Hendra virus infection in a veterinarian

To the Editor: In their report of Hendra virus infection acquired by a veterinarian from an infected horse, Hanna et al1 mention that the likely reservoir for this virus is fruit bats (Pteropus spp.), and suggest that transmission of the virus to horses may be via contamination of pasture by birth products from fruit bats.

During 5 years of fieldwork in north-eastern Australia for my PhD thesis on Toxocara pteropodis, an intestinal roundworm of flying foxes,2 which included hundreds of hours observing fruit bats in their natural habitats, not once did I come across a case of natural birth or abortion in fruit bats away from their communal roosts (“camps”), which were always within pockets of dense forest, such as mangrove, eucalyptus or melaleuca swamps. Furthermore, the three coastal fruit bat species exhibited a short, well defined birthing season, generally over 3 weeks from late October through to November. The birthing season of the wide-ranging, inland little red flying fox, P. scapulatus, is 6 months out of phase with this; it produces its young in May3 in remote inland camps. During birth, which is a short process lasting usually less than an hour, the mother bat remains alone, quite separate from and ignored by her neighbours.

All my observations of flying fox births were during daylight hours, and in the camps. While it is possible that an individual female might give birth away from her camp while out feeding at night, this would seem to be such an isolated event as to exclude it from being a reliable, and therefore major, transmission route for the virus. Moreover, the first recorded cases of equine and human infection occurred in the month of September,1 further diminishing the likelihood of birth products being the mode of transmission from bats.

On the other hand, while feeding in mango trees or on other exotic or native fruits and blossoms growing in horse paddocks, these bats do defecate and urinate frequently; this, to my mind, may be a more likely infection route. Resting in camps, individual bats urinate indiscriminately, contaminating any neighbours roosting below. While out collecting flying foxes for my research, I found it impossible to avoid aerial contamination by their excrement — although I do not recall ever experiencing symptoms suggestive of Hendra virus infection.