Climatic factors may trigger outbreak of tularaemia (rabbit fever)

What causes an outbreak of tularaemia (rabbit fever) has until now been a mystery, and where the bacteria go between outbreaks is still unknown. Climatic factors have now been shown to be a possible trigger for outbreaks of the disease in a study carried out by Thomas Palo, Mid Sweden University, and Clas Ahlm and Arne Tärnvik, Umeå University.

The investigation, which is being published in the journal Ecology and Society, demonstrates that the incidence of the disease in humans correlates more strongly with variations in climate than with variations in the hare population.

Rabbit fever is a disease caused by the bacterium Francisella tularensis, and it affects humans and animals at irregular intervals. It has long been thought that the disease gathers momentum among small mammals, such as hares, and is then transmitted to humans by mosquitoes or through contact with smitten animals.

“Hares are victims of the disease just as much as humans, but they are much more susceptible and die of it,” says Professor Thomas Palo.

The study shows that climatic variation and the flow of our waterways can be triggering factors for increased incidence. It may be that in certain years there is an accumulation of stagnant water where both the bacteria and mosquitoes thrive. These situations occur irregularly and are dependent on the climate. The study demonstrates that cold winters one or two years before an outbreak lead to slower flow rates in waters, which may entail an increased risk of an outbreak of tularaemia. Another finding of the study is that no increase in rabbit fever is expected as a result of a warmer climate in the future.