Evaluation of protective immunity against experimental Dirofilaria immitis infection in Beagle dogs

Prevention of heartworm is a key goal of pet wellness. An experimental trial was carried out to induce the immunologic protection against Dirofilaria immitis infection in dogs during the period from July 2005 to November 2006.  To evaluate the three protocols of immunization, dogs were separately immunized with gamma-irradiated infective larvae; with chemical abbreviation of infection; with chemical abbreviation plus Freund's complete adjuvant respectively. Each trial consisted of immunized and control groups and each group composed of two dogs. All dogs used for this study were subcutaneously challenged with 100 intact third-stage larvae at designated times after the last immunization following the above three protocols. The dogs were euthanized and necropsized between 120 to 175 days after challenge infection for the worms in the right ventricle of the heart and pulmonary arteries. Number of worms and sexes were determined. A mean of 36 worms from the immunized groups with irradiated L3; 33 worms from the chemically-abbreviated group whereas 13 worms from the chemical abbreviation plus Freund's complete adjuvant group were recovered. The percentages of the average protection in three groups were 45.80%, 55.05% and 77.90% respectively. The adjuvant enhanced the protective immunity against L3 challenge infection. The ELISA values do not explain the intensity of the protection, but shown adequately the immunized dogs responding to the immunization performed in this experiment. Key words: Heartworm, protective immunity, chemical-abbreviation, gamma-irradiated larvae DOI = 10.3329/bjvm.v5i1.1323 Bangl. J. Vet. Med. (2007). 5 (1 & 2): 93-98