Epidemiological survey of Neorickettsia risticii in equids from the State of Rio de Janeiro, Brazil

Abstract

Equine neorickettsiosis (EN), also known as Potomac Horse Fever, is a non-contagious disease caused by the bacterium Neorickettsia risticii of the Anaplasmataceae family. The objectives of this study were to detect the presence of anti-N. risticii antibodies by the indirect immunofluorescence assay (IFA) and of its DNA by qPCR in equids at high and low altitude regions in the State of Rio de Janeiro, Brazil, and to identify factors associated with seropositive equids by multiple logistic regression analysis. The frequency of anti-N. risticii antibodies was 16.05% (n=113/704). The animal age and breeding region were the factors that influenced the seropositivity rate for N. risticii in the equids (p<0.05). Equids from the lowland region had higher seropositivity (p<0.05; OR=5.87) compared to those of the mountain region. The presence of snails on the farm was a factor associated with this result (p<0.05; OR=2.88). In the lowland region, age of the animal and site of breeding were protective factors for the detection of antibodies anti-N. risticii in equids, with lower frequency of seropositivity in younger animals (p<0.05; OR=0.06) and in animals raised in dry areas (p<0.05; OR=0.22). The presence of the target DNA of N. risticii by qPCR was not observed in any of the samples tested. The existence of seropositive equids for N. risticii demonstrates a possible circulation of this agent in the studied area, and that the age related characteristics and equids breeding region are important factors regarding seropositivity in the State of Rio de Janeiro.

Putative Equine Neorickettsiosis in a Mare from Southern Brazil

“…Interestingly it was suggested that a disease named "churrío" or "churrido", known for at least 100 years occurring during the summer in southern Brazil and Uruguay, is, in fact, equine neorickettiosis [8] and might have been introduced to North America from South America [31]. These findings associated with the serological evidence of the presence of N. risticii in other states from Brazil, such as Rio de Janeiro [26], Santa Catarina and São Paulo [17] and with the wide distribution of NR in North America, India and Europe [7,31]; suggest that EN is probably underdiagnosed in Brazil. In addition, the etiology of equine enterocolitis in Brazil should be more thoroughly investigated to associate the causative pathogens and reduce economic losses.…”

“…The biochemical assays revealed an increase in fibrinogen concentration (600 mg/dL, reference range: <400) without any alteration to the total plasma protein concentration. Hemogasometry revealed metabolic acidosis (BE (ecf) = -2.9 mEq/L, reference range: 0-6) (cHCO 3 = 22.7 mEq/L, reference range: [24][25][26][27][28][29][30]. No alteration was identified in the analysis of the peritoneal fluid.…”