Seroprevalence of Heartland Virus Antibodies in Blood Donors, Northwestern Missouri, USA

This is the authors' abstract. We don't add key points for this paper.

We estimated the seroprevalence of Heartland virus antibodies to be 0.9% (95% CI 0.4%-4.2%) in a convenience sample of blood donors from northwestern Missouri, USA, where human cases and infected ticks have been identified.Although these findings suggest that some past human infections were undetected, the estimated prevalence is low.I n 2012, Heartland virus, a novel virus in the family Phe- nuiviridae, genus Phlebovirus, was identified in blood specimens obtained from 2 residents (men) of northwestern Missouri, USA (1).Given the clinical manifestations of illness and history of tick bites of the patients, both men were initially believed to have ehrlichiosis but they failed to improve after being given doxycycline.Before identification of Heartland virus in these 2 patients, to our knowledge, there were no known phleboviruses that caused human disease in the United States (1,2).Subsequent field work identified Amblyomma americanum ticks, which are widely distributed across the eastern and central United States, as the likely vector for the virus (3,4).Wild animals in Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Maine, Missouri, New Hampshire, North Carolina, Tennessee, Texas, and Vermont have been found to be seropositive for Heartland virus antibodies (5).Investigations are underway to identify more disease cases, but little is known about the incidence of Heartland virus infection in humans.The objective of this study was to estimate the seroprevalence of antibodies against Heartland virus in a convenience sample of blood donors who reside in northwestern Missouri where human cases and infected ticks have been identified (1,3,6). The StudyBecause the anticipated seroprevalence of Heartland virus was unknown, we calculated a sample size that would enable us to conclude with reasonable confidence that infections were rare in case no positive results were detected.To this end, we calculated that serum from 500 individual blood donors was required to infer that the true prevalence was <0.5% with 95% confidence.In addition, this sample size ensured that the prevalence would be estimated with precision no worse than ± 4.5% with 95% confidence.Most blood donors in northwestern Missouri donate through community blood drives operated by the Community Blood Center of Greater Kansas City (Kansas City, MO, USA).Specimens were collected from consecutive blood drives conducted during November 4-December 3, 2013.The study population included blood donors >16 years of age who had adequate residual specimens remaining after standard screening was performed.We originally intended to include residents of 15 counties surrounding the area where the first cases were identified (Figure ).However, because 5 of those counties had <5 donations, analysis was restricted to residents of the remaining 10 counties.At the time of donation, blood donors consented to have residual specimen used for research.If a donor did not provide this consent, their sample was excluded.All specimens were deidentified before shipment to the Centers for Disease Control and Prevention (CDC; Fort Collins, CO, USA) for testing.The only data included with the specimens were patient age, sex, and county of residence.Testing of deidentified, residual samples was deemed by CDC to not involve human subjects under 45 CFR 46.102 (https://www.hhs.gov/ohrp/regulations-and-policy/regula-tions/regulatory-text/index.html#46.102),and human subjects regulations were not applicable.We screened all serum specimens for IgG against Heartland virus by using a Clinical Laboratory Improvement Amendments-approved microsphere assay as described (7).For specimens yielding IgG-positive results, we performed a more specific plaque reduction neutralization test (PRNT), which can differentiate between related phleboviruses in the United States, by using Vero E6 cells to confirm the presence of virus-specific neutralizing antibodies and a 90% plaque reduction criteria (8,9).