Bourbon virus in New York: The First Confirmed Human Case

Bourbon virus in New York has been confirmed in a human for the first time. The infection was identified not by detecting the virus itself, but by observing how the patient’s immune response changed between two blood samples: the level of neutralizing antibodies rose several-fold.

The rare virus is believed to spread through the bite of Amblyomma americanum, commonly known as the lone star tick because adult females carry a pale spot on their backs. Bourbon virus was first identified in 2014 after a fatal illness in Bourbon County, Kansas. Only a small number of human infections have been documented since then.

How the infection was identified

The researchers examined blood samples from 107 people between 20 and 93 years of age. All had been treated in Suffolk County on Long Island between 2019 and 2024 for an acute febrile illness following a recent tick bite.

Samples were sent to the New York State Department of Health and tested for antibodies against three tick-borne viruses: Bourbon, Heartland, and Powassan. The laboratory used a plaque-reduction neutralization test, which measures whether antibodies in a person’s blood can prevent viral particles from infecting cells.

Two participants had neutralizing antibodies against Bourbon virus. One additional participant had antibodies against Heartland virus. None tested positive for neutralizing antibodies against Powassan virus.

A single positive antibody result, however, does not necessarily prove a recent infection. Antibodies may remain in the bloodstream long after an earlier exposure. Paired samples collected at different times provide much stronger evidence.

In one patient, the Bourbon virus antibody titer increased at least fourfold. Such a rise is considered evidence of an acute or recent infection and enabled the researchers to confirm the first recognized human case in New York State.

The patient developed severe illness and required hospitalization. Reported symptoms included profound fatigue and intense headaches. A more familiar tick-borne infection was initially suspected, and the patient was treated with doxycycline, but the antibiotic did not improve the illness.

Why the diagnosis can be missed

The early symptoms of Bourbon virus disease overlap with those of several other tick-borne infections. Patients may develop fever, fatigue, headache, muscle or joint pain, rash, nausea, and reduced numbers of white blood cells and platelets.

The condition can therefore resemble Lyme disease, ehrlichiosis, or anaplasmosis. Lyme disease and several other tick-borne illnesses are caused by bacteria and may respond to antibiotics. Bourbon virus is viral, so antibiotics have no effect on it.

There is currently no widely available commercial diagnostic test. Suspected samples must be sent to specialized public health laboratories, increasing the likelihood that mild, unusual, or unexpected cases remain undiagnosed.

No vaccine or specific antiviral medicine is available. Treatment is supportive and may include fluids, pain and fever control, and hospitalization for patients with severe disease.

What the study cannot establish

The findings do not reveal how common Bourbon virus is in the general population of New York. The participants were not a random population sample; they were people who had already developed fever after a tick exposure. The analysis was also limited to 107 patients from one county.

The diagnosis was based on antibodies rather than direct detection of viral RNA in the bloodstream. The sharp increase in antibody titer between paired samples makes the evidence for recent infection considerably stronger, but serology does not replace broad access to direct diagnostic testing.

The main finding is not that a completely new virus suddenly appeared in New York. Earlier surveillance had already detected evidence of Bourbon virus circulation in local ticks and wildlife. The new study provides convincing evidence that the virus can also infect people in the region.

For clinicians, this means that rare viral infections should be considered when a patient develops a severe febrile illness after a tick bite, particularly when standard tests are negative and antibiotic treatment does not help.