Posted Jan. 14, 2015
The devastating impact of white-nose syndrome on bat colonies in eastern North America is due in part to the seasonal dynamics of infection and transmission, according to a new study led by scientists at the University of California-Santa Cruz. “Host and pathogen ecology drive the seasonal dynamics of a fungal disease, white-nose syndrome” was published Dec. 3, 2014, in the Proceedings of the Royal Society B: Biological Sciences.
Researchers discovered that the Pseudogymnoascus destructans fungus can infect nearly every bat in a colony during the winter while the bats are hibernating. Bats that survive the winter are able to clear the infection during summer when their body temperatures are increased, which prevents fungal growth. Yet the high infection rate during hibernation leads to greater mortality rate at a time when bat populations are naturally at their lowest, before the females give birth in the summer.
“It hits when the population is at its smallest, and, by the end of winter, nearly 100 percent of the bats in a cave can be infected, which helps explain why it has such large impacts,” said Kate Langwig, a graduate student at UC-Santa Cruz and lead author of the paper.
The study provides the first description of the dynamics of fungal infection and transmission in bats. The findings are in striking contrast with most infectious diseases, according to senior author Marm Kilpatrick, PhD, associate professor of ecology and evolutionary biology at UC-Santa Cruz.
||Little brown bats in a New York hibernation cave exhibit white fungal growth on their muzzles. (Photo by Nancy Heaslip, New York Department of Environmental Conservation)
“For many diseases, population density and social interactions play a big role in transmission, but these bats are actually very social and live in dense colonies in both summer and winter,” he said. “In this case, transmission is tied to hibernation and body temperature. When the bats start hibernating, it’s almost like they become petri dishes for this fungus to grow on.”
P destructans thrives in cold environments and grows superficially on exposed skin on the bats’ noses, ears, and wings. During hibernation, the body temperatures of bats drop to the cold ambient temperatures of their hibernacula. The fungus proliferates at these temperatures, which range from 2 to 12ºC.
Over the course of the winter hibernation period, the infection spreads throughout the bat colony. Most of the deaths are in late winter, when both infection prevalence and infection loads are highest.
Researchers studied six species of bats, testing them for infection with the fungus during three key periods of their annual cycle: fall, when the bats mate outside the hibernacula; winter, when they go into hibernation; and summer, when they migrate to maternity sites, and the females give birth.
Low levels of fungal infection were detected during the fall, probably as a result of bats coming into contact with spores of the fungus inside the hibernacula. The fact that bats are not transmitting the infection during the migratory period is important in limiting the rate at which it is spreading geographically, according to the researchers.
The study provides critical information for planning strategies to manage white-nose syndrome.