Secondary bacterial infection in plasma endotoxin levels and the acute-phase response of mice infected with Trypanosoma brucei brucei.

Murine Trypanosoma brucei brucei infection leads to elevated plasma endotoxin-like activity levels not related to parasitaemia levels accompanied by the development of acute-phase response and increased plasma levels of serum amyloid P (SAP) and haptoglobin (Hp). To determine the source of the endotoxin-like activity and role of secondary bacterial infection in the pathogenesis of trypanosomosis, infected mice were treated with the antibiotic ciprofloxacin. Plasma endotoxin-like activity levels, irrespective of treatment, were elevated three- to fourfold, beginning 7 days after infection. Plasma protein concentrations increased markedly following infection from 7 days after infection (DAI). Peak Hp and SAP concentrations in ciprofloxacin-treated and -untreated infected mice were attained 7 and 14 DAI, respectively. Thereafter, both protein levels gradually declined until the end of the experiment, but Hp levels for non-treated mice declined up to 21 DAI and thereafter significantly increased on 28 and 35 DAI. Whole-trypanosome lysate and the membrane-enriched fraction demonstrated endotoxin-like activity, with the former having higher levels. The results suggest that the endotoxin-like activity in trypanosome fractions and plasma of infected mice is due to the trypanosome. Further elevation of haptoglobin during the late stages of infection in non-treated mice suggests the involvement of secondary bacterial infection.