SYDNEY: Climatic extremes like frequent droughts and floods, associated with global warming, can trigger epidemics that could potentially wipe out livestock or wildlife.

A new study suggests that such extremes are capable of altering normal host-pathogen relationships, causing a "perfect storm" of multiple infectious outbreaks.

The study, by a team, comprising scientists from the Universities of California, Illinois and Minnesota, examined outbreaks of canine distemper virus (CDV) in 1994 and 2001 that claimed large numbers of lions in Tanzania's Serengeti National Park and Ngorongoro Crater.

Extreme drought had preceded both these fatal viral outbreaks that reduced the lion population of Cape Buffalo.

The lions suffered heavy tick infestations that became even more common in their diet. These parasites are normally present in lions at harmlessly low levels.

The CDV suppressed the lions' immunity, which allowed the elevated levels of blood parasites to reach fatally high levels, leading to mass deaths.

In 1994, the number of lions in the Serengeti study area dropped by more than 35 percent after the double infection. Similar losses occurred in the Crater die-off in 2001.

The lion populations recovered within three to four years after each event, but most climate change models predict increasing frequency of droughts in East Africa.

"The study illustrates how ecological factors can produce unprecedented mortality events and suggests that co-infections may lie at the heart of many of the most serious die-offs in nature," said Craig Packer, of University of Minnesota.

The findings of the study have been published in the latest issue of the journal PLOS ONE.