Impact of rotavirus vaccine introduction in Abidjan, Côte d'Ivoire

Côte d'Ivoire introduced rotavirus vaccine in March 2017. Rotavirus surveillance is conducted at Centre Hospitalier Universitaire de Yopougon in Abidjan, the capital city. Children <5 years of age are enrolled in rotavirus surveillance if admitted to the hospital with acute gastroenteritis. We used sentinel surveillance data from 2014 through mid-2019 to compare trends in rotavirus pediatric gastroenteritis hospitalizations before and after rotavirus vaccine introduction. We used Poisson regression to analyze changes in rotavirus prevalence, adjusting for calendar month and accounting for total monthly admissions; January 2014 - December 2016 was considered "pre-vaccine," and January 2017 - June 2019 was considered "post-vaccine." Age distribution and severity were compared between periods using the Mann-Whitney U test. Rotavirus-positive admissions declined 51% (95% CI: 28%-67%), from 31.5% pre-vaccine to 14.9% afterward. The median age of rotavirus-positive children increased from 7 months (interquartile range [IQR]: 5-11) in the pre-vaccine period to 11 months (IQR: 7-18, p = .005) in the post-vaccine period. The median severity score decreased from 11 to 9 (p = .008) among all children, and from 12 pre- to 10.5 post-vaccine (p = .35) among rotavirus-positive children. Our findings suggest that rotavirus vaccine introduction contributed to reduced rotavirus hospitalization in Abidjan and possibly more broadly.

Genotypic characterization of rotavirus in children under 5 years circulating in Côte D'Ivoire from 2010 to 2013

Background

Rotavirus infection is the most common cause of severe gastroenteritis in children under five years of age in both developed and developing countries. The World Health Organisation (WHO) recommends the surveillance of rotavirus strains prior to vaccine introduction in all applicable countries. The objective of this study was to describe the epidemiological characteristics as well as to determine the circulating genotypes of rotaviruses in Côte d’Ivoire prior to vaccine introduction.

Methods

The study included children under five years of age who met the inclusion criteria after informed consent had been sort from their parents or guardians. Rotavirus VP6 antigens were detected for each stool sample using Enzyme Immunoassay (EIA). Genotyping of positive EIA samples was performed by reverse-transcriptase-PCR (RT-PCR) assays.

Results

A total of 684 children were recruited. Children aged between 6 and 11 months were the most represented with 34%. Rotavirus VP6 antigens were found in 27.1% (186/684) of samples tested. Commonly detected G genotypes included G12 (46.6% (82/176) and G1 (13.1% (23/176) whilst P[8] (49.8% (91/183) was the most predominant P genotype. Rotavirus G12P[8] was the most predominant strain circulating in Côte d’Ivoire within the period of study and constituted 26.6% of all strains detected.

Conclusion

The monitoring of circulating strains will help guide decision-makers in the choice of vaccine. Genotypic variability of circulating rotavirus strains over the years implies there is a need for continuous rotavirus strain surveillance even after vaccine introduction.

[Value of gastric fluid to start antibiotics in premature babies suspected of having early neonatal bacterial infection]

The objective of this study was to evaluate the value of direct examination and culture of gastric fluid in the treatment of early neonatal bacterial infections (INBP) in pre-term infants.

MATERIALS AND METHODS

Observational study conducted over 6 months in a Type III center. All hospitalized premature babies who had routine gastric fluid sampling at birth during the period of the study were included. They were classified into two groups: premature infants with probable or suspected infection and treated as such (Group 1) and premature infants with no infection or only having colonization (Group 2).

RESULTS AND DISCUSSION

In total, 255 pre-term infants were included in the study. Group 1 consisted of 127 newborns and group 2 consisted of 128 newborns. The direct gastric fluid examination was positive in 51 newborns in Group 1 and in 46 newborns in group 2. The culture was positive in 25 newborns in group 1 and eight newborns in group 2. Direct examination of gastric fluid of the 255 children studied had low sensitivity (40.1%) and low specificity (64%) of INBP, with 52.6% positive predictive value (PPV) and 51.8% negative predictive value (NPV). The gastric fluid culture was specific (93.7%) of the INBP, sensitivity was low (19.6%), with PPV at 75.7% and NPV at 54%.

CONCLUSION

These results undermine the relevance of the direct examination of gastric fluid in the delicate diagnosis of INBP. This direct examination has a low PPV and NPV. It is advisable not to start or stop antibiotic therapy solely on this argument; however, it can guide the choice of antibiotic therapy and remains useful for this reason. The culture of gastric fluid has very good specificity (93.7%).

Is K-O Tab 1-2-3((R)) long lasting on non-polyester mosquito nets?

Many societies use locally sourced mosquito nets made from a variety of materials. For protecting against malaria these require regular re-treatment with insecticide. K-O Tab 1-2-3 is a 'dip-it-yourself' long-lasting formulation with time-limited interim recommendation from WHO for treatment of washed white and coloured polyester nets for up to 15 washes. To determine wash-resistance on different fabrics, nets made of polyester, polyethylene, cotton or nylon were treated with K-O Tab 1-2-3 and washed up to 20 times using standard WHO washing procedures. Efficacy was assessed using cone and cylinder bioassays and tunnel tests, and deltamethrin content using high-pressure liquid chromatography. Polyethylene and cotton nets treated with K-O Tab 1-2-3 and washed 20 times achieved the WHO threshold of >80% mortality in tunnel tests. Polyethylene matched the performance of polyester in all bioassays in contrast to cotton and nylon which produced low mortality and knock-down in cone and cylinder bioassays. After 20 washes 16.5% of the loading dose of deltamethrin remained on the polyester nets compared with 28.7% on polyethylene, 38.9% on cotton and 2.2% on nylon. Cotton nets retained a high concentration of insecticide but the relatively poor performance in terms of knock-down and mortality suggest most insecticide is bound within the cotton fibres rather than on the surface. K-O Tab 1-2-3 renders insecticide wash fast on polyethylene nets, less so on cotton and nylon. Nets made from polyethylene can be treated in the home to render the insecticide long lasting.

[Generalized tetanus with otitic portal of entry after using intra-auricular traditional remedies in a 2 old child]

A case of tetanus with uncommon way of contamination was found in the paediatric department of the Yopougon teaching hospital in Côte d'Ivoire. A two-year-old child, without vaccination against tetanus and suffering from a chronic otitis presented a generalized tetanus, after the use of traditional local remedies in his ear. Through this observation, the authors want to make population aware of the detrimental effects of traditional local auricular remedies and want to advise all physicians to make a serotherapy and/or a vaccination against tetanus to all children with chronic otitis in our area.

Chlorfenapyr: a pyrrole insecticide for the control of pyrethroid or DDT resistant Anopheles gambiae (Diptera: Culicidae) mosquitoes

Owing to the development and spread of pyrethroid resistance in Anopheles gambiae in Africa there is an urgent need to develop alternative insecticides to supplement the pyrethroids. Chlorfenapyr is a pyrrole insecticide first commercialized for the control of agricultural pests and termites. Performance against An. gambiae bearing kdr (pyrethroid and DDT resistance) or Ace-1(R) insensitive acetylcholinesterase (organophosphate and carbamate resistance) mechanisms was studied using a variety of adult bioassay tests including a simulated-experimental hut system (tunnel tests) that allows uninhibited mosquito behaviour/insecticide interactions. Strains resistant to pyrethroids and organophosphates showed no cross resistance to chlorfenapyr. In cone bioassays on treated netting the mortality of adult mosquitoes showed an unexpected curvilinear response, with highest mortality occurring at intermediate dosages. Adults expressed irritability to chlorfenapyr at higher dosages, which might explain the dosage-mortality trend. Toxic activity of chlorfenapyr was slow compared to conventional neurotoxic insecticides and additional mortality occurred between 24h and 72 h. In tunnel tests, the dosage-mortality trend showed a more typical sigmoid response and most mortality occurred during the first 24h. Mosquito penetration through the holed, treated netting showed only limited inhibition and blood-feeding was not inhibited. Mortality rates in the kdr strain exposed to chlorfenapyr treated netting in tunnel tests were much higher than with permethrin treated netting over the same 100-500 mg/m(2) dosage range. Chlorfenapyr has potential for malaria control in treated-net or residual spraying applications in areas where mosquitoes are pyrethroid resistant. For treated-net applications chlorfenapyr might be combined with pyrethroid as a mixture to provide personal protection as well as to give control of resistant mosquitoes.

Multiple insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus from Benin, West Africa

Because free-insecticide treated net distribution is planned in Benin (West Africa) during the next few years, we investigated the type, frequency and distribution of insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus mosquitoes in four localities selected on the basis of contrasting agricultural practices, use of insecticides and environment. Bioassays with WHO diagnostic test kits were carried out using pyrethroid, carbamate, organophosphate and organochlorine insecticides. An. gambiae mosquitoes were identified to species and to M or S molecular forms using PCR techniques. Molecular and biochemical assays were carried out to identify kdr and Ace.1 mutations in individual mosquitoes and to detect any increase in the activity of enzymes typically involved in insecticide metabolism (oxidase, esterase and glutathion-S-transférases). WHO diagnostic tests showed high frequency of resistance in An. gambiae and Cx. quinquefasciatus to permethrin and DDT in three areas. This was consistent with the presence of target site insensitivity due to kdr mutation and to increased metabolism through enzymatic activity. Kdr was expressed in both M and S forms. However, less than 1% of An. gambiae or Cx. quiqnuefasciatus showed the presence of the Ace.1(R) mutation. Carbamate/OP resistance was present at higher frequency in Culex than in An. gambiae. Dieldrin resistance was present in both species at all four localities. A higher frequency of pyrethroid-resistance was found in An. gambiae mosquitoes collected in urban areas compared to those collected in rice growing areas. The expansion of vegetable growing within urban areas probably contributed to selection pressure on mosquitoes. The detection of multiple resistance mechanisms in both An. gambiae and Cx. quinquefasciatus in Benin may represent a threat for the efficacy of ITNs and other forms of vector control such as indoor residual spraying in the future.

Efficacy of permethrin-treated uniforms in combination with DEET topical repellent for protection of French military troops in Côte d'Ivoire

In 2000, 22,000 French military personnel were deployed overseas. The French military health service implemented a vector control strategy including personal protection by the use of permethrin preimpregnated battlefield uniforms (BFUs) and the application on the skin of a topical repellent (50% DEET). In 2000, French forces used an industrial process to impregnate cloth with permethrin by soaking it before cut-out of the BFU. A study was implemented in four experimental huts in Côte d'Ivoire to assess the field efficacy of the impregnated BFUs and their resistance to washing. Taking into account the systematic variations in each variable in the field and using a modeling based on logistic regression and discriminant analysis, this study showed that after 6 h without reapplication, the protective effects of the use of DEET as skin repellent was not significant, perhaps due to the high density of Anopheles mosquitoes during the night catching sessions and an average time of effective repellency of < 2 or 3 h in the field. The analysis also showed that the French process of industrial impregnation of permethrin of the BFU offered in 2000 some protection from mosquito bites but not enough to reduce significantly the incidence of malaria among nonimmune troops. No positive or negative interaction was noted when DEET and the impregnated BFUs were used together.

Experimental hut comparisons of nets treated with carbamate or pyrethroid insecticides, washed or unwashed, against pyrethroid-resistant mosquitoes

The efficacy against mosquitoes (Diptera: Culicidae) of a bednet treated with carbamate insecticide [carbosulfan capsule suspension (CS) 200 mg/m(2)] was compared with four types of pyrethroid-treated nets in veranda-trap huts at Yaokoffikro near Bouaké, Côte d'Ivoire, where the malaria vector Anopheles gambiae Giles carries the kdr gene (conferring pyrethroid resistance) at high frequency and Culex quinquefasciatus Say is also pyrethroid resistant. Pyrethroids compared were lambdacyhalothrin CS 18 mg/m(2), alphacypermethrin water dispersible granules (WG) 20 mg/m(2), deltamethrin 50 mg/m(2) (Permanet) and permethrin emulsifiable concentrate (EC) 500 mg/m(2). Insecticidal power and personal protection from mosquito bites were assessed before and after the nets were used for 8 months and hand washed five times in cold soapy water. Before washing, all treatments except permethrin significantly reduced blood-feeding and all had significant insecticidal activity against An. gambiae. The carbosulfan net gave significantly higher killing of An. gambiae than all pyrethroid treatments except the Permanet. Against Culex spp., carbosulfan was more insecticidal and gave a significantly better protective effect than any of the pyrethroid treatments. After washing, treated nets retained various degrees of efficacy against both mosquito genera - but least for the carbosulfan net. Washed nets with three types of pyrethroid treatment (alphacypermethrin, lambdacyhalothrin, permethrin) gave significantly higher mortality rates of Culex than in huts with the same pyrethroid-treated nets before washing. After five washes, the Permanet, which is sold as a long-lasting insecticidal product, performed no better than the other nets in our experimental conditions.

Efficacy of mosquito nets treated with insecticide mixtures or mosaics against insecticide resistant Anopheles gambiae and Culex quinquefasciatus (Diptera: Culicidae) in Côte d'Ivoire

Only pyrethroid insecticides have so far been recommended for the treatment of mosquito nets for malaria control. Increasing resistance of malaria vectors to pyrethroids threatens to reduce the potency of this important method of vector control. Among the strategies proposed for resistance management is to use a pyrethroid and a non-pyrethroid insecticide in combination on the same mosquito net, either separately or as a mixture. Mixtures are particularly promising if there is potentiation between the two insecticides as this would make it possible to lower the dosage of each, as has been demonstrated under laboratory conditions for a mixture of bifenthrin (pyrethroid) and carbosulfan (carbamate). The effect of these types of treatment were compared in experimental huts on wild populations of Anopheles gambiae Giles and the nuisance mosquito Culex quinquefasciatus Say, both of which are multi-resistant. Four treatments were evaluated in experimental huts over six months: the recommended dosage of 50 mg m(-2) bifenthrin, 300 mg m(-2) carbosulfan, a mosaic of 300 mg m(-2) carbosulfan on the ceiling and 50 mg m(-2) bifenthrin on the sides, and a mixture of 6.25 mg m(-2) carbosulfan and 25 mg m(-2) bifenthrin. The mixture and mosaic treatments did not differ significantly in effectiveness from carbosulfan and bifenthrin alone against anophelines in terms of deterrency, induced exophily, blood feeding inhibition and overall mortality, but were more effective than in earlier tests with deltamethrin. These results are considered encouraging, as the combination of different classes of insecticides might be a potential tool for resistance management. The mixture might have an advantage in terms of lower cost and toxicity.

Resistance to carbosulfan in Anopheles gambiae from Ivory Coast, based on reduced sensitivity of acetylcholinesterase

Resistance to carbosulfan, a carbamate insecticide, was detected in field populations of the malaria vector mosquito Anopheles gambiae Giles (Diptera: Culicidae) from two ecologically contrasted localities near Bouaké, Ivory Coast: rural M'bé with predominantly M form of An. gambiae susceptible to pyrethroids; suburban Yaokoffikro with predominantly S form of An. gambiae highly resistant to pyrethroids (96% kdr). The discriminating concentration of 0.4% carbosulfan (i.e. double the LC100) was determined from bioassays with the susceptible An. gambiae Kisumu strain. Following exposure to the diagnostic dosage (0.4% carbosulfan for 1 h), mortality rates of female An. gambiae adults (reared from larvae collected from ricefields) were 62% and 29% of those from M'bé and Yaokoffikro, respectively, 24 h post-exposure. Exposure for 3 min to netting impregnated with the operational dosage of carbosulfan 200 mg/m2 gave mortality rates of 88% of those from M'bé and only 12.2% for Yaokoffikro. In each case the control untreated mortality rate was insignificant. Biochemical assays to detect possible resistance mechanism(s) revealed the presence of insensitive AChE in populations of An. gambiae at both localities, more prevalent in the S form at Yaokoffikro than in M form at M'bé, as expected from bioassays results. Our study demonstrates the need to monitor carbamate resistance among populations of the An. gambiae complex in Africa, to determine its spread and anticipate vector control failure if these insecticides are employed.

[An experimental tool essential for the evaluation of insecticides: the testing huts]

The following study analyses the potentialities of the experimental huts built in M'be Valley (Côte d'Ivoire) where the evaluations of the insecticide products have been carried out for many years in line with the WHOPES protocol on the methodology of stage 2 assays. Starting a testing station first requires a good knowledge of the sensitivity of Anopheles gambiae to the main insecticide families. Then thanks to the experimental huts the efficacy of the various means of treatment can be compared with the one in untreated huts; this study focuses on house spraying using 100 mg a.i./m2 and bednets impregnated with lambda-cyhalothrin at a dose of 15 mg a.i./m2. The fipronil used in house spraying doesn't show any repellent effect, however it does have an irritating effect that increases the natural exophily of An. gambiae females entering the testing huts. The blood-feeding rate recorded in the treated huts was reduced to 24% and to 38% mortality rate consisting mainly of a 24 hours delayed mortality. The bednets treated with lambda-cyhalothrin have greatly reduced the contact between man and vector since the entry rate of An. gambiae females was cut down by 68% compared to the control. The exophily of this anopheles was twofold greater with the impregnated bednets and the blood-feeding rate reduced to 47%. Finally the global mortality rate, two thirds of immediate mortality, one third of delayed mortality, reached 35%. The experimental huts in the M'be Valley therefore provide essential information regarding the selection of the most efficacious insecticides against An. gambiae. This experimental method must be extended to other sites in order to finalize ever more selective and appropriate means of control against nuisance and disease-vector mosquitoes.

Olyset Net efficacy against pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus after 3 years' field use in C te d'Ivoire

Pyrethroid-impregnated bednets are advocated for personal protection against malaria vectors. To avoid the need for periodic re-treatment, it would be advantageous to have nets that retain insecticidal efficacy for years and withstand repeated washing. Such a type of commercially produced bednet with permethrin 2% incorporated in polyethylene fibres (trademark Olyset Net supplied by Sumika Life-Tech Co., Osaka, Japan) was evaluated against mosquitoes in veranda-trap huts at Yaokoffikro, near Bouaké, C te d'Ivoire, by standard WHOPES phase II procedures. Four Olyset Nets were compared with a standard untreated polyester net as control. They comprised three examples previously used in a village for over 3 years (one washed, one dirty, one very dirty) and a previously unused Olyset Net, newly unwrapped, from the same original batch. Bioassays with 3 min exposure of susceptible Anopheles gambiae Giles (Diptera: Culicidae) gave >99% mortality of female mosquitoes tested on the 'new' Olyset Net. The used Olyset Nets gave mortality rates averaging 83% for the washed net, 85% for the dirty net and 55% for the very dirty net (within 24-h following 3 min exposure). Thus, Olyset Nets were found to remain remarkably effective against susceptible An. gambiae for at least 3 years under field conditions. Wild pyrethroid-resistant populations of Culex quinquefasciatus Say and An. gambiae (savanna cytotype with 96% kdr) were assessed during June-August 1999 for their responses to sleepers protected by nets in the experimental huts. With regard to hut entry by foraging female mosquitoes, Olyset Nets showed some deterrency against An. gambiae (44% reduction by the new net, approximately 20% by the dirty nets, none by the washed net), but not against Cx. quinquefasciatus. Among mosquitoes entering the hut with untreated control net, 30-34% tried to leave (exophily) but were caught in the verandah trap. The permethrin repellency of Olyset Nets increased exophily by 19% for An. gambiae and 14% for Cx. quinquefasciatus. Blood-feeding rates were 16% An. gambiae and 35% Cx. quinquefasciatus in the hut with sleeper under the untreated net (showing considerable prevention of biting), 22-26% of both species in huts with washed or dirty used Olyset Nets (not significantly different from control), while the biting success rate of Cx. quinquefasciatus (but not kdr An. gambiae) was more than halved by the 'new' Olyset Net. Mortality rates of pyrethroid-resistant An. gambiae and Cx. quinquefasciatus from the huts were, respectively, 3% and 8% with the untreated polyester net, 27.5% and 17% with the 'new' Olyset, 15% and 17.5% with the washed Olyset, 16-25% and 17-20% with dirty old Olyset Nets. Kill differences between nets are significantly different for both An. gambiae and Cx. quinquefasciatus. Unfortunately the washed used Olyset Net showed least activity against resistant mosquitoes, despite its greatest activity against susceptible An. gambiae. In each case there was evidence that a high proportion of mosquitoes failed to feed through the net (many of them dying from starvation when they could not leave the closed hut), with indications that dirty Olyset nets enhanced this protective value.

Combined pyrethroid and carbamate 'two-in-one' treated mosquito nets: field efficacy against pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus

A new approach is proposed in the treatment of mosquito nets, using a 'two-in-one' combination of pyrethroid and non-pyrethroid insecticides applied to different parts of bednets. The objectives are mainly to overcome certain limitations of pyrethroid-impregnated bednets currently recommended for malaria control purposes. Apart from developing alternatives to pyrethroid dependency, we sought to counteract pyrethroid irritant effects on mosquitoes (excito-repellency) and resistance to pyrethroids. The idea takes advantage of the presumed host-seeking behaviour of mosquitoes confronted by a net draped over a bed, whereby the mosquito may explore the net from the top downwards. Thus, nets could be more effective if treated on the upper part with residual non-irritant insecticide (carbamate or organophosphate) and with a pyrethroid on the lower part. Sequential exposure to different insecticides with distinct modes of action is equivalent to the use of a mixture as a potential method of managing insecticide resistance. We also intended to improve the control of nuisance mosquitoes, especially Culex quinquefasciatus Say (Diptera: Culicidae) that often survive pyrethroids, in order to encourage public compliance with use of insecticide-treated nets (ITNs). Polyester bednets were pretreated with residual pyrethroid (bifenthrin 50 mg/m2 or deltamethrin 25 mg/m2) on the lower half and with carbamate (carbosulfan 300 mg/m2) on the upper half to minimize contact with net users. Unreplicated examples of these 'two-in-one' treated nets were field-tested against wild mosquitoes, in comparison with an untreated net and bednets treated with each insecticide alone, including PermaNet wash-resistant formulation of deltamethrin 50 mg/m2. Overnight tests involved volunteers sleeping under the experimental bednets in verandah-trap huts at Yaokofikro, near Bouaké in C te d'Ivoire, where the main malaria vector Anopheles gambiae Giles, as well as Culex quinquefasciatus Say, are highly resistant to pyrethroids. Efficacy of these ITNs was assessed in the huts by four entomological criteria: deterrency and induced exophily (effects on hut entry and exit), blood-feeding and mortality rates (immediate and delayed). Overall, the best impact was achieved by the bednet treated with carbosulfan alone, followed by 'two-in-one' treatments with carbosulfan plus pyrethroid. Blood-feeding rates were 13% An. gambiae and 17% Cx. quinquefasciatus in huts with untreated nets, but only 3% with carbosulfan ITNs, 7-11% with combined ITN treatment, 6-8% An. gambiae and 12-14% Cx. quinquefasciatus with pyrethroid alone. Mosquitoes that entered the huts were killed sooner by nets with combined treatment than by pyrethroid alone. Mortality-rates in response to ITNs with carbosulfan (alone or combined with pyrethroid) were significantly greater for Cx. quinquefasciatus, but not for An. gambiae, compared to ITNs with only pyrethroid. About 20% of sleepers reported potential side-effects (headache and/or sneezing) from use of ITN treated with carbosulfan alone. Further development of this new 'two-in-one' ITN concept requires a range of investigations (choice of effective products, cost-benefit analysis, safety, etc.) leading to factory production of wash-resistant insecticidal nets treated with complementary insecticides.

[Impact of resistance of Anopheles gambiae s.s. to permethrin and deltamethrin on the efficacy of impregnated mosquito nets]

Trials to assess the impact of resistance of Anopheles gambiae s.s. to permethrin and deltamethrin on the efficacy of insecticide-treated bednets were carried out from October 1997 to April 1998 in six experimental huts at the Yaokoffikro testing station in Côte d'Ivoire. Six polyester bednets were used. Two bednets were treated with permethrin at a dose of 500 mg/m2 and two with deltamethrin at 25 mg/m2. The remaining two untreated bednets served as controls. The number of Anopheles gambiae s.s. entering the hut was reduced 18% with permethrin-treated bednets and 43% with deltamethrin-treated bednets. Threefold fewer female mosquitoes were found under insecticide-treated bednets than under untreated nets (controls). The number of mosquitoes passing through the treated net was threefold lower. The number of mosquitoes exiting from the treated bednets increased twofold. The blood-feeding rate dropped by 55%. Forty percent of mosquitoes entering the permethrin-treated bednets and 56% entering the deltamethrin-treated bednets died. Immediate mortality was always greater (> 85%) than delayed mortality (< 15%). Bioassays confirmed the results from hut experiments. A lower knockdown effect was recorded with permethrin in the resistant strain. Conversely deltamethrin showed the same knockdown effects in the susceptible (Kisumu) and resistant (Yaokoffikro) strain. Mortality rates were low with both permethrin and deltamethrin. This study shows that, even in areas where Anopheles gambiae s.s. is resistant to permethrin and deltamethrin, bednets treated with these insecticides remain effective and can still be considered as an excellent method of personal protection.

[Laboratory evaluation of alpha-cypermethrin insecticide efficacy on Anopheles gambiae populations of Côte d'Ivoire resistant to permethrin and deltamethrin]

Susceptibility tests were carried out in laboratory conditions to evaluate the efficacy of alpha-cypermethrin (a synthetic pyrethroid never used in Côte d'Ivoire) for malaria vector control. Five wild populations of Anopheles gambiae originating from M'bé, Yaokoffikro, Korhogo, Kafiné and Daola and two laboratory reared strains (Kisumu susceptible and Kou permethrin resistant selected strain) were tested. The diagnostic dosage of alpha-cypermethrin for the sensitive strain Kisumu was 2.5 x 10(-3)%. A comparative study of the susceptibility of samples of wild populations of An. gambiae was carried out according to the WHO standard susceptibility test. Impregnated papers with 4% DDT, 0.25% permethrin, 0.025% deltamethrin and 0.0025% alpha-cypermethrin were used. The results showed that except for mosquitoes from M'bé, all the other populations were resistant to these insecticides. Bioassays were carried out with alpha-cypermethrin at the operational dosage of 20 mg a.i./m2 on the same population and laboratory reared strains. The results showed the efficacy of this insecticide on both the Kisumu strain and the population from M'bé, a maintained efficacy for the Daloa, Kafiné and Korhogo mosquito populations, but the wild anopheline population from Yaokoffikro clearly appeared fully resistant.