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.

Infectious disease in an era of global change

“…Similarly, evidence suggests that populations of the black flying fox in Australia, a key reservoir of Hendra virus, have moved 100 km southward in the past 100 years owing to climatic changes. This shifting range likely caused Hendra virus to spill over into southern horse populations, and these horses subsequently infected humans 19 , 20 . Patterns of change are likely occurring in other bat populations globally but remain understudied — a clear cause for concern given the crucial role bat populations play as a reservoir host for several high-fatality pathogens 21 .…”

Henipaviruses—A constant threat to livestock and humans

“…A second outbreak in Queensland, Australia also occurred in 1994 and affected 2 horses and 1 person. However, this event was only recognized in 1995, after the infected person died from relapsing encephalitis [19,21].…”

The Hendra virus vaccine: perceptions regarding the role of antibody titre testing

“…It will likely be lower after 12 months, and the rate of decline and individual variation that is likely to occur between horses warrants further research. 21 More longitudinal field studies, like Tan et al, 16 looking at responses to the vaccine in the field over time will contribute to this knowledge. Until then, the titre of 64 remains an arbitrary value.…”