Experimental infection of horses with Hendra virus/Australia/horse/2008/Redlands

Abstract

Hendra virus (HeV) is a highly pathogenic zoonotic paramyxovirus harbored by Australian flying foxes with sporadic spillovers directly to horses. Although the mode and critical control points of HeV spillover to horses from flying foxes, and the risk for transmission from infected horses to other horses and humans, are poorly understood, we successfully established systemic HeV disease in 3 horses exposed to Hendra virus/Australia/Horse/2008/Redlands by the oronasal route, a plausible route for natural infection. In 2 of the 3 animals, HeV RNA was detected continually in nasal swabs from as early as 2 days postexposure, indicating that systemic spread of the virus may be preceded by local viral replication in the nasal cavity or nasopharynx. Our data suggest that a critical factor for reducing HeV exposure risk to humans includes early consideration of HeV in the differential diagnosis and institution of appropriate infection control procedures.

Figure 1

Temperature transponder data for horse 1 during experimental infection with Hendra virus, Australia. Before viral challenge, each mare was fitted with an intrauterine (transcervical) temperature transponder to allow continuous recording of core body temperature. Temperature was measured every 15 minutes in each horse. Solid line represents the moving average based on 20 temperature readings.

Figure 2

Rectal temperatures (A) and heart rates (B) of each horse after experimental infection with Hendra virus, Australia. Data were collected by using an electronic monitor 2×/d, along with comments on general demeanor. Data were used to determine a humane endpoint for each animal.

Figure 3

Brain vasculitis in horse experimentally infected with Hendra virus, Australia. A) Parenchyma and B) ovary of horse 2. Original magnification ×200.

Figure 4

Lymphadenitis with syncytial cell formation in horse 2 experimentally infected with Hendra virus (HeV), Australia. Immunohistochemical staining of HeV N protein showing presence of antigen in red. Original magnification ×200.

Figure 5

Dilation of lymphatic vessels and ventral lung lobe margins of horse 3 experimentally infected with Hendra virus, Australia. Original magnification ×10.

Figure 6

Relative abundance of Hendra virus (HeV) P RNA in different horse tissues at postmortem examination after experimental infection with HeV, Australia. Values are expressed relative to ribosomal 18S copies. Tissue origins are indicated along the y-axis. *Sample not available for testing.