Immunological Response to Experimental Echinococcosis in Meriones unguiculatus

Abstract

Varying doses of protoscolices of Echinococcus granulosus were injected intraperitoneally into Mongolian jirds, Swiss mice, and golden hamsters. After 4 months the animals were killed and the numbers of developing cysts counted. Jirds were by far the most susceptible hosts. Doses of 500 protoscolices produced 100% infection rates in both weanlings and adults. Comparable infection rates in weanling mice required inocula of 5,000 protoscolices, but even at this dose hamsters were refractory to infection. Three of 5 jirds developed pulmonary cysts after intravenous administration of 500 protoscolices. Serologic responses in infected jirds were followed using the indirect hemagglutination tests and a purified fraction of hydatid cyst fluid (HCF) as antigen. Titers reached a plateau after 15 weeks and were maintained for several months. Much brisker serologic responses occurred in animals sensitized with the antigenic fraction in various adjuvant vehicles. At no time during infection did jirds show any evidence of immediate hypersensitivity to HCF in direct skin tests, passive cutaneous anaphylactic tests, or after intravenous challenge with antigen. After artificial immunization with hapten-conjugated antigens or HCF, jirds underwent a fatal shock following intravenous challenge with antigen. HCF provoked the appearance of circulating antibodies which were capable of sensitizing normal recipients for passive systemic anaphylaxis after a latent period of 72 hr. It is concluded that the failure of the infected jird to develop immediate hypersensitivity responses to E. granulosus represents a marked deviation from the parrern of the immune response in echinococcosis in man and domestic animals and must be considered in the future use of this animal in experimental studies on the host-parasite relationship.