Antibodies to Aqx toxin of Actinobacillus equuli in horses and foals.

The research examined the presence of antibodies to Aqx toxin, a part of Actinobacillus equuli bacteria, in adult horses and foals. It was found that these antibodies were prevalent in both adult horses and foals after intake of colostrum, but not in foals before colostrum intake.

Introduction to Actinobacillus equuli and the Aqx Toxin

• Actinobacillus equuli is a bacterium that is normally found in the oral flora of horses.
• Despite its usual benign presence, A. equuli is associated with diseases in horses, most notably a fatal form of septicaemia in newborn foals. This deadly condition is believed to be related to the inability of the foal’s immune system to receive passive transfer of immunities from the mother through colostrum (a form of milk produced by the mammary glands of mammals during pregnancy which contains antibodies to protect the newborn against disease).
• One particular protein of A. equuli, named Aqx, is a pore-forming toxin from the RTX family which has been found to be cytotoxic to horse lymphocytes (a type of white blood cell that plays a crucial role in the immune system).

Detection of Antibodies to Aqx in Horses

• The research aimed to detect the presence of antibodies to the Aqx toxin in horse serum, collected from individuals across multiple regions.
• The antibodies to Aqx were found in the serum of adult horses and also in the serum of foals, but only if tested 24 hours after birth and initial colostrum intake.

Implication of Results

• The study shows that newborn foals, within their first few hours of life, do not have an immune response to the Aqx toxin as evidenced by the absence of antibodies in their serum prior to colostrum intake.
• The presence of the antibodies to the Aqx toxin after the intake of colostrum supports the importance of this initial feeding in passively transferring necessary immunities from the mother to the newborn.
• Despite being part of the regular oral microbiota of horses, A. equuli and its Aqx toxin could present a risk to horse health, especially in foals who have not been able to benefit from passive immunoglobulin transfer via colostrum.