Analysis of the Rickettsia africae genome reveals that virulence acquisition in Rickettsia species may be explained by genome reduction

<p>Abstract</p> <p>Background</p> <p>The <it>Rickettsia </it>genus includes 25 validated species, 17 of which are proven human pathogens. Among these, the pathogenicity varies greatly, from the highly virulent <it>R. prowazekii</it>, which causes epidemic typhus and kills its arthropod host, to the mild pathogen <it>R. africae</it>, the agent of African tick-bite fever, which does not affect the fitness of its tick vector.</p> <p>Results</p> <p>We evaluated the clonality of <it>R. africae </it>in 70 patients and 155 ticks, and determined its genome sequence, which comprises a circular chromosome of 1,278,540 bp including a <it>tra </it>operon and an unstable 12,377-bp plasmid. To study the genetic characteristics associated with virulence, we compared this species to <it>R. prowazekii</it>, <it>R. rickettsii </it>and <it>R. conorii</it>. <it>R. africae </it>and <it>R. prowazekii </it>have, respectively, the less and most decayed genomes. Eighteen genes are present only in <it>R. africae </it>including one with a putative protease domain upregulated at 37°C.</p> <p>Conclusion</p> <p>Based on these data, we speculate that a loss of regulatory genes causes an increase of virulence of rickettsial species in ticks and mammals. We also speculate that in <it>Rickettsia </it>species virulence is mostly associated with gene loss.</p> <p>The genome sequence was deposited in GenBank under accession number [GenBank: <ext-link ext-link-type="gen" ext-link-id="NZ_AAUY01000001">NZ_AAUY01000001</ext-link>].</p

Особенности ценообразования на рынке экскурсионных услуг Крыма

Цель статьи – анализ специфики ценообразования на экскурсионные услуги в Крыму как важного фактора развития этого рынка

Identification of Rickettsial Infections by Using Cutaneous Swab Specimens and PCR

To determine the usefulness of noninvasive cutaneous swab specimens for detecting rickettsiae, we tested skin eschars from 6 guinea pigs and from 9 humans. Specimens from eschars in guinea pigs were positive for rickettsiae as long as lesions were present. Optimal storage temperature for specimens was 4°C for 3 days

Why Are There So Few Rickettsia conorii conorii-Infected Rhipicephalus sanguineus Ticks in the Wild?

The bacterium Rickettsia conorii conorii is the etiological agent of Mediterranean spotted fever (MSF), which is a life-threatening infectious disease that is transmitted by Rhipicephalus sanguineus, the brown dog tick. Rh. sanguineus-R. conorii conorii relationships in the wild are still poorly understood one century after the discovery of the disease. In this study, we collected naturally infected ticks from the houses of people afflicted by MSF in Algeria. Colonies of both infected and non-infected ticks were maintained in our laboratory, and we studied the effect of temperature variations on the infected and non-infected ticks. We did not observe any major differences between the biological life cycle of the infected and non-infected ticks held at 25°C. However, a comparatively higher mortality relative to the control group was noticed when R. conorii conorii-infected engorged nymphs and adults were exposed to a low temperature (4°C) or high temperature (37°C) for one month and transferred to 25°C. R. conorii conorii-infected Rh. sanguineus may maintain and serve as reservoirs for the Rickettsia if they are not exposed to cold temperatures. New populations of ticks might become infected with Rickettsiae when feeding on a bacteremic animal reservoir

Are vertebrates reservoir hosts for rickettsia?

Rickettsiae sensu stricto are the bacteria from the genus Rickettsia. Many of them are responsible for human arthropod-borne (fleas, lice, ticks, mites) diseases. One hundred years after having detected rats as reservoirs of Rickettsia typhi, it is important to assemble the current knowledge on the role of vertebrates in the rickettsial epidemiology. For the agent of Mediterranean spotted fever, R. conorii, dogs are thought to be an intermittent reservoir. R. rickettsii, the agent of Rocky Mountain spotted fever, is capable of infecting dogs, although, in this case they are most likely accidental hosts ; wild animals are the more probable reservoirs. R. felis is the cause of emerging spotted fever in humans ; studies showed that opossums in the USA may be its reservoir. Finally, hematophagous arthropods are considered to be the principal vectors and reservoirs for rickettsiae, although vertebrates may be secondary reservoirs in particular ecosystems that favour the persistence of rickettsiae and in which humans may become accidentally infected.Les rickettsies, sensu stricto, sont des bactéries du genre Rickettsia. Elles sont responsables de maladies humaines transmises par des arthropodes (puces, poux, tiques, acariens). Cent ans après la mise en évidence de l’agent du typhus (Rickettsia typhi) ayant comme réservoir le rat, il est important de faire un point des connaissances concernant le rôle des vertébrés dans le cycle des rickettsies. Pour R. conorii, agent de la fièvre boutonneuse méditerranéenne, le chien est considéré comme un réservoir intermittent. R. rickettsii, agent de la fièvre pourprée des montagnes rocheuses, infecte le chien qui joue plus un rôle de sentinelle que de réservoir, celui-ci étant dévolu à des animaux sauvages. Parmi les rickettsioses émergentes, la fièvre boutonneuse à puces due à R. felis fait l’objet d’études en particulier aux États-Unis où l’opossum est suspecté d’être un réservoir. En plus des arthropodes hématophages vecteurs et réservoirs principaux, les vertébrés constituent bien des réservoirs secondaires dans des écosystèmes donnés qui permettent la persistance des rickettsies et dans lesquels l’homme peut s’infecter accidentellement

Rickettsia felis–associated Uneruptive Fever, Senegal

During November 2008–July 2009, we investigated the origin of unknown fever in Senegalese patients with a negative malaria test result, focusing on potential rickettsial infection. Using molecular tools, we found evidence for Rickettsia felis–associated illness in the initial days of infection in febrile Senegalese patients without malaria

Eschar and neck lymphadenopathy caused by Francisella tularensis after a tick bite: a case report

<p>Abstract</p> <p>Introduction</p> <p>In 25 to 35% of cases, the aetiological agent of scalp eschar and neck lymphadenopathy after a tick bite remains undetermined. To date, <it>Rickettsia slovaca</it>, <it>Rickettsia raoultii </it>and more recently <it>Bartonella henselae </it>have been associated with this syndrome.</p> <p>Case presentation</p> <p>A four-year-old Caucasian boy was admitted to hospital with fever, vomiting and abdominal pain. On physical examination, an inflammatory and suppurating eschar was seen on the scalp, with multiple enlarged cervical lymph nodes on both sides. Although no tick was found in this scalp lesion, a diagnosis of tick-borne lymphadenopathy was suggested, and explored by serology testing and polymerase chain reaction of a biopsy from the eschar. <it>Francisella tularensis </it>DNA was found in the skin biopsy and the serology showed titres consistent with tularaemia.</p> <p>Conclusion</p> <p>This is, to the best of our knowledge, the first reported case of scalp eschar and neck lymphadenopathy after tick bite infection caused by <it>F. tularensis.</it></p