Two tick-borne viruses – Heartland virus and Bourbon virus – have killed at least seven people in the US so far and appear to be spreading. Nebraska has just become the ninth state to detect one or both viruses in local ticks. New York also recently reported its first case of Bourbon virus in a person.
“Are these viruses going to keep expanding in ticks? Are we going to see more and more cases of human infections? These are questions that a lot of my colleagues and I are wondering about,” says at the University of Nebraska Medical Center.
Heartland virus was first reported in and Bourbon virus in after they were discovered in people who had become severely unwell or died after being bitten by ticks. Since then, they have been found to be transmitted by lone star ticks (Amblyomma americanum), named for the white, vaguely star-shaped spot on the female’s back.
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Historically, lone star ticks were only found in south-eastern states of the US, but they have been due to factors like climate change and reforestation of previously cleared areas.
Heartland virus or Bourbon virus, or both, have been found in lone star ticks in Missouri, Kansas, Illinois, Alabama, Georgia, New York, Pennsylvania and Virginia. These ticks also recently became established in Nebraska, leading Fauver and his colleagues to investigate whether they have brought the viruses with them.
The team analysed more than 7000 lone star ticks collected by the Nebraska Department of Health and Human Services from multiple locations across the state between 2022 and 2026. Both viruses were detected in ticks from Sarpy County, and Heartland virus was found in ticks from Richardson County. These are in the south-east of Nebraska, suggesting lone star ticks migrated from neighbouring Missouri and Kansas.
At this point, no one in Nebraska is known to have contracted these emerging viruses from tick bites. However, there is a “very real possibility” that human infections have occurred and gone undiagnosed, says Fauver. This is because the symptoms can be mistaken for those of other tick-borne illnesses or non-tick-related viruses, he says. Common symptoms include fever, fatigue, headache, loss of appetite, muscle or joint aches and nausea.
Research suggests that only a small proportion of people who become infected with Heartland virus or Bourbon virus become severely unwell. Analysis of blood samples collected from hundreds of people in Missouri have found that almost 1 per cent have neutralising antibodies to and , indicative of previous infections. “But it’s not like 1 per cent of people in Missouri have had these illnesses,” says Fauver.
There are no commercial tests for Heartland virus or Bourbon virus, so they are only detected when blood samples from hospitalised patients are sent for analysis at specialised laboratories, like at the Centers for Disease Control and Prevention (CDC).
Heartland virus is named after the Heartland Regional Medical Center in St. Joseph, Missouri, where it was in blood samples from two men who were hospitalised with severe illness after being bitten by ticks on their respective farms. Both men recovered, but one reported ongoing fatigue and headaches for years afterwards.
Since then, people have been found to be infected with Heartland virus in central and eastern states of the US, and at least four have died. The most , reported last October, was that of a 32-year-old Connecticut woman who had been exposed to ticks on a recent hiking trip. She died of a cardiac arrest, with an autopsy finding Heartland virus in her brain.
Bourbon virus is named after Bourbon County, Kansas, where the of a human infection occurred in a man who noticed a tick on his shoulder after working outdoors on his property in 2014. He died soon afterwards from multi-organ failure. Since then, Bourbon virus has been detected in a small number of other people, some of whom have died.
New York, which is being increasingly colonised by lone star ticks, recently reported its first human infection with Bourbon virus. A man in his 60s contracted the virus after being bitten by multiple ticks while working outdoors on Long Island, . The man, who recovered, was discovered to have Bourbon virus after a sample of his blood was sent to the New York State Department of Health by a research team led by at Stony Brook University in New York.
“Bourbon virus is likely more prevalent than we think in our region and other cases are likely not being diagnosed,” Marcos said in a announcing the case last month. Heartland virus has also been detected in a small number of people in New York who have become unwell following tick bites, with the .
“I think it’s a reasonable deduction that as lone star ticks expand their range, more and more people are at risk of getting exposed to Heartland virus and Bourbon virus,” says Fauver.
Lone star ticks feed on animals like white-tailed deer and raccoons that have been found to have antibodies to Heartland virus and Bourbon virus, suggesting the viruses may continuously cycle between the ticks and these animals, says Fauver. “But there’s still a lot we don’t know.”
Lone star tick bites are also known for causing alpha-gal syndrome, which makes people allergic to red meat, and ehrlichiosis, characterised by fever, aches and headache. Lyme disease, which has similar symptoms, is caused by the black-legged tick (Ixodes scapularis). Ehrlichiosis and Lyme disease can be treated with antibiotics, whereas there are no antivirals or other treatments available for Heartland virus and Bourbon virus.
Continuous monitoring of the viruses is crucial so people can take precautions to protect themselves, says Fauver. “We’ll be going back and testing these sites [in Nebraska] to see if the viruses continue to show up, so that public health communications can be made to folks in these areas,” he says. “Obviously, you always want to avoid tick bites, but if you know you’re in a hotspot area where these viruses are circulating, you might want to be extra cautious.”
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