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Biomedical subjects

F Chandre

Publications and source records attributed to F Chandre.

34 records · Page 2Linked to original sources
PubMed2000

[Impact of pyrethrin resistance on the efficacity of impregnated mosquito nets in the prevention of malaria: results of tests in experimental cases with deltamethrin SC].

The effects of impregnated bednets treated with deltamethrin at a dosage of 25 mg a.i./m2 were evaluated at two testing stations in Côte d'Ivoire. The first one was located in Yaokoffikro, where Anopheles gambiae s.s. are resistant to pyrethroids (including deltamethrin), and the second in M'be, close to a large rice-growing area where An. gambiae s.s. are susceptible pyrethroids. In both situations, treating bednets with deltamethrin was very effective in limiting contact between man and vector. 72% fewer female An. gambiae entered the huts in the susceptible area, whereas a decrease of 43% was recorded in the resistant area, indicating that deltamethrin still has a certain repellent effect on resistant populations of An. gambiae s.s. Overall mortality induced by bednets treated with insecticide was significantly higher in the resistant area (56.4% as versus 44.3%). An explanation for this apparent paradox is that the mosquitoes being less repelled by the insecticide remain on the treated material for longer periods of time and most of them eventually die. The results of this study indicate that bednets treated with deltamethrin are an effective prophylactic measure even in areas where An. gambiae s.s. are resistant to pyrethroids and should still be considered as a practical means of personal protection against malaria even in pyrethroid resistance areas with high frequency of kdr resistance genes.

Animals↗
PubMed1999

Status of pyrethroid resistance in Anopheles gambiae sensu lato.

The present study confirms the presence of pyrethroid resistance among Anopheles gambiae s.l mosquitos in Côte d'Ivoire and reports the observation of such resistance in two other countries in West Africa (Benin and Burkina Faso). Malaria vector populations from Cameroon (Central Africa), Senegal (West Africa) and Botswana (southern Africa) were found to be susceptible to pyrethroids. In the most resistant mosquito populations, resistance to permethrin was associated with reduced mortality, not only with respect to this compound but also towards deltamethrin. Moreover, a significant increase in knockdown time was observed in some mosquito populations before any decrease in mortality, suggesting that knockdown time could be a good indicator for the early detection of pyrethroid resistance. In view of the current extension of such resistance, there is an urgent need to set up a network in Africa to evaluate its development. It is also vital that the impact of this resistance on pyrethroid-impregnated bednets be assessed.

Africa↗
PubMed1999

[Systemic action of ivermectin on Culex quinquefasciatus and Simulium squamosum].

The mortality of Culex quinquefasciatus mosquitoes having fed ten days earlier on a chicken treated by 2,000 micrograms/kg of ivermectin (about ten times the therapeutic dosage) is about 25% higher than the mortality recorded on mosquitoes having fed on a non treated chicken. This systemic effect occurs only if the blood meal takes place between 7 and 31 hours after the administration of the drug. However, no systemic effect is recorded either with the C. quinquefasciatus mosquito or with the Simulium squamosum black fly when they are fed on human beings treated at the therapeutic dose.

Animals↗
PubMed1999

Pyrethroid cross resistance spectrum among populations of Anopheles gambiae s.s. from Côte d'Ivoire.

Field samples of Anopheles gambiae s.s. from Côte d'Ivoire were tested with 5 pyrethroids (cyfluthrin, lambda-cyhalothrin, alpha-cypermethrin, deltamethrin, permethrin), 1 pseudo-pyrethroid (etofenprox), and an organochlorine (DDT). With the use of World Health Organization diagnostic tests, 5 out of 6 samples were found cross-resistant to these insecticides. A strong decrease in knockdown effect and mortality was also observed when testing deltamethrin-impregnated nettings. With a polymerase chain reaction amplification of specific alleles diagnostic test, resistance was found associated with the presence of a kdr mutation. The strong correlation between kdr allelic frequency and resistance to DDT or etofenprox indicated that kdr was the main resistance factor for these 2 insecticides. On the contrary, a lower correlation was observed between kdr frequency and resistance to 4 of the 5 pyrethroids tested, suggesting that another mechanism was also involved, likely a metabolic detoxification. These results point out the necessity to monitor pyrethroid resistance and the presence of kdr before implementation of any impregnated bed-net programs for malaria control.

Alleles↗
PubMed1999

Current distribution of a pyrethroid resistance gene (kdr) in Anopheles gambiae complex from west Africa and further evidence for reproductive isolation of the Mopti form.

In the field, the kdr mutation, involved in pyrethroid resistance, has been found widely distributed in the Savanna form of Anopheles gambiae s.s., but never in wild populations of the Mopti form or An. arabiensis, even in areas where both occur in sympatry with resistant Savanna populations. Under laboratory conditions, Mopti and Savanna forms were fully able to interbreed and the kdr mutation was transmissible from one form to the other. Both forms appeared to be exposed to pyrethroid selection pressure in the field. The absence of the kdr mutation in the Mopti form and the total lack of Mopti-Savanna heterozygotes in field populations provides further evidence of a pre-copulatory barrier to gene flow between these two forms. Molecular markers, including kdr, are powerful tools for studying population genetics and circulation of resistance genes, and should be used through an integrated approach for a better understanding of the speciation process.

Africa, Western↗
PubMed1999

[Efficacy of permethrin-impregnated Olyset Net mosquito nets in a zone with pyrethroid resistant vectors. I--Entomologic evaluation].

The efficacy of permethrin-treated Olyset Net mosquito nets on malaria transmission and morbidity was studied in Kafine, a village located in the savanna region of the Cote d'Ivoire in Africa. After collecting sociodemographic, entomological, and parasitological data, bednets were distributed first in the southern half of the village and then in the whole village. Throughout the study period, mosquito specimens were captured on the skin of inhabitants at four points in the village between 6 PM and 6 AM both inside (but outside bednets) and outside houses. Prior to distribution of bednets, the mean biting rate (MBR) by Anopheles gambiae was 77.4 bites per man per night (b/m/n). The mean parturity rate (MPR) was 40.6 p. 100, the sporozootic index (SI) was 0.99 p. 100, and the mean entomological inoculation rate (MEIR) was 0.7 infectious bites per man per night (b+/m/n). Six months after distribution of bednets in the southern half of the village, MBR was 80.2 b/m/n, MPR was 32 p. 100, SI was 1.8 p. 100, and MEIR was 0.83 b+/m/n. After extending distribution to the whole village, data from November 1996 to July 1997 were as follows: MBR, 67.8 b/m/n; MPR, 20.1 p. 100; SI, 0.65 p. 100; and MEIR, 0.66 p. 100. From August 1977 to July 1998, data were as follows: MBR, 102.6 b/m/n; MPR, 26.2 p. 100; SI, 1.15 p. 100; and MEIR, 0.74 b+/m/n. Comparative analysis of these data showed that use of bednets had no effect on the bite or entomological inoculation rate. This is in agreement with the documented resistance of vectors in the study zone to permethrin. Despite the known stimulation/repulsion effect of permethrin, use of treated bednets had no real impact on transmission. This inefficacy could be related to the high prevalence (80 p. 100) of the Kdr gene (responsible for resistance) in the savanna form of Anopheles gambiae.

Adolescent↗
PubMed1998

Molecular characterization of pyrethroid knockdown resistance (kdr) in the major malaria vector Anopheles gambiae s.s.

Pyrethroid-impregnated bednets are playing an increasing role for combating malaria, especially in stable malaria areas. More than 90% of the current annual malaria incidence (c. 500 million clinical cases with up to 2 million deaths) is in Africa where the major vector is Anopheles gambiae s.s. As pyrethroid resistance has been reported in this mosquito, reliable and simple techniques are urgently needed to characterize and monitor this resistance in the field. In insects, an important mechanism of pyrethroid resistance is due to a modification of the voltage-gated sodium channel protein recently shown to be associated with mutations of the para-type sodium channel gene. We demonstrate here that one of these mutations is present in certain strains of pyrethroid resistant A. gambiae s.s. and describe a PCR-based diagnostic test allowing its detection in the genome of single mosquitoes. Using this test, we found this mutation in six out of seven field samples from West Africa, its frequency being closely correlated with survival to pyrethroid exposure. This diagnostic test should bring major improvement for field monitoring of pyrethroid resistance, within the framework of malaria control programmes.

Alleles↗
PubMed1998

Pyrethroid resistance in Culex quinquefasciatus from west Africa.

Pyrethroid resistance was investigated in thirty-three samples of Culex quinquefasciatus Say from twenty-five cities in Côte d'Ivoire and Burkina Faso. Permethrin resistance ratios at LC50 ranged from 9.5- to 82-fold in Côte d'Ivoire and from 17- to 49-fold in Burkina Faso. For deltamethrin, resistance ratios were lower and ranged from nine to thirty-eight in both countries. A strain was selected with permethrin to investigate resistance mechanisms. After forty-two generations of selection, permethrin resistance level reached 3750-fold, but deltamethrin resistance remained unexpectedly unchanged. This indicated that a specific mechanism was involved in permethrin resistance. Synergist assays and biochemical tests indicated that resistance was partly due to P450-dependent oxidases. A target site insensitivity (kdr) was also involved, associated with DDT cross resistance and a dramatic loss of permethrin knockdown effect on adults. This resistance should be taken into consideration when planning the use of pyrethroid-impregnated materials in urban areas, as Culex is by far the main source of nuisance. Any failure in nuisance control due to resistance is likely to demotivate people in using impregnated materials.

Africa, Western↗
PubMed1998

Origin and prevention of airport malaria in France.

Since 1969, 63 cases of airport malaria have been reported in Western Europe, 24 of which occurred in France. Most were due to Plasmodium falciparum. In 1994, 7 cases occurred in and around Roissy Charles de Gaulle airport (CDG), showing 4 types of contamination: among employees working on airstrips or opening containers, among residents living near the airport, among people living at some distance from the airport after a secondary transport of vectors, and by vectors transported in luggage. In-flight or stop-over infection is not considered as airport malaria. The infective anophelines originated from airports where malaria transmission occurs, mostly in subsaharan Africa. A tentative list is given taking into account aerial traffic with France. Surveys in the airports of Dakar (Senegal), Cotonou (Benin), Abidjan (Cote d'Ivoire) and Yaoundé (Cameroun) found potential vectors in all of these from July to September. After 1994, the Contrôle Sanitaire aux Frontières (CSF) in charge at CDG concentrated its efforts on the flights at risk, as well as information and sensitization of airline companies, which resulted in 73% and 87% of the flights at risk being properly disinsected in 1995 and 1996. Despite pyrethroid resistance in Anopheles gambiae s.s. in West Africa, the efficacy of aircraft spraying with permethrin aerosols is still acceptable. However, surveillance of resistance should be improved and search for nonpyrethroid insecticides suitable for aircraft strongly encouraged.

Africa, Western↗
PubMed1998

The acetylcholinesterase gene Ace: a diagnostic marker for the Pipiens and Quinquefasciatus forms of the Culex pipiens complex.

The taxonomy of the Culex pipiens complex remains a controversial issue in mosquito systematics. Based on morphologic characters, 2 allopatric taxa are recognized, namely Cx. pipiens (including the form "molestus") in temperate areas and Cx. quinquefasciatus in tropical areas. Here we report on variability at the nucleotide level of an acetylcholinesterase gene in several strains and natural populations of this species complex. Few polymorphisms were found in coding regions within a subspecies but many polymorphisms were observed between subspecies in noncoding regions. We describe a method based on a restriction enzyme polymorphism in polymerase chain reaction-amplified DNA, in which the presence or absence of one restriction site discriminates Cx. pipiens, Cx. quinquefasciatus, and their hybrids. This technique reliably discriminates mosquitoes from more than 30 worldwide strains or populations. Polymerase chain reaction amplification of specific alleles may also be a useful tool for characterizing specific alleles of each sibling taxon.

Acetylcholinesterase↗
PubMed1997

Distribution of organophosphate and carbamate resistance in Culex pipiens quinquefasciatus (Diptera: Culicidae) in West Africa.

The distribution of organophosphate and carbamate resistance was investigated in 33 samples of Culex pipiens quinquefasciatus Say from 25 cities in Côte d'Ivoire and Burkina Faso. Organophosphate resistance levels were higher in Côte d'Ivoire than in Burkina Faso. Chlorpyrifos resistance ratios at LC95 ranged from 4 to 30 times in Côte d'Ivoire and from 3 to 6 times in Burkina Faso. For temephos, ratios ranged from 3 to 18 and from 1 to 2, respectively. Of 27 samples from Côte d'Ivoire, 25 also displayed cross resistance to carbamates as shown by a mortality plateau in bioassays with propoxur and carbosulfan (similar to chlorpyrifos). Cross resistance to organophosphates and carbamates was caused by an insensitive acetylcholinesterase allele (AceR). This gene was absent from Burkina Faso, except in Niangoloko near the Côte d'Ivoire border. Organophosphate resistance also was associated with the presence of A2-B2 overproduced esterases which had higher frequencies in Côte d'Ivoire (75-100%) than in Burkina Faso (40-50%). Two other esterases with the same electrophoretic mobility as C2 from Puerto Rico and B1 from California were identified for the 1st time in West Africa. "C2" was widespread, whereas "B1" was present in only a few mosquitoes from Côte d'Ivoire. These differences in resistance patterns should be taken into consideration in planning urban mosquito control strategies within 2 countries.

Africa, Western↗
PubMed1997

Ivermectin and moxidectin in two filarial systems: resistance of Monanema martini; inhibition of Litomosoides sigmodontis insemination.

Effects of ivermectin and moxidectin were compared on two filarial species: Monanema martini which presents dermal microfilariae and induces Onchocerca-like lesions in its natural murid host Lemniscomys striatus, and Litomosoides sigmodontis (= L. carinii). M. martini microfilariae showed an unusual resistance to ivermectin, in vitro and in vivo; moxidectin was no more efficient. However, the two drugs used at high concentrations deeply altered the uterine embryogenesis, but had no lethal effect on adult filariae. L. sigmodontis blood microfilariae showed a great susceptibility to moxidectin, similar to that previously described for ivermectin. The two drugs also induced a long term effect because they inhibited the insemination of the female filariae. This result reinforces the observations made by other authors on the human parasite, Onchocerca volvulus.

Animals↗
PubMed1993

Effect of ivermectin on two filaria-vector pairs. Brugia malayi-Aedes aegypti; Litomosoides sigmodontis-Bdellonyssus bacoti.

The effect of ivermectin was studied on two filaria-vector pairs, Brugia malayi-Aedes aegypti and Litomosoides sigmodontis-Bdellonyssus bacoti. The rodent hosts, respectively Mastomys coucha and Meriones unguiculatus, were treated with ivermectin doses of 0.05 mg/kg, or 0.2 mg/kg or 2 mg/kg. Batches of vectors were fed on rodents, infected or not, treated or not, from H7 to D43 post-ivermectin. Vector survival was observed and dissections were performed to study the filarial development. It appears that ivermectin has no systemic effect on vectors, or very little. The drug acts on transmission because it affects the microfilariae. Transmission of L. sigmodontis is blocked because microfilariae are eliminated from the blood. Transmission of B. malayi is blocked although microfilaremia remains present at a low level. Two particular features are observed: microfilariae are hyper-ingested, but they do not cross the stomach wall (in contrast, they cross at a high rate in the control batch of Aedes, due to the "stomach wall limitation"). These events might be explained by a muscular passivity of the microfilariae treated with ivermectin. Transmission of the two filarioid species is restored normally about D25-40 post ivermectin because a new population of microfilariae has appeared. These ivermectin experiments emphasize the diversity and complexity of two important phases of the filarial cycle in the vector: the ingestion of microfilariae and the passage through the stomach wall.

Aedes↗
PubMedDate not supplied

Natural swarming behaviour of the molecular M form of Anopheles gambiae.

In Anopheles gambiae, as in most species of mosquitoes, mating is initiated in flight. The males aggregate in aerial swarms and conspecific females individually fly to these swarms where they mate with males. In this study, we investigated the swarming behaviour of A. gambiae and conducted 2 surveys in the rice field area of the Vallée du Kou in Burkina Faso in 1999 and 2002. A high number of anopheline mosquitoes were observed in this area and both molecular M and S forms of A. gambiae were found in sympatry. Swarms formed a few minutes after sunset in different places and no obvious markers were associated with their occurrence. However, swarms occurred close to cow herds generally in open flat areas, 2-3 m above the ground. Overall, 2829 anopheline mosquitoes were collected from 21 swarms composed primarily of males. A few specimens of Culex quinquefasciatus were collected from 3 swarms. Although both molecular M and S forms were found in sympatry in the village, swarms were composed almost exclusively of the molecular M form. This suggests that there are alternative swarming habits for both molecular M and S forms of A. gambiae in nature.

Africa, Western↗
PubMedDate not supplied

[Anopheline population genetics].

Population genetic studies of vectors are essential for (i) the determination of their taxonomic status and consequently the definition of their vectorial role in the transmission of pathogenic agents; (ii) the evaluation of the species genetic variability and the estimation of their capacities of adaptation to selection pressure; (iii) an estimation of gene flow among populations in order to evaluate their degree of isolation and gene circulation, especially resistance genes. Among the malaria vectors taken as examples on three continents, Africa, South-East Asia and Latin America, the large majority of the species showed an important polymorphism. The Gambiae Complex, which is by far the most studied one, includes at present 7 species with the recent description of An. quadriannulatus A and B from Ethiopia. An. gambiae s.s. includes itself 5 chromosomal forms. One of them, the Mopti form, should be considered as a species unto itself. For An. arabiensis, a strong differentiation has been observed among the populations from Senegal and the Indian Ocean Islands. The kdr mutation, which confers resistance to pyrethroid knockdown effect, has never been found either in the Mopti form, or An. arabiensis, indicating a restricted gene flow between these latter two and An. gambiae s.s. The speciation process of the Gambiae Complex seems to be a recent phenomenon due to environmental selection pressure. Species of the Funestus Group are distinguishable by morphological characters. The genetic study of An. funestus s.s. did not show the presence of a complex, in spite of high polymorphism and population structure. Anophelines from eastern areas present an important biodiversity. The Minimus Complex includes two species, A and C, which are widely distributed in South-East Asia. Species A is strongly endophilic, on the contrary species C is at once more exophilic and zoophilic. The latter species might have been selected by DDT indoor house spraying. After numerous taxonomic investigations, the Dirus Complex includes now 7 species. In Latin America, An. pseudopunctipennis clustered into three geographic populations which are under a speciation process. One covers North America and Guatemala, the other South America and Belize, whilst the last one is restricted to Grenada Island. On the contrary, An. darlingi showed little morphologic and genetic variability throughout the species geographic range suggesting the existence of a single species. The main objective of these studies is to implement a more selective approach of vector control programs in relation to the incriminated species, their bioecology and their role in malaria transmission. The improvement of efficiency and selectivity of vector control is becoming a major goal in order to make the best out of the available tools and control the impact of interventions on the environment.

Africa↗