Abstract
Rickettsia are obligate intracellular bacteria often associated with ticks and best known for causing human diseases (rickettsiosis), including typhus fever and sporadic cases of serious infection. In this study, we conducted a large survey of ticks in French Guiana to understand the overall diversity of Rickettsia in this remote area largely covered by dense rainforests. Out of 819 individuals (22 tick species in six genera), 252 (30.8%) samples were positive for Rickettsia infection. Multilocus typing and phylogenetic analysis identified 19 Rickettsia genotypes, but none was 100% identical to already known Rickettsia species or strains. Among these 19 genotypes, we identified two validated Rickettsia species, Rickettsia amblyommatis (spotted fever group) and Rickettsia bellii (bellii group), and characterized a novel and divergent Rickettsia phylogenetic group, the guiana group. While some tick hosts of these Rickettsia genotypes are among the most common ticks to bite humans in French Guiana, their potential pathogenicity remains entirely unknown. However, we found a strong association between Rickettsia genotypes and their host tick species, suggesting that most of these Rickettsia genotypes may be nonpathogenic forms maintained through transovarial transmission.
Highlights
Rickettsia are obligate intracellular bacteria often associated with ticks and best known for causing human diseases, including typhus fever and sporadic cases of serious infection
The detection rate of Rickettsia did not co-vary with the screening effort, i.e., the number of examined specimens per tick species (Spearman’s rank correlation, n = 22, rs = 0.20, p = 0.37): the tick species observed with Rickettsia infections were not those for which we examined more specimens
This is best exemplified by (1) Rickettsia-positive tick species for which we examined few specimens, such as I luciae (n = 6 examined specimens and all were Rickettsia-positive) and A. goeldii (n = 5 examined specimens and 4 were Rickettsia-positive), and (2) Rickettsia-negative tick species for which we examined a large number of specimens, such as A. oblongoguttatum (n = 95 examined specimens but none positive) and D. nitens (n = 97 examined specimens but none positive) (Fig. 1, Tables 1 and S1)
Summary
Rickettsia are obligate intracellular bacteria often associated with ticks and best known for causing human diseases (rickettsiosis), including typhus fever and sporadic cases of serious infection. The best known Rickettsia species are major human pathogens that include the etiological agents of the epidemic typhus, R. prowazekii, the Rocky Mountain spotted fever, R. rickettsii, and the flea-borne spotted fever, R. felis[1,4,5]. Most of these pathogenic Rickettsia species have a zoonotic life cycle and are transmitted by blood-feeding arthropods such as ticks, mites, lice and fleas, which commonly serve as ecological bridges for transmission from wildlife to humans and domestic animals[1,4,5]. Three Rickettsia groups – the spotted fever group, the typhus group and the transitional group – are the subject of intensive study since they all include major pathogenic species and are commonly found in blood-feeding arthropods[1]. We examined and discussed their genetic proximity with known Rickettsia species and strains
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