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Malaria has long constituted a major public health problem for French Guyana, limiting its demographic and economic development. From 1949 to 1960, due to chemoprophylaxis and DDT spraying in houses, the number of malaria cases decreased markedly. After 1975, important migratory movements contributed to increasing the incidence of malaria. In 1989, numerous cases were observed when some 500 immigrants settled in a formerly uninhabited area, known as Cabassou BP 134. It is located 7 km (S-E) from the main city of Cayenne and bordered by secondary forest and swamps. The entomological study initiated in 1990 included weekly biting-landing catches (3 hours) on human bait in houses from dusk onwards as well as locating breeding places around the settlement to collect larvae by dipping. Anopheles specimens were identified and the females dissected to detect infections by Plasmodium and also to determine the rate of parous specimens. Control measures included deltamethrin (15 mg/m2) and DDT (2 g/m2) spraying, every four months, of interior walls and thermal fogging of naled around the houses. Cold ULV aerosol of fenitrothion (500 ml/ha) was also used to treat the swamp borders. In April 1990, a health education programme was begun and in June, 288 impregnated bednets (deltamethrin 15 mg/m2) were treated. From 1990 to 1998, 1,588 (498 larvae + 1090 adults) Anopheles (Nyssorhynchus) were collected: An. aquasalis 797 (311 L + 486 A). An. braziliensis 139 (87 L + 52 A). An. darlingi 652 (100 L + 552 A). No infected female was found among the 710 dissected. The number of malaria cases decreased abruptly in the fall of 1990 when An. darlingi disappeared and only one case due to P. vivax was detected between 1995 and 1998. An. darlingi (parous rate = 72%) appears to be the main if not the sole vector of malaria in this locality. As in the past, a focus of malaria appears when immigrants from endemic countries settle in a formerly uninhabited place where An. darlingi are breeding.

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A programme of surveillance was initiated in 1992, in the French Riviera, to detect a possible introduction of Aedes albopictus from Italy and to prevent nuisances caused by mosquitoes in the touristic localities of the Côte d'Azur. In five years, numerous mosquito breeding places have been located. Nine species have been collected: Anopheles claviger, An. plumbeus, Aedes geniculatus, Ae. vittatus, Culex hortensis, Cx. impudicus, Cx. pipiens, Culiseta fumipennis, Cs. longiareolata but no Ae. albopictus was found. Nuisances were mainly due to hypogean populations of Cx. pipiens. Breeding places in urban sites have been controlled or suppressed. The discovery of an important larval population of An. plumbeus in an urban area might further stress the importance of this species already suspected to transmit indigenous malaria in cities.

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Prediction and prevention of dengue epidemics are based on informations gathered about the mosquito vector species, the dengue types transmitted, the vertebrate hosts and their environment. Although Aedes aegypti is the most important vector, other Aedes may also propagate the dengue viruses. The populations of vector mosquitoes are evaluated through several indices: Breteau and/or positive house index, number of indoor resting Aedes females, etc.... The four dengue types can replicate in vertebrate hosts beside humans and in other mosquito species than Ae. aegypti. The incidence of dengue on a population is largely variable according to the immunity status, the vector competence and the virus strains. Concomitant infections by two types of dengue virus or by an another pathogen (Alphavirus) have been observed. The environmental factors influencing the dengue ecosystem are mostly climatic (temperature, rainfall, wind) but also anthropic (transportation means, public buildings). Prevention of dengue epidemics must be based on public health education in schools, community participation, epidemiological surveillance linked with good vector control teams. Nevertheless intensive research on dengue and the actions undertaken for the last forty years, dengue remains the first cause of viral morbidity worldwide.

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Since the 1940s, the dengue epidemics occur more and more often in the Pacific islands with an increased severity. For example, in New Caledonia, outbreaks of dengue-like diseases have been reported since the end of the last century but the first epidemic due to an identified virus occurred in 1942-1943 and was caused by the DEN-1 type. The next, due to the DEN-2 type, was reported thirty years later, in 1972-1973. After that, three outbreaks burst between 1975 and 1990, caused successively by dengue types 1, 4 and 3 but from 1985, human strains of different types were isolated at the same time. The vector control measures, mainly aerial ULV spraying had a variable efficacy. The most important vector was Aedes aegypti but dengue virus strains were also isolated from other mosquito species (Aedes vigilax, Culex annulirostris, C. bitaeniorhynchus, Coquillettidia xanthogaster); their role in the interhuman transmission of dengue was not demonstrated. In New Caledonia, the development of international travels, an extension of suburbs and an increased insecticide resistance of Ae. aegypti are the obvious causes of the problem but an unknown transmission cycle, involving different hosts and vectors may also be suspected.

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Psorophora lineata, a very large-sized mosquito, has rarely been collected in French Guiana. From specimens obtained in 1942-1991, data on morphology, bionomics, local distribution and disease relations are given. P. lineata may be considered as a potential vector of arboviruses.

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The authors report the result of an entomological study in the southeastern France. It is the first time that Phlebotomus perfiliewi is described in that country.

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In the course of a dengue outbreak, 765 larvae and 20 pupae were collected in Noumea and in Wallis island around patients premises, to investigate a possible natural infection. On 15 pools made of 335 Aedes aegypti larvae and pupae, 3 appeared to be infected. Dengue virus type 1 was the only serotype identified. Minimum infection rate reached 1: 112. In New Caledonia, the local strains of Aedes aegypti can insure the survival of dengue 1 virus between outbreaks, due to a vertical infection of their progeny.

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An entomological survey conducted at the international airports of the Fiji Islands showed Aedes albopictus breeding in the protective area of Nadi airport. No Aedes aegypti nor Anopheles accidentally imported have been seen during the visit. Aedes vexans, A. pseudoscutellaris, A. burnetti, A. vigilax, Culex annulirostris, C. quinquefasciatus and a species of the pipiens complex have been collected incidentally out of airport areas. Due to the presence of Aedes albopictus, a new and important epidemiological risk must be considered now in Fiji Islands. Vector control measures must be taken urgently. These results demonstrate the necessity to maintain a strict vector surveillance in international airports.

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From 1971 to 1980, dengue outbreaks occurred in New-Caledonia due to dengue viruses type 2, 1 and 4 successively. After an eclipse of four years, dengue reappeared in 1985 through 1988. Out of 109 cases confirmed by virus isolation, dengue serotypes 1, 2, 3 and 4 caused 15, 23, 17 and 54 cases respectively; in 28 other cases, the Flavivirus type could not be identified and in 26 cases an Alphavirus (Ross River) was pointed out. The DEN 3 virus, unknown in New-Caledonia before 1985, was discretely transmitted until 1988. The 1989 outbreak showed the necessity of rigorous vector control measures.

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A survey conducted in eight airports of the South pacific, yielded 2,044 larvae and 136 adult forms, belonging to 25 Culicidae species. Breeding places were found in every airport, either within the perimeter (6 airports) or in the protective zone. Some potentially dangerous vectors were identified: Aedes aegypti (4 airports), Ae. polynesiensis, Ae. vigilax, Anopheles farauti (2 airports), Culex annulirostris, C. p. quinquefasciatus. Vector control measures should be strengthened to suppress every breeding place within the airport perimeter.

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Culex bitaeniorhynchus, reported from New Caledonia after a single collection of larvae in Noumea in 1952, has been found in two other localities, on the south-west and on the north-east coasts. The morphological features show some differences between the local population and the forms from the Oriental Region. Adults have been caught during the hot and rainy season, by light traps mainly. The females have been very rarely collected on human bait. Though found naturally infected by dengue 4 virus, that species is not likely to have an epidemiological importance in New Caledonia. It seems doubtful that it has been imported recently.

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Viruses isolated during 1979 and 1980 from patients with polyarthritis in New Caledonia and Wallis and Futuna Islands have been found to be more closely related to Ross River virus than any other regional Alphavirus. On the basis of virulence in suckling mice the majority of these isolates were found to be more closely related to the NB5092 strain of Ross River virus than to the prototype T48 strain.

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A parasitological survey has been conducted in the localities of New Caledonia where foci of subperiodic bancroftian filariasis, transmitted by Aedes vigilax, had been observed in 1950-1957. The microfilaremia indices obtained in 1979-1980 are generally lesser than in the past. Some foci on the west coast, have disappeared; the other ones are spread along the coasts in the north, north-west, north-east and east of the mainland, one is located in Ouvea island. Aedes vigilax is highly prevalent in the surroundings of the foci; infection rate is low (0.5%).

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From 1975, epidemiological studies on arboviral diseases, conducted in New Caledonia, Vanuatu, Wallis and Horne Islands, have shown that 11 species of mosquitoes may harbour viruses in natural conditions. Virus isolations were attempted from 1,025 pools of Culicidae totalizing 32,182 individuals belonging to 5 genera and 21 species. Viral infections have been demonstrated in 76 pools (7.4%). The species harbouring viruses were: Aedes aegypti, Ae. alternans, Ae. notoscriptus, Ae. vexans, Ae. vigilax, Culex annulirostris, C. bitaeniorhynchus, C. iyengari, Culex pipiens quinquefasciatus, Coquillettidia xanthogaster. Among the strains definitively identified, dengue 1 virus was recovered from Ae. aegypti, Ae. polynesiensis, Ae. vigilax, dengue 4 virus was obtained from Ae. aegypti, Ae. vigilax, C. xanthogaster, C. annulirostris. Ross River virus was identified in Ae. vigilax and C. quinquefasciatus. The infected mosquitoes originated from New Cadedonia, Vanuatu (Aoba), Wallis and Horne Islands.

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During an outbreak of arboviral diseases in the South-West Pacific islands, from 1979 to 1980, patients sera examined in New Caledonia revealed 43 cases of epidemic polyarthritis due to Ross River virus. Viral strains were obtained from 16 of these patients. After isolation of the virus in newborn mice, the inoculation of C6/36, PS-EK and Vero cells allowed the identification of these strains by hemagglutination inhibition and complement fixation tests. This was the first time that cases of polyarthritis caused by RR virus were observed in New Caledonia, Vanuatu, Wallis and Futuna.

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After imported cases, a dengue outbreak, caused by type 4 virus, affected 11 per cent of the habitants of Thio, New Caledonia. Distribution of cases by sex, by ethnic and age group, by locality and by week is established on cases confirmed by serology and/or by virus isolation. Clinical aspect was classical but liver and digestive tract of patients were frequently affected. Five haemorrhagic forms were observed. Aedes aegypti was found in each visited house; pooled specimens were found infected by type 4 virus.

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Human filariasis caused by the aperiodic form of Wuchereria bancrofti is one of the main epidemiological problems in Wallis and Futuna Islands. The ecologic features and the Public-health Service actions for survey and control of this endemic disease are described. Biological and clinical results were very satisfactory.

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