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  Director : Anna-Bella Failloux-Manuellan (afaillou@pasteur.fr)


  abstract

 

Arboviruses such as dengue and yellow fever are studied through the analysis of populations of Aedes vectors (Aedes aegypti and Aedes albopictus) endemic to the tropical region. Population genetic approaches combined with experimental infections and molecular phylogeny are used to better define the epidemiology of these diseases in different situations: in areas where the two species co-exist or in regions where both dengue and yellow fever rage.



  report

cale

Disruptions of environment and human population growth disturb ecosystems and thus, shape vector-transmitted diseases. Humans through insecticide use to control vectors, deforestation, urbanization, increase of commercial traffics alter vector populations and their genetic composition. What is the impact of such changes in vector population demography and genetic structure? Which role has competition between vector species in the epidemiology of dengue and yellow fever?

A. Population genetic structure and vector competence

Mosquito populations display different susceptibility to arbovirus infections. By estimating population genetic structure and vector competence, we have identified three major groups: (1) the sylvan form, Ae. ae. formosus from West Africa and some islands in the Indian Ocean, (2) the domestic form, Ae. ae. aegypti from Southeast Asia and South America and (3) Ae. ae. aegypti populations from the South Pacific islands. Mosquitoes from the domestic form are highly susceptible to dengue infection whereas those from the sylvan form are less susceptible.

1. Aedes populations from Brazil: Ricardo Lourenço de Oliveira (Post-doc, Institute of Oswaldo Cruz, Rio de Janeiro, Brazil)

To eradicate yellow fever transmission, campaigns of control have been implemented in the South American continent during the last century. Ae. aegypti, eliminated from most countries, has re-infested the region. Based on population genetic studies and estimations of vector competence, we have demonstrated that Ae. aegypti is more susceptible to both dengue and YF viruses than Ae. albopictus. Considering the high densities of Ae. albopictus in rural areas and of Ae. aegypti in towns, the risk of dengue epidemics and yellow fever urbanization in Brazil is more real than ever.

2. Aedes aegypti in Martinique: Anna-Bella Failloux, André Yébakima (Vector Control of Martinique)

In the Caribbean, dengue has become a major problem in public health when the first cases of dengue hemorrhagic fever were described in Cuba in 1981. The vector Ae. aegypti has been subjected to intensive control for decades. Mosquito populations from Martinique are more differentiated than those from French Guiana whereas infection rates are very heterogeneous for Martinique populations. Mosquito populations from French Guiana are genetically closer to Asian populations than to Martinique ones.

3. Aedes mosquitoes implicated to dengue transmission in Cambodia: Christophe Paupy (PhD student)

The introduction of Ae. aegypti in South-East Asia led to the replacement of native species such as Ae. albopictus by competition. Coincidentally, dengue hemorrhagic fever emerged, in 1954 in Manilla.

Within a population, interactions between individuals of two different sympatric species could shape their evolution. Co-structuration of Ae. aegypti and Ae. albopictus is examined in different foci of dengue in Cambodia. How competition could explain the replacement of Ae. albopictus by Ae. aegypti and which impact has dengue infection on this interaction?

4. Development of genetic markers in Ae. aegypti: Karine HUBER (Post-doc)

Genetic variation is examined using an array of molecular genetic tools. Besides isoenzymes, RAPDs, RFLPs, ITS regions and microsatellites, new techniques have evolved with the advent of PCR technology such as AFLP (amplified fragment length polymorphism) technique. This new tool for DNA fingerprinting is based on the detection of genomic restriction fragments by PCR amplification using both principles of RFLP and techniques such as RAPDs . It generates an extensive level of polymorphism between individuals. Tested on mosquitoes from Cambodia, this marker gives the same pattern of differentiation as isoenzymes and microsatellites. Moreover, it can distinguish the two forms of Ae. aegypti (Ae. ae. aegypti and Ae. ae. formosus).

5. Oral susceptibility Aedes mosquitoes: Marie VAZEILLE

By experimental infections, we have demonstrated that Ae. albopictus is less susceptible than Ae. aegypti to dengue infection and susceptibility tends to increase with increasing generations in the laboratory whatever the mode of production of the virus (cell culture, various number of passages on mosquitoes) and the geographic origin of the isolate. This observation only concerns samples recently colonized in laboratory. Susceptibility tends to be acquired with increasing generations in insectarium. These observations demonstrate the importance of considering the colonization history of mosquitoes when assessing their susceptibility to infection with dengue viruses.

B. Phylogenetic studies of Aedes mosquitoes (Anna-Bella Failloux)

The mosquito genus Aedes contains more than 900 species divided into 38 subgenera. In the subgenus Stegomyia, 110 species have been described and divided into seven groups. Around 40 taxa have been analysed at three mitochondrial genes: cytochrome b oxidase, cytochrome oxidase II and NADH dehydrogenase 5. We are able to distinguish two major lineages: the Ae. aegypti group and the Ae. albopictus group. Within the Ae. aegypti group, we can define populations from Africa and those from South America and South-East Asia.

C. Other activities

- Other scientific projects

Our unit is implicated in two PTR programs:

- PTR n°23 coordinated by Armelle Delecluse on the molecular basis of mosquito-arbovirus interactions in the midgut epithelium (is there a receptor to dengue virus? What is the replication rate of dengue virus in the mosquito?)

- PTR n° 28 coordinated by Valérie Choumet on Molecular evolution of snake venom enzymes (Thomas Garrigues, PhD student)

Molecular phylogenetic of the genus Vipera s.l. has been analyzed using nucleotides sequences of the mitochondrial cytochrome b gene and the subunit 2 of NADH dehydrogenase (ND2). The genus Vipera has been incriminated in particular venom poisonings in Southeast France. Is it due to imported species or species newly appeared in the region after interbreeding between two different species?

Phylogenetic analysis has shown that: (1) within the genus Vipera, two main lineages can be described: the oriental group and the European group, (2) among the European species, distinction is done between the French and the Italian sub-species and (3) the population incriminated in venom poisonings with neurological signs forms a sister group with French Vipera aspis.

- Medical and Veterinary Entomology Reference Centre

Several thousands of insects are classified and registered in a database now composed of about 95,000 mosquito and 6,000 tick specimens. Only three institutions shelter collections of insects of medical interest in France: the Institute of Research for Development, the National Museum of Natural History and the Pasteur Institute.

- Training in medical entomology (every two years)

This unique French course in medical entomology of 8 weeks gives a good introduction to medical entomology.

Photo: Aedes aegypti, the vector of dengue and yellow fever : the dark form (Ae. ae. formosus) and the light form (Ae. ae. aegypti).

Keywords: dengue, yellow fever, Aedes aegypti, population genetics, vector competence



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
  DELACOURTIE, Claudine, (cdelac@pasteur.fr) FAILLOUX-MANUELLAN, Anna-Bella, Institut Pasteur (afaillou@pasteur.fr) GARRIGUES, Thomas, PhD student

HUBER, Karine, Post-doc

PAUPY, Christophe, PhD student

LOURENCO DE OLIVEIRA, Ricardo, Post-doc

AYAD, Nadia (nayad@pasteur.fr)

BRION, Myriam (mbrion@pasteur.fr)

DELACOURTIE, Claudine (cdelac@pasteur.fr)

LECOQ, Marie-Thérèse (mthl@pasteur.fr)

MOUSSON, Laurence (lmousson@pasteur.fr)

SCAEROU, Christelle (cscaerou@pasteur.fr)

VAZEILLE, Marie (vazeille@pasteur.fr)

VILLERET, Régine (villeret@pasteur.fr)


Activity Reports 2002 - Institut Pasteur
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