Routes of Hendra Virus Excretion in Naturally-Infected Flying-Foxes: Implications for Viral Transmission and Spillover Risk

Abstract

Pteropid bats or flying-foxes (Chiroptera: Pteropodidae) are the natural host of Hendra virus (HeV) which sporadically causes fatal disease in horses and humans in eastern Australia. While there is strong evidence that urine is an important infectious medium that likely drives bat to bat transmission and bat to horse transmission, there is uncertainty about the relative importance of alternative routes of excretion such as nasal and oral secretions, and faeces. Identifying the potential routes of HeV excretion in flying-foxes is important to effectively mitigate equine exposure risk at the bat-horse interface, and in determining transmission rates in host-pathogen models. The aim of this study was to identify the major routes of HeV excretion in naturally infected flying-foxes, and secondarily, to identify between-species variation in excretion prevalence. A total of 2840 flying-foxes from three of the four Australian mainland species (Pteropus alecto, P. poliocephalus and P. scapulatus) were captured and sampled at multiple roost locations in the eastern states of Queensland and New South Wales between 2012 and 2014. A range of biological samples (urine and serum, and urogenital, nasal, oral and rectal swabs) were collected from anaesthetized bats, and tested for HeV RNA using a qRT-PCR assay targeting the M gene. Forty-two P. alecto (n = 1410) had HeV RNA detected in at least one sample, and yielded a total of 78 positive samples, at an overall detection rate of 1.76% across all samples tested in this species (78/4436). The rate of detection, and the amount of viral RNA, was highest in urine samples (>serum, packed haemocytes >faecal >nasal >oral), identifying urine as the most plausible source of infection for flying-foxes and for horses. Detection in a urine sample was more efficient than detection in urogenital swabs, identifying the former as the preferred diagnostic sample. The detection of HeV RNA in serum is consistent with haematogenous spread, and with hypothesised latency and recrudesence in flying-foxes. There were no detections in P. poliocephalus (n = 1168 animals; n = 2958 samples) or P. scapulatus (n = 262 animals; n = 985 samples), suggesting (consistent with other recent studies) that these species are epidemiologically less important than P. alecto in HeV infection dynamics. The study is unprecedented in terms of the individual animal approach, the large sample size, and the use of a molecular assay to directly determine infection status. These features provide a high level of confidence in the veracity of our findings, and a sound basis from which to more precisely target equine risk mitigation strategies.

Climate Change Could Increase the Geographic Extent of Hendra Virus Spillover Risk

“…HeV spills over to horses from two of the four Australian flying fox species (Smith et al 2014; Edson et al 2015; Martin et al 2016). We treated these species as two separate reservoir host systems (Smith et al 2014; Edson et al 2015; Martin et al 2018) that were geographically limited to the areas colonisable by P. alecto and P. conspicillatus (Soberón et al 2005; Martin et al 2016).…”

“…Hendra virus (HeV, Paramyxoviridae: Henipavirus ) is another bat-borne virus that spills over into domestic animals, in its case horses, and then people with high case fatality rates of 50–75% (Halpin et al 2011; Smith et al 2014; Edson et al 2015; Martin et al 2016). It was discovered in 1994 in a Brisbane suburb in Queensland, Australia, with two of the four Australian mainland flying fox species, Pteropus alecto and P. conspicillatus , as its major reservoir hosts (Halpin et al 2011; Smith et al 2014; Edson et al 2015; Martin et al 2016), although antibodies against HeV are commonly found in P. scapulatus and P. poliocephalus (Young et al 1996; Plowright et al 2008).…”

“…It was discovered in 1994 in a Brisbane suburb in Queensland, Australia, with two of the four Australian mainland flying fox species, Pteropus alecto and P. conspicillatus , as its major reservoir hosts (Halpin et al 2011; Smith et al 2014; Edson et al 2015; Martin et al 2016), although antibodies against HeV are commonly found in P. scapulatus and P. poliocephalus (Young et al 1996; Plowright et al 2008). HeV is closely related to Nipah virus, which is also a Henipavirus from pteropodid bats.…”

Virus discovery in bats

“…Bat urine and faeces have been favoured as non-invasive samples for virus discovery, however active bat catching and sampling can give more accurate calculations of viral prevalence. In the case of Hendra virus, urine was the most significant form of virus transmission, with higher titres of virus seen in urine compared to specimens such as nasal swabs, faecal samples and serum 21 . Pooled urine can be collected from plastic sheets laid below bat colonies and stored in a viral transport medium at À808C for later analysis 22 .…”

No Evidence of Hendra Virus Infection in the Australian Flying‐fox Ectoparasite Genus Cyclopodia

“…The spillover of Hendra virus (HeV) into horses, and subsequent transmission to humans, has resulted in fatal respiratory and neurological disease (Field et al., ; Playford et al., ). Australian flying‐foxes of the genus Pteropus are considered to be the reservoir host of HeV (Halpin et al., ; Field et al., ), with recent research demonstrating that Pteropus alecto and Pteropus conspicillatus are the predominant hosts of this virus (Smith et al., ; Edson et al., ; Goldspink et al., ). The most parsimonious hypotheses on the mode of HeV transmission, both between flying‐foxes, and from flying‐foxes to horses, propose direct or indirect contact with infected urine (Field et al., , ; Smith et al., ; Edson et al., ), although neither transmission cycle has been conclusively demonstrated.…”