Amblyomma sculptum: genetic diversity and rickettsias in the Brazilian Cerrado biome

Abstract

Amblyomma sculptum (Ixodida: Ixodidae) Berlese, 1888 is the most important tick vector in Brazil, transmitting the bioagent of the most severe form of spotted fever (SF) in part of the Cerrado (in the states of Minas Gerais and São Paulo). In another part of the Cerrado (Central-West region of Brazil), a milder form of SF has been recorded. However, neither the rickettsia nor the vector involved have been characterized. The aim of the current study was to analyse genetic variation and the presence of rickettsia in A. sculptum in Cerrado, from silent areas and with the milder form of SF. Samples were subjected to DNA extraction, amplification and sequencing of 12S rDNA, cytochrome oxidase subunit II and D-loop mitochondrial genes (for tick population analyses), and gltA, htrA, ompA and gene D (sca4) genes for rickettsia researches. Exclusive haplotypes with low frequencies, high haplotype diversity and low nucleotide diversity, star-shaped networks and significant results in neutrality tests indicate A. sculptum population expansions in some areas. Rickettsia amblyommatis, Candidatus Rickettsia andeanae and Rickettsia felis were detected. The A. sculptum diversity is not geographically, or biome delimited, pointing to a different potential in vector capacity, possibly associated with differing tick genetic profiles.

Seasonal dynamics, geographical range size, hosts, genetic diversity and phylogeography of Amblyomma sculptum in Argentina

“…Thus, the degree of genetic structure detected in this work for A. sculptum is not associated to low host vagility. Similar genetic variability was reported by Bitencourth et al (2017) in A. sculptum populations of the Cerrado biogeographic provinces sensu Morrone (2006) of Brazil. Beati et al (2013) suggest that host availability is not a limiting factor for the dispersion of the species belonging to the A. cajennense complex.…”

Genetic diversity, population structure and rickettsias in Amblyomma ovale in areas of epidemiological interest for spotted fever in Brazil

“…Despite the relevance of A. ovale to public health in Brazil, this is the first study to analyze the intraspecific genetic diversity of this ixodid in an attempt to help understand SF epidemiology. The number of haplotypes detected (11–33) resembles that observed for other Amblyomma species (Beati et al ., ; Bitencourth et al ., , ). These haplotypes were exclusive to each analyzed biome area, with ARF I showing the highest number of haplotypes (Fig.…”

“…Amongst other factors, such genetic variation may increase or decrease the potential for carrying and transmitting pathogens. In turn, this may influence the formation of foci or risks of infection, altering the epidemiological scenario of the disease (Araya‐Anchetta et al ., ; Bitencourth et al ., , ). Although the importance of A. ovale to SF epidemiology is well‐established, no studies have investigated the intraspecific variations associated with the presence of rickettsia.…”

Diversity of rickettsiae and potential vectors of spotted fever in an area of epidemiological interest in the Cerrado biome, midwestern Brazil

“…Phylogenetic analysis (Figs S1 and S2) supports the absence of geographic and biome delimitation in A. sculptum , as previously reported by Bitencourth et al . ().…”

“…Furthermore, milder cases of SF have been recorded in the midwestern region of Brazil (Oliveira et al ., ), suggesting that rickettsia other than R. rickettsii , the principal rickettsia transmitted by A. sculptum , may be involved in epidemic cycles in Goiás. The presence of A. sculptum females and males in areas in Goiás, where there are no confirmed cases of SF, point to it being a possible area of concern and, as there are no serological reports of SF in animals, these data underscore the importance of surveillance work in these areas, especially as the population of this vector in the Cerrado is expanding (Bitencourth et al ., ).…”