By Drs. Carol Castellares and Mar Faraco
In August 2026, a recently confirmed case of Bourbon virus disease (BRBV) in Suffolk County, USA, made the news, highlighting another tick-borne disease that many people have never heard of. Bourbon virus is a rare virus transmitted mainly through the bite of an infected “lone star” tick. It was first identified in 2014 in Bourbon County, Kansas, and only a few human cases have been reported in the United States.
The infectious agent
Bourbon virus (BRBV) is an emerging arbovirus belonging to the genus Thogotovirus, within the family Orthomyxoviridae. It was first identified in 2014 following the death of a patient with a history of a tick bite in Bourbon County, Kansas (United States).
BRBV is a single-stranded RNA virus closely related to other members of the genus Thogotovirus, including Dhori, Jos, Araguari, Upolu, and Batken viruses.
Since its identification, only a small number of confirmed clinical cases have been described, all of them in the United States. However, several serological studies conducted in both animals and humans indicate that circulation of the virus may be considerably more widespread than reported cases suggest. For this reason, BRBV is considered a rare emerging pathogen, although it is probably underdiagnosed due to the nonspecific nature of its clinical manifestations, its similarity to other tick-borne diseases, the limited availability of commercial diagnostic tests, and the low level of clinical suspicion.
The vector and reservoirs
BRBV is transmitted to humans mainly through the bite of the “lone star” tick (Amblyomma americanum), which is considered the main vector of the virus. This species is widely distributed across the central, southern, and eastern regions of the United States.
The virus appears to be maintained in nature by various wild and domestic mammals. These include the white-tailed deer (Odocoileus virginianus), considered the main reservoir, as well as raccoons (Procyon lotor), opossums (Didelphis virginiana), cottontail rabbits, squirrels, horses (Equus caballus), and domestic animals such as dogs (Canis lupus familiaris) and cats (Felis catus).
Geographic distribution
Up to 2026, all confirmed clinical cases of BRBV infection have been reported in the United States. The first cases were reported in the states of Kansas, Missouri, and Oklahoma, which are considered the initial core area of virus circulation. Subsequently, evidence of BRBV circulation has been found in other regions, including North Carolina, Virginia, and New York. In 2026, the first confirmed human case in New York State was reported, corresponding to an infection previously acquired in Suffolk County (Long Island). This expands the known geographic distribution of the disease and reinforces the hypothesis that the virus circulates more widely than reported clinical cases suggest.
The existence of silent virus circulation is supported by several seroprevalence studies. In Missouri, a study conducted in the St. Louis area detected neutralizing antibodies against BRBV in 3 of 440 serum samples (0.7%), demonstrating previous undiagnosed infections. Likewise, neutralizing antibodies have been identified in people in North Carolina with no history of illness compatible with BRBV infection. In Suffolk County (New York), a study involving patients with fever following a tick bite detected neutralizing antibodies in 2 of 107 individuals; in one of them, seroconversion with a fourfold increase in antibody titre was observed, consistent with a recent infection.
Entomological surveillance also demonstrates active BRBV circulation in tick populations. One of the most relevant studies was conducted at the Tyson Research Center (Missouri), where 2,778 ticks were analysed, approximately 99% of which were Amblyomma americanum. Fourteen pools tested positive for BRBV, with estimated infection rates ranging from 1.5 to 14 per 1,000 ticks. The main circulation hotspots were located in the areas known as “North Gate” and “Bunker 51”. In addition, the virus has also been detected in ticks collected in Kansas, Missouri, and North Carolina.
The recent confirmation of the first human case in New York, together with the geographic expansion of Amblyomma americanum and the high seroprevalence observed in animals and humans, supports the hypothesis that BRBV is an emerging pathogen with stable enzootic circulation and a substantial degree of underdiagnosis.
The disease
The incubation period of BRBV is not known precisely, although symptoms are estimated to appear a few days after the bite of an infected tick. The initial clinical presentation is nonspecific and can be confused with other tick-borne diseases, such as ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever, or Heartland virus disease, making early recognition of the infection difficult.
The most common symptoms include acute-onset fever, severe fatigue, weakness, headache, loss of appetite, nausea, vomiting, myalgia, and arthralgia. Some patients develop a diffuse skin rash or petechiae on the soft palate and lower extremities.
The clinical course may progress to multiorgan failure, shock, and death, particularly in older patients or those with underlying medical conditions. Reported cases have shown little or no response to empirical treatment with doxycycline, a finding that may help in the differential diagnosis from bacterial tick-borne infections.
Diagnosis
There are currently no commercially authorized tests for the diagnosis of BRBV infection. Diagnostic confirmation requires specialized techniques (RT-PCR, PRNT), mainly available at the CDC and at some state public health laboratories in the United States.
The CDC recommends considering these tests in patients who develop an acute febrile illness within three months of possible tick exposure, particularly between April and October, when vector activity is highest. Diagnostic suspicion should be increased in the presence of leukopenia, thrombocytopenia, and elevated liver enzymes without another apparent cause, as well as in patients with suspected tick-borne disease who do not improve after empirical treatment with doxycycline.
Treatment and prevention
There are currently no specific antiviral drugs or authorized vaccines for the prevention or treatment of BRBV infection. Clinical management is supportive.
Prevention is based on reducing the risk of tick exposure. Measures include the use of approved repellents containing DEET or icaridin on exposed skin, permethrin for treating clothing and outdoor equipment, wearing protective clothing, avoiding contact with dense vegetation and tall grass, performing body checks after outdoor activities, and removing attached ticks as soon as possible.
Bourbon virus. Source: CDC.
Recommended reading
- https://people.com/first-case-of-bourbon-virus-confirmed-in-new-york-12032269
- About Bourbon Virus. https://www.cdc.gov/bourbon-virus/about/index.html
- Evidence of Heartland and Bourbon Viruses Transmitted by Ticks in Suffolk County, New York. https://www.ajtmh.org/view/journals/tpmd/115/1/article-p140.xml
- Evidence of Human Bourbon Virus Infections, North Carolina, USA. https://pubmed.ncbi.nlm.nih.gov/39387510/
- https://www.ecdc.europa.eu/en/disease-vectors/prevention-and-control/protective-measures-ticks
