An initial survey of 150 horses from Thailand for anti-Pythium insidiosum antibodies

Abstract Objectives: Pythium insidiosum causes a deadly condition, called pythiosis, in humans and other animals. The organism has been identified in tropical and subtropical environments worldwide. Since 1985, human pythiosis has been increasingly reported from Thailand. Seroprevalence studies estimated that ~32,000 Thai people have been exposed to the pathogen. In 2018, the first animal pythiosis case in Thailand was diagnosed in a horse. In this study, we surveyed anti-P. insidiosum antibodies in a sample of the Thai equine population. Results: Serum samples were available from 150 out of 6,353 registered horses distributed across Thailand. ELISA detected the anti-P. insidiosum antibodies in three horses. Immunochromatography and Western blot confirmed the presence of the antibodies in one of the ELISA-positive horses. Based on one positive out of 150 tested, the Pythium seroprevalence in the Thai equine population was 0.7%, which is 10 times higher than that of the Thai human population. The seroprevalence of the anti-P. insidiosum antibodies in a small sample of horses suggests a higher incidence of pythiosis in horses than in humans. Larger studies will be necessary to obtain the full picture of the epidemiology of animal pythiosis in Thailand.