veterinarian. “Our goal is to inform and educate cattle producers across the country about this potential threat.”

West Virginia is a hotbed for the Asian longhorned tick. Jerry Yates, the state’s Beef Quality Assurance coordinator, said help in dealing with the invasive pest can’t come soon enough.

“We’re polluted with them,” said Jerry Yates, stationed at West Virginia University’s Reymann Memorial Farm in Wardensville. “It’s a good bet if a cattle farmer around here doesn’t already have this tick on their place, they’ll get it sooner or later.”

Yates also manages the West Virginia Bull Evaluation Program, overseeing sire performance testing that evaluates the genetic potential and feed efficiency of bulls. He’s seeing a lot of bull buyers actually choosing to purchase bulls from tick-infested herds—something that goes against most rules of livestock biosecurity.

“Bull buyers who already have theileriosis on their farms would be ill-advised to introduce tick-naïve animals into their herds,” Yates explained. “They’re better off buying bulls that have lived through the infection.”

Indeed, when a herd is constantly exposed to ticks in an endemic region, most cattle develop pre-immunity early in life. As a result, the herd achieves “endemic stability,” whereupon infection rates can be incredibly high, but visible sickness and death drop significantly.

“The good news is that over time the animal builds a natural resistance to the ticks,” said Cassandra Olds, Kansas State University entomologist. “And so in places where we've seen hyper infestations, tick levels have now gone back down to normal because the animals naturally acquired resistance.”

Yates reminds producers, though, that commonsense biosecurity would say that acquiring livestock from regions where the Asian longhorned tick is endemic poses a risk of introducing the disease into previously unaffected areas or naïve herds. 

Calves do not receive protective immunity to Theileria through colostrum. Because there is no in-utero transmission, every calf is born completely naïve. In endemic zones, up to 80% of calves are infected by three months of age, experiencing a mild form of the disease while they build their own cell-mediated immunity.

Because immunity relies on a delicate balance between the host’s immune system and the active parasite, any major physiological stressor can break this suppression. Calving, weaning, transportation, or poor nutrition can cause the parasite to flare up, leading to a sudden relapse of clinical anemia and illness.

There’s currently no specific treatment for theileriosis, and no vaccinations to protect cattle. Essentially, products labeled for on-animal tick control are effective against Asian longhorned ticks, according to Oklahoma State University Extension livestock entomologist Jonathan Cammack.

While preferring temperate, humid climates in pastures and meadows, this tick is highly adaptable. It can enter a dormant state to survive freezing winter temperatures. Livestock entomologists agree it is an incredibly resilient invasive species with unique biological traits that allow it to quickly populate and survive in diverse environments.

According to the University of Missouri Extension, beef producers who have lost cattle to Theileria orientalis may qualify for financial assistance through USDA’s Livestock Indemnity Program.

Globally, theileriosis poses a severe threat to livestock economics, causing a 1% to 5% baseline mortality rate that can spike up to 50% or more in highly virulent strains or stressed, naive herds.