A novel model of lethal Hendra virus infection in African green monkeys and the effectiveness of ribavirin treatment

Abstract

The henipaviruses, Hendra virus (HeV) and Nipah virus (NiV), are emerging zoonotic paramyxoviruses that can cause severe and often lethal neurologic and/or respiratory disease in a wide variety of mammalian hosts, including humans. There are presently no licensed vaccines or treatment options approved for human or veterinarian use. Guinea pigs, hamsters, cats, and ferrets, have been evaluated as animal models of human HeV infection, but studies in nonhuman primates (NHP) have not been reported, and the development and approval of any vaccine or antiviral for human use will likely require efficacy studies in an NHP model. Here, we examined the pathogenesis of HeV in the African green monkey (AGM) following intratracheal inoculation. Exposure of AGMs to HeV produced a uniformly lethal infection, and the observed clinical signs and pathology were highly consistent with HeV-mediated disease seen in humans. Ribavirin has been used to treat patients infected with either HeV or NiV; however, its utility in improving outcome remains, at best, uncertain. We examined the antiviral effect of ribavirin in a cohort of nine AGMs before or after exposure to HeV. Ribavirin treatment delayed disease onset by 1 to 2 days, with no significant benefit for disease progression and outcome. Together our findings introduce a new disease model of acute HeV infection suitable for testing antiviral strategies and also demonstrate that, while ribavirin may have some antiviral activity against the henipaviruses, its use as an effective standalone therapy for HeV infection is questionable.

FIG. 1.

Average time to death. Shown is the therapeutic effect of ribavirin treatment at 24 h prior to infection (pre) and 12 or 48 h postinfection on the time to death. Black bars represent average time to death for each group. Error bars represent the standard error of the mean of three animals.

FIG. 2.

Radiological and gross pathological changes in lungs of Hendra virus-infected African green monkeys. Radiologic progression of respiratory disease in animal HeV6 (Table 1), who was euthanized on day 8 due to severe respiratory distress. First evidence of congestion is observed on day 7 p.i., and infection rapidly progressed to diffuse interstitial infiltrates and pulmonary consolidation by day 8 p.i. R, right side.

FIG. 3.

Gross pathological changes observed during HeV infection of African green monkeys. Shown are gross pathological changes associated with the end stage of lethal HeV infection in African green monkeys. (A) Sanguinous froth exuding from nares; (B) enlarged lungs with multifocal areas of congestion and hemorrhage; (C) congestion of the brain (black arrows).

FIG. 4.

Histological changes and tropism of HeV in tissues from infected African green monkeys. Shown are histological changes associated with the end stage of lethal HeV infection in African green monkeys (animal HeV1; Table 1). (A) Phosphotungstic acid-hematoxylin (PTAH) staining of lung lobe showing an abundance of polymerized fibrin in and around the alveolar spaces; (B) localization of HeV antigen by immunohistochemical (IHC) stain in the alveolar septae and within a lung blood vessel showing endothelial syncytia (inset); (C) IHC stain of HeV antigen in the brain stem; (D) detection of HeV antigen in neuron cell body and axon as well as surrounding cells.

FIG. 5.

Virus replication in tissues of HeV-infected African green monkeys. Virus replication was determined in tissues of HeV-infected animals by virus titration (A) and TaqMan RT-PCR (B) as described in Materials and Methods. For each treatment group, tissue samples from three animals were assayed and analyzed and the mean TCID₅₀ or relative HeV N expression values were calculated. The error bars represent the standard error of the mean. The TCID₅₀ titers are calculated per gram (gr) of tissue. LN, lymph node.

FIG. 6.

Virus detection in samples from HeV-infected African green monkeys. TaqMan RT-PCR was used to determine the relative HeV N expression levels in oral (A), nasal (B), and rectal (C) swabs as well as in whole blood (D) on days 1, 3, 5, 7, and 9 postinfection. For each treatment group, samples from three animals were assayed and analyzed and the mean relative HeV N expression values were calculated. The error bars represent the standard error of the mean.