Association of microbiologic flora with clinical, endoscopic, and pulmonary cytologic findings in foals with distal respiratory tract infection.

This study investigates the infectious agents causing undifferentiated distal respiratory tract disease in young horses, commonly known as foals. The research found the bacterium Streptococcus zooepidemicus to be the predominant form of bacteria found in these diseases, and also highlighted the usefulness of the Agar gel immunodiffusion (AGID) test in identifying foals exposed to certain bacteria, despite the test not always correlating with bacterial culture results.

Objective and Methodology

• In this research, the team aimed to establish the infectious agents causing episodes of undifferentiated distal respiratory tract disease in foals aged between 1 to 8 months old. This disease often results in symptoms like nasal discharge, cough, and pneumonia.

• The researchers attempted to identify the probable causes for these episodes of illness by culturing samples from the proximal and distal airways of clinically ill foals, before any treatments had been provided.

• 101 foals were chosen for the culture exercise, which was done for aerobic and anaerobic bacteria and viruses like rhinoviruses, equine arteritis virus, equine herpesvirus subtype 1 [EHV-1], influenza virus, and adenovirus.

Findings

• The research did not find any viruses in swab or bronchial lavage airway specimens in foals. EHV-1 was found in two of 47 foals with an increase in seroconversion. The other viruses showed low and decreasing serotiters, likely due to maternally derived antibodies.

• The bacterium Streptococcus zooepidemicus was the predominant organism identified, found in 88 out of 101 cases. It was accompanied by alpha-hemolytic streptococci (8 cases), Bordetella bronchiseptica (13 cases), Staphylococcus epidermidis (9 cases), and other organisms in lesser frequency.

Agar Gel Immunodiffusion (AGID) test

• The Agar gel immunodiffusion (AGID) test proved useful in detecting foals exposed to Rhodococcus equi, a bacterium that can cause severe pneumonia in foals. However, the results from this test did not correspond well with the bacterial culture results, as 34% of foals that tested negative in the culture tested positive in the AGID test.

In conclusion, the study found Streptococcus zooepidemicus to be the predominant bacterial species causing distal respiratory tract disease in foals. Furthermore, the AGID test could be a valuable tool, despite its strayed correlation with bacterial culture results.