Last year, a man living in the United States died shortly after being exposed to ticks. At the time, scientists couldn’t identify any of the usual culprits of tick-borne illnesses in his blood, such as the bacterium that causes Rocky Mountain spotted fever. However, their search did reveal a virus that didn’t appear to match any known viruses, which prompted further investigation into the unusual case. Now, after several months of analysis of the isolated pathogen, scientists have finally managed to identify the novel species of virus, which appears to belong to the same family of viruses to which the influenza viruses belong. The findings have been published in Emerging Infectious Diseases.
The patient was a previously healthy man in his 50s living in Bourbon County, Kansas. He had been doing some work outdoors in late spring last year which exposed him to the ticks. A few days before becoming ill with diarrhea and weakness, he found several tick bites on his body and one swollen tick still on his shoulder. His symptoms worsened and he developed a fever, chills and a lack of appetite, which prompted him to seek medical attention.
Because of his apparent exposure to arthropod parasites, the man was prescribed antibiotics for his presumed tick-borne illness and sent home, but the next day his level of consciousness began to deteriorate, so he was admitted to the hospital. Alongside a slight fever, the man had an increased heart rate and blood pressure, but nothing seemed to stand out as unusual. Further tests, however, revealed that his white blood cell and platelet (clotting cells) counts were down.
Over the next few days, his condition deteriorated further despite antibiotic therapy and tests were negative for all the common tick-borne bacterial pathogens, such as Borrelia which causes Lyme disease. The man then experienced multi-organ failure and consequently died 11 days after first becoming ill.
Scientists continued to scour his blood for the potential cause, which led them to an unknown virus that was later identified as a member of the Thogotovirus genus, which belongs to the same family as all three influenza viruses, the Orthomyxoviridae. The virus was named Bourbon virus because of the area the infected man came from.
Although other thogotoviruses are associated with ticks, only two of those previously identified have been known to infect humans, and these have only been found in a handful of individuals in Europe, Asia and Africa. What is interesting is that these two viruses caused brain inflammation in patients, such as encephalitis, not decreases in blood cells. The Kansas man’s symptoms were actually more similar to those found in patients with ehrlichiosis, a rare tick-borne bacterial illness also found in the United States.
Although this is the first known case of Bourbon virus, that doesn’t necessarily mean the virus hasn’t been around for long. Epidemiologist Erin Staples points out to USA Today that it is perfectly possible many people have been infected, but that the virus usually only causes a very mild illness. Now that we have sophisticated diagnostic and surveillance techniques, it is possible more cases may be identified in the future.