Echinococcus granulosus: Acute systemic allergic reactions to hydatid cyst fluid in infected sheep

Abstract

Sheep with naturally acquired infections of Echinococcus granulous and uninfected sheep were injected intravenously with hydatid cyst fluid, and the clinical, cardiopulmonary, hematological, and pathological effects were recorded. The clinical response of infected sheep was severe, and one animal died. Cardiopulmonary changes included a “triple response” of the systemic blood pressure ending in prolonged hypotension and pulmonary arterial and intrapleural hypertension. An immediate, severe neutropenia was followed by a rebound neutrophilia and eosinophilia. Packed cell volume and plasma protein concentration were increased, and coagulation time was prolonged. Pathological changes, confined to the lungs, consisted of congestion, periarteriolar and peribronchiolar hemorrhage, edema, and sequestration of polymorphonuclear cells in the alveolar capillaries. The clinical signs after injection were mild or absent in noninfected sheep. The initial changes in systemeic and pulmonary pressures were similar to those in the infected animals; however, these pressures reverted to preinjection levels by 5 min after injection. The neutrophil response in control animals was identical to that in infected animals, and three control animals had a marked eosinophilia at 24 hr. Pathological changes were less marked in the noninfected animals. The responses of hydatid-infected sheep to hydatid fluid injection suggest anaphylaxis because of their similarity to the manifestations of experimental anaphylaxis in sheep and other ungulates. Although there were statistically significant differences in the responses of infected and noninfected sheep, they were differences in degree rather than kind. Two control sheep were infected with single cysticerci of Taenia hydatigena, and this related larval cestode may have produced sensitization to E. granulosus antigens. The mechanism of the reactions occurring in sheep neither infected with T. hydatigena nor with demonstrable agglutinating antibody to E. granulosus antigens is unknown. These reactions may be manifestations of the primary toxicity of hydatid cyst fluid; however, that sensitization to unknown antigens could have produced cross-reactivity to E. granulosus antigens remains a possibility.