A study published yesterday in the Journal of Infectious Diseases based on plasma antibody testing suggests that a rare tick-borne virus is circulating more widely in the United States than previously thought.

Scientists from Takeda Manufacturing in Austria used sensitive live-virus neutralization tests to analyze the prevalence of antibodies against Bourbon virus (BRBV) and related Thogotoviruses in pooled plasma-derived immunoglobulin (IG) collected from people in the United States and the European Union from 2006 to 2024.

First identified in the United States in 2014, BRBV is caused by a bite from the lone star tick (Amblyomma americanum). It can cause severe illness in people with weakened immune systems but is likely underrecognized because it often causes only mild or non-specific symptoms and occurs primarily in rural areas with limited surveillance, the researchers said.

“Only a few human cases have been confirmed, but small studies suggest ~1% of people may have been exposed,” they noted. “As climate change expands the habitats of ticks and the animals that carry them, these viruses may spread into new regions.”

None of the IG preparation lots contained detectable neutralizing antibodies against Thogotovirus or Dhorivirus, and EU IG was largely non-reactive. But BRBV-neutralizing antibody concentrations in US IG showed a borderline-significant increase over time.

These results highlight the need for improved tick surveillance and awareness of particularly vulnerable people about their need to protect themselves against emerging tick-borne viruses.

“These results highlight the need for improved tick surveillance and awareness of particularly vulnerable people about their need to protect themselves against emerging tick-borne viruses,” the authors wrote.

The levels of BRBV-neutralizing antibodies detected in IG, however, were not considered potent enough to support their use for the prevention or treatment of BRBV, they added.

In an accompanying editorial, Michael Busch, MD, PhD, and colleagues from Vitalant Research Institute in San Francisco said that donor-based emerging infectious disease surveillance using IG products “will accelerate identification of newly circulating pathogens, prospective assessment of consequent population immunity, and development and deployment of MCM [medical countermeasures].”