Heartland Virus in Humans and Ticks, Illinois, USA, 2018–2019

Holly C. Tuten; Kristen L. Burkhalter; Kylee R. Noel; Erica J. Hernandez; Seth Yates; Keith Wojnowski; John Hartleb; Samantha Debosik; April Holmes; Christopher M. Stone

Disclosures

Emerging Infectious Diseases. 2020;26(7):1548-1552. 

In This Article

The Study

The suspected sites of human exposure were determined according to case-patient interviews conducted by local county health departments (Figure). Two of the 3 sites were in an area considered endemic for A. americanum ticks, and the other site was near the putative current northern distribution range limit for this tick vector.

Figure.

Tick collection sites associated with 2 cases of Heartland virus infection in humans, Kankakee and Williamson Counties, Illinois, USA, 2019. Locations of the counties are indicated by red dots on the Illinois map.

For case-patient 1, the potential exposure site was an ≈40-acre rural homestead in Kankakee County, which had an assemblage of barnyard animals, including chickens, goats, horses, and turkeys (site 1) and a small amount of forest surrounded by extensive cropland. For case-patient 2, in Williamson County, a potential exposure site consisted of 2 adjacent lakeshore campgrounds located within a heavily wooded wildlife refuge (site 2) and another was a suburban home with sparse tree cover (site 3). We observed deer at site 1 during collection visits on June 21 and 25, 2019, and deer, coyotes, and racoons at site 2 during visits on July 11 and 12, 2019. A pet dog lived at the residence at site 3, which we visited on July 11, 2019.

We collected ticks by dragging along 150-m transects (sites 1 and 2) and with carbon dioxide traps consisting of a 1 m2 white cloth laid on the ground with 0.5 kg of dry ice left in the center to sublimate for 2 hours before returning to collect ticks (sites 1–3). We collected live ticks into 14-mL plastic centrifuge tubes (TPP, https://www.tpp.ch) that had been modified by applying carpet tape between the lid and tube mouth. We added ticks through a tape-covered hole punched in the center of the paper-backed side of the tape; the sticky side of the tape facing the tube interior immobilized the ticks before they could exit, enabling their secure transport while alive (Video, https://wwwnc.cdc.gov/EID/article/26/7/20-0110-V1.htm). Ticks were either kept alive (site 1) or killed in the field at the end of the day and kept on dry ice (sites 2 and 3) during transport to the Illinois Natural History Survey Medical Entomology Laboratory (Champaign, IL, USA), where they were identified and sorted by species, life stage, and sex[11,12] on a chill table and maintained at −80°C. Ticks were then shipped on dry ice to the CDC Arboviral Diseases Branch (Fort Collins, CO, USA) for Heartland and Bourbon virus testing, where tick pool homogenization, RNA extraction, and virus screening were performed by real-time PCR as previously described.[2,13] The prevalence of virus infection from pooled samples was calculated by using PooledInfRate, which implements a bias-corrected maximum-likelihood estimation method.[14]

A total of 70 pools of adult ticks and 23 pools of nymphs were tested (Table 1). The median pool size for adult ticks was 10 (range 1–10) and for nymphs was 30 (range 3–33). A single pool of male A. americanum ticks from each county was positive for HRTV (cycle threshold values of 21.7 for site 1 and 24.1 for site 2 by first PCR, 23.2 and 25.3 after confirmation by second PCR); Bourbon virus was not detected. The estimated prevalence of HRTV in adult male A. americanum ticks was 9.46/1,000 ticks at site 1 and 7.60/1,000 ticks at site 2 (Table 2).

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