[Arboviruses also have an American dream]. / Les arbovirus ont aussi leur « rêve américain ¼.

Some arboviruses that originated in the Old World have been introduced by humans into the American continent. The first of them was the yellow fever virus, coming from the West African coast with slaves in the 17th-19th centuries, followed by dengue viruses, which were always prevalent within the Americas. Next was theWest Nile virus, introduced in New York in 1999, that spread in only a few years over the whole continent. Then, Chikungunya virus arrived on Saint Martin Island in 2013 after its outbreak in Polynesia; it is now widespread in the Caribbean Islands and on the American continent from the United States to Brazil. Finally, Zika virus, already active in Asia and in the South Pacific region, was introduced in Brazil and spread between the southern part of United States and south Brazil. These unexpected emergences are the consequence of the generalization of transoceanic trading; so, it is humans who are truly responsible for such transportation of viruses from the African and Asian continents. The mechanisms of virus establishment in unusual ecosystems have to be analyzed in order to understand the conditions for the circulation of the viruses, which supposes an adaptation to new hosts and vectors that are sometimes local species (like Culex vectors of West Nile virus) but mainly previously introduced mosquitoes (like Aedes aegypti and/or Aedes albopictus). Over time, all these vectors developed a strong anthropophily and, most of them, a remarkable adaptation to urban environment; hence, these arboviruses can disseminate both in rural and urban context. This type of arboviral emergences will certainly continue in the following years and we must imperatively develop preventive strategies by detecting virus mutations with capacity for emergence, enhancing the sensibility and rapidity of epidemiological surveillance, and becoming ready to face such events that cause a truly international health crisis.

Insects as vectors: systematics and biology.

Among the many complex relationships between insects and microorganisms such as viruses, bacteria and parasites, some have resulted in the establishment of biological systems within which the insects act as a biological vector for infectious agents. It is therefore advisable to understand the identity and biology of these vectors in depth, in order to define procedures for epidemiological surveillance and anti-vector control. The following are successively reviewed in this article: Anoplura (lice), Siphonaptera (fleas), Heteroptera (bugs: Cimicidae, Triatoma, Belostomatidae), Psychodidae (sandflies), Simuliidae (black flies), Ceratopogonidae (biting midges), Culicidae (mosquitoes), Tabanidae (horseflies) and Muscidae (tsetse flies, stable flies and pupipara). The authors provide a rapid overview of the morphology, systematics, development cycle and bio-ecology of each of these groups of vectors. Finally, their medical and veterinary importance is briefly reviewed.

[Bats and Viruses: complex relationships]. / Chauves-souris et virus: des relations complexes.

With more than 1 200 species, bats and flying foxes (Order Chiroptera) constitute the most important and diverse order of Mammals after Rodents. Many species of bats are insectivorous while others are frugivorous and few of them are hematophagous. Some of these animals fly during the night, others are crepuscular or diurnal. Some fly long distances during seasonal migrations. Many species are colonial cave-dwelling, living in a rather small home range while others are relatively solitary. However, in spite of the importance of bats for terrestrial biotic communities and ecosystem ecology, the diversity in their biology and lifestyles remain poorly known and underappreciated. More than sixty viruses have been detected or isolated in bats; these animals are therefore involved in the natural cycles of many of them. This is the case, for instance, of rabies virus and other Lyssavirus (Family Rhabdoviridae), Nipah and Hendra viruses (Paramyxoviridae), Ebola and Marburg viruses (Filoviridae), SARS-CoV and MERS-CoV (Coronaviridae). For these zoonotic viruses, a number of bat species are considered as important reservoir hosts, efficient disseminators or even directly responsible of the transmission. Some of these bat-borne viruses cause highly pathogenic diseases while others are of potential significance for humans and domestic or wild animals; so, bats are an important risk in human and animal public health. Moreover, some groups of viruses developed through different phylogenetic mechanisms of coevolution between viruses and bats. The fact that most of these viral infections are asymptomatic in bats has been observed since a long time but the mechanisms of the viral persistence are not clearly understood. The various bioecology of the different bat populations allows exchange of virus between migrating and non-migrating conspecific species. For a better understanding of the role of bats in the circulation of these viral zoonoses, epidemiologists must pay attention to some of their biologic properties which are not fully documented, like their extreme longevity, their diet, the population size and the particular densities observed in species with crowded roosting behavior, the population structure and migrations, the hibernation permitting overwintering of viruses, their particular innate and acquired immune response, probably related at least partially to their ability to fly, allowing persistent virus infections and preventing immunopathological consequences, etc. It is also necessary to get a better knowledge of the interactions between bats and ecologic changes induced by man and to attentively follow bat populations and their viruses through surveillance networks involving human and veterinary physicians, specialists of wild fauna, ecologists, etc. in order to understand the mechanisms of disease emergence, to try to foresee and, perhaps, to prevent viral emergences beforehand. Finally, a more fundamental research about immune mechanisms developed in viral infections is essential to reveal the reasons why Chiroptera are so efficient reservoir hosts. Clearly, a great deal of additional work is needed to document the roles of bats in the natural history of viruses.

[Japanese encephalitis: a fast-changing viral disease]. / Encéphalite japonaise : une maladie virale en pleine évolution.

The following aspects are dealt with in this article: 1) current geographical distribution of Japanese encephalitis; 2) clinical patterns of Japanese encephalitis; 3) vertebrate hosts of Japanese encephalitis virus; 4) vectors of JE virus; 5) epidemiological locations (endemic area, endemoepidemic area, epidemic area); 6) unknown epidemiological aspects; 7) JE virus serotypes; 8) evolution of the disease and recent epidemiological changes; 9) phylogenetic origin of the JE virus; 10) ecological changes in the past, factors in the emergence of the disease; and 11) the future: Can we predict how the situation will evolve?

Global change: impact, management, risk approach and health measures--the case of Europe.

Global changes, including an increase in trade and global warming, which act on the environment, are likely to impact on the evolution of pathogens and hence of diseases. To anticipate the risks created by this new situation, a French group of experts has developed a method for prioritising animal health risks. This is a two-phase method: the first step is to identify the diseases whose incidence or geographical distribution could be affected by the changes taking place, and the second step is to evaluate the risk of each of these diseases. As a result of this process, six priority diseases were selected: bluetongue, Rift Valley fever, West Nile fever, visceral leishmaniasis, leptospirosis and African horse sickness. The main recommendations were: to develop epidemiological surveillance, to increase knowledge of epidemiological cycles, to develop research into these diseases and to pool cross-border efforts to control them.

[Ecology of vector systems: a tangle of complexity]. / L'écologie des systèmes vectoriels: une somme de complexités.

The long co-evolutionary process between arthropods and microorganisms has resulted in a wide variety of relationships. One such relationship involves a wide range of infectious agents (virus, bacteria, protozoa, helminthes) that use blood-feeding arthropods (insects and mites) as vectors for transmission from one vertebrate to another. Transmission involves three components, i.e., microorganism, vector(s), and vertebrate host(s). Study under natural conditions has shown that the underlying mechanisms are extremely complex with circulation of the infectious agents depending on numerous conditions linked not only to bioecology but also to genetic factors in all three component populations. The role of arthropods sometimes goes beyond that of a transmitter of disease. In some cases they also serve as reservoirs or disseminators. In addition changes in the environment whether due to natural causes or human activities (e.g. pollution, agropastoralism, urbanization, transportation network development, and climate change) can have profound and rapid effects on the mechanisms underlying these vector systems. In short the ecology of vector systems closely reflects the extreme complexity of epidemiological studies on diseases caused by infectious agents depending on this type of transmission. As a result prediction of infectious risks and planning of preventive action are difficult. It appears obvious that a good understanding of vector systems in their natural context will require a truly ecological approach to the diseases that must be the focus of extremely close epidemiologic surveillance. Achieving this goal will necessitate more than the skills of physicians and veterinarians. It will require the contribution of specialists from a variety of fields such as microbiology, entomology, systematics, climatology, ecology, urbanism, social sciences, economic development, and many others.

Sex-specific and blood meal-induced proteins of Anopheles gambiae midguts: analysis by two-dimensional gel electrophoresis.

BACKGROUND: Anopheles gambiae is the main vector of Plasmodium falciparum in Africa. The mosquito midgut constitutes a barrier that the parasite must cross if it is to develop and be transmitted. Despite the central role of the mosquito midgut in the host/parasite interaction, little is known about its protein composition. Characterisation of An. gambiae midgut proteins may identify the proteins that render An. gambiae receptive to the malaria parasite. METHODS: We carried out two-dimensional gel electrophoresis of An. gambiae midgut proteins and compared protein profiles for midguts from males, sugar-fed females and females fed on human blood. RESULTS: Very few differences were detected between male and female mosquitoes for the approximately 375 silver-stained proteins. Male midguts contained ten proteins not detected in sugar-fed or blood-fed females, which are therefore probably involved in male-specific functions; conversely, female midguts contained twenty-three proteins absent from male midguts. Eight of these proteins were specific to sugar-fed females, and another ten, to blood-fed females. CONCLUSION: Mass spectrometry analysis of the proteins found only in blood-fed female midguts, together with data from the recent sequencing of the An. gambiae genome, should make it possible to determine the role of these proteins in blood digestion or parasite receptivity.

Genetic differentiation of the dengue vector, Aedes aegypti (Ho Chi Minh City, Vietnam) using microsatellite markers.

Dengue haemorrhagic fever emerged in the 1950s and has become a major public health concern in most Asian countries. In Vietnam, little is known about the intraspecific variation of the vector and its consequences on vectorial capacity. Here we report the use of microsatellite markers to differentiate Aedes aegypti populations in Ho Chi Minh City, a typical, overcrowded Asian city. Six microsatellite loci, with 5-14 alleles per locus, were scored in 20 mosquito samples collected in 1998 in Ho Chi Minh City. We found substantial differentiation among Ae. aegypti populations from the outskirts, whereas populations from the centre of the city showed less differentiation. These results are consistent with the hypothesis that populations of Ae. aegypti in central Ho Chi Minh City are panmictic because there are abundant larval breeding sites and an abundance of humans for adults to feed upon. In contrast, populations on the outskirts become differentiated largely through the processes of genetic drift because larval breeding sites are not as abundant. These findings implicate human activities associated with urbanization, as factors shaping the genetic structure of Ae. aegypti populations.

Temporal genetic variation in Aedes aegypti populations in Ho Chi Minh City (Vietnam).

Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population density over time. The larval habitats of this species being unevenly distributed and transient (depending on cycles of drought and flood), the forces generating temporal variation in gene frequencies in populations are studied. We sampled seven mosquito populations from Ho Chi Minh City (Vietnam) and its suburbs on five occasions between April 1999 and August 2000. We investigated genetic variation by studying isoenzyme and microsatellite polymorphism and susceptibility to a dengue 2 virus strain. Ae. aegypti populations collected during the dry season (January-April) showed genetic differentiation (F(ST) = 0.016, P < 10(-6) for isoenzymes) and showed more differentiated infection rates of the dengue 2 virus. The genetic structure of the population is less marked during the rainy season (F(ST) = 0.081, P < 10(-6)). Thus, environmental factors, such as rainfall and factors related to human activity, such as breeding site density and insecticide treatment, control the genetic structure of Ae. aegypti populations in the short term. The implications of studies of this kind for the design of future control programmes are discussed.

Isoenzyme differentiation of Aedes aegypti populations in French Guiana.

Population genetics of peri-domestic Aedes aegypti (Diptera: Culicidae), vector of dengue and yellow fever, were investigated by gel electrophoresis of 10 enzyme loci in 14 samples of mosquito larvae collected in 1997-1998 from localities separated by distances of 3-275 km in French Guiana. Genetic differentiation between geographical populations was generally high (mean FST = +0.111, P < 10(-5)) even among seven sites <30 km apart (FST = +0.137, P < 0.05), but not positively correlated with distance. Thus, Ae. aegypti comprises a mosaic of genetically differentiated populations in French Guiana. This may be attributed to reinvasion from diverse origins through repeated founder events after this vector species was eliminated during the 1940s to 1960s.

Population structure of Aedes albopictus from La Réunion Island (Indian Ocean) with respect to susceptibility to a dengue virus.

Ten F1 Aedes albopictus samples collected from Réunion Island in the Indian Ocean were tested for oral susceptibility to dengue 2 virus and 20 were analysed for genetic polymorphism by starch gel electrophoresis. Data from infection rates defined two distinct geographical areas: east coast vs. west coast. Genetic differentiation was found to be dependent on ecological factors and the biological characteristics of Ae. albopictus. These results have implications for the vector ecology and pattern of migration, and have importance in the understanding of dengue transmission.

Population genetic structure and competence as a vector for dengue type 2 virus of Aedes aegypti and Aedes albopictus from Madagascar.

Starch gel electrophoresis was used to assess the polymorphism of 7 isoenzymes in single mosquitoes (field-collected F0 or F1 generation) for Aedes albopictus (8 strains) from northern Madagascar. Mosquitoes of the F2 generation (3 strains of Aedes aegypti and 10 strains of Ae. albopictus) were tested for oral susceptibility to dengue type 2 virus. Aedes aegypti was less susceptible to viral infection than Ae. albopictus. The genetic differentiation was less high between Ae. albopictus populations collected in agglomerations connected by highly frequented roads, indicating that human ground transportation favors mosquito dispersal. These results have implications for the ecology, pattern of migration, and relative importance in epidemic transmission of dengue viruses between the 2 Aedes species.

Aedes aegypti in French Guiana: susceptibility to a dengue virus.

Twenty-seven samples of Aedes aegypti (F1 generation) from French Guiana were tested for their susceptibility to dengue serotype 2 virus. Very high infection rates were observed by indirect fluorescent antibody (IFA) test. Ae. aegypti samples were pooled according to two groups: the first group (N=10) represented mosquitoes from the urbanized area of Cayenne and surroundings, and the second group (N=17) corresponded to mosquitoes collected in the countryside. Infection rates were found to be similar in these two cases. These findings are discussed in relation with the history of Ae. aegypti in this part of the world.

Pathogen-specific resistance to Rift Valley fever virus infection is induced in mosquito cells by expression of the recombinant nucleoprotein but not NSs non-structural protein sequences.

Rift Valley fever virus (RVFV) is an arbovirus of the BUNYAVIRIDAE: family, causing recurrent disease outbreaks in Africa. Natural vertebrate hosts include cattle and humans. Several mosquito species belonging to the AEDES: and CULEX: genera act as vectors of this phlebovirus. To test whether pathogen-derived resistance against RVFV could be induced by expressing genomic sequences in mosquito cells, as has been shown for La Crosse and dengue 2 viruses, we generated various recombinant Semliki Forest viruses expressing the S segment (or its genes) in the genomic or antigenomic sense. Expression of the N but not the NSs gene interfered with the production of RVFV in mosquito cells and this phenomenon was RNA- but not protein-dependent. These results raise questions on the molecular mechanisms involved in virus resistance.

Aedes aegypti in Tahiti and Moorea (French Polynesia): isoenzyme differentiation in the mosquito population according to human population density.

Genetic differences at five polymorphic isoenzyme loci were analyzed by starch gel electrophoresis for 28 Aedes aegypti samples. Considerable (i.e., high Fst values) and significant (i.e., P values >10(-4)) geographic differences were found. Differences in Ae. aegypti genetic structure were related to human population densities and to particularities in mosquito ecotopes in both Tahiti and Moorea islands. In highly urbanized areas (i.e., the Papeete agglomeration), mosquitoes were highly structured. Recurrent extinction events consecutive to insecticidal treatments during dengue outbreaks tend to differentiate mosquito populations. In less populated zones (i.e., the east coast of Moorea and Tahiti), differences in ecotope characteristics could explain the lack of differentiation among mosquitoes from rural environments such as the east coast of Tahiti where natural breeding sites predominate. When the lowest populated zones such as Tahiti Iti and the west coast of Moorea are compared, mosquito are less differentiated in Moorea. These results will be discussed in relation to the recent findings of variation in mosquito infection rates for dengue-2 virus.

[The state of vector-borne diseases in Indonesia]. / La situation des maladies à vecteurs en indonésie.

From epidemiological point of view, Indonesia is an extremely interesting area owing its insular structure and ecological, anthropological, cultural and economical diversity. As everywhere, vector-borne diseases are the result of complex and variable epidemiological systems, subject both to biogeographical rules and human activity. Two main arboviroses are present in Indonesia: dengue and Japanese encephalitis. Dengue appears as an endemoepidemic disease and is mostly circumscribed to urban areas. Haemorrhagic cases were first observed in 1968; since then, the incidence has been constantly increasing and the disease is now one of the principal causes of child lethality. Japanese encephalitis is a rural endemic disease transmitted by rice-field mosquitoes; its incidence remains relatively low since pigs, which are usual link-hosts for the virus, are uncommon in this mainly Muslem country. Human clinical cases are recorded from non-Muslem islands such as Bali or Irian Jaya which raises the question of immunisation for travellers. Recently, Japanese encephalitis was observed on east of the Wallace line which had been considered as the eastern cut-off line. Malaria is common throughout the country, Plasmodium vivax being the most frequent species. Some of the Anopheline vectors are related to brackish water as are coastal species; others have been favoured by rice growing. Several species bite and rest outdoors, rendering control measures complex. Moreover, chloroquine resistance is increasing in both P. falciparum and P. vivax. All three filaria species responsible for human lymphatic filariasis exist in Indonesia. Bancroft filariasis is present in rather limited foci on most of the islands; malayan filariasis is very prevalent on many islands, mostly in coastal areas, and Timor filariasis exist only on a few small islands. These parasitic diseases are cumulative and do not practically endanger the health of travellers. In the past, plague was common on Java island, but today, human cases are very rare. Scrub typhus is prevalent everywhere, as is murine typhus, being very frequent in harbour cities and one of the main causes of hospitalisation for febrile syndromes.. On the whole, the situation of several of these diseases has been worsening in Indonesia for about thirty years. Although epidemiological situations constantly evolve, two recent occurrences should be paid particular attention: -transmigration which is now a national priority and greatly facilitates the spread of many pathogens, arboviroses or chloroquine-resistant plasmodia, but also of rats, mosquitoes, etc. -deforestation due either to land-farming by Javanese transmigrants or to sudden climatic changes such as El Niño in 1997. Such deep ecological transformations may have considerable and unforeseeable consequences on the epidemiology of vector-borne diseases in Indonesia.

Aedes albopictus from Albania: a potential vector of dengue viruses.

Aedes albopictus collected in Durazzo, the main port of Albania, were tested for oral susceptibility to dengue type 2 virus and their infection rates were compared to those of an Aedes aegypti strain (Paea) and another strain of Ae. albopictus (Tananarive). Infection rates for the Albanian Ae. albopictus were dose dependent, ranging from 38.9 +/- 13.6% to 85.1% with the titer of the meal increasing from 10 x 8.1 to 10 x 9.1 50% mosquito infectious doses (MID50)/ml. The percentage of infected females was lower for the Ae. albopictus Durazzo strain than for the Ae. aegypti Paea strain: 38.9 +/- 13.6% compared with 92.4 +/- 4.9% for a meal of 10 x 8.1 MID50/ml, respectively. However, the difference was less when the titer of the meal was increased: 85.1% compared with 100% for a meal of 10 x 9.1 MID50/ml, respectively. The infection rate was also lower for the Durazzo strain than for the Tananarive strain of Ae. albopictus. The degree of viral replication in infected females was not significantly different in the 3 strains tested and we were able to demonstrate the ability of females from the Durazzo strain to transmit the virus in the course of a blood meal. Our results lead us to conclude that Ae. albopictus from Albania could serve as a vector for dengue virus.

[Genetic control of vectorial competence in Aedes mosquitoes]. / Contrôle génétique de la compétence vectorielle des moustiques du genre Aedes.

The transmission of pathogens by arthropods is dependent on the relationships that exist between the pathogen, the invertebrate host (the vector) and the vertebrate host, each of which is influenced by environmental variations. Particular attention is given to the knowledge of intrinsic factors and the mechanisms controlling the ability of vectors to transmit pathogens (viruses or parasites). Polymorphism in the expression of susceptibility to oral infection has been shown to occur among geographical samples of mosquitoes. It has been proven that intraspecific variations in vector competence are controlled by one or more genes and expressed in variable proportions within a mosquito population. Recent advances in molecular biology have facilitated accessibility of nucleic acid sequence data. These new techniques allow one to analyse the genotype distribution within and among populations. Population genetic studies are currently used to understand the evolution of species differentiation and provide indications on genetic relationship among field vector populations. Estimations of gene flow with respect to vector capacity have provided rich insight into vector species complexes. Knowledge of intraspecies variation is important for the understanding of vector transmission, disease epidemiology and disease control. In this article, two examples are presented to illustrate the contribution of population genetic studies to the understanding of epidemiology of arthropod-borne diseases: Aedes polyneniensis, a vector of human lymphatic filariasis and Aedes aegypti, the vector of dengue viruses.