Rickettsial spotted fever in capoeirão village, Itabira, Minas Gerais, Brazil.

The study explores infection rates of spotted fever rickettsia, a bacteria infamous for causing Brazilian spotted fever, among humans, dogs, horses, and ticks in a rural area in Itabira City, Minas Gerais state, Brazil. Through the use of lab tests, the researchers found infection rates were highest in horses, followed by dogs, then humans, but very low among ticks.

Study Purpose and Methodology

• The goal of this study was to gain insight into the prevalence of spotted fever rickettsia, a bacteria that causes Brazilian Spotted Fever (BSF), in an endemic area in Brazil. A specific area in Minas Gerais State, known as Itabira City, was chosen for this research.
• The researchers collected samples from humans, dogs, horses, and adult Amblyomma cajennense ticks, all of which are common in the selected area. The tick species A. cajennense has been implicated in the transmission of the bacteria causing BSF in Brazil.
• They used an Immunofluorescence Assay (IFA) to identify the presence of antibodies against Rickettsia rickettsii, the bacteria that causes BSF, in these samples. In addition, ticks were also tested using the hemolymph test and Polymerase Chain Reaction (PCR) targeting the htrA and the gltA genes.

Results of the Study

• The study revealed various infection rates among the test subjects, with horses displaying the highest rate of 100%, meaning all tested horses showed the presence of antibodies against the bacteria.
• Dogs had the second highest detection rate at 81.3%, whilst 8.2% of the human samples resulted in a positive response for the antibodies. This indicates a significant spread of the bacteria within these populations.
• Interestingly, none of the 356 tick specimens tested positive for Rickettsia via either hemolymph test or PCR. Despite being cited as possible vectors, the lack of infection in the sampled ticks suggests a low infection rate among this tick population in this specific area.

Implications of the Study

• The results suggest considerable circulation of the Rickettsia bacteria among horses and dog populations. Consequently, horses and dogs can potentially serve as sentinel species for BSF in the studied area.
• Despite the significant infection rates among these mammal subjects, the surprisingly low infection rate among the ticks begs further investigation. It raises questions about other potential vectors or transmission routes in the spread of BSF.