Bourbon Virus in Field-collected Ticks, Missouri, USA

Harry M. Savage; Kristen L. Burkhalter; Marvin S. Godsey, Jr.; Nicholas A. Panella; David C. Ashley; William L. Nicholson; Amy J. Lambert

Disclosures

Emerging Infectious Diseases. 2017;23(12):2017-2022. 

In This Article

Abstract and Introduction

Abstract

Bourbon virus (BRBV) was first isolated in 2014 from a resident of Bourbon County, Kansas, USA, who died of the infection. In 2015, an ill Payne County, Oklahoma, resident tested positive for antibodies to BRBV, before fully recovering. We retrospectively tested for BRBV in 39,096 ticks from northwestern Missouri, located 240 km from Bourbon County, Kansas. We detected BRBV in 3 pools of Amblyomma americanum (L.) ticks: 1 pool of male adults and 2 pools of nymphs. Detection of BRBV in A. americanum, a species that is aggressive, feeds on humans, and is abundant in Kansas and Oklahoma, supports the premise that A. americanum is a vector of BRBV to humans. BRBV has not been detected in nonhuman vertebrates, and its natural history remains largely unknown.

Introduction

Bourbon virus (BRBV) was first isolated from blood samples from a hospitalized male resident of Bourbon County, Kansas, USA.[1] He was >50 years of age and previously healthy. Several days before becoming ill in late spring 2014, he reported several tick bites and an engorged tick on his shoulder. Initial symptoms included nausea, weakness, and diarrhea.[1] On day 2 after symptom onset, he had experienced fever, anorexia, chills, headache, myalgia, and arthralgia. On day 4 after onset, he was hospitalized. Physical examination found a papular rash on his trunk. The patient had a temperature of 37.3°C and laboratory findings of leukopenia, lymphopenia, thrombocytopenia, hyponatremia, and increased levels of aspartate aminotransferase and alanine aminotransferase. He was treated with intravenous fluids and doxycycline for possible tickborne illness. Serologic assays for the causative agents of Rocky Mountain spotted fever, tularemia, brucellosis, babesiosis, and Q fever were negative, as were molecular tests for Ehrlichia spp. and Anaplasma phagocytophilum and blood smears for Babesia.[1] The patient died 11 days after symptom onset.

Virologic tests on EDTA-treated blood and separated serum collected from the patient on day 9 after symptom onset were negative for Heartland virus (HRTV; family Bunyaviridae, genus Phlebovirus),[1] a recently described tickborne virus.[2,3] However, during plaque reduction neutralization tests for HRTV antibody, heterologous (non-HRTV) viral plaques were observed. Subsequently, plaque assay results revealed distinct plaques 3 days after inoculation within wells inoculated with blood and serum.[1] Electron microscopy of virus particles demonstrated filamentous and spherical particles consistent with the morphology of the family Orthomyxoviridae. Full-length sequencing and phylogenic analysis demonstrated that the virus was new, most closely but distantly related to the Old World virus Dhori virus, and a member of the genus Thogotovirus.[1,4] This new virus was named Bourbon virus after the county of residence of the patient. BRBV is the first human pathogen of the genus Thogotovirus to be identified in the New World.[4]

In May 2015, the Centers for Disease Control and Prevention (CDC) and the Oklahoma State Department of Health reported that a Payne County, Oklahoma, USA, resident became ill and tested positive for antibodies to BRBV by plaque reduction neutralization tests (E. Staples, O. Kosoy, CDC, pers. comm., 2016 Dec 5). The patient recovered fully.

In response to the report of the fatal BRBV case from eastern Kansas in 2014, we retrospectively tested ticks for BRBV that were collected during spring and summer 2013 from 6 sites in northwestern Missouri, ≈240 km from Bourbon County (Figure 1). We had originally collected, identified, pooled, and processed these tick samples as part of an ongoing HRTV surveillance program.[5] The goals of our retrospective analysis were to determine whether BRBV was present in the neighboring state of Missouri, to incriminate possible vector species, and to determine which life history stages are involved in virus transmission to humans.

Figure 1.

Locations of 6 tick sampling sites surveyed in northwestern Missouri, USA, during 2013 (indicated by site numbers), showing proximity of site to Bourbon County, Kansas (bottom center of map). Inset maps show location of area in main map (top, dashed box) and location of state of Missouri in the United States (bottom, gray shading). Co., County.

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