Sleep during experimental trypanosomiasis in rabbits.

Trypanosoma brucei subspecies cause the human condition known as "sleeping sickness." In rabbits, these organisms induce a chronic and ultimately fatal disease characterized by periodic parasitemia. To characterize sleep alterations during a chronic infectious condition and to determine how immune stimulation of the host, as reflected by cyclic parasitemia, is related to altered somnolence, we monitored sleep and other clinical indices in rabbits inoculated subcutaneously with Trypanosoma brucei brucei. Within four days, infected rabbits developed fever, reduced food intake, and other signs of infectious illness concurrent with the onset of parasitemia were evident. The initial febrile episodes were transient, recurring in temporal correlation with parasitemia. Time spent in slow-wave sleep and delta-wave amplitude during slow-wave sleep increased significantly in association with the onset of febrile episodes, despite an overall trend toward decreases in these parameters. Because each episode of parasitemia presents an immune stimulus to the infected host, the periodic enhancement of sleep observed in this model is consistent with the hypothesis that immune stimulation is correlated with increased somnolence. The data further indicate that sleep alterations occur not only during acute infections, as previously reported, but during chronic infections as well.