Immunologic and hematologic responses in ponies with experimentally induced Strongylus vulgaris infection.

The research study investigates the immune and blood responses in ponies infected with the parasite Strongylus vulgaris. The study looks into how varying degrees of infection affect the immune response and the overall impact of a re-infection on ponies’ immune system.

Experimental Setup

• Four ponies were experimentally infected with Strongylus vulgaris, a common parasite in horses.
• Two of the ponies were injected with 200 larvae while the other two received 700 larvae.
• The same ponies were then re-inoculated with the same amount of larvae 34 weeks after the first injection.
• These four ponies were compared with five helminth-free ponies to see the difference in immune responses.

Initial Responses

• The ponies injected with S vulgaris produced an antigen-induced lymphocyte response between 1.5 to 3 weeks after infection but it didn’t persist over time.
• This response was followed by a biphasic complement-fixing antibody response and then a biphasic eosinophilia (increase in eosinophils, a type of white blood cell).

Impact of Larval Load

• The antibody titer (concentration) to S vulgaris antigen was higher in ponies injected with 700 larvae compared to those injected with 200 larvae.
• In ponies injected with 700 larvae, the second peak in antibody titer and number of eosinophils was observed earlier than in those injected with 200 larvae. It subsided from around 24 weeks after injection.

Impact of Reinfection

• After reinoculation, an increased degree of lymphocyte responsiveness was observed but by 17 weeks after this reinoculation, only the primary peak in the absolute number of eosinophils indicated an anamnestic response (immune response upon exposure to the same antigen).
• Significantly, no antibodies were detectable after reinoculation, unlike the initial infection.
• The prepatent period for S vulgaris infection (time from infection to detection) was noted to be 24 to 25 weeks.