The Heartland virus continues to be found in southeastern states, as recent study results identified the virus in lone star ticks in Georgia.
The virus is a rare source of disease in humans. Prior studies have shown other mammalian species have antibodies suggesting exposure to the virus, but humans remain the only species known so far to become ill from naturally acquired infection.
A scientific article, published in April by Emerging Infectious Diseases, describes isolation of the Heartland virus in pooled samples from about 9,400 ticks collected during 2018-19 in a rural area that has white-tailed deer known to be seropositive for antibodies to the virus and is near the site of a confirmed infection in a human. The authors isolated DNA of the Heartland virus in three of 960 pools of samples.
Gonzalo Vazquez-Prokopec, PhD, who is a research professor in environmental sciences at Emory University and the corresponding author of the article, said the wildlife reservoir for the virus remains unknown and the lone star tick’s wide range of hosts—from deer to turkeys—adds difficulty in identifying that reservoir. Now that his team has identified an area with evidence of the virus, he said, the researchers can help identify which animals could be reservoirs and which seasons are associated with the most infections.
That study starts this summer with capture of wild rodents, identification of any antibodies against the Heartland virus, and expansion to other small mammal species.
A 2018 article in the American Journal of Tropical Medicine and Hygiene indicates researchers identified Heartland virus–neutralizing antibodies in blood that had been collected from deer in southern states since 2001. Positive samples came from deer in Arkansas, Florida, Georgia, Kentucky, Louisiana, North Carolina, Oklahoma, South Carolina, and Tennessee from 2001-15.
Dr. Vazquez-Prokopec said his research team’s recent article shows that virus sequences from Georgia are distinct from those collected in neighboring states, suggesting the virus may have been circulating long term and evolving in each location.
“We cannot say that the virus is spreading,” he said. “It could be that we’re getting better at detecting it because now we have better tools—molecular tools—to detect it in ticks.”
Aaron Brault, PhD, is a virologist and team lead for the diagnostic and reference team at the Division of Vector-Borne Diseases in the Arboviral Diseases Branch of the Centers for Disease Control and Prevention. He noted that prior study results have identified cats, dogs, goats, horses, coyotes, moose, opossums, raccoons, and white-tailed deer with neutralizing antibodies that suggest exposure to the Heartland virus, but none of those animals has had observed clinical signs of infection.
Among a wide range of species inoculated with the virus under experimental conditions, only mice bred to have compromised immune systems developed disease. Dr. Brault said blood samples from animals exposed to the virus in the wild have had higher antibody responses, perhaps because of the effects of tick saliva in suppressing local immune responses or because of the cumulative responses to multiple tick bites.
Dr. Brault noted that it’s possible a small unrecognized portion of animals could become infected and show clinical signs. Veterinarians would have an important role of identifying any such cases, he said.
Data on distribution of lone star ticks indicate the ticks are expanding their range northward, and he sees potential for the range of the Heartland virus to expand with its suspected tick vectors. Veterinarians who submit ticks for identification can help show where any range expansion is occurring and help identify risk to humans.