Le paludisme urbain côtier à Cotonou (République du Bénin) : étude entomologique

Une étude de la transmission du paludisme à Cotonou, ville côtière, a été réalisée au cours d'une surveillance entomologique de 12 mois dans trois quartiers représentatifs de différents aspects de la ville. La densité du vecteur (#A. gambiae$ s.l.) varie selon le degré d'urbanisation des quartiers. Le nombre moyen annuel de piqûres est égal à 1179 au centre de la ville, 3666 dans les quartiers périphériques et 3363 en zones intermédiaires. L'indice sporozoïtique moyen est de 1,7 %. Au centre de la ville, la transmission est saisonnière et dure 3 mois pendant lesquels 33 piqûres infectées sont reçues par homme. L'indice sporozoïtique maximum observé est de 12 % avec un taux quotidien d'inoculation de 1,02. En ceinture autour de la ville, la transmission est également saisonnière mais dure huit mois pendant lesquels 58 piqûres d'anophèles infectés sont reçues par homme. Contrairement à d'autres villes continentales d'Afrique intertropicale, l'intensité de la transmission à Cotonou est élevée et est de 46 piqûres infectées/homme/an. (Résumé d'auteur

Combining indoor residual spraying with chlorfenapyr and long-lasting insecticidal bed nets for improved control of pyrethroid-resistant Anopheles gambiae: an experimental hut trial in Benin.

BACKGROUND: Neither indoor residual spraying (IRS) nor long-lasting insecticidal nets (LLINs) are able to fully interrupt transmission in holoendemic Africa as single interventions. The combining of IRS and LLINs presents an opportunity for improved control and management of pyrethroid resistance through the simultaneous presentation of unrelated insecticides. METHOD: Chlorfenapyr IRS and a pyrethroid-impregnated polyester LLIN (WHO approved) were tested separately and together in experimental huts in southern Benin against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus. The bed nets were deliberately holed with either six or 80 holes to examine the effect of increasing wear and tear on protectiveness. Anopheles gambiae were genotyped for the kdr gene to assess the combination's potential to prevent the selection of pyrethroid resistance. RESULTS: The frequency of kdr was 84%. The overall mortality rates of An. gambiae were 37% and 49% with the six-hole and 80-hole LLINs, respectively, and reached 57% with chlorfenapyr IRS. Overall mortality rates were significantly higher with the combination treatments (82-83%) than with the LLIN or IRS individual treatments. Blood feeding (mosquito biting) rates were lowest with the 6-hole LLIN (12%), intermediate with the 80-hole LLIN (32%) and highest with untreated nets (56% with the 6-hole and 54% with the 80-hole nets). Blood feeding (biting) rates and repellency of mosquitoes with the combination of LLIN and chlorfenapyr IRS showed significant improvement compared to the IRS treatment but did not differ from the LLIN treatments indicating that the LLINs were the primary agents of personal protection. The combination killed significantly higher proportions of Cx. quinquefasciatus (51%, 41%) than the LLIN (15%, 13%) or IRS (32%) treatments. CONCLUSION: The chlorfenapyr IRS component was largely responsible for controlling pyrethroid-resistant mosquitoes and the LLIN component was largely responsible for blood feeding inhibition and personal protection. Together, the combination shows potential to provide additional levels of transmission control and personal protection against pyrethroid-resistant mosquitoes, thereby justifying the additional resources required. Chlorfenapyr has potential to manage pyrethroid resistance in the context of an expanding LLIN/IRS strategy

Molecular evidence of incipient speciation within Anopheles gambiae s.s. in West Africa

We karyotyped and identified by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis Anopheles gambiae s.s. samples collected in several African countries. The data show the existence of two non-panmictic molecular forms, named S and M, whose distribution extended from forest to savannahs, Mosquitoes of the S and M forms are homosequential standard for chromosome-2 inversions in forest areas. In dry savannahs, S is characterized mainly by inversion polymorphisms typical of Savanna and Bamako chromosomal forms, while M shows chromosome-2 arrangements typical of Mopti and/or Savanna and/or Bissau, depending on its geographical origin. Chromosome-2 inversions therefore seem to be involved in ecotypic adaptation rather than in mate-recognition systems. Strong support for the reproductive isolation of S and M in Ivory Coast comes from the observation that the kdr allele is found at high frequencies in S specimens and not at all in chromosomal identical M specimens. However, the kdr allele does not segregate with molecular forms in Benin

Etude de la morbidité palustre et de la gravité des accès pernicieux chez les porteurs du trait drépanocytaire

Une étude a été conduite en zone de forte transmission permanente du paludisme à #Plasmodium falciparum$ pour comparer la fréquence et la gravité des accès palustres chez les enfants de la naissance à 15 ans appartenant à différents groupes hémoglobiniques; 291 enfants se présentant dans un dispensaire périphérique et 467 à l'hôpital ont été examinés. Le diagnostic des accès palustres a été établi sur des critères cliniques, parasitologiques et évolutifs. Le seuil de parasitémie pathogène paraît similaire pour tous les types d'hémoglobine. Il a été estimé à 3000 hématies parasitées par mm3. Les accès palustres simples ou pernicieux sont significativement plus fréquents chez les sujets ayant une hémoglobine normale que chez les autres. La létalité due au paludisme est supérieure à 3 % chez les enfants AA, alors qu'aucun décès n'a pu être attribué au paludisme chez les porteurs du trait drépanocytaire. La fréquence du gène S s'est révélée significativement moindre (p < 0,05) chez des enfants présentant un accès palustre que dans tous les autres groupes d'enfants. Il apparaît que la plus faible fréquence et la moindre gravité des accès palustres chez les porteurs du trait drépanocytaire pourraient expliquer, en zone d'holoendémie, une mortalité réduite dans l'enfance chez ces sujets par rapport aux autres sujets. (Résumé d'auteur

Chemical composition and insecticidal activity of plant essential oils from Benin against Anopheles gambiae (Giles)

BACKGROUND: Insecticide resistance in sub-Saharan Africa and especially in Benin is a major public health issue hindering the control of the malaria vectors. Each Anopheles species has developed a resistance to one or several classes of the insecticides currently in use in the field. Therefore, it is urgent to find alternative compounds to conquer the vector. In this study, the efficacies of essential oils of nine plant species, which are traditionally used to avoid mosquito bites in Benin, were investigated. METHODS: Essential oils of nine plant species were extracted by hydrodistillation, and their chemical compositions were identified by GC-MS. These oils were tested on susceptible “kisumu” and resistant “ladji-Cotonou” strains of Anopheles gambiae, following WHO test procedures for insecticide resistance monitoring in malaria vector mosquitoes. RESULTS: Different chemical compositions were obtained from the essential oils of the plant species. The major constituents identified were as follows: neral and geranial for Cymbopogon citratus, Z-carveol, E-p-mentha-1(7),8-dien-2-ol and E-p-mentha-2,8-dienol for Cymbopogon giganteus, piperitone for Cymbopogon schoenanthus, citronellal and citronellol for Eucalyptus citriodora, p-cymene, caryophyllene oxide and spathulenol for Eucalyptus tereticornis, 3-tetradecanone for Cochlospermum tinctorium and Cochlospermum planchonii, methyl salicylate for Securidaca longepedunculata and ascaridole for Chenopodium ambrosioides. The diagnostic dose was 0.77% for C. citratus, 2.80% for E. tereticornis, 3.37% for E. citriodora, 4.26% for C. ambrosioides, 5.48% for C. schoenanthus and 7.36% for C. giganteus. The highest diagnostic doses were obtained with S. longepedunculata (9.84%), C. tinctorium (11.56%) and C. planchonii (15.22%), compared to permethrin 0.75%. A. gambiae cotonou, which is resistant to pyrethroids, showed significant tolerance to essential oils from C. tinctorium and S. longepedunculata as expected but was highly susceptible to all the other essential oils at the diagnostic dose. CONCLUSIONS: C. citratus, E. tereticornis, E. citriodora, C. ambrosioides and C. schoenanthus are potential promising plant sources for alternative compounds to pyrethroids, for the control of the Anopheles malaria vector in Benin. The efficacy of their essential oils is possibly based on their chemical compositions in which major and/or minor compounds have reported insecticidal activities on various pests and disease vectors such as Anopheles

Loss of protection with insecticide-treated nets against pyrethroid-resistant Culex quinquefasciatus mosquitoes once nets become holed: an experimental hut study

ABSTRACT: BACKGROUND: An important advantage of pyrethroid-treated nets over untreated nets is that once nets become worn or holed a pyrethroid treatment will normally restore protection. The capacity of pyrethroids to kill or irritate any mosquito that comes into contact with the net and prevent penetration of holes or feeding through the sides are the main reasons why treated nets continue to provide protection despite their condition deteriorating over time. Pyrethroid resistance is a growing problem among Anopheline and Culicine mosquitoes in many parts of Africa. When mosquitoes become resistant the capacity of treated nets to provide protection might be diminished, particularly when holed. An experimental hut trial against pyrethroid-resistant Culex quinquefasciatus was therefore undertaken in southern Benin using a series of intact and holed nets, both untreated and treated, to assess any loss of protection as nets deteriorate with use and time. RESULTS: There was loss of protection when untreated nets became holed; the proportion of mosquitoes blood feeding increased from 36.2% when nets were intact to between 59.7% and 68.5% when nets were holed to differing extents. The proportion of mosquitoes blood feeding when treated nets were intact was 29.4% which increased to 43.6-57.4% when nets were holed. The greater the number of holes the greater the loss of protection regardless of whether nets were untreated or treated. Mosquito mortality in huts with untreated nets was 12.9-13.6%; treatment induced mortality was less than 12%. The exiting rate of mosquitoes into the verandas was higher in huts with intact nets. CONCLUSION: As nets deteriorate with use and become increasingly holed the capacity of pyrethroid treatments to restore protection is greatly diminished against resistant Culex quinquefasciatus mosquitoes

Parasitémies à Plasmodium falciparum ou P. malariae chez les porteurs du trait drépanocytaire dans différents biotopes du Bénin

La prévalence du paludisme en fonction du phénotype de l'hémoglobine et la fréquence du gène S ont été recherchées dans deux différents biotopes du Bénin. Dans aucun d'eux, la prévalence du paludisme n'est significativement différente entre les porteurs du trait drépanocytaire et les autres. De même, la prévalence du trait drépanocytaire n'est pas modifiée par l'âge. En revanche, en région holoendémique, la densité parasitaire moyenne à #P. falciparum$ est significativement plus faible chez les sujets AS que chez les sujets AA. La présence du trait drépanocytaire ne réduit pas le risque d'infection palustre mais semble diminuer l'importance de la parasitémie. (Résumé d'auteur