Mesenteric lymphangitis and sepsis due to RTX toxin-producing Actinobacillus spp in 2 foals with hypothyroidism-dysmaturity syndrome.

This study investigates two cases of foal infection by Actinobacillus bacteria which cause mesenteric lymphangitis and sepsis, noting a potential link between the occurrence of these infections and hypothyroidism-dysmaturity syndrome in the foals.

Background

• The research focuses on a type of bacteria known as Actinobacillus suis-like organisms (ASLOs) which are known to inhabit the genital, respiratory, and digestive tracts of healthy adult horses, as well as horses with respiratory disease, and septic foals.

Case Studies

• The study focuses on two foals born on separate farms and suffering from congenital hypothyroidism-dysmaturity syndrome, a condition that resulted in the contraction of carpal flexor tendons and thyroid hyperplasia.
• These foals were found to have been infected with ASLOs, which led to conditions such as thrombotic and necrotizing mesenteric lymphangitis and lymphadenitis; one of them had mandibular prognathism as well.

Bacterial Isolation and Identification

• The researchers then isolated ASLOs from the tissues of these animals, specifically their intestines. These organisms were then subjected to biochemical testing and mass spectrometric analysis.
• Through this process, they were unable to identify ASLOs conclusively. Simultaneously, they performed a comparative genetic analysis of these isolates along with similar others, in the process studying the phylogeny of three specific genes and checking for the presence of specific toxins.

Reclassification of the Isolates

• The two isolates were eventually classified as Actinobacillus suis sensu stricto and A equuli ssp haemolyticus, based on the characteristic presence and absence of specific toxins.
• Based on their genotypic analysis, the researchers were also able to reclassify three other equine ASLOs and two of five A equuli isolates as A equuli subsp haemolyticus, asserting that toxin genotyping plays a crucial role in the accurate classification of actinobacilli.

Conclusion

• This study highlights the significance of toxin genotyping in accurately identifying and classifying Actinobacillus bacteria, particularly in the case of infections in foals suffering from hypothyroidism-dysmaturity syndrome.
• The researchers also underline the importance, in the light of these findings, of studying such bacteria and the diseases they cause, given the frequent contact human populations have with horses and related species.