Clinical evaluation of the serodiagnostic value of enzyme-linked immunosorbent assay for Rhodococcus equi infection in foals.

This research article reports on the use of an enzyme-linked immunosorbent assay (ELISA) to detect the presence of antibodies against Rhodococcus equi infection in foals. The results suggest that high optical density (OD) readings may indicate a severe infection.

Methodology and Results

• The researchers used an ELISA test to identify the presence of serum IgG antibodies against Tween 20-extracted antigen of strain ATCC 6939 in foals in Hidaka, Japan.
• The study involved 752 foals showing various signs of infectious disease.
• Based on findings from previous studies, the researchers set an OD value of more than 0.3 as the benchmark for a positive result. Of the 752 sick foals, 138 had an OD value of 0.3 or above and were identified as ‘suspected of R. equi infection’.
• The age distribution of the 138 seropositive foals was significant, with most (64%) aged between 31 and 60 days. There was a notable decrease in subjects beyond this age range.

Interpretation of Findings

• Twenty-five percent of the suspected foals (34 out of 138) had an OD value of over 0.9 in addition to high blood leucocyte counts and serum fibrinogen and alpha-globulin levels.
• These foals were treated with antibiotics before and after serodiagnosis. Ninety-one percent (126 out of 138) recovered, while 9% did not show any improvement in their health condition.
• The foals that did not improve even after treatment showed symptoms of suppurative pneumonia and lymphadenitis of gut-associated lymph nodes accompanied by abdominal abscesses at necropsy. R. equi was identified in all isolates from the pulmonary and abdominal abscesses.
• These findings suggest that high OD values might correlate with a severe disseminated infection with R. equi.