When wild house mice become sick, they spend time away from their social groups, which leads to a decrease in their potential for disease transmission. A new study was revealed by evolutionary biologists from the University of Zurich, in collaboration with the ETH Zurich. Models focused on predicting the spread of infectious diseases like influenza or Ebola in humans, that can be improved through these results. Animals that become sick can change their behavior and, as an example, become less active. Patricia Lopes from the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, the study’s lead author, says that previous research in wild animals has generally ignored how this change in behavior may affect social contacts in a group, and how these changes can impact the transmission of a disease.
Sick mice remove themselves from the group and are not avoided by the others. Experimental manipulations of free-living mice, radio frequency tracking of animals, social network analysis and disease modeling, were used to tackle this problem. They simulated an infection by injecting the mice with lipopolysaccharides, which results in an immune response and generalized disease symptoms. A paper was published in the journal Scientific Reports where the team revealed that sick mice become disconnected from their social groups.
Mice are able to detect other sick mice, so it was surprising to find that the animals in the same social group did not avoid the sick mouse. They even continued interacting with the sick mouse, and other mice more or less, in the same way as before the experimental infection. The sick mouse removed itself from the group. Relatives in the same group may be protected by the behavior of the sick mouse, so as not to catch the disease.
The researchers used mathematical models to predict how an infectious disease would spread, considering the changes in behavior of the sick animals. They believe that the speed and extent of disease spread are greatly reduced.
This study contributes to our understanding of the complexity inherent to disease transmission, and the importance of changes in behavior of sick animals, for predicting the outcome of disease and sickness outbreaks. Humans are also known to alter their behaviors when sick, and the study confirms these findings. These effects are possible in behavioral symptoms, including influenza and Ebola.
-Dr Fredda Branyon