Review of Temephos Discriminating Concentration for Monitoring the Susceptibility of Anopheles labranchiae (Falleroni; 1926); Malaria Vector in Morocco

In Morocco; the resistance monitoring of Anopheles labranchiae larvae to temephos is done using discriminating concentration of 0.125?mg; which is half of the WHO recommended dose for Anopheles. However; this dosage seemed to be too high to allow an early detection of the resistance and its revision was found necessary. The present study was carried out during May-June 2008 and 2009 in nine provinces from the north-west of the country. The aim was to determine the lethal concentrations LC100 of temephos for the most susceptible populations and to define the discriminating dosage as the double of this value. The bioassays were conducted according to WHO standard operating protocol to establish the dose-mortality relationship and deduct the LC50 and LC95. The results of this study indicated that the LC100 obtained on the most susceptible populations was close to 0.05?mg/L. Therefore; the temephos discriminating dosage for susceptibility monitoring of An. labranchiae larvae in Morocco was set to be 0.1?mg

Challenges in Malaria Vector Control; is the Use of DDT The Best Option?

Malaria is an infection caused by a protozoan parasite of the genus Plasmodium; four species of which infect human beings; the most common being Plasmodium vivax and most deadly being Plasmodium falciparum. The Anopheles mosquito serves as Plasmodium's delivery system; or vector. Only female mosquitoes can transmit it since males don't take blood meals. Anopheles mosquitoes bite mainly during night time hours and early hours in the morning (IDRC; 2008)

Malaria Vaccine:The Pros and Cons

Background: Malaria is an important parasitic disease of humans caused by infection with a parasite of the genus Plasmodium and transmitted by female anopheles. Infection caused by P. falciparum is the most serious of all the other species (P. ovale; P. vivax and P. malariae) especially in terms of morbidity and mortality hence the reason why most of the research has been focussed on this species. The disease affects up to about 40 per cent of the world's population with around 300-500 million people currently infected and mainly in the tropics. It has a high morbidity and mortality especially in resource-poor tropical and subtropical regions with an economic fall of about US$ 12 billion annually in Africa alone. relevant literatures were reviewed from medical journals; library search and internet source. Other relevant websites like PATH; Malaria Vaccine Initiative and Global Fund were also visited to source for information. The key words employed were: malaria; vaccine; anopheles mosquito; insecticide treated bed-nets; pyrethroids and Plasmodium. several studies have underscored the need to develop an effective human malaria vaccine for the control and possible eradication of malaria across the globe with the view to reduce the morbidity and mortality associated with the disease; improve on the social and economic losses and also protect those at risk. It is very obvious that the need for effective human malaria vaccine is not only to serve those living in malaria endemic regions but also the non-immune travellers especially those travelling to malaria endemic areas; this would offer cost effective means of preventing the disease; reducing the morbidity and mortality associated with it in addition to closing the gap left by other control measures. It is very obvious that there is no single control measure known to be effective in the control of malaria; hence the need for combination of more than one method with the aim of achieving synergy in the total control and possible eradication of the disease. It suffices to say that despite the use of combination of more than one method (e.g. drugs treating patients; breaking the life cycle of the vector mosquito using larvicides; clearing swamps and other mosquito breeding sites); no much progress was made towards achieving this goal; hence the renewed interest especially with regards to vaccine development

Transmission Dynamics of Malaria in Four Selected Ecological Zones of Nigeria in the Rainy Season

Background: Two of the problems of malaria parasite vector control in Nigeria are the diversity of Anopheline vectors and large size of the country. Anopheline distribution and transmission dynamics of malaria were therefore compared between four ecotypes in Nigeria during the rainy season. Methods: Polymerase chain reaction (PCR) was used in molecular identification after morphological identification microscopically. Enzyme linked immunorsorbent assay (ELISA) was used for the blood meal analysis and sporozoite detection. Results: Five species were identified out of 16;410 anophelines collected. An. gambiae s.s made up approximately 29.2-36.6of the population in each zone. All five species acted as vectors for P. falciparum . An. gambiae s.s had the highest sporozoite rate. The most infected mosquitoes were found in the rain forest. More blood meals were taken from bovids; except the savannah forest; where 73.3were on humans and Human Blood index (HBI) was 57.3. The Entomological inoculation rate (EIR) was a mean of 13.6 ib/p but was highest in the rainforest zone. Conclusions and limitations: This study demonstrates the complex distribution of anophelines and the considerable variations in the intensity of malaria transmission in Nigeria. We highlight the need to consider diverse epidemiological situations when planning countrywide control programmes

La presence des bovins comme hotes alternatifs peut-elle modifier le comportement trophique des vecteurs du paludisme en zone de foret?

Des enquetes entomologiques longitudinales ont ete effectuees de novembre 1998 a novembre 2000 en vue de determiner le comportement trophique des anopheles en presence de bovins comme hotes alternatifs a l`homme dans deux localites de la zone de foret du sud Cameroun; Obala et Nkolbisson. Les collectes des moustiques ont eu lieu a l`interieur des habitations par pulverisation intra domiciliaire et a l`exterieur a l`aide de captures sous moustiquaire piege avec comme appats l`homme et le veau. L`origine du repas de sang et l`infectivite des moustiques ont ete identifiees par la technique ELISA (Enzyme Linked Immunosorbent Asay). Au total; 992 anopheles appartenant a 8 especes ont ete collectees au cours de cette etude. An. funestus etait l`espece la plus abondante a Obala tandis qu`An. nili predominait a Nkolbisson. Le taux d`anthropophilie etait plus eleve chez les moustiques collectes a l`interieur des habitations que chez ceux collectes a l`exterieur sous moustiquaire piege. An. gambiae et An. funestus ont montre une nette preference pour l`homme tandis qu`An. nili a pique indifferemment l`homme et le boeuf. An. gambiae etait de loin le vecteur principal dans les deux sites d`etude avec 24 cas d`infections sur les 42 trouves. Ces resultats montrent que les vecteurs en zone de foret peuvent diversifier la source de leur repas de sang en presence d`hotes alternatifs tels que les bovins. Toutefois; il serait important de comprendre si l`introduction de l`elevage de bovins dans cette region pourrait influencer le cycle de transmission du paludisme

Epidemiological Importance of the Anopheles Nili Group of Malaria Vectors in Equatorial Villages of Cameroon; Central Africa

From March 1999 to March 2007; entomological surveys were conducted in eight riverside locations of the equatorial domain in Cameroon; to assess the contribution of Anopheles nili group to malaria transmission. Results showed that the anthropophilic Anopheles nili; Anopheles carnevalei and Anopheles ovengensis were involved in 5-68of the Plasmodium falciparum entomological inoculation rates (EIRs) in all the study sites. Alongside; vectors such as Anopheles Gambiae; Anopheles moucheti; Anopheles funestus; Anopheles marshallii and Anopheles hancocki also took a substantial part to these transmission rates in sympatric conditions. Anopheles nili s.s. was the major vector in villages situated near the Sanaga river; with more than 100 infective bites/person/year. Its true Plasmodium falciparum infections rates ranged from 1.4to 6.1. Anopheles carnevalei and Anopheles ovengensis were mainly distributed in the equatorial cross-bordering areas; where they contributed for less than 30of the Plasmodium falciparum EIRs in villages located along the Nten river and Congo river networks. These findings confirm Anopheles nili s.s. as a major malaria vector mosquito; and also provided more data regarding the epidemiological role of Anopheles carnevalei and Anopheles ovengensis througout the central African region

Pyrethroid Resistance in a Major African Malaria Vector Anopheles arabiensis from Mamfene; Northern KwaZulu-Natal; South Africa

A population of Anopheles arabiensis; a major malaria vector in South Africa; was collected during 2005 from inside sprayed houses in Mamfene; northern KwaZulu-Natal; South Africa; using window exit traps. None of these specimens (n = 300 females) was found to be infected with Plasmodium falciparum. Insecticide susceptibility assays on 2-3 day old F1 progeny usingWHOsusceptibility kits revealed 100susceptibility to bendiocarb; resistance to deltamethrin (95.91) was suspected; while resistance to permethrin (78.05) was confirmed. The knockdown resistant (kdr) genotype was not found in the surviving mosquitoes. Biochemical analysis using enzyme assays showed elevated levels of monooxygenase that correlated with the permethrin bioassay data. While elevated levels of non-specific esterase were found in some families (11/12 for a- and 6/12 for Beta-esterases); the data did not show any correlation with the permethrin bioassay. Analysis of permethrin and bendiocarb tolerant lines; selected in the laboratory to characterise biochemical resistance profiles; showed increased levels of non-specific esterase and monooxygenase activity in the case of the permethrin-selected cohorts; and elevated glutathione S-transferases and general esterases in that of the bendiocarb-selected line. Synergist assays; using piperonyl butoxide; confirmed the involvement of monooxygenase and glutathione S-transferase in pyrethroid and bendiocarb resistance. This study underlines the importance of routine surveillance for insecticide susceptibility in wild anopheline populations

Vector Species Composition and Malaria Infectivity Rates in Mkuzi; Muheza District; North-Eastern Tanzania

Entomological surveys were conducted in Mkuzi village in Muheza District; north-east Tanzania from April to September 2003. The objectives were to determine the species composition and infectivity rates of mosquitoes in Mkuzi village. Mosquito collection was done using CDC light trap and pyrethrum spray catch (PSC) techniques. The light trap: spray catch ratio was 2.2:1. A total of 2157 mosquitoes were collected (light trap= 1483; PSC= 674). Anopheles gambiae s.s. accounted for 56.7(N=1224) of all mosquitoes collected. Other species were An. funestus complex (19.2) and Culex quinquefasciatus (24.1).The mosquito density per room was 74.15 and 33.7 for light trap and PSC techniques; respectively. A total of 1637 Anopheles mosquitoes were tested for circumsporozoite protein by Enzyme linked Immunosobent Assay (ELISA). The overall infectivity rate for circumsporozoite protein for P. falciparum in Anopheles mosquitoes was 21.14(346/1637). Species-specific infectivity rates were 22.7(278/1224) in An. gambiae s.s. and 24.0(68/283) in An. funestus funestus; 0(0/80) for An. rivulorum and 0(0/50) for An.parensis. Blood meal analysis indicated that 92.3of An. gambiae s.s; 88.9of An. funestus s.s.; 64.5of An. rivulorum and 67.7of An. parensis had taken blood meal from human hosts. In conclusion; malaria transmission in Mkuzi area of Muheza district is mainly by the highly anthropophagic An. gambiae s.s. and An. funestus s.s. More studies are needed to identify the seasonal variation of species composition and transmission dynamics in this village

Repellency Property of Long Chain Aliphatic Methyl Ketones against Anopheles gambiae s.s

Long chain aliphatic methyl ketone series of C7-C15 were tested for repellency activity against the malaria transmitting mosquito Anopheles gambiae s.s. All methyl ketones produced a dose dependent (P0.001) repellency response with 2-tridecanone giving comparable protection efficacy to DEET at 10 and 1concentrations. Aliphatic methyl ketones of C7-C10 had lower activity than those of C11-C15. However; within this range compounds with odd carbon atoms (2-undecanone; 2-tridecanone and 2-pentadecanone) were more effective than compounds with even carbon atoms (2-decanone and 2- dodecanone). Comparable repellency activity of 2-tridecanone to DEET show that; it may save as Anopheles gambiae s.s. mosquito repellent

Malaria vectors and transmission dynamics in coastal south-western Cameroon

Background: Malaria is a major public health problem in Cameroon. Unlike in the southern forested areas where the epidemiology of malaria has been better studied prior to the implementation of control activities; little is known about the distribution and role of anophelines in malaria transmission in the coastal areas. Methods: A 12-month longitudinal entomological survey was conducted in Tiko; Limbe and Idenau from August 2001 to July 2002. Mosquitoes captured indoors on human volunteers were identified morphologically. Species of the Anopheles gambiae complex were identified using the polymerase chain reaction (PCR). Mosquito infectivity was detected by the enzyme-linked immunosorbent assay and PCR. Malariometric indices (plasmodic index; gametocytic index; parasite species prevalence) were determined in three age groups (5yrs; 5-15yrs; 15yrs) and followed-up once every three months. Results: In all; 2;773 malaria vectors comprising Anopheles gambiae (78.2); Anopheles funestus (17.4) and Anopheles nili (7.4) were captured. Anopheles melas was not anthropophagic. Anopheles gambiae had the highest infection rates. There were 287; 160 and 149 infective bites/person/year in Tiko; Limbe and Idenau; respectively. Anopheles gambiae accounted for 72.7; An. funestus for 23and An. nili for 4.3of the transmission. The prevalence of malaria parasitaemia was 41.5in children 5 years of age; 31.5in those 5-15years and 10.5in those 15years; and Plasmodium falciparum was the predominant parasite species.Conclusions: Malaria transmission is perennial; rainfall dependent and An. melas does not contribute to transmission. These findings are important in the planning and implementation of malaria control activities in coastal Cameroon and West Africa

Occurrence of the leucine-to-phenylalanine knockdown resistance (kdr) mutation in Anopheles arabiensispopulations in Tanzania; detected by a simplified high-throughput SSOP-ELISA method

Background: Molecular markers of insecticide resistance can provide sensitive indicators of resistance development in malaria vector populations. Monitoring of insecticide resistance in vector populations is an important component of current malaria control programmes. Knockdown resistance (kdr) confers resistance to the pyrethroid class of insecticides with cross-resistance to DDT through single nucleotide polymorphisms (SNPs) in the voltage-gated sodium channel gene. Methods: To enable detection of kdr mutations at low frequency a method was developed that uses polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA)-based technology; allowing rapid; reliable and cost-effective testing of large numbers of individual mosquitoes. This was used to assay mosquitoes from sites in lower Moshi; Tanzania. Results: Sequence-specific oligonucleotide probes (SSOP) were used for simultaneous detection of both East and West African kdr mutations with high specificity and sensitivity. Application of the SSOP-ELISA method to 1;620 field-collected Anopheles arabiensis from Tanzania identified the West African leucine-phenylalanine kdr mutation in two heterozygous individuals; indicating the potential for resistance development that requires close monitoring. Conclusion : The presence of the West African kdr mutation at low frequency in this East African population of An. arabiensis has implications for the spread of the kdr gene across the African continent

Effective population size of Anopheles funestus chromosomal forms in Burkina Faso

Background: As Anopheles funestus is one of the principal Afro-tropical malaria vectors; a more complete understanding of its population structure is desirable. In West and Central Africa; An. funestus population structure is complicated by the coexistence of two assortatively mating chromosomal forms. Effective population size (Ne) is a key parameter in understanding patterns and levels of intraspecific variation; as it reflects the role of genetic drift. Here; Ne was estimated from both chromosomal forms; Kiribina and Folonzo; in Burkina Faso. Methods: Short-term Ne was estimated by evaluating variation at 16 microsatellite loci across temporal samples collected annually from 2000-2002. Estimates were based on standardized variance in allele frequencies or a maximum likelihood method. Long-term Ne was estimated from genetic diversity estimates using mtDNA sequences and microsatellites. Results: For both forms; short-term and long-term Ne estimates were on the order of 103 and 105; respectively. Long-term Ne estimates were larger when based on loci from chromosome 3R (both inside and outside of inversions) than loci outside of this arm. Conclusion: Ne values indicate that An. funestus is not subject to seasonal bottlenecks. Though not statistically different because of large and overlapping confidence intervals; short-term Ne estimates were consistently smaller for Kiribina than Folonzo; possibly due to exploitation of different breeding sites: permanent for Folonzo and intermittent for Kiribina. The higher long-term Ne estimates on 3R; the arm carrying the two inversions mainly responsible for defining the chromosomal forms; give natural selection broader scope and merit further study

Efficacy of bifenthrin-impregnated bednets against Anopheles funestus and pyrethroid-resistant Anopheles gambiae in North Cameroon

Background: Recent field studies indicated that insecticide-treated bednets (ITNs) maintain their efficacy despite a high frequency of the knock-down resistance (kdr) gene in Anopheles gambiae populations. It was essential to evaluate ITNs efficacy in areas with metabolic-based resistance. Methods: Bifenthrin was used in this experiment because it is considered a promising candidate for bednets impregnation. Nets were treated at 50 mg/m2; a dose that has high insecticidal activity on kdr mosquitoes and at 5 mg/m2; a dose that kills 95of susceptible mosquitoes under laboratory conditions with 3 minutes exposure. Bednets were holed to mimic physical damage. The trial was conducted in three experimental huts from Pitoa; North-Cameroon where Anopheles gambiae displays metabolic resistance and cohabits with An. funestus. Results: Bifenthrin at 50 mg/m2 significantly reduced anophelines' entry rate (80). This was not observed at 5 mg/m2. Both treatments increased exophily in An. gambiae; and to a lesser extent in An. funestus. With bifenthrin at high dosage; over 60reduction in blood feeding and 75-90mortality rates were observed in both vectors. Despite presence of holes; only a single An. gambiae and two An. funestus females were collected inside the treated net; and all were found dead. The same trends were observed with low dosage bifenthrin though in most cases; no significant difference was found with the untreated control net. Conclusion: Bifenthrin-impregnated bednets at 50 mg/m2 were efficient in the reduction of human-vector contact in Pitoa. Considerable personal protection was gained against An. funestus and metabolic pyrethroid resistant An. gambiae populations

Transmission vectorielle du paludisme en savane arborée à Gansé en Cote d'Ivoire

Un suivi entomologique longitudinal a ete realise a Ganse; un village du Nord-Est de la Cote d'Ivoire; entre juillet 2000 et juillet 2001. L'objectif de cette etude etait de repertorier les especes vectrices des Plasmodium par capture des moustiques sur des volontaires; recolter des larves dans diff e rents types de gites et evaluer l'implication de ces especes dans la transmission du paludisme. Quatre especes appartenant au genre Anopheles ont ete recoltees dans le village. La technique ELISA d'identification des antigenes CSP de Plasmodium a montre que trois de ces especes etaient ve c t rices. Ces especes appartenaient au complexe An. gambiae (An. gambiae s.s. a 100); au groupe An. funestus (An. funestus s.s. a 95;6) et au groupe An. nili (An. nili s.s. a 100). Les indices sporozoitiques moyen etaient de 5;9pour An. gambiae s.l.; 4;3pour les Anopheles du groupe funestus et 2;6pour les Anopheles du groupe nili. Les principaux gites larvaires etaient des points d'eau temporai es tels que des flaques pour An. gambiae s.l.; des cours d'eau a vegetation dressee pour les Anopheles du groupe funestus et le fleuve Comoe pour les Anopheles du groupe nili. La presence de ces trois especes avec des pics d'abondance observes respectivement en mai; en septembre et en juillet; assure une transmission quasi permanente de P. falciparum. Cette transmission est importante car on a pu enregistrer jusqu'a 410 piqures infectees par homme et par an. Dans cette localite; nous avons montre la presence d'An. rivulorum-like mais surtout le role important d'An. nili s.s. dans la transmission et la complexite du systeme vectoriel dans la region

Donnees recentes sur la sensibilite d'Anopheles arabiensis et d'Anopheles funestus aux pyrethrinoides et au DDT sur les Hautes Terres Centrales de Madagascar -Resultats preliminaires montrant une absence de la mutation kdr chez An. arabiensis

"Recent observations on the sensitivity to pyrethroids and DDT of Anopheles arabiensis and Anopheles funestus in the central Highlands of Madagascar; preliminary resultson the absence of the kdr mutation in An. arabiensis"". Anopheles arabiensis and Anopheles funestus are the principal vectors of malaria on the central highlands of Madagascar. These two species of mosquito are directly or indirectly the targets of indoor insecticide spread. The survey of the susceptibility of these two vectors to insecticides is essential specifying for the anti-vectorial current directives and for the future programs. This paper describes : - the recent tests of susceptibility and the study of the knock-down effect of four pyrethroids (deltamethrin 0.50"