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Life cycle, growth characteristics and host cell response of Rickettsia helvetica in a Vero cell line
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Bacteriology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm, Center for Clinical Research Dalarna.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology. (Faciliteter; BioVis)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Bacteriology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Medicinska och farmaceutiska vetenskapsområdet, centrumbildningar mm, Center for Clinical Research Dalarna.
2012 (English)In: Experimental & applied acarology, ISSN 0168-8162, E-ISSN 1572-9702, Vol. 56, no 2, 179-187 p.Article in journal (Refereed) Published
Abstract [en]

Rickettsia helvetica, a spotted fever rickettsia and emerging pathogen with Ixodes ricinus ticks as the main vector, is an agent of human disease and may cause febrile illness as well as meningitis. In three parallel series the isolated standard type of R. helvetica, obtained from a PCR-positive I. ricinus tick, was high-passaged and propagated in a Vero cell line. By using quantitative real-time PCR, the generation time from inoculation to stationary phase of growth was calculated to 20-22 h. In the static cultivation system the stationary phase was observed from the seventh day after inoculation, and there was no observed degradation of R. helvetica DNA during the 14 days studied. Microscopy showed that the organisms invaded the host cells rapidly and were primarily found free in the cytoplasm and only occasionally located in the nucleus. Four days after inoculation some of the host cells were broken and many indifferent stages of cytoplasmic organic decomposition were seen. However the R. helvetica organism did not show any morphologic alterations and the number of organisms was stable after the replication peak which may indicate that R. helvetica is adapted to growth in a Vero cell line and/or that the phase of degradation occurs later than the 14 days studied. The findings differ from what has been reported for other rickettsiae of the spotted fever group and may be of importance for invasiveness and virulence of R. helvetica.

Place, publisher, year, edition, pages
2012. Vol. 56, no 2, 179-187 p.
Keyword [en]
rickettsia, qPCR, vero cells, life cycle, ultrastructure
National Category
Microbiology
Research subject
Infectious Diseases
Identifiers
URN: urn:nbn:se:uu:diva-166778DOI: 10.1007/s10493-011-9508-7ISI: 000299078900010OAI: oai:DiVA.org:uu-166778DiVA: diva2:477690
Note

Correction in: Experimental and Applied Acarology, Vol 56, Issue 2, pp 189-190

DOI: 10.1007/s10493-011-9509-6

Available from: 2012-01-13 Created: 2012-01-13 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Epidemiological and Bacteriological Aspects of Spotted Fever Rickettsioses in Humans, Vectors and Mammals in Sweden
Open this publication in new window or tab >>Epidemiological and Bacteriological Aspects of Spotted Fever Rickettsioses in Humans, Vectors and Mammals in Sweden
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Rickettsiae are obligate intracellular gram-negative bacteria transmitted by arthropod vectors. Rickettsiae sometimes cause disease in humans, typically with high fever, headache and occasionally an eschar.

In Sweden, Rickettsia helvetica, belonging to the spotted fever group, is the only tick-transmitted rickettsia found free in nature. The pathogenic roll of R. helvetica has not been fully investigated, but it has been implicated in aneruptive fever and cardiac disease.

This thesis describes parts of the transmission pathways of rickettsiae in Sweden. Rickettsia infection rates in ticks collected from birds were analysed, and the birds’ role as disseminators and reservoirs was studied. We found that more than one in ten ticks was infected with rickettsia bacteria, predominantly R. helvetica, and that migrating birds contribute not only to long-distance dispersion of bacteria, but also to an inflow of novel and potentially pathogenic rickettsia species, in this case R. monacensis and R. sp. strain Davousti-like species, into Sweden.

Further, wild and domestic animals were found to have seroreactivity against R. helvetica, which shows that they are exposed and susceptible to rickettsia. Their role as reservoirs has not been determined, yet they may indirectly be involved in transmission of rickettsia to humans by infected ticks feeding on them.

The seroreactivity in humans was also studied. Patients investigated for suspected Borrelioses and blood donors had detectable antibodies against Rickettsia spp., with the highest prevalence detected in the suspected Borreliosis group. This shows that humans in Sweden are exposed to and develop an immune response against rickettsia. The suspicion that R. helvetica may cause severe symptoms was verified by a patient with subacute meningitis where the bacterium was shown for the first time to cause an invasive infection with CNS involvement and where the bacterium was isolated from the patient’s cerebrospinal fluid.

Growth characteristics and morphology of R. helvetica were studied to better understand invasiveness and virulence. The findings indicate that the invasiveness is comparable with other rickettsia, though R. helvetica seems to have a stable but slightly slower growth. 

Rickettsia helvetica is endemic in Sweden and therefore needs to be considered when investigating disease after a tick bite.

Abstract [sv]

Rickettsia är en liten, strikt intracellulär, gramnegativ bakterie som sprids med vektorer som fästingar, löss och loppor. Bakterien kan orsaka Rickettsios hos människa, en sjukdom där de vanligaste symtomen är hög feber, huvudvärk, muskelvärk och i vissa fall ett bettmärke (eschar). I Sverige är Rickettsia helvetica, som tillhör spotted fever gruppen (SFG), den enda fästingöverförda rickettsia bakterien som hittats allmänt i naturen. Patogeniciteten för R. helvetica är ofullständigt utredd, men ”aneruptive fever” och hjärtmuskelinflammation har rapporterats.

Avhandlingen beskriver delar av smittkedjan för SFG rickettsia i Sverige. Bakteriernas förekomst i fästingar plockade från fåglar har studerats, likaså det ekologiska tryck som flyttfåglars bärarskap av infekterade fästingar bidrar med när de korsar olika världsdelar. Mer än var tionde fästing var infekterad med rickettsia bakterier, i huvudsak R. helvetica. Det visade sig att flyttfåglar bidrar inte bara till långväga spridning av bakterier utan även till införsel av nya potentiellt patogena rickettsiaarter, i detta fall identifierades R. monacensis och en R. sp strain Davousti liknande art.

Vidare analyserades seroreaktivitet mot Rickettsia helvetica hos både tamdjur och vilda djur, vilket visade på antikroppsutveckling, som uttryck för smittexposition, i mer än vart femte djur. Djurens roll som reservoar för bakterien är inte klarlagd, men oavsett är djuren indirekt involverade i spridningen av bakterien till människa via infekterade fästingar som suger blod.

Seroreaktivitet hos människa har också studerats. Patienter, provtagna på grund av misstanke om borreliainfektion, samt blodgivare hade detekterbara antikroppar mot Rickettsiae, med högst prevalens i gruppen med misstänkt borreliainfektion. Fynden visar att människor i Sverige är exponerade för och utvecklar en immunreaktion mot rickettsia. Att R. helvetica skulle kunna ge allvarlig sjukdom verifieras av ett patientfall med subakut meningit där bakterien för första gången visats ge invasiv infektion med påverkan på nervsystemet (CNS engagemang) och där bakterien isolerats från patientens ryggmärgsvätska. 

Morfologi och tillväxtegenskaper för R. helvetica undersöktes för att bättre förstå bakteriens invasivitet och virulens. Fynden indikerar att invasiviteten är jämförbar med andra rickettsiaarter men R. helvetica verkar ha en stabil men något långsammare tillväxt.

Rickettsia helvetica är endemisk i Sverige och måste tas i beaktande vid sjukdomsutredning efter ett fästingbett.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 888
Keyword
Rickettsia helvetica, ticks, cultivation, serology, polymerase chain reaction (PCR), DNA sequencing, western blot, electron microscopy, meningitis, seroprevalence
National Category
Clinical Laboratory Medicine Microbiology Microbiology in the medical area
Identifiers
urn:nbn:se:uu:diva-197277 (URN)978-91-554-8639-6 (ISBN)
Public defence
2013-05-22, Hörsalen, Klinisk Mikrobiologi, Akademiska Sjukhuset, Dag Hammarskjöldsväg 17, Ing D1, Uppsala, 13:00 (Swedish)
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Supervisors
Available from: 2013-04-26 Created: 2013-03-21 Last updated: 2013-08-30Bibliographically approved

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Lukinius, AgnetaNilsson, Kenneth

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