Hendra virus infection dynamics in Australian fruit bats

Abstract

Hendra virus is a recently emerged zoonotic agent in Australia. Since first described in 1994, the virus has spilled from its wildlife reservoir (pteropid fruit bats, or 'flying foxes') on multiple occasions causing equine and human fatalities. We undertook a three-year longitudinal study to detect virus in the urine of free-living flying foxes (a putative route of excretion) to investigate Hendra virus infection dynamics. Pooled urine samples collected off plastic sheets placed beneath roosting flying foxes were screened for Hendra virus genome by quantitative RT-PCR, using a set of primers and probe derived from the matrix protein gene. A total of 1672 pooled urine samples from 67 sampling events was collected and tested between 1 July 2008 and 30 June 2011, with 25% of sampling events and 2.5% of urine samples yielding detections. The proportion of positive samples was statistically associated with year and location. The findings indicate that Hendra virus excretion occurs periodically rather than continuously, and in geographically disparate flying fox populations in the state of Queensland. The lack of any detection in the Northern Territory suggests prevalence may vary across the range of flying foxes in Australia. Finally, our findings suggest that flying foxes can excrete virus at any time of year, and that the apparent seasonal clustering of Hendra virus incidents in horses and associated humans (70% have occurred June to October) reflects factors other than the presence of virus. Identification of these factors will strengthen risk minimization strategies for horses and ultimately humans.

Figure 1. Map of Australia with flying fox distribution, Hendra virus spillover locations and flying fox sampling locations.

Sampled roost sites were identified in three geographically disparate sampling locations: south-east Queensland (SEQ), far north Queensland (FNQ) and the Northern Territory (NT). The SEQ sampling location includes the sampled roost sites and spillover locations from Murwillimbah to Tewantin; the FNQ sampling location includes sampled roost sites and spillover locations from Gordonvale to Clifton Beach, and north to the tip of Queensland; the NT sampling location includes sampled roost sites identified in the Northern Territory, remote from any spillover locations.