Infection with vibrio fetus in the inununologically immature fetal calf

Viable cultures of Vibrio fetus were injected into the placental cavities of cows between 122 and 249 days of pregnancy. Cows inoculated between 122 and 182 days of pregnancy aborted dead fe­tuses 5-7 days (average of 5.6 days) after inocu­lation, whereas those infected after that time aborted live fetuses 9-20 days (average of 13.3 days) later. V. fetus was recovered from the lung and abomasum and occasionally from the liver, spleen, and brain. Partially macerated calves, aborted between 129 and 187 days of gestation, showed no remarkable gross or microscopic le­sions. Serum samples were not available for anal­ysis from these calves. Gross lesions in fetuses aborted after 222 days of gestation consisted of a necrotizing placentitis, fibrinous peritonitis and pleuritis, and hepatitis. Microscopic changes were predominately of a proliferative nature and in­cluded reticuloendothelial hyperplasia and plasma cell infiltrates in the lamina propria of the tubular organs. Elevated levels of immunoglobulin M with questionable antibody specificity were observed in the late-term fetuses. Cows developed specific an­tibody titers in comparable periods of time. The results suggested that fetal calves exposed to V. fetus prior to 188 days of gestation were incapable of developing the immune response necessary for overcoming the infection. Fetuses infected after 212 days of gestation resisted the infection to a greater degree, as determined by morphologic and humoral observations. However, the late-term fe­tuses were unable to respond with the same degree of specificity of antibodies as was observed in the adult cows.