Lymphadenitis in experimental murine toxoplasmosis induced by intramuscular injection of tachyzoites.

When tachyzoites (RH strain) of Toxoplasma gondii are injected intramuscularly, experimental mice survive up to 7 days, 1-2 days longer than those infected intraperitoneally. We observed sequential histopathological changes in inguinal lymph nodes after intramuscular injection of tachyzoites to thighs of specific pathogen free (SPF) mice. Initial findings on 1 or 3 days after the injection were reactive germinal centers, distended sinuses and epithelioid cell clusters in cortical and paracortical regions. Later on 5 days after the injection, however, effacement of nodal structure with depletion of cells and focal necrosis were observed. Necrotizing lymphadenitis in the experimental murine toxoplasmosis suggests the causal relation between T. gondii infection and the human disease.