Identifying Hendra virus diversity in pteropid bats

Abstract

Hendra virus (HeV) causes a zoonotic disease with high mortality that is transmitted to humans from bats of the genus Pteropus (flying foxes) via an intermediary equine host. Factors promoting spillover from bats to horses are uncertain at this time, but plausibly encompass host and/or agent and/or environmental factors. There is a lack of HeV sequence information derived from the natural bat host, as previously sequences have only been obtained from horses or humans following spillover events. In order to obtain an insight into possible variants of HeV circulating in flying foxes, collection of urine was undertaken in multiple flying fox roosts in Queensland, Australia. HeV was found to be geographically widespread in flying foxes with a number of HeV variants circulating at the one time at multiple locations, while at times the same variant was found circulating at disparate locations. Sequence diversity within variants allowed differentiation on the basis of nucleotide changes, and hypervariable regions in the genome were identified that could be used to differentiate circulating variants. Further, during the study, HeV was isolated from the urine of flying foxes on four occasions from three different locations. The data indicates that spillover events do not correlate with particular HeV isolates, suggesting that host and/or environmental factors are the primary determinants of bat-horse spillover. Thus future spillover events are likely to occur, and there is an on-going need for effective risk management strategies for both human and animal health.

Figure 1. Phylogenetic tree (neighbour-joining, p distance) of the hypervariable region from nucleotide 1500 to 2240 (bat isolates of HeV are represented in red, horse isolates in blue.

Bat variants sequenced from PCR amplification are indicated in pink and horse and human variants in black. Yeppoon collection 15/8/09, Cedar Grove collection 5/8/09, Tolga Scrub collection 24/8/09).

Figure 2. Map of Queensland with outbreaks in horses (blue circles) and sites of HeV detection from flying fox roosts (red squares).

Figure 3. Phylogenetic tree of full length HeVgenome (bat isolates are represented in red, horse isolates are represented in blue).

Figure 4. Variability map of the number of changes/100 nucleotides of HeV genome utilising the 12 full length sequences.

Coding regions for the six major viral proteins are indicated beneath variability map.

Figure 5. Comparison of the phylogenetic tree from two regions of the HeV genome a) nucleotides1561–2385 and b) nucleotides 4288–5065.