Serum-mediated Haemonchus contortus larval aggregation differs by larval stage and is enhanced by complement

Area of Science:

• Veterinary Parasitology
• Immunology
• Sheep Health

Background:

• Haemonchus contortus is a major gastrointestinal nematode parasite of small ruminants.
• Immune responses, including antibody and complement, are crucial for controlling parasitic infections.

Purpose of the Study:

• To investigate the role of complement/antibody complexes in Haemonchus contortus larval aggregation.
• To assess the influence of host breed resistance and infection status on this aggregation.
• To determine how larval maturation affects aggregation in vitro.

Main Methods:

• Larval binding assays using H. contortus larval stages (L3, exsheathed L3, L4).
• Incubation with serum from parasite-naïve or primed St. Croix (resistant) and Suffolk (susceptible) lambs.
• Manipulation of serum components (complement, antibody) to assess their role in aggregation.

Main Results:

• No significant difference in L3 aggregation based on breed or infection status.
• Exsheathed L3 and L4 aggregation was reduced with primed Suffolk (susceptible) serum compared to L3.
• Removal of complement or antibody abolished aggregation; their combined depletion and restoration confirmed their essential role.
• IgG binding to larvae within aggregates was confirmed using fluorescence-labeled antibodies.

Conclusions:

• Complement/antibody complexes induce Haemonchus contortus larval aggregation, inhibiting motility.
• This aggregation mechanism may be critical for the early clearance of H. contortus infections in sheep.
• Breed resistance and infection status influenced aggregation, particularly in susceptible breeds.