Surveillance for Heartland Virus (Bunyaviridae:Phlebovirus) in Missouri During 2013: First Detection of Virus in Adults ofAmblyomma americanum(Acari: Ixodidae)

Abstract

During 2013, we collected and tested ticks for Heartland virus (HRTV), a recently described human pathogen in the genus Phlebovirus (Bunyaviridae), from six sites in northwestern Missouri. Five sites were properties owned by HRTV patients, and the sixth was a conservation area that yielded virus in ticks during 2012. We collected 39,096 ticks representing five species; however, two species, Amblyomma americanum (L.) (97.6%) and Dermacentor variabilis (Say) (2.3%), accounted for nearly all ticks collected. We detected 60 HRTV-positive tick pools and all were composed of A americanum: 53 pools of nymphs, six pools of male adults, and one pool of female adults. This is the first record of HRTV in adult ticks. Virus was detected at five properties that yielded A. americanum ticks, including properties owned by four of five patients. Virus was detected at two sites that yielded virus in 2012. Detection of virus in multiple years indicates that the virus persists in ticks within a relatively small geographic area, although infection rates (IR) may vary greatly among sites and between years at a site. IR per 1,000 A. americanum in northwestern Missouri during the April-July 2013 study period were as follows: all adults, IR = 1.13; adult females, IR = 0.33; adult males, IR = 1.90; and nymphs, IR = 1.79. The IR in nymphs, the stage with the largest data set, corresponds to 1/559 infected ticks. Having robust estimates of IR in various stages for A. americanum should lead to more accurate public health messaging and a better understanding of virus transmission.

Heartland Virus Exposure in White-Tailed Deer in the Southeastern United States, 2001–2015

“…Human disease has been reported in nine states, mainly in the Midwestern and southern United States. [1][2][3][4] The virus is most likely transmitted by the lone star tick Amblyomma americanum and has been isolated from wild-caught ticks in the vicinity of the first reported human cases, 5,6 as well as experimentally transmitted by co-feeding between A. americanum ticks. 7 Amblyomma americanum has a vast and expanding geographical range including 39 states and the District of Columbia, predominantly in the southeastern states (as far west as Texas), and extending north through the mid-Atlantic and New England regions.…”

“…There was a significant association with moderate and heavy tick burdens and HRTV seropositivity, which is consistent with other evidence of A. americanum being the primary vector for HRTV. [5][6][7] In addition, HRTV-exposed deer have been detected in most of the states where human cases of HRTV-associated disease have been documented. The presence of seropositive and tick-laden WTD in an area may be another useful indicator for the presence or increased circulation of HRTV in a given area, alerting human health providers and specialists to the potential of human HRTV infections.…”

Experimental Infection of White-Tailed Deer (Odocoileus virginanus) with Heartland Virus

“…3 The virus is most likely transmitted by ticks, namely Amblyomma americanum, and has been isolated from wild-caught ticks in the vicinity of the first reported human cases. 5,6 Antibodies reactive with HRTV have been detected in freeranging white-tailed deer (WTD) (Odocoileus virginianus), moose (Alces alces), raccoons (Procyon lotor), and coyotes (Canis latrans) in the central and eastern United States. [7][8][9] Heartland virus, however, has not been detected in any naturally infected, seropositive animals to date.…”

Tick-Borne Zoonoses in the United States: Persistent and Emerging Threats to Human Health

“…In 1999, E. ewingii , initially described from four patients from Missouri, was recognized as another cause of ehrlichiosis in humans (Buller et al 1999). In 2009, Heartland virus, the first pathogenic tick-borne phlebovirus in the United States, was described from two patients in northwestern Missouri and later detected in field collected A. americanum ticks (McMullan et al 2012; Savage et al 2013, 2016). …”