Environmental Challenges and Co-Infection Modulate Resistance and Tolerance Against Trypanosoma Cruzi and Trichinella Spiralis in Rats.

To overcome infection, hosts employ two defense strategies: resistance (which limits pathogen fitness), and tolerance (which reduces infection damage). These strategies may be influenced by environmental challenges such as food shortage, social conflict, and co-infections. Here, our objective was to assess defense strategies in rats infected with Trichinella spiralis and/or Trypanosoma cruzi under environmental challenges. After four weeks of treatment with environmental challenges (food restriction [0/1] and/or social conflict [0/1]), rats were exposed to Tri. spiralis [0/1] and/or Try. cruzi [0/1]. Six weeks postinoculation, we measured parasite intensity and several indicators of health or pathology. Tolerance to Try. cruzi increased in the presence of social conflict and food restriction. Coinfected animals showed reduced tolerance compared to mono-infected. However, food-restricted mono-infected rats had lower tolerance than other groups. No significant differences were found in resistance to Try. cruzi. Tolerance to Tri. spiralis was higher in food-restricted rats and Coinfected rats. Moreover, we found a potential shift in defense strategy: rats that are mono-infected and exposed to social conflict may be more resistant but less tolerant to Tri. spiralis than all other experimental groups. Overall, our findings highlight that defense strategies are context-dependent in the nematode-protozoan infection model studied, and provide evidence of a shift in the defense strategy to accommodate during environmental challenges. Given that rodents play a key role as reservoirs of zoonotic pathogens, understanding the range and variability of defense strategies in these animals is of utmost importance.