A mild form of strangles caused by an atypical Streptococcus equi.

The research discusses a mild strain of the bacterial disease ‘strangles’ in horses, caused by an unusual variant of Streptococcus equi, and its extensive subclinical presence in a large breeding farm.

Identification of Atypical Strangles

In the study, a milder case of strangles was identified at a large horse breeding farm. This form was caused by an unusual variant of Streptococcus equi, a bacterium that typically leads to the disease. The variant was distinct from the typical strain as its mucoid capsule – a sticky, sugary coating that defends the bacterium and helps it to stick to surfaces – disappeared after 24 hours of culture, resulting in a matt-type bacterial colony.

• Signs of this mild form of strangles included a brief fever lasting 24-48 hours, a heavy nasal discharge, and loss of appetite.
• In approximately half of the infected animals, moderate enlargement of the mandibular lymph nodes (found in the lower jaw area) was noted, often leading to rupture or necessitating drainage.

Investigation of Subclinical Infections

The study also employed a serological test – specifically, a passive hemagglutination antibody test, where red blood cells clump together in the presence of certain types of antibodies, to detect disease exposure. This test revealed that unnoticed or non-symptomatic (subclinical) infections of this atypical strangles form were widespread among the horses in the breeding farm. These silent carriers increase the chances of spreading the unidentified variant of the bacterium across the farm and beyond.

The research underscores the importance of recognizing and addressing atypical variants of common disease-causing organisms, such as the S. equi variant leading to a milder form of strangles, which can lead to widespread subclinical infections that risk large scale outbreaks if ignored.