Equine Granulocytic Anaplasmosis, A Neglected Disease: Risk Factors Associated with Prevalence of Antibodies in Equines

Anaplasma phagocytophilum, a tick-borne bacterium that causes granulocytic anaplasmosis, is a neglected pathogen in Brazil, and is diagnosed in several species of domestic and wild animals as well as in humans.

This study aimed to investigate the prevalence of anti-A. phagocytophilum antibodies in Equidae from the state of Rio de Janeiro and to identify possible risk factors for infection.

A total of 612 blood samples were collected from horses from 15 municipalities within the state. Moreover, an epidemiological questionnaire was administered to evaluate aspects related to seroreaction, taking into account the spatial distribution (properties, municipalities, and mesoregions), management practices, signs of disease, and the individual state of the animals. For the diagnosis, indirect immunofluorescence was performed.

In the present study, 124 (20.26%), out of a total of 612, animals with anti-A. phagocytophilum IgG antibodies at titers of 1:80 were detected. Multivariate logistic regression analysis showed that the presence of the infection at the property (P <0.0001) and the origin (P = 0.0095) of the horse were the true risk factors for infection in the state of Rio de Janeiro.

This allows to infer that the bacterium is distributed in all mesoregions of the state of Rio de Janeiro and that animals from other states can introduce the infection and make a property a focus of disease; it can also be inferred that these properties are important in the maintenance of the disease and the permanence of bacteria circulating in horses. It is also noteworthy that this was the first identification of mules as hosts of A. phagocytophilum infection.