Bourbon Virus

• Bourbon virus is a newly discovered RNA virus that causes serious illness in humans.
• The Lone Star tick carries the Bourbon virus in the southern U.S. and Midwest.
• Bourbon virus is uncommon, and it is unclear how often ticks may carry or transmit it to humans.
• The cases that have been reported of Bourbon virus infection have been severe and progressive, sometimes resulting death.
• Tests for the Bourbon virus are only available from specialty laboratories such as that of the U.S. Centers for Disease Control and Prevention (CDC). It is likely to be under-reported because testing is not commonly available at this time.
• Both tick numbers and tick-transmitted diseases are on the rise.
• Ticks can transmit many types of diseases depending on the species of tick and geographic location.

Of the viruses of the genus Thogotovirus (family Orthomyxoviridae) known to cause human disease, Bourbon virus is the most recently discovered. Bourbon virus got its name from the location where the first human case was discovered. In 2014, a man became seriously ill in Bourbon County, Kansas, several days after working outdoors and finding several engorged ticks attached to him. Multiple tests for bacterial and viral causes did not detect a cause of the illness. After an 11-day illness during which he continued to have fevers, he developed multi-organ failure and died. The CDC performed reverse transcriptase polymerase chain reaction (RT-PCR) testing on samples of his blood, initially looking for Heartland virus. The CDC instead discovered a novel RNA virus, and further analysis confirmed that it belonged to the Thogotovirus genus. Bourbon virus is the only one of the three viruses of this type (including Thogoto and Dhori viruses) to be found in the United States. The others were found in Nigeria.

Surveillance testing of ticks has been conducted since 2015 in Bourbon and Linn Counties after the new virus was discovered. The majority of ticks collected have been soft-bodied ticks of the species Amblyomma americanum (also called the Lone Star tick), which was found to carry both Heartland virus and Bourbon virus. It is still unclear how frequently the tick species acquires or transmits Bourbon virus. Only a few cases of Bourbon virus disease have been reported since 2015 in the southern U.S. and Midwest.

In addition to Heartland and Bourbon virus, the Lone Star tick can carry and transmit Powassan virus, which causes a serious encephalitis. Its range is mainly in the Southeast U.S. but can be found in the Northeast and Midwest. The Lone Star tick can also transmit southern tick-associated rash illness (STARI) and ehrlichiosis. It also is associated with meat allergy (alpha gal syndrome) that causes mild to severe reactions (including anaphylaxis) after eating red meat.

Bourbon virus causes Bourbon virus disease.

The bite of the Lone Star tick (Amblyomma americanum) transmits the virus. Thus, the risk factors for Bourbon virus disease include activities that increase the risk of tick bites from this tick species. The Lone Star tick inhabits the Southeastern U.S. and Midwest, but it is spreading to the north and west. Researchers don't know whether the Bourbon virus spreads via this tick in other areas or by other insects.

The risk factors for Lone Star tick bites include hiking or walking in wooded grassy areas. Unlike other tick-borne diseases, it is not known how long the tick must be attached to transmit Bourbon virus.

Bourbon virus disease does not appear to spread from person to person or from an animal to a human.

The incubation period for Bourbon virus disease is not known, but at least two cases have described tick bites within 3 days of developing symptoms. It is not known whether the virus may have been transmitted by other tick bites earlier than these.

Very little is known about Bourbon virus disease. Based on the few cases reported so far, symptoms and signs include fevers, extreme fatigue, pale pink rash, nausea, vomiting, severe headache, and body aches. Laboratory findings include low white blood cell count (leukopenia), low platelet count (thrombocytopenia), and elevation of liver enzyme tests.

The CDC is able to test for the genetic material of Bourbon virus using PCR techniques.

Emergency specialists, internal medicine specialists (including critical care and hospital medicine specialists), pediatricians, and infectious disease specialists are most likely to play roles in managing a case of Bourbon virus disease in the hospital.

There is no currently recommended antiviral medicine for this virus, and antibiotics are not useful for treating viruses. The treatment of Bourbon virus disease focuses on supportive care, which treats the symptoms of the disease as it progresses. A patient may need critical care in an intensive care unit, including respiratory and other support.

Studies of Bourbon virus infection in mice suggest a possible role of deficient immunity to viral infections in causing disease. Treatment of mice with alpha-interferon, as well as antiviral drugs used to treat other RNA viruses, were found to effectively reduce viral replication. Both ribavirin and favipiravir (T-705; 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) were tested. While ribavirin and alpha-interferon are commercially available drugs, favipiravir is an investigational drug that has shown promise against influenza and some hemorrhagic fever viruses. It is possible that one or more of these drugs may be useful in treating human Bourbon virus infections in the future. Favipiravir may also hold promise in preventing the disease after exposure (prophylaxis).

There are no known home remedies for treating Bourbon virus disease.

The prognosis and overall survival rate of Bourbon virus disease have not been determined because of the limited number of known cases. At least two of the individuals with Bourbon virus disease, one in Kansas, and one in Missouri, have died.

For now, based on limited knowledge, it is possible that people can prevent Bourbon virus disease by preventing bites from Lone Star ticks. You can prevent tick bites when hiking by staying on trails and avoiding areas of high grass or that are wooded, as well as wearing long sleeves and long pants, and tucking hems into socks. Clothing and camping gear can be treated with 0.5% permethrin products. Use insect repellants that are U.S. Environmental Protection Agency (EPA)-registered and contain 2-undecanone, DEET, picaridin, IR3535, para-menthane-diol, or oil of lemon eucalyptus. Treat clothing, boots, and tents with products containing 0.5% permethrin. EPA has an online repellent search tool that can help with choosing the best options.