First detection of heartland virus (Bunyaviridae: Phlebovirus) from field collected arthropods

Abstract

Heartland virus (HRTV), the first pathogenic Phlebovirus (Family: Bunyaviridae) discovered in the United States, was recently described from two Missouri farmers. In 2012, we collected 56,428 ticks representing three species at 12 sites including both patients' farms. Amblyomma americanum and Dermacentor variabilis accounted for nearly all ticks collected. Ten pools composed of deplete nymphs of A. americanum collected at a patient farm and a nearby conservation area were reverse transcription-polymerase chain reaction positive, and eight pools yielded viable viruses. Sequence data from the nonstructural protein of the Small segment indicates that tick strains and human strains are very similar, ≥ 97.6% sequence identity. This is the first study to isolate HRTV from field-collected arthropods and to implicate ticks as potential vectors. Amblyomma americanum likely becomes infected by feeding on viremic hosts during the larval stage, and transmission to humans occurs during the spring and early summer when nymphs are abundant and actively host seeking.

Figure 1.

Map of northwestern Missouri indicating location of 12 arthropod sampling sites on 9 properties sampled during 2012. See Table 1 for details.

Figure 2.

Unrooted phylogenetic tree based upon partial nonstructural protein (NSs) open reading frame of the Small (S) segment nucleotide sequences (∼670 bp) for representative viruses of the genus Phlebovirus inferred by the maximum likelihood (ML) method. Tree is drawn to scale with branch lengths representing the number of nucleotide substitutions per site. Bootstrap values expressed as percentage of 2,000 replicates. GenBank accession numbers for non-Heartland virus strains appear next to virus names.