Abstract
Rickettsiae have worldwide occurrence and rickettsiosis are widely recognized as emerging infections in several parts of the world. For decades, it was thought that a single pathogenic tick-borne spotted fever group (SFG), Rickettsia, occurred in each continent. Nowadays, thanks to molecular biology, new species of Rickettsia responsible for disease in humans are continuously identified worldwide. In a framework of diagnostic activities of the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise “G. Gaporale” and considering some reports of suspected human clinical cases of rickettsiosis, a survey on ticks collected form animals and humans was carried out with the aim to identify the Rickettsia species circulating in Abruzzi and Molise regions. A total of 603 ticks, previously identified at species level by morphology, pooled into 178 tick samples, were tested by pan-Rickettsia RealTime PCR. DNA from specimens positive for Rickettsia spp. was then sequenced in order to identify the Rickettsia species involved. The highest infection rate was detected in Dermacentor marginatus followed by Ixodes ricinus. The selected targets for this purpose were OmpA and gltA. Rickettsia slovaca, Rickettsia monacensis, Rickettsia massiliae, Rickettsia conorii, Rickettsia aeschlimannii, Rickettsia helvetica, Rickettsia raoultii, and Rickettsia felis – like organisms were identified in this study. These are the first data available in the literature for the circulation of SFG Rickettsia species in the selected geographical area. Results made evidence of high rate of infection in ticks. All Rickettsia species detected have been previously involved in human infection. The diversity of Rickettsia detected, and tick species collected reflects the biodiversity in term of wildlife and environment of the area. An association between Rickettsia species, ticks, and the relationships with vertebrate host species are discussed. Due to the peculiar eco-biology of each Rickettsia species, the use of diagnostic tools able to identify Rickettsia at the species level is thus recommended in order to assess the risk for humans and to elucidate more precise etiological diagnosis in clinical cases.
Highlights
Rickettsiae are obligate intracellular bacteria transmitted by ticks, fleas, lice, and mites
It was assumed that R. conorii sbsp conorii was the only agent of spotted fever group (SFG) Rickettsia circulating in Italy, and that the classical clinical manifestation of Mediterranean spotted fever (MSF) was the only one developed after the infection in humans
Thanks to the improved diagnostic skills and, mainly, to the use of molecular tools, different SFG Rickettsia have been identified in the Italian territory including Rickettsia slovaca, Rickettsia aeschlimanni, Rickettsia massilliae, Rickettsia monacensis, Rickettsia conorii subspecies
Summary
Rickettsiae (family Rickettsiaceae, order Rickettsiales) are obligate intracellular bacteria transmitted by ticks, fleas, lice, and mites. Different Rickettsia species isolated from ticks were not considered pathogenic for humans for years or decades until a definitive association with human disease was established, such as the emblematic case of Rickettsia massiliae in Europe [2]. Rickettsia conorii subspecies (sbsp) conorii the agent of Mediterranean spotted fever (MSF) is considered endemic mainly in the central and southern Regions of the Mediterranean [2]. In Italy, according to the Italian National Institute of Health [8], around 10,000 cases have been reported in the period 1996–2009. These cases are mainly described in warmer areas of the country, namely in central southern Italy and in the main islands. Rickettsia raoulti, Rickettsia helvetica, and Rickettsia hoogstraalii, [1,2,11,12,13,14]
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