# The mosaic of Rickettisae from the Caatinga Biome, Brazil: New records and first interactions

## TL;DR

This study identifies new Rickettsia species and tick associations in Ceará, Brazil, expanding understanding of rickettsiosis in the region.

## Contribution

First detection of Rickettsia amblyommatis and R. asembonensis in Ceará and the first interaction between Rickettsia parkeri and Amblyomma parvum.

## Key findings

- Rickettsia amblyommatis and R. asembonensis were detected for the first time in northeastern Brazil.
- A new association between Rickettsia parkeri and Amblyomma parvum was identified.
- The study contributes to understanding the eco-epidemiological profile of Rickettsiae in Ceará.

## Abstract

Rickettsiosis are infections that have worldwide distribution, also occurring in all regions of Brazilian territory and being distributed across its various biomes. The most relevant rickettsiosis in Brazil is Spotted Fever (SF), a potentially lethal zoonosis. Although cases of SF have been confirmed in southeastern Brazil, the epidemiological situation in the Northeast remains poorly understood. The aim of this study was to analyze the circulation and identification of Rickettsia species in the state of Ceará, a northeastern state with confirmed SF cases since 2010. In parallel, we identified potential vectors, as to contribute to the development of an eco-epidemiological profile of Rickettsiae in the state. Genomic DNA samples, extracted from ticks collected in areas with suspected cases, were analyzed via PCR to detect Rickettsia spp., with positive samples undergoing further characterization and genomic sequencing for ompB (SFG-IF/SFG-TG IR) and htrA (17Kd1/17Kd2) genes via Nested PCR. Our results detected, for the first time, the presence of Rickettsia amblyommatis and R. asembonensis in the region. These findings demonstrated the geographical expansion of Rickettsiae in northeastern Brazil. Additionally, we identified the first interaction between Rickettsia parkeri and Amblyomma parvum, signaling a potential change in our understanding of interactions between these species. Altogether, our study reveals a new panorama regarding Rickettsiae in northeastern Brazil.

Rickettsiae are bacteria spread mainly by ticks and fleas that can cause diseases in humans and animals. This study focused on identifying different species of Rickettsia and their potential tick carriers in the state of Ceará, Brazil. We examined 1,359 samples from ticks collected on animals and in the environment. After initial testing, 82 samples showed signs of Rickettsia bacteria, and we successfully identified specific species in 37 of them using genetic analysis. Notably, this research found Rickettsia amblyommatis and Rickettsia asembonensis circulating in the region for the first time, adding to our understanding of local bacteria and their tick hosts. We also discovered a new association between the tick Amblyomma parvum and Rickettsia parkeri, a species linked to mild human infections. These findings help map which ticks carry which bacteria, offering insights into how Rickettsiae spread in the environment. This is crucial for public health planning, as some species can cause illness in humans. By identifying these bacteria and their carriers, this research contributes to a better understanding of disease risks in Ceará and similar regions worldwide.