Experimental immunization of ponies with Strongylus vulgaris radiation-attenuated larvae or crude soluble somatic extracts from larval or adult stages.

The study examines the efficacy of two methods of immunizing ponies against Strongylus vulgaris infection: one using irradiated larvae and the other using crude soluble homogenates from either the larvae or adult stages of the parasite.

About the Experiment

• Yearling ponies were brought up in parasite-free conditions and divided into three groups for different forms of immunization and a control group.
• The groups were immunized either with radiation-attenuated third-stage larvae dubbed L3, soluble adult somatic extracts or larval somatic extracts. The extracts also contained excretory/secretory products from the insect’s in vitro culture. The control group was given a placebo.
• Each group was immunized twice. The irradiated larvae were given orally while the extracts or controls were injected with an adjuvant into the ponies’ muscle tissue.

Post Immunization Assessment

• About six weeks after the second immunization, all ponies were exposed to the parasite.
• Six weeks post-challenge, necropsy examinations were conducted.
• The group receiving the irradiated larvae showed the fewest post-exposure clinical signs and lesions, indicating protection from infection at a rate of 91%, determined by the minimal larval recoveries from the animals’ arterial dissections.

Results Analysis

• The soluble antigen recipients did not differ much from the control group in terms of larval recoveries, equating their susceptibility levels to the challenge.
• Compared to the control group, the soluble antigen recipients showed more clinical signs and lesions, raising concerns that parenteral immunization might intensify the post-challenge inflammatory responses.
• The immunization with irradiated larvae resulted in an increased count of certain white blood cells known as eosinophils, antibody recognition of S. vulgaris L3 surface antigens and showed signs of encouraging a ‘cytophilic’ antibody response that facilitated degranulation, a process where cells release antimicrobial cytotoxic molecules.