Heartland virus (HRTV), an emerging infection first detected in lone star ticks in Missouri in 2009, has spread to lone star ticks in Georgia, a study published in Emerging Infectious Diseases reports.
HRTV disease is transmitted by the bite of an infected Amblyomma americanum tick, named “lone star” because of the silver-white spot on the female scutum (back).
“By … sampling … in an area with reported exposure to HRTV in wildlife and humans and testing for infection in thousands of ticks from multiple sites and physiologic stages, we confirmed the presence of HRTV in Georgia,” the authors write.
“This information about the expanding geographic range of lone star ticks, combined with increased human presence in tick-infested habitats, can be used to improve strategies for preventing tick bites and to alert physicians about this emerging tickborne virus infection,” a press release by the Centers for Disease Control and Prevention notes.
Persistent field and lab work led to HRTV discovery in Georgia
The search for infected lone star ticks began after a retroactive analysis confirmed that a person who died in Georgia in 2005 from an unidentified illness was infected with HRTV. A subsequent analysis of serum samples collected earlier from local white-tailed deer showed that the deer had been exposed to HRTV since at least 2001, according to a press release by Emory University.
These discoveries prompted local researchers to investigate whether lone star ticks in rural, woodsy central Georgia were carrying HRTV.
Lead study author Yamila Romer, MD, an infectious disease clinician and microbiologist in the department of environmental sciences at Emory University in Atlanta, and her colleagues collected samples of ticks in 2018 at 26 sites near the location of the patient who died and the seropositive deer. In 2019, they focused their collections on the two sites that had provided the most ticks in 2018.
From April to October in both years, the research team visited sites weekly to swish white flannel flags through underbrush. They picked off adult and nymph Amblyomma americanum ticks, placed them into vials, and transported them to their lab. They sorted 9,294 ticks by sex, life stage, and collection site. Then they crushed the ticks and extracted their RNA.
To confirm viral infection, the team tested RNA extracted from cell culture supernatants using a real-time polymerase chain reaction test specific for HRTV.
In the three pools of ticks that tested positive for HRTV, the researchers found a minimum infection rate of 0.46/1,000 ticks, suggesting that about 1 of every 2,000 ticks carried HRTV. They sequenced the genome of the three isolates and found that the genomes were similar to one another but were very different from the genomes from HRTV samples taken outside Georgia.
Catherine A. Hill, PhD, a professor of entomology and vector biology and the interim head of the department of entomology at Purdue University in West Lafayette, Ind., was impressed with the researchers’ discovery.
“Heartland virus is difficult to detect,” she said in an email. “The prevalence of human cases is low, and the virus appears to be present at very low levels in populations of lone star tick. The investigators went to some lengths to survey for the virus, collect, and process thousands of ticks – and they found the needle in the haystack.” Dr. Hill was not involved in the study.