Effects of a chronic wasting infection on skeletal muscle size and contractile properties.

To evaluate the effects of chronic infection on skeletal muscle dimensions and contractile properties, we used a hamster model of visceral leishmaniasis, a parasitic infection of the reticuloendothelial system produced by Leishmania donovani (LD). To distinguish between effects of reduced caloric intake and infection per se, we also studied healthy control animals and noninfected animals subjected to caloric restriction. Three muscles were tested in vitro: plantaris, soleus, and diaphragm. Both caloric restriction and LD infection caused loss of body weight and reduced muscle cross-sectional areas and wet weights. The interventions had variable effects on in vitro contractile properties, the most pronounced being reduction in peak tension in response to tetanic stimulation. Tension loss was 35-45%, except for a loss of 65% in plantaris of LD-infected animals. We conclude that chronic LD infection affects skeletal muscles in both indirect and direct ways. 1) Reduced caloric intake due to anorexia decreases muscle size and active tension. Disuse probably enhances this effect in limb muscles. 2) Infection produces profound weakness of inactive fast-twitch muscle by unknown mechanisms.