Hendra virus: Epidemiology dynamics in relation to climate change, diagnostic tests and control measures

Abstract

Hendra virus (HeV) continues to pose a serious public health concern as spillover events occur sporadically. Terminally ill horses can exhibit a range of clinical signs including frothy nasal discharge, ataxia or forebrain signs. Early signs, if detected, can include depression, inappetence, colic or mild respiratory signs. All unvaccinated ill horses in areas where flying foxes exist, may potentially be infected with HeV, posing a significant risk to the veterinary community. Equivac® HeV vaccine has been fully registered in Australia since 2015 (and under an Australian Pesticides and Veterinary Medicines Authority special permit since 2012) for immunization of horses against HeV and is the most effective and direct solution to prevent disease transmission to horses and protect humans. No HeV vaccinated horse has tested positive for HeV infection. There is no registered vaccine to prevent, or therapeutics to treat, HeV infection in humans. Previous equine HeV outbreaks tended to cluster in winter overlapping with the foaling season (August to December), when veterinarians and horse owners have frequent close contact with horses and their bodily fluids, increasing the chance of zoonotic disease transmission. The most southerly case was detected in 2019 in the Upper Hunter region in New South Wales, which is Australia's Thoroughbred horse breeding capital. Future spillover events are predicted to move further south and inland in Queensland and New South Wales, aligning with the moving distribution of the main reservoir hosts. Here we (1) review HeV epidemiology and climate change predicted infection dynamics, (2) present a biosecurity protocol for veterinary clinics and hospitals to adopt, and (3) describe diagnostic tests currently available and those under development. Major knowledge and research gaps have been identified, including evaluation of vaccine efficacy in foals to assess current vaccination protocol recommendations.

Keywords: Biosecurity; Climate change; HeV, Hendra virus; Infectious disease; LAMP, Loop-mediated isothermal amplification; MFI, Median fluorescent intensity; NSW, New South Wales; NiV, Nipah virus; OIE, World Organization for Animal Health; One health; PC, Physical containment; PPE, Personal protective equipment; QLD, Queensland; RNA, Ribonucleic acid; SNT, Serum neutralization test; Se, Sensitivity; Sp, Specificity; Vaccine; Zoonosis; iELISA, Indirect enzyme-linked immunosorbent assay; qRT-PCR, Real-time reverse transcription polymerase chain reaction; sG, Soluble G.

Fig. 1

Hendra virus spillover events categorized by postcode in Queensland and New South Wales from 1994 to 2010 (left); and from 2011 to 2019 (right).

Fig. 2

Flowchart of a strict Hendra virus biosecurity protocol. HeV, Hendra virus; EDTA, ethylenediaminetetraacetic acid; PPE, personal protective equipment.

Fig. 3

Flowchart of a less rigorous Hendra virus biosecurity protocol. HeV, Hendra virus; EDTA, ethylenediaminetetraacetic acid; PPE, personal protective equipment.

Fig. 4

Flowchart of diagnostics procedures for HeV exclusion and confirmatory tests. qRT-PCR, real-time reverse transcription polymerase chain reaction; Indirect ELISA, indirect enzyme-linked immunosorbent assay; EDTA, ethylenediaminetetraacetic acid; CPE, cytopathic effect.