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Chikungunya: target cells virus identified

Researchers of Institute Pasteur and CNRS have just marked a projection in the comprehension of the disease due to the virus Chikungunya (disease of “the curved man”), which currently prevails in India and in Gabon, while identifying for the first time of the target cells of the virus. Their results, carried out in collaboration with clinicians of the island of the Meeting, are published in PLoS Pathogens and PLoS ONE.
The Chikungunya virus, discovered in Tanzania in 1952, and the disease which it causes up to now were studied very little. The epidemic which A prevails in islands of the Indian Ocean in 2005-2006 (270 000 cases) had led to the mobilization of a dozen teams from the Pasteur Institute in Paris, from now on committed in the study of this neglected disease. Pasteurian teams had in particular recalled the evolutionary history of the Chikungunya virus in the Indian Ocean, thanks to the sequencing of several viral strains having circulated during the epidemic (see communicated of May 23, 2006). Chikungunya since caused a vast epidemic in India, making between 1,4 and 6,5 million case between 2005 and 2007, and currently touches Gabon, where some 11.500 cases were indexed since mid-April 2007.
The first question-key for the study of the pathogenesis of this disease relates to the tropism of the virus: which are the cells which it infects in the organization? The study now published in PLoS Pathogens aimed at answering this question. It was carried out by the team of Olivier Schwartz - Unit Virology (CNRS URA 3015) at the Pasteur Institute -, in collaboration with several teams of the Pasteur Institute and the Hospital complex Southern Meeting.
The researchers first of all adapted tools (cytometry of flow, immunofluorescence, electronic microscopy…) allowing to visualize and quantify the virus. They thus could show in vitro that this one did not multiply in the circulating blood cells (lymphocytes, monocytes), but that he retorted himself in the macrophages (phagocytic cells of origin blood and located in fabrics). These cells could thus be implied in the infection of fabrics that one knows touched by the disease, like the muscles and the articulations. The virus also infects the majority of the cells known as “adherent”: epithelial cells endothéliales, cells, fibroblasts… The researchers wish today to identify the ways of entries of the virus in these cellular types, and to also better include/understand the interactions of the virus with the immune system. Their work could right now make it possible to test drugs in cellular culture, in order to select those which inhibit the infection of the target cells. In parallel, another study undertaken by Pierre-Emmanuel Ceccaldi and Simona Ozden in the Unit Epidemiology and physiopathology of the viruses oncogenes (CNRS URA 3015) to the Pasteur Institute, directed by Antoine Gessain, in collaboration with other teams of the Institute Pasteur, Institute of Myologie of Paris, and with clinicians of Saint-Denis of the Meeting, made it possible to show that, at the infected people, certain cells present in muscular fabric are targets of the Chikungunya virus. Their work, recently published in PLoS ONE, is based on the study of biopsies of patients. They found in a biopsy taken in acute phase of the disease at a patient, and in another taken at a later stage in another patient, than the cells precursors of the muscular cells - satellite cells - were infected by the virus. Moreover, these cells prove, in cellular culture, very permissive with the virus. The authors seek today to know if these cells would not play a part of “tank” of the virus, which would explain the repetitions of the muscular pains observed among certain patients.
These first key stages of the study of Chikungunya are new results - after the sequencing of the virus of the Indian Ocean published last year - strong mobilization of the researchers of Institut Pasteur, which works also in particular on the transmission mother-child, the physiopathology of the disease, the relations between the virus and the mosquitos vectors, and currently séquencent stocks of viruses which circulate in Gabon*.

News inside News:

Complete sequencing of the genomes of 6 viral strains
Researchers at the Institut Pasteur have managed to retrace the origin and evolution of the Chikungunya virus in the Indian Ocean through complete sequencing of the genome of six viral strains isolated from patients from Reunion Island and the Seychelles, as well as through partial sequencing of the viral protein E1 from 127 patients from the Indian Ocean islands (Reunion,Madagascar, Seychelles, Mauritius, Mayotte). Their study, published in PLoS Medicine, opens up new research paths that should help to explain the magnitude of the epidemic and the occurrence of severe forms of the disease.

For the first time ever, the complete genome sequences of the Chikungunya virus have been identified from viral isolates obtained from a low number of cell culture passages and therefore very close to the clinical virus, whereas to date the complete genomes identified were those of laboratory strains. This study, started at the National Reference Centre for Arboviruses, was continued on a large scale by the Institut Pasteur's technological platform Genotyping of Pathogens and Public Health . This work was undertaken in order to gain a better understanding of the origin and evolution of the viruses responsible for an epidemic of unprecedented magnitude. This outbreak started in early 2005 in Comoros, and has caused 248,000 cases in the Reunion Island between March 2005 and April 28, 2006 and 5834 cases in Mayotte, 8976 cases in the Seychelles, 6000 cases in Mauritius.

The study was supervised by Sylvain Brisse, head of the Pathogen Genotyping and Public Health Platform at Pasteur Genopole Ile-de-France, and Isabelle Schuffenecker of the Arbovirus National Reference Centre in Lyon, in collaboration with several teams from the Institut Pasteur in Paris, and with clinicians and virologists from the Reunion island, Madagascar (Institut Pasteur), Mayotte et the Seychelles.

The study shows that the Indian Ocean viral strains are closely related to each other and are related to East, Central and South African strains isolated between 1952 and 2000. The viruses that emerged in the Indian Ocean were therefore probably imported from the African continent. This scenario is compatible with the human population exchanges between East Africa and the Comoros where the epidemic started in early 2005. Moreover, changes that occurred in the viral genome as the epidemic progressed, especially the emergence and predominance of a particular genotype since September 2005, suggest an adaptive evolution of the viral strains.

Sequencing of the complete genome of a viral strain isolated from the cerebrospinal fluid (CSF) of a Reunion Island patient suffering from meningo-encephalitis revealed several mutations causing amino acid substitutions specific to this clinical isolate. Studies are currently underway to establish whether these substitutions are linked to the neurovirulence of the Chikungunya virus, on the one hand, and to greater efficiency of viral multiplication, on the other hand.

The viruses' " molecular signatures ", which constitute genetic fingerprints, in virus envelope protein E1 have also been found. As the three dimensional structure of E1 in a very similar alphavirus, the Semliki Forest virus, had already been ascertained by Felix Rey's team, this made it possible to provide a model of the structure of E1 of the Chikungunya virus in order to locate the mutations. One of these signatures(" E1 226 " : see figure below), not found early on in the epidemic, became predominant in Reunion Island strains from September 2005, and therefore shortly before the epidemic explosion. The authors suggest that this signature may confer an advantage and favour the multiplication of the virus in Aedes albopictus, its vector (protein E1 is in fact involved in attaching the virus to the mosquito's cell membranes).

The magnitude of the epidemic in the Indian Ocean and the description of new clinical froms of the disease has underlined "the critical lack of understanding of the physiology of the disease and the biology of the virus", as the authors point out.

The molecular data presented here is a first step to bridge this gap of knowledge and opens the way to functional studies. A dozen teams at the Institut Pasteur have indeed been working for several weeks on unveiling the mysteries of Chikungunya virus. Their research should, at middle-term, contribute to the development of tools to help combat this neglected disease.

References:
) “Characterization of reemerging Chikungunya virus”: PLoS Pathogens, June 2007. Marion Sourisseau (1), Clementine Schilte (2), Nicoletta Casartelli (1), Celine Trouillet (1), Florence Guivel-Benhassine (1), Dominika Rudnicka (1), Nathalie Ground-Fuller (1), Karin the Russet-red one (9), Marie-Christine Prevost (3), Hafida Fsihi (4), Marie-Pascale Frenkiel (5), Fabien Strainer (1), Philippe V.Afonso (6), Pierre-Emmanuel Ceccaldi (6), Simona Ozden (6), Antoine Gessain (6), Isabelle Schuffenecker (10), Bruno Verhasselt (11), Alessia Zamborlini (12), Ali Saib (12), Felix A. Rey (7), Fernando Arenzana-Seisdedos (8), Philippe Desprès (5), Alain Michault (9), Matthew L. Albert (2) and Olivier Schwartz (1) 1. Unit Virus and Immunity, Pasteur Institute, Paris; 2. Group Immunobiologie of the dendritic cells, Inserm U818, Institut Pasteur 3. Electronic platform of microscopy, Pasteur Institute 4. Department Infection and Epidemiology, Pasteur Institute 5. Unit molecular Interactions Flavivirus-Hosts, Pasteur Institute 6. Unit of épidemiologiie and physiopathology of the viruses oncogenes, Pasteur Institute 7. Unit of Structural Virology, Pasteur Institute; 8. Laboratory of Molecular Viral Pathogenesis, Pasteur Institute 9. Laboratory of Microbiology, Hospital complex Southern Meeting, Island of the Meeting 10. Center National Reference of Arbovitus, Lyon 11. Ghent University, Belgium 12 Hospital Saint-Louis, Paris. 1,6,7,8: CNRS URA 3015
2) “satellite Human muscle cells have targets of Chikungunya virus infection”: PLoS ONE, June 13, 2007. Simona Ozden (1), Michel Huerre (2), Jean-Pierre River (3), Lark L. Coffey (4), Philippe V. Afonso (1), Vincent Mouly (5), Jean de Monredon (6), Jean-Christophe Roger (6), Mohamed El Amrani (6), Jean-Luc Yvin (7), Marie-Christine Jaffar (8), Marie-Pascale Frenkiel (4), Marion Sourisseau (9), Olivier Schwartz (9), Gillian Butler-Browne (5), Philippe Desprès (4), Antoine Gessain1 and Pierre-Emmanuel Ceccaldi (1) 1. Unit of epidemiology and physiopathology of viruses oncogènes-CNRS URA1930, Pasteur Institute; 2. Unit Seeks and appraises Histotechnologie and Pathologie, Institut Pasteur 3. Service of Anatomopathologie, CHD Felix Guyon, Saint-Denis of the Meeting 4. Unit molecular Interactions Flavivirus-Hosts, Pasteur Institute 5. Inserm Pierre U787-University and Marie Curie-Institute of Myologie, Salpétrière Pity, Paris 6. Service of Neurology, CHD Felix Guyon, Saint-Denis of the Meeting 7. Service of Internal medicine, CHD Felix Guyon, Saint-Denis of the Meeting 8. Laboratory of Biology, CHD Felix Guyon, Saint-Denis of the Meeting 9. Unit Virus and Immunity, Pasteur Institute, Paris


Contacts :
Service de presse de l'Institut Pasteur :
Nadine Peyrolo ou Corinne Jamma
01 40 61 33 41
cjamma@pasteur.fr
Service de presse du CNRS :
Cécile Pérol
01 44 96 43 09
cecile.perol@cnrs-dir.fr

Notes: * In collaboration with the unit of tropical virology of the IMTSSA, in Marseilles

In The Image 2-
Three dimensional model of envelope protein E1 in Chikungunya virus in position 226, indicated by the white star, could explain specific adaptation to the vector mosquito, Aedes albopictus.

Release link: http://www.cnrs.fr/