Control of the Aedes vectors of the dengue viruses and Wuchereria bancrofti: the French Polynesian experience.

In most of the 130 islands of French Polynesia, the stenotopic mosquitoes Aedes aegypti (the main local vector for the viruses causing dengue) and Aedes polynesiensis (the main local vector of Wuchereria bancrofti) share many breeding sites in water containers such as discarded cans, coconut shells, buckets and water-storage pots and drums. In addition to selective application of insecticides, non-polluting methods of controlling these mosquitoes have been evaluated during the last decade in two main ecological situations: (1) villages, where Aedes breeding sites are typically peridomestic; and (2) flooded burrows of land crabs, the major source of Ae. polynesiensis throughout the South Pacific region. Large-scale trials of biological control agents, such as mosquito fish (Gambusia affinis and Poecilia reticulata) and copepods (Mesocyclops aspericornis), and of integrated-control strategies have demonstrated the efficacy of certain techniques and control agents against the target Aedes populations in some village situations. Generally, mechanical methods (the use of layers of polystyrene beads against mosquito larvae and pupae, and screening against adult mosquitoes) were more efficient than use of the biological control agents. By integrating several methods of control, mosquito densities (as measured by human-bait collections and larval surveys) were reduced significantly compared with the results of concurrent sampling from untreated villages, and control remained effective for months after the interventions ceased. In land-crab burrows, the first attempts to control Aedes larvae used bacterial agents (Bacillus thuringiensis) and predatory copepods gave disappointing results. Mesocyclops aspericornis could be an effective control agent if the burrows were constantly flooded, but most burrows dry out and refill periodically, so copepod populations do not survive. As it proved difficult to reach all corners of the long sinuous burrows with any control agent, larvicidal (chlorpyrifos-methyl) baits were developed for foraging crabs to carry into their burrows. This novel technique proved to be effective and could become the method of choice for treating crab burrows. Further research is underway to find the optimum (biological or chemical) larvicidal ingredient for the crab bait. Despite the ecological and logistical challenges of controlling the Aedes vectors of the dengue viruses and W. bancrofti in so many scattered islands, the French Polynesian experience indicates that relatively simple methods can be integrated and applied effectively and economically. Operationally, however, success also depends on a strong political commitment and on at-risk communities that are sufficiently motivated to maintain a good level of Aedes control.

[Features of larval development in Simulium buissoni Roubaud, 1906, and S. sechani Craig and Fossati, 1995 (Diptera: Simuliidae) in the Marquesas Archipelago (French Polynesia)]. / Caractéristiques du développement larvaire de Simulium buissoni Roubaud, 1906, et de S. sechani Craig et Fossati, 1995 (Diptera: Simuliidae) dans l'archipel des Marquises (Polynésie Française).

Two anthropophilic species are known from the Marquesas archipelago (French Polynesia): Simulium buissoni Roubaud, 1906 and S. sechani Craig & Fossati, 1995. The need to control them requires good knowledge about their larval growth, larvae being the only stage actually susceptible to control. A biometric study based on cephalic measures of the two species, shows that they both have seven larval instars. Size variations following species and sampling sites are examined, as are variations of the sex of the two last larval instars. A recolonization experiment, after treatment of a part of a river, allows us to quantify larval growing length of S. buissoni, which is about 12 days. These data allow us to determine the optimal treatment frequency.

[Aspects of the aggressivity cycle of Simulium buissoni Roubaud, 1906 (Diptera: Simuliidae) in Nuku-Hiva, Marquesas Archipelago (French Polynesia)]. / Aspects du cycle d'agressivité de Simulium buissoni Roubaud, 1906 (Diptera: Simuliidae) à Nuku-Hiva, Archipel des Marquises (Polynésie Française).

High density of haematophagous blackflies on Nuku-Hiva Island (Marquesas archipelago, French Polynesia) is a handicap to its optimal development. The present study contains observations from many sampling sites to examine aggressive periods of Simulium buissoni Roubaud, 1906. Density of aggressive females is very high, principally in highly irrigated sites of the island. Biting rates show low variation between days, and a diurnal activity, with a poorly pronounced circum-meridian maximum. Parity rates show great variation between sampling stations, but are lowest during the day. A hypothesis of greater spatial dispersion of nulliparous females allows explanation of much of the observed variation. Sampling in and out of a house shows exophily of blackflies. Proportion of parous females is greater in the house. Data collected over a long period show that earlier densities were greater than recent ones. Perturbation of the environment is probably the basis of this decrease.

The impact of 34 years of massive DEC chemotherapy on Wuchereria bancrofti infection and transmission: the Maupiti cohort.

Semi-annual mass DEC chemotherapy combined with vector control at the beginning of the programme, has been administered on the remote island of Maupiti (French Polynesia) since 1955 (except two periods in 1960-67 and 1970-74). The results of two surveys in 1985 and 1989, reporting 0% microfilaraemia, led to the hope that the eradication of lymphatic filariasis had been achieved. We combined parasitological criteria (microfilaraemia by membrane filtration), immunological (antigenaemia and serum levels of specific IgG antibodies) and molecular (PCR-based evaluation of infection in mosquitoes) techniques and found only good control of the parasite: We found residual microfilaraemia in 0.4% of the sample (mean level in carriers: 101.2 mf/ml), antigenaemia in 4.6% (mean level in positive persons: 714.4 units/ml) and specific IgG in 21.6% (including in one very young child). In addition, an infection rate of 1.4% was calculated in the Aedes polynesiensis vector population. These data, obtained in 1997 just before a hurricane, were partially confirmed in 1999 (0.1% of infection rate in the vector). Together with the possibility of some resistance to DEC, various epidemiological factors critical for the eradication of lymphatic filariasis are discussed.

[Distribution of Simulium buissoni Roubaud, 1906 and S. sechani Craig & Fossati, 1995 (Diptera: Simuliidae) in Nuku-Hiva and Eiao (Marquesas Archipelago, French Polynesia)]. / Répartition de Simulium buissoni Roubaud, 1906 et S. sechani Craig & Fossati, 1995 (Diptera: Simuliidae) à Nuku-Hiva et Eiao (Archipel des Marquises, Polynésie Française).

Nuku-Hiva and Eiao are the only islands of the Marquesas archipelago where blackflies bite humans. Knowledge of the geographic distribution of species is necessary to optimize control operations. Looking at frequency distributions of labral fan rays numbers from a large sample of larvae allowed redefinition of species. Simulium sechani Craig & Fossati, 1995, become the only species represented in Eiao. This species live in Nuku-Hiva too, but is limited to the external part of the main caldera. Presence of S. buissoni Roubaud, 1906, in all part of the island is confirmed, as is presence of S. hukaense Séchan, 1983 but in reduced number. Large samples of S. sechani extends its labral fan rays numbers. Stability of the described repartition over several decades is shown.

[Tentative discrimination of adult female simulids (Diptera: Simuliidae) in Nuku-Hiva (Marquesas Archipelago, French Polynesia)]. / Tentative de discrimination des femelles adultes de simulies (Diptera: Simuliidae) à Nuku-Hiva (Archipel des Marquises, Polynésie Française).

Simulium sechani Craig & Fossati, 1995 was recently found for the first time in a part of Nuku-Hiva Island. This species coexists with Simulim buissoni Roubaud 1906, the dominant species, and always regarded as the main biting fly on the island. The problem is that optimisation of control operations needs a good knowledge of targets. The unknown female of S. sechani is the reason of this study. This study used samples collected before the description of S. sechani to try to correlate its geographical extent with easy to use biometrical parameters, and then give a first look at the possibilities of determination of adult females. Parameters used are: the numbers of maxillary and mandibular teeth, the dimension of the third antenna article and the number of apical hairs, the width and depth of the ventral plate space, and the number of hairs on the radial vein of the wing. Analysis of frequency distributions in relation with sampling sites and trapping hosts did not allow us to find convenient diagnosis characters, but contributed to new questions about isolation of insect populations in valleys and hosts usually used.

The blackfly Simulium buissoni and infection by hepatitis B virus on a holoendemic island of the Marquesas archipelago in French Polynesia.

The hematophagous blackfly Simulium buissoni causes skin lesions on an island in the Marquesas archipelago that is holoendemic for hepatitis B virus (HBV). To test the hypothesis of the possible role of this fly in the transmission of hepatitis B, 506 children (age range 2-11 years) were examined for the presence of skin lesions, and attempts were made to detect HBV DNA in and on blackflies using two polymerase chain reaction methods. The mean number of skin lesions showed a positive correlation with the age of these children (r = 0.12, P < 0.05). Furthermore, it was significantly higher in the rural zone than in the urban zone (mean +/- SD 41.02 +/- 31.71 versus 17.73 +/- 13.43; P < 0.05), and showed a correlation with a higher infection rate (73.9% versus 41.3%). Of the 45 pools of 10 insects tested, HBV DNA was not detectable on the inside of the insect, but was detectable on the flies (1-10 particles/insect in three positive pools). Infection by HBV conveyed by the flies is theoretically possible, but their indirect role via the numerous skin lesions caused on children is likely to explain such a high level of transmission.

Release of Mesocyclops aspericornis (Copepoda) for control of larval Aedes polynesiensis (Diptera: Culicidae) in land crab burrows on an atoll of French Polynesia.

On Tereia Island, Rangiroa Atoll, 14,321 land crab burrows were treated with the copepod Mesocyclops aspericornis from January to June 1986, to control larvae of Aedes polynesiensis marks. In October 1987, the entire island of Tereia was retreated (17,300 burrows), and the neighboring island, Voisin, was left untreated as a control. From 5 to 15 mo after treatment, burrows with M. aspericornis contained an average of 2 Ae. polynesiensis immatures compared with 97 immatures from untreated burrows. Long-term larval control was successful in low-lying areas where burrows remained wet or were reflooded. Although there may have been other contributing factors, the major reason for lack of persistence of M. aspericornis in burrows over the entire island appeared to be poor resistance to desiccation. From all treated burrows in October 1987, M. aspericornis subsequently was found in 89.5, 39.1, and 24.1% of burrows sampled 5, 8, and 15 mo after treatment, respectively. The broad-scale results for Tereia indicated that there was no reduction of adult biting indices when compared with Voisin. Mark-release experiments on four occasions indicated that Ae. polynesiensis had a limited flight range and that the probability for interisland movement was low.

Cumulative mortality rates in Aedes polynesiensis after feeding on polynesian Wuchereria bancrofti carriers treated with single doses of ivermectin, diethylcarbamazine and placebo.

During a therapeutic trial, batches of 672 to 1979 laboratory-bred Aedes polynesiensis, the mosquito vector of lymphatic filariasis in French Polynesia, were fed on Wuchereria bancrofti carriers one, three and six months after they had been treated with either single doses of ivermectin at 100 mcg/kg, diethylcarbamazine (DEC) at 3 and 6 mg/kg or placebo. High mortality rates were observed during the 15-day period following the blood-meal in mosquitoes fed on carriers treated with microfilaricidal drugs and were significantly higher in mosquitoes fed on carriers treated with ivermectin than in those fed on carriers treated with DEC. Though its intensity decreased with the passage of time, the phenomenon was observed in mosquitoes fed on carriers up to six months after treatment, especially in those fed on carriers treated with ivermectin. By decreasing the number of mosquitoes able to transmit the infection, this lethal effect on Ae. polynesiensis might represent an additional advantage of ivermectin in lymphatic filariasis control programs.

Oral infection of Aedes polynesiensis by Wuchereria bancrofti by using parafilm membrane feeding.

In order to construct a cDNA library from third-stage larvae (L3) of Wuchereria bancrofti var. pacifica, the Parafilm membrane feeding method is proposed for the oral infection of Aedes polynesiensis. Heparinized blood supplemented with 5.10(-3) M ATP was put in the feeder with carbon dioxide provided as additional phagostimulant. The results of this artificial infection feeding method were compared with those obtained when mosquitoes fed directly on the forearm of a microfilaremic patient. The number of females feeding through the artificial membrane was smaller than on the patient's forearm (32.1 vs. 84.8%). The mean number of L3s obtained per female was not statistically different between the 2 feeding methods; however, the total number of L3s obtained from 100 females allowed to feed in each group was twice as high in the natural feeding method.

Ivermectin for treatment of bancroftian filariasis in French Polynesia: efficacy in man, effect on transmission by vector Aedes polynesiensis.

Forty male Polynesian W. bancrofti carriers with mf counts greater than or equal to 20/ml were treated with a single ivermectin 50, 100, 150 or 200 mcg/kg dose. Following therapy, mf levels fell to less than 1% of pretreatment levels in the carriers treated with the 3 highest doses. After one month, negativation rate was 40% in patients treated with a 50 mcg/kg dose, significantly lower than in patients treated with higher doses. Recurrence of microfilaremia was observed by 3 months, mf recurrence percentages were significantly lower in patients treated with the 3 highest doses than in patients treated with a 50 mcg/kg dose. At 6 months, mf recurrence percentages reached 49.8, 12.6, 14 and 5.4% of pretreatment levels in carriers treated with 50, 100, 150 and 200 mcg/kg, respectively. No significant difference was observed between mf levels by group at 6 and 12 months. With respect to efficacy, a dose greater than or equal to 100 mcg/kg appeared superior to 50 mcg/kg dose; no significant difference between the 3 highest doses was observed. Some patients developed headache, myalgia and fever within 24 hours following therapy, none of adverse reactions were considered serious. In vector Ae. polynesiensis fed on carriers 6 months after treatment, average numbers of mf ingested and average numbers of L3 cephalic larvae were lower than those observed in mosquitoes fed on non-treated carriers with comparable mf counts.(ABSTRACT TRUNCATED AT 250 WORDS)

[Proposal for a testing protocol of insecticides against the copepod crustacean Mesocyclops aspericornis Daday 1906]. / Proposition de protocole de test insecticide vis-à-vis du crustacé copépode Mesocyclops aspericornis Daday 1906.

A method to determine the susceptibility of Mesocyclops aspericornis to insecticides is proposed. Tests were carried out by placing adults females in 100 ml of insecticide solution at 3 temperatures (20 degrees C, 25 degrees C, 30 degrees C). Mortality was scored 24 h after treatment. The results show a low variability of the insecticide effectiveness at these temperatures.

[Evaluation of larvicide susceptibility of Culicidae in French Polynesia]. / Evaluation de la sensibilité aux larvicides de Culicidés de Polynésie française.

Larval tests on 4th-stage Aedes aegypti, Aedes polynesiensis and Culex quinquefasciatus of French Polynesia, according to the WHO method, demonstrate susceptibility of these species to organophosphorous compounds and less susceptibility to insect growth regulators.

[A study of ivermectin in the treatment of lymphatic filariasis due to Wuchereria bancrofti var. pacifica in French Polynesia]. / Etude de l'ivermectine pour le traitement de la filariose lymphatique due à Wuchereria bancrofti var. pacifica en Polynésie française.

Forty carriers of 20 or more W. bancrofti var. pacifica per ml were blind administered ivermectin at 50, 100, 150 or 200 mcg/kg doses. The rate of successful treatment was 100% with the 4 dosages. The percentage cure rate and the decrease percentage in the microfilarial count were significantly higher in persons treated with 100, 150 and 200 mcg/kg than in persons treated with 50 mcg/kg. Frequency and intensity of side-reactions were similar to those observed during treatment with DEC; they were more frequent and severe in persons with greatest microfilaremia but did not depend on the dosage. Ivermectin in 100 mcg/kg single-dose, administered once a year, is the best candidate to replace DEC in mass treatments.

[Studies on the Simulium damnosum complex in West Africa - V. Morphological identification of the females in Ivory Coast (author's transl)]. / Etude du complexe Simulium damnosum en Afrique de l'Ouest. V. Identification morphologique des femelles en Cote d'Ivoire.

The morphological identification of adult females of the Simulium damnosum complex is essential for studies on the ecology and vector potential of the species concerned. Detailed morphological studies of adult females obtained at breeding sites, where larvae had been identified cytotaxonomically, allowed the establishment of an identification key. This key, based on morphological characters of the antennae and maxillae, is dealing with the six species of the complex known to occur in the Ivory Coast. It has been used, with success, during ecological and epidemiological studies in the field.