Researchers have found that sick house mice isolate themselves from the rest of their social group. This is in contrast to previous beliefs that the healthy animals were the ones avoiding their sick conspecifics. This new knowledge will help scientists better understand disease transmission in wild animal populations. The findings are in a paper just published in the journal Scientific Reports.
There has been little research on how diseases spread in wild animal populations. This is partially due to the difficulties of conducting studies on free-roaming wild animals. Previously, it was generally believed that animals in social groups would avoid sick members, slowing down the rate of disease transmission.
Researchers from the University of Zurich studied a large group of wild house mice in Illnau, Switzerland. The mice lived in a large barn and were free to come and go as they pleased. The barn’s mice had been tracked by scientists since 2002. Researchers set up artificial nest boxes, which the mice used regularly. The mice were then fitted with tracker tags and given individual identities for the study.
The team injected some of the mice with lipopolysaccharides (LPS) from bacterial cell walls. The LPS injections caused mild infection symptoms, including lethargy. The effect was short-lasting and not ultimately harmful to the mice. Another group of mice were injected with a saline injection as a control.
The researchers found that the sick mice spent more time away from their social group. They isolated themselves through their own behaviors, not because of actions by healthy mice. In fact, the non-LPS mice didn’t avoid their sick conspecifics as previous research had suggested. Instead, the healthy mice continued normal interactions with their sick companions and showed no avoidance behaviors. This shows that the sick mice were making a personal choice to stay away from the rest of the group.
The research team believes that the sick mice were staying away from their social group in order to reduce disease transmission. Their social groups consist mainly of relatives, giving an evolutionary advantage to mice that attempt to reduce the spread of illness. The authors hope that their findings can provide new insight into how diseases spread in wild animal populations, especially ones that form close-knit social groups. The findings may also help explain human behavioral responses to infectious diseases.
Patricia C. Lopes, Per Block, and Barbara König. Infection-induced behavioural changes reduce connectivity and the potential for disease spread in wild mice contact networks. Scientific Reports (2016).