Serological and molecular detection of Anaplasma phagocytophilum in Thoroughbred horses from Chilean racecourses.

This research carries out serological and molecular tests on thoroughbred horses within Chile to detect Anaplasma phagocytophilum, a bacterium that causes equine granulocytic anaplasmosis (EGA). The study also explores the correlation between the bacterium’s presence and certain hematological findings, and it determines the virus’s genetic relation to strains in the USA and Europe.

Methodology

• The study was conducted on 457 thoroughbred horses, taken from racecourses in three different Chilean cities: Santiago, Viña del Mar, and Concepción.
• To detect the presence of A. phagocytophilum, a complete blood count was carried out, and the researchers utilized a real-time PCR that targets the msp2 gene.
• For serological detection, an Indirect fluorescent antibody test (IFAT) was used to detect IgG antibodies against A. phagocytophilum. This was carried out on horses from two of the racecourses (Santiago and Vina del Mar).

Findings

• The occurrence of A. phagocytophilum, as detected by real-time PCR, was found to be 13.6%, with the highest occurrence found in Santiago (26.5%), followed by Concepción (9%), and the lowest in Viña del Mar (5%).
• The overall frequency of IgG antibodies to A. phagocytophilum was 7.9%, with 9.9 % found in Santiago and 6.5 % in Viña del Mar. Only three animals from Santiago Racecourse tested positive in both the real-time PCR and serology tests.
• The researchers found that PCR-positive horses from Santiago racecourse exhibited significantly lower hemoglobin, mean corpuscular value (MCV), and mean corpuscular hemoglobin concentration (MCHC) but higher eosinophil counts.
• When performing a phylogenetic analysis based on the msp2 gene, the researchers discovered that the A. phagocytophilum sequences found in their study were closely related to A. phagocytophilum sequences from the USA and Europe.

Significance

• This marks the first time that Anaplasma phagocytophilum DNA has been detected in Chile, highlighting the bacterium’s presence and potential veterinary public health risks.
• The results show a significant association between A. phagocytophilum infection and altered hematological values in horses, which could inform diagnostic procedures and treatments.
• The genetic similarity found between sequences of A. phagocytophilum in Chile and those in the USA and Europe suggests potential transmission routes and calls for further exploration and epidemiological studies.