Vertebrate Host Susceptibility to Heartland Virus

Abstract

Heartland virus (HRTV) is a recently described phlebovirus initially isolated in 2009 from 2 humans who had leukopenia and thrombocytopenia. Serologic assessment of domestic and wild animal populations near the residence of 1 of these persons showed high exposure rates to raccoons, white-tailed deer, and horses. To our knowledge, no laboratory-based assessments of viremic potential of animals infected with HRTV have been performed. We experimentally inoculated several vertebrates (raccoons, goats, chickens, rabbits, hamsters, C57BL/6 mice, and interferon-α/β/γ receptor-deficient [Ag129]) mice with this virus. All animals showed immune responses against HRTV after primary or secondary exposure. However, neutralizing antibody responses were limited. Only Ag129 mice showed detectable viremia and associated illness and death, which were dose dependent. Ag129 mice also showed development of mean peak viral antibody titers >8 log₁₀ PFU/mL, hemorrhagic hepatic lesions, splenomegaly, and large amounts of HRTV antigen in mononuclear cells and hematopoietic cells in the spleen.

Keywords: Ag129 mice; HRTV; Heartland virus; chickens; goats; hamsters; host susceptibility; mice; mouse model; phlebovirus; rabbits; raccoons; vector-borne infections; vertebrates; virulence; viruses; zoonoses.

Figure 1

Dose response of Heartland virus (HRTV)–infected interferon α/β/γ receptor–deficient (Ag129) mice. Mice of either sex were inoculated with 10⁴–10° PFU of HRTV/0.1 mL of inoculum. Mice were observed daily for death through day postinoculation 24. A) Percentage survival. B) Dose-associated HRTV viremias determined by plaque assays on Vero E6 cells. Different groups of 5 mice inoculated with the same dose of HRTV were bled every third day. Thus, a decrease in viremia was observed for the 10² PFU dose inoculum group days postinoculation 5 and 6. Error bars indicate SD.

Figure 2

Pathologic changes associated with infection of interferon-α/β/γ receptor–deficient (Ag129) mice with Heartland virus (HRTV). A) Mouse showing typical clinical signs of HRTV infection (ruffled fur, hunched posture, and squinting eyes). B) Dissected mouse showing an enlarged pale spleen (arrow). C–E) Hematoxylin and eosin staining (left panels) and immunohistochemical staining (right panels) for HRTV nucleocapsid protein of spleen (C), liver (D), and kidney (E) of Ag129 mice at 5–7 days postinoculation with 10⁴ PFU virus. Original magnifications: C, ×100; D, ×50; E, ×100.