Social network structure is robust to parasite induced changes in contact behavior of domestic sheep

To understand infections affect populations, it’s important to understand
the relationship between parasitism and social behavior. Parasites can
disrupt social networks in two main ways: by changing the behavior of
infected individuals—often leading to decreased activity—and by prompting
uninfected individuals to alter their behavior, such as avoiding those
showing signs of illness. These behavioral adjustments can shift group
dynamics and influence how parasites spread. In this study, we explored
how a parasitic nematode infection influences both individual social
interactions and the structure of social networks in sheep. We created
three experimental treatments, each replicated across four independent
groups: (1) all individuals infected (Parasitised), (2) all individuals
uninfected (Non-parasitised), and (3) a mixture of infected and uninfected
individuals (Mixed). We tracked social contact patterns using proximity
loggers over four stages of infection: prior to infection, the pre-patent
period, the patent phase, and after the infection had cleared. Our
findings revealed that infected lambs—whether in fully parasitised or
mixed groups—engaged in fewer social contacts after becoming infected.
Interestingly, in the mixed groups, uninfected lambs did not reduce their
interactions with infected group members, maintaining contact levels
similar to those before infection. These results indicate that parasitic
infections can alter social behaviors across an entire group, and that the
behavioral responses may depend not only on an individual's infection
status but also on the composition and responses of the social group as a
whole.