Lesions in guinea pigs infected with Coxiella burnetii strain M-44.

Guinea pigs inoculated with the live M-44 vaccine strain of Coxiella burnetii were examined grossly and microscopically for the presence of Q fever-related lesions. Mild myocarditis was observed in 38% of the infected animals but in none of the control animals. Livers showed significant incidence of hepatitis, necrosis, and granuloma formation, especially during the first eight days of the infection. A much lower incidence of splenitis was also found but was considered to be of borderline significance. Generally, lesions were mild in nature, and none seemed to endanger the life of the animal or to cause observable distress.