Does the disturbance of bat roosts increase Hendra risk?

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The flying fox roosts enrolled in the study. Image: PLOS ONE
The flying fox roosts enrolled in the study. Image: PLOS ONE

A study has found no evidence that disturbing the roosts of bats increased their excretion of Hendra virus.

Hendra virus, which is capable of infecting horses, is carried by the native Australia fruit bats known as flying foxes.

Humans are able to catch the virus from contact with the bodily fluids of infected horses. Of seven known Hendra cases in humans, four have proved fatal.

The researchers said the increased urban presence of flying foxes often provoked negative community sentiments because of the Hendra exposure risk, resulting in calls for the dispersal of urban flying-fox roosts.

However, it has been suggested that disturbing urban roosts may result in an increase in Hendra infection in flying foxes because of increased stress, creating a greater risk of spillover of the disease.

Hume Field and his colleagues sought to examine the impact of roost modification and dispersal on the dynamics of Hendra infection in flying foxes, as well as monitoring levels of the stress hormone, cortisol, in their urine.

Their work centered on 21 roosts during the 15-month study period. They comprised 11 primary roosts and 10 secondary roosts, with the majority in Queensland.

They found the mean prevalence of Hendra virus in urine samples collected before roost disturbance at 4.9 percent. The prevalence during roost disturbance was 4.7 percent, while afterwards it was found to be 3.4 percent. The researchers described the differences as small and non-significant.

The differences found in mean urine cortisol concentrations were similarly described as small and non-significant.

The researchers did, however, find an underlying association between cortisol concentration and season, and cortisol concentration and region, suggesting that other – plausibly biological or environmental – variables played a role in cortisol concentration dynamics.

“We found no statistical association between flying-fox roost disturbance and Hendra virus urinary excretion prevalence, indicating that roost disturbance does not precipitate increased Hendra virus infection and excretion in dispersing flying-foxes,” they reported in the open-access peer-reviewed journal, PLOS ONE.

“Further, we found no fundamental statistical association between roost disturbance and urinary cortisol concentration.”

They said that the levels of behavioural distress associated with roost disturbance appeared to be affected by the nature and timing of the activity, which highlighted the need for a “best practice” approach to dispersal or roost modification.

The researchers said the mobility of flying-foxes provided some capacity for them to escape human disturbance, but their increasing urban presence may subject them to chronic roost disturbance and harassment, the consequences of which remained unknown.

They found no evidence of Hendra virus excretion in single species roosts of little red and grey-headed flying-foxes, which was consistent with previous findings. The findings suggested these species may be less efficient hosts than black or spectacled flying-foxes.

The research team said the findings should provide a robust platform for informed public discussion and policy development in relation to Hendra virus and flying fox management in Australia.

“The absence of any detected increase in Hendra virus excretion associated with roost disturbance does not negate the ‘background’ exposure risk for horses, and the need for horse owners to adopt and maintain recommended risk management strategies,” they added.

Field was joined in the research by Daniel Edson, Less McMichael, Nina Kung, Craig Smith, David Jordan and David Mayer.

Edson D, Field H, McMichael L, Jordan D, Kung N, Mayer D, et al. (2015) Flying-Fox Roost Disturbance and Hendra Virus Spillover Risk. PLoS ONE 10(5): e0125881. doi:10.1371/journal.pone.0125881
The full study can be read here

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