Rhodococcal antigen: Evaluation of the antigenic unit using horse blood serum in the prolonged complement fixation test

Аннотация

Background and Aim. Rhodococcus equi pneumonia occursendemically on some farms, whereas on
other  it occurs sporadically or is not detected at all. On endemic farms, the prevalence and severity of the disease may also vary seasonally. This study aimed to assess the seroprevalence of R. equi infection in horses from selected regions of Kazakhstan.

Materials and Methods. A serological study was conducted to assess the prevalence of Rhodococcus equi infection in horses. A total of 260 serum samples collected from four administrative regions (Astana city, Erementau district, Shieli district, and Zhanakorgan district) were examined using the prolonged complement fixation test (PCFT). Statistical analysis included descriptive statistics, distribution assessment, and one-way analysis of variance.

Results. The overall seroprevalence was 19.6%. The highest seroprevalence was observed in the Erementau district (41.8%) and Astana city (36.0%), whereas the lowest was recorded in the Shieli district (12.0%), with an intermediate value in the Zhanakorgan district (17.1%). No statistically significant differences in mean seroprevalence were detected between districts (p = 0.231). However, analysis at the individual farm level revealed a highly heterogeneous, clustered distribution of the pathogen. The distribution of seropositivity was markedly right-skewed, with a median of 15%, and 25% of farms were completely free of infection. At the same time, localized outbreaks with infection rates of up to 66.7% were detected. The antibody titers were predominantly at the 1:10 level (56.9%), which, together with the focal distribution pattern, suggests endemic circulation of the pathogen.

Conclusion. The findings indicate that epidemiological surveillance should be shifted from territorial to farm-level monitoring in order to ensure more targeted detection and control of infection foci.