A new tick-borne disease is killing cattle in the US

A new tick-borne disease is killing cattle in the US

In the spring of 2021, Cynthia and John Grano, who own a cattle operation and sell performance horses in Culpeper County, Virginia, started noticing some of their cows slowing down and acting “spacey.” They figured the animals were suffering from anaplasmosis, a common infectious disease that causes anemia in cattle. Their veterinarian Melinda McCall warned them that another parasite-borne disease was rapidly spreading in the area.

After a third cow died the Granos decided that they would test their blood. The test was positive for the disease, theileria. The cows died without any treatment. Cynthia saw a cow that had been separated from the herd in September. By then, Cynthia had lost seven cows and seven calves. She was walking up to the cow when it suddenly charged at Cynthia, knocking her over and breaking her shoulder blade. The cow was dead by that afternoon.

Cattle owners like the Granos are not alone. This new disease is affecting livestock producers across the country. Even though the disease is rapidly spreading west, researchers aren’t sure how it will develop in the United States. The disease could spread rapidly across the country if states fail to control it. This could lead to massive production losses for individual operations as well as the entire industry.

Theileria, which is in the same family as malaria, is being transmitted largely through the Asian longhorned tick, an invasive species first discovered in the US in 2017. The tick is native to Japan, China, Russia, Korea, and China. Theileria has spread to the US. It has been detected in cattle in West Virginia and Kansas. Some sale barns in Virginia saw the prevalence of theileria increase from two to 20 percent in just two years.

Theileria can cause cows to abort their fetuses. Anemia can also result in the death of a cow. In Australia, where the disease has been spreading since 2012 and now affects a quarter of the cattle, theileria costs the beef industry an estimated $19.6 million a year in reduced milk and meat yields, according to a 2021 paper. In Japan and Korea, the combined loss is an estimated $100 million annually. Kevin Lawrence, an associate professor at Massey University who studies theileria in New Zealand, says that country has managed to avoid abortions because 95 percent of cows calve in the spring there, the same season he’s seen theileria infecting cows. Calving season in the USA can occur all year. He says, “I think in America you’re going to be seeing abortions.” “You’re going see deaths.”

Yet, the US livestock industry seems to be trying to minimize concern, despite acknowledging the danger posed by theileria. According to the National Cattlemen’s Beef Association (one of the largest cattle lobbying organizations), the incidences of the disease in the United States are rare. That contradicts the experience of McCall, the Granos’ veterinarian, who in 2020 encountered theileria in 40 of the Virginia farms she serves. McCall says that it will cause a lot of economic losses for producers, regardless of whether they are aware.

tick's eye view through the grass of a cow


The US Department of Agriculture has funded cooperative agreements with the Virginia-Maryland College of Veterinary Medicine and the University of Georgia to better understand the distribution of the disease and the Asian longhorned tick, respectively. McCall and others feel that the agency has not done enough. McCall states that it is difficult to get the USDA to pay attention because they don’t believe it’s causing many problems. “And that’s like, ‘Wow, you have no idea how many problems it’s causing and how widespread it could be.'”

In a 2019 paper about monitoring the Asian longhorned tick, the USDA acknowledged it failed to contain the problem. It says that its original goal was to eradicate the tick species. The tick’s spread has made it impossible to achieve that goal. Now, the agency and its partners seem to be playing catch-up to the dismay of researchers.

There is no national program to combat infestation. Denise Bonilla is the USDA’s cattle fever tick program coordinator. She says that the USDA doesn’t have enough funds to create a framework for this issue. Although she says that the agency has not been behind, she adds that “if you ask someone whose animals died if the effort to control theileria is happening fast enough, they will probably tell you no.”

Vaccines are still items on a wishlist. People in the field cannot access vaccines and treatments for infection until they are widely available. Sometimes even that process has been slow or nonexistent. The Asian longhorned tick continues its rapid growth. The US could face a serious public health crisis if it spreads diseases to humans as it has in other countries.

It can be difficult to pinpoint when an invasive species makes landfall, but research scientist Andrea Egizi remembers when the Asian longhorned tick first crossed her radar. Egizi, who runs a tick-borne disease lab at Rutgers University, was sitting in a monthly meeting in 2017 with various state agency representatives. Tadhgh Rainey (head of the Hunterdon County Department of Health’s mosquito and vector disease control section) mentioned that a local resident showed him a sample of ticks she had found on her sheep. Unknowingly, she had thousands of ticks on clothes. They looked like tiny particles of dust. Rainey noticed that the ticks’ mouth parts were larger than the others. He also noted that the body was more circular than any other species.

Egizi volunteered to perform a genetic assessment, which revealed a 99.9 percent match to the Asian longhorned tick, making this the first confirmed sighting of the species in the wild in the United States. Egizi was shocked and unsure of who to alert. She contacted Rutgers University’s Center of Vector Biology and notified the USDA and the US Centers for Disease Control and Prevention. Egizi claims that the USDA was eventually given responsibility for tracking the tick because it poses a greater threat to livestock than it does to human health.

Thanks to studies of the tick’s behavior in other countries, we know that it is a major cattle pest and a “frequent” parasite to people, according to a paper co-authored by Egizi. It can transmit the SFTS virus to humans and can cause Japanese spotted fever. The tick prefers to feed on domestic animals and wild animals in the US. Theileria–in particular a virulent genotype called Theileria Orientalis Ikeda–has been known to exist in the US about as long as the Asian longhorned tick.

Scientists don’t know whether the tick or theileria entered the country first. The most plausible explanation is that the tick came to the country uninfected and was fed by a cow infected with some other disease. Theileria spreads through blood. It can also be transmitted by common needles, lice, mosquitos and biting flies. The Asian longhorned tick is a powerful vector for the disease. The tick can reproduce the disease easily. The Asian longhorned tick is parthenogenetic, which means that females can reproduce with or without a male. It reproduces faster than other sexual species, such as the blacklegged tick (also known as the deer tick), which is found in the eastern United States. Every female can lay 1,000 to 2,000 eggs at a time and thousands of ticks can be found on a single animal, according to the CDC.

“We started getting more reports that it’s in more New Jersey counties, more states,” says Egizi. “And it spiraled from there.”

Since the discovery in the US in 2017, the Asian longhorned tick has spread to as many as 17 states. There have been increasing reports of tick-borne diseases in cattle and humans as the tick’s range has expanded. Though he did not get sick, a 66-year-old man in Yonkers, New York, in 2018 became the first person in the US to suffer a confirmed bite from an Asian longhorned tick; they were found on his mowed lawn. And according to an internal USDA email, there have been five collections since 2017 of the tick hosting on humans in Fairfax County, Virginia. According to USDA data, there have been ticks detected on human hosts in New York, Pennsylvania, Maryland and New York.

closeup of tick, also a blade of dry grass with a cluster of ticks
Many longhorn ticks can cluster on a single stalk until a host passes close enough.


Both researchers and those in the livestock industry stress that theileria cannot make people who eat the infected meat sick, but some worry about the link regardless. Jaydee Hanson is the Center for Food Safety’s policy director. He says that any sick animal should be removed form the meat production system. He says that sick meat and dairy animals are more susceptible to illnesses such as Shiga toxin-producing E.coli and salmonella.

However, at the moment, sick cows are not being removed from their herd. Steve Hopkins, a Virginia farmer, believes that infected cows should remain unaffected to build immunity. Treatments have been successful in Australia with the antiprotozoal buparvaquone. However, the drug remains in the cow’s system for too long to be considered safe for use in food animals. It is not allowed to be used outside of the lab.

Even tracking the spread of the disease is challenging. There is currently no national testing program or requirement for sick animals to be culled. A blood test for theileria costs about $50, though the hope is to reduce the price to $5 or $10. Even if theileria is suspected, livestock producers don’t always test. John Grano said they didn’t test the cow that was charged Cynthia, though symptoms of theileria include weakness and fever. In an email obtained through a public records request, a USDA epidemiology officer informed Bonilla, the USDA coordinator, in July 2022 about Asian longhorned ticks found on a bull at a Kentucky stockyard the previous month. “The state informed all producers about the possibility of the animals having [Asian-longhorned ticks] and the need for treatment, but I don’t know yet if they have done any environmental sampling on those farms or additional follow-up (I am assuming probably not To stem the spread, researchers who MIT Technology Review talked to say that there must be a vaccine as well as an FDA-approved treatment. The only way to prevent tick spread is to reduce tick reproduction, which is difficult considering the Asian longhorn’s propensity to breed quickly and host on many domestic and wild animals.

The FDA has not approved any therapeutics for theileria. Vaccines are still years away. Lawrence says that no one in New Zealand has been working on a vaccine after theileria outbreaks for over a decade. Results from buparvaquone, the antiprotozoal drug, are “often variable,” noted a 2021 paper he co-authored. David Emery, an Australian leading theileria researcher, is currently researching a way of preventing the spread of the disease by injecting cattle infected with blood. This seems to cause milder symptoms than tick-borne diseases. In an email, he stated that this was how he hoped to protect cattle from being moved into endemic areas. Although there has been work on a vaccine in Korea and Japan, results were mixed, a 2021 paper of his noted.

Theileria has made life a bit complicated for Kevin Lahmers, a veterinary pathologist at Virginia Tech. His job is to determine why an animal died or became sick. He conducts necropsies and examines tissue under a microscope. He also teaches and conducts research in applied diagnostics. However, his specialty is pathogen discovery and “messing about” with DNA sequencing.

” “There’s a lot failure associated with exploring new avenues,” says he. “I’m willing .”

to fail This adventurous attitude led him to investigate a series of cattle deaths. In 2017, he was the first to connect a sick cow in Virginia to theileria from Asian longhorned ticks.

Since then, Lahmers has become a leading researcher on theileria in the US. Last November, he had applied six more times for two separate USDA grants to help him fund diagnostic testing and interventions. This could have allowed him to research a preventative such as a vaccine. He felt that he couldn’t convince the reviewers about the national significance and importance of each grant. The USDA stated in a statement to MIT Technology Review that it makes science-based decisions based upon several factors. This includes current status and animal disease characteristics. Lahmers was frustrated because he tried to sound the alarm in a thoughtful way. Agriculture is the largest industry in Virginia and cattle are the second-highest commodity, with an economic impact of $70 billion. Lahmers, who spent his childhood shadowing his father’s veterinarian on house visits, believes that if he raises alarms about theileria, buyers may not be interested in Virginia cattle.

Kevin Lahmers, a veterinary pathologist at Virginia Tech, is working to advance theileria research.


“What I want to do is help people raise happy, healthy cows and be profitable,” Lahmers says. “If I am so bold and aggressive to raise all the alarms I can, then that will actually harm the group that you’re trying to be part. The livestock industry and its allies have become increasingly defensive. The National Cattlemen’s Beef Association and five other organizations have collectively spent $200 million over the past twenty years lobbying against climate policies that would limit meat production. Last year, when Colorado’s governor encouraged people to forgo meat for one day a week, the governor of Nebraska, which has an $11.8 billion livestock industry, called it “an attack on our way of life.”

But the USDA and cattle lobbyists–which claim they are seeing more infections than ever before–seem to be warming up to theileria research. After years of being without support, Lahmers signed several cooperative agreements with the Animal and Plant Health Inspection Service (a USDA branch) to increase surveillance to other states, improve diagnostic testing and begin preliminary research into a possible vaccine.

But by this point, Lahmers says that theileria has become endemic. It is here to stay in at least some of the eastern United States’ established populations. It can also spread to other areas if infected cows are moved. Climate change could help extend its range into new areas; scholarship on other tick species has shown that climate change is likely causing ticks in the US to migrate northward and to be active earlier in the season as temperatures warm.

It is possible that the country will soon be infested. The tick is also a vector of other pathogens, including the Bourbon and Heartland viruses.

The Asian longhorned tiger is expected to be found east of the Mississippi, as well as in Kansas, Oklahoma, Texas.” Lahmers states. He predicts that the tick’s reach will expand to Canada and the West Coast in the coming years.

Britta Lokting is a journalist based in New York.

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