How lambs control infection with Ostertagia circumcincta

Area of Science:

• Veterinary immunology
• Parasitology
• Quantitative genetics

Background:

• Nematode infections pose significant challenges in livestock.
• Understanding host-parasite interactions is crucial for developing effective control strategies.
• Ostertagia circumcincta is a major gastrointestinal nematode affecting sheep.

Purpose of the Study:

• To investigate the host immune response to Ostertagia circumcincta in lambs.
• To determine the mechanisms of genetic resistance in lambs against nematode infection.
• To identify specific immune components responsible for controlling parasite burden.

Main Methods:

• Quantitative genetic analyses of faecal egg counts and worm length in over 500 Scottish Blackface lambs.
• Measurement of nematode numbers and adult female worm length.
• Assessment of the association between immune responses and parasite characteristics, specifically the IgA response to fourth-stage larvae.

Main Results:

• Substantial genetic variation was observed in faecal egg counts and worm length, but not worm numbers.
• A strong relationship exists between decreased worm length and reduced parasite fecundity.
• The IgA response to fourth-stage larvae was strongly and consistently associated with reduced worm length, accounting for most variation.

Conclusions:

• Genetic resistance in lambs to O. circumcincta primarily involves control of worm growth, not worm numbers.
• The IgA immune response mediates suppression of worm growth and fecundity.
• IgA-mediated suppression is the major mechanism of resistance against O. circumcincta in lambs.