This is the second in a series of three articles documenting the geographical distribution of 41 dominant vector species (DVS) of human malaria. The first paper addressed the DVS of the Americas and the third will consider those of the Asian Pacific Region. Here, the DVS of Africa, Europe and the Middle East are discussed. The continent of Africa experiences the bulk of the global malaria burden due in part to the presence of the An. gambiae complex. Anopheles gambiae is one of four DVS within the An. gambiae complex, the others being An. arabiensis and the coastal An. merus and An. melas. There are a further three, highly anthropophilic DVS in Africa, An. funestus, An. moucheti and An. nili. Conversely, across Europe and the Middle East, malaria transmission is low and frequently absent, despite the presence of six DVS. To help control malaria in Africa and the Middle East, or to identify the risk of its re-emergence in Europe, the contemporary distribution and bionomics of the relevant DVS are needed. A contemporary database of occurrence data, compiled from the formal literature and other relevant resources, resulted in the collation of information for seven DVS from 44 countries in Africa containing 4234 geo-referenced, independent sites. In Europe and the Middle East, six DVS were identified from 2784 geo-referenced sites across 49 countries. These occurrence data were combined with expert opinion ranges and a suite of environmental and climatic variables of relevance to anopheline ecology to produce predictive distribution maps using the Boosted Regression Tree (BRT) method. The predicted geographic extent for the following DVS (or species/suspected species complex*) is provided for Africa: Anopheles (Cellia) arabiensis, An. (Cel.) funestus*, An. (Cel.) gambiae, An. (Cel.) melas, An. (Cel.) merus, An. (Cel.) moucheti and An. (Cel.) nili*, and in the European and Middle Eastern Region: An. (Anopheles) atroparvus, An. (Ano.) labranchiae, An. (Ano.) messeae, An. (Ano.) sacharovi, An. (Cel.) sergentii and An. (Cel.) superpictus*. These maps are presented alongside a bionomics summary for each species relevant to its control.

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The dominant Anopheles vectors of human malaria in Africa, Europe and the Middle East: occurrence data, distribution maps and bionomic précis

The incubation period for malaria parasites within the mosquito is exquisitely temperature-sensitive, so that temperature is a major determinant of malaria risk. Epidemiological models are increasingly used to guide allocation of disease control resources and to assess the likely impact of climate change on global malaria burdens. Temperature-based malaria transmission is generally incorporated into these models using mean monthly temperatures, yet temperatures fluctuate throughout the diurnal cycle. Here we use a thermodynamic malaria development model to demonstrate that temperature fluctuation can substantially alter the incubation period of the parasite, and hence malaria transmission rates. We find that, in general, temperature fluctuation reduces the impact of increases in mean temperature. Diurnal temperature fluctuation around means >21°C slows parasite development compared with constant temperatures, whereas fluctuation around <21°C speeds development. Consequently, models which ignore diurnal variation overestimate malaria risk in warmer environments and underestimate risk in cooler environments. To illustrate the implications further, we explore the influence of diurnal temperature fluctuation on malaria transmission at a site in the Kenyan Highlands. Based on local meteorological data, we find that the annual epidemics of malaria at this site cannot be explained without invoking the influence of diurnal temperature fluctuation. Moreover, while temperature fluctuation reduces the relative influence of a subtle warming trend apparent over the last 20 years, it nonetheless makes the effects biologically more significant. Such effects of short-term temperature fluctuations have not previously been considered but are central to understanding current malaria transmission and the consequences of climate change.

https://www.pnas.org/content/pnas/106/33/13844.full.pdf

Understanding the link between malaria risk and climate.

Males and females of nearly all animals differ in their body size, a phenomenon called sexual size dimorphism (SSD). The degree and direction of SSD vary considerably among taxa, including among populations within species. A considerable amount of this variation is due to sex differences in body size plasticity. We examine how variation in these sex differences is generated by exploring sex differences in plasticity in growth rate and development time and the physiological regulation of these differences (e.g., sex differences in regulation by the endocrine system). We explore adaptive hypotheses proposed to explain sex differences in plasticity, including those that predict that plasticity will be lowest for traits under strong selection (adaptive canalization) or greatest for traits under strong directional selection (condition dependence), but few studies have tested these hypotheses. Studies that combine proximate and ultimate mechanisms offer great promise for understanding variation in SSD and sex differences in body size plasticity in insects.

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Sex differences in phenotypic plasticity affect variation in sexual size dimorphism in insects: from physiology to evolution.

Background: Indoor-based anti-vector interventions remain the preferred means of reducing risk of malaria transmission in malaria endemic areas around the world. Despite demonstrated success in reducing humanmosquito interactions, these methods are effective solely against endophilic vectors. It may be that outdoor locations serve as an important venue of host seeking by Anopheles gambiae sensu lato (s.l.) mosquitoes where indoor vector suppression measures are employed. This paper describes the host seeking activity of anopheline mosquito vectors in the Punta Europa region of Bioko Island, Equatorial Guinea. In this area, An. gambiae sensu stricto (s.s.) is the primary malaria vector. The goal of the paper is to evaluate the importance of An gambiae s.l. outdoor host seeking behaviour and discuss its implications for anti-vector interventions. Methods: The venue and temporal characteristics of host seeking by anopheline vectors in a hyperendemic setting was evaluated using human landing collections conducted inside and outside homes in three villages during both the wet and dry seasons in 2007 and 2008. Additionally, five bi-monthly human landing collections were conducted throughout 2009. Collections were segregated hourly to provide a time distribution of host-seeking behaviour. Results: Surprisingly high levels of outdoor biting by An. gambiae senso stricto and An. melas vectors were observed throughout the night, including during the early evening and morning hours when human hosts are often outdoors. As reported previously, An. gambiae s.s. is the primary malaria vector in the Punta Europa region, where it seeks hosts outdoors at least as much as it does indoors. Further, approximately 40% of An. gambiae s.l. are feeding at times when people are often outdoors, where they are not protected by IRS or LLINs. Repeated sampling over two consecutive dry-wet season cycles indicates that this result is independent of seasonality. Conclusions: An. gambiae s.l. mosquitoes currently seek hosts in outdoor venues as much as indoors in the Punta Europa region of Bioko Island. This contrasts with an earlier pre-intervention observation of exclusive endophagy of An. gambiae in this region. In light of this finding, it is proposed that the long term indoor application of insecticides may have resulted in an adaptive shift toward outdoor host seeking in An. gambiae s.s. on Bioko Island.

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Outdoor host seeking behaviour of Anopheles gambiae mosquitoes following initiation of malaria vector control on Bioko Island, Equatorial Guinea.

Tithonia diversifolia is an invasive weed commonly found in tropical ecosystems. In this work, we investigate the influence of different abiotic environmental factors on the plant's metabolite profile by multivariate statistical analyses of spectral data deduced by UHPLC-DAD-ESI-HRMS and NMR methods. Different plant part samples of T. diversifolia which included leaves, stems, roots, and inflorescences were collected from two Brazilian states throughout a 24-month period, along with the corresponding monthly environmental data. A metabolomic approach employing concatenated LC-MS and NMR data was utilised for the first time to study the relationships between environment and plant metabolism. A seasonal pattern was observed for the occurrence of metabolites that included sugars, sesquiterpenes lactones and phenolics in the leaf and stem parts, which can be correlated to the amount of rainfall and changes in temperature. The distribution of the metabolites in the inflorescence and root parts were mainly affected by variation of some soil nutrients such as Ca, Mg, P, K and Cu. We highlight the environment-metabolism relationship for T. diversifolia and the combined analytical approach to obtain reliable data that contributed to a holistic understanding of the influence of abiotic environmental factors on the production of metabolites in various plant parts.

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Effect of the environment on the secondary metabolic profile of Tithonia diversifolia : a model for environmental metabolomics of plants

Distribution of the molecular forms of Anopheles gambiae and pyrethroid knock down resistance gene in Nigeria.

st , 2 nd , 3 rd and 4 th instars larval, pupal and adult stages were observed from day 1 to 6 using six replicates of each water sample. The number of eggs laid (fecundity) by the emerged adults were estimated using counting microscope. Level of development in emerged adults was determined using the wing size. The analysis of the physicochemical parameters of the water samples was carried out in the Nigerian Institute of Marine and Oceanography. The physicochemical characteristics were compared with the rates of development and fecundity of the Anopheline species. Statistical analysis using ANOVA indicates no significant difference (P > 0.05) in the hatchability of the eggs. However, the rates of larval development to pupal stage and subsequent adult emergence showed a level of significant difference (P 0.05). This study provides information on mosquito ecology in relation to breeding habitat which may have bearing on vector population and distribution as well as malaria transmission in a particular area.

/pdf/physico-chemical-characteristics-of-anopheles-breeding-sites-325qj23bw0.pdf

Physico-chemical characteristics of Anopheles breeding sites: Impact on fecundity and progeny development

Extracts from the leaf of Tithonia diversifolia used in folk medicine for treatment of various ailments were tested for antimalaria and mosquito repellency properties in experimental animals and human volunteers, under the laboratory conditions. Comparison of the effectiveness of Chloroquine with the aqueous and methanolic extracts from the plant (T. diversifolia) showed that Chloroquine was 100% effective in clearing the parasite while the aqueous and methanolic extracts were 50 and 74% effective in clearing the parasites respectively. Both aqueous and methanolic extracts were more effective when administered before the onset of the infection, probably indicating the time-dependency of the antimalaria effects. Earlier application of the extracts at the onset of the malaria symptoms was more effective in reducing the parasitemia within a few days. The administration of the plant extracts during the malaria episode was also effective with longer period of administration. The LC50 of the aqueous extract in mice was 1.2ml/100g body weight while the Maximum Tolerated Dose (MTD) was found to be 1.0ml/g. The repellent activity of volatile oil at different concentrations was measured by protection period against the bites of Anopheles gambiae, Aedes aegypti andCulex quinquefasciatus. The volatile oil extract showed higher repellent effect onA. gambiae at higher concentrations however its repellent and protective effects at various concentrations on all other species of mosquito tested can not be underestimated.

	 

	Key words: Tithonia diversifolia, aqueous, methanolic, volatile oil extracts,chloroquine, Plasmodium berghei, mosquitoes.

https://africaneditors.org/journal/JMPR/full-text-pdf/24480-129826

Anti-malarial and repellent activities of Tithonia diversifolia (Hemsl.) leaf extracts

Background & objectives: Anopheline mosquitoes consist of a large number of species each of which differs from another in population, resting and feeding behaviour in relation to the prevailing conditions in the locality. A longitudinal study was carried out to investigate the population dynamics, resting and feeding behaviour of the major anopheline species found in a rain forest zone of Nigeria. Methods: Mosquitoes resting and biting indoors were collected using WHO standard techniques and supplemented with outdoor-biting collections in the study areas between January and December 2004. Samples were sorted and identified microscopically for morphological features while molecular identification was carried out using polymerase chain reaction (PCR) techniques. Results: PCR-based tests showed that both indoor and outdoor collections constitute three groups of Anopheles mosquitoes, An. gambiae s.l. Giles (68.6%), An. funestus Giles (30.7%) and An. moucheti Evans (0.7%). Of the 1,342 female Anopheles mosquitoes collected indoors, 799 were caught resting and 543 were caught biting. The outdoor-biting population accounted for 28.8% of the total collections (n =1885). There was no significant difference (p >0.05) in the biting activities (indoors and outdoors) of these species in four villages. However, An. arabiensis and An. moucheti were more exophagic with >60% of their biting occurring outdoors while An. gambiae and An. funestus were more endophagic with >55% of their biting occurring indoors. The human-vector contact with An. gambiae and An. funestus (indoors) was about 73.3 and 66.7%, respectively as against 27.7% in An. arabiensis and 25.3% in An. moucheti. This gave the corresponding man-biting rates (MBR) of 17.5 bites/man/ night for An. gambiae, 14.6 bites/man/night for An. funestus, 6.7 bites/man/night for An. arabiensis and 4.3 bites/man/night for An. moucheti. Moreover, the number of An. gambiae and An. funestus caught resting indoors was significantly higher than the other two species (p <0.05). The wet season collections showed that An. gambiae caught were more than 67% of the total catch while An. arabiensis was predominant in the dry season (χ 2 = 75.44, df = 3, p <0.01). Interpretation & conclusion: The present study highlights some aspects of the behaviour of anopheline mosquitoes in southern Nigeria which is an important component of epidemiological study of malaria. This information provides basis to the understanding of the role played by the identified anopheline species in malaria transmission and a baseline to formulate malaria control programme.

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Behaviour and population dynamics of the major anopheline vectors in a malaria endemic area in southern Nigeria.

Background & objectives: Pyrethroid insecticide resistance in the malaria vector Anopheles gambiae Giles is mainly associated with reduced target site sensitivity arising from a single point mutation in the sodium channel gene, often referred to as knockdown resistance (kdr). This resistance mechanism is widespread in West Africa and was reported for the first time in Nigeria in 2002. Here we present changes in the susceptibility/resistance status of the molecular ‘M’ and ‘S’ forms of An. gambiae and the frequency of the kdr alleles from 2002–05.

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I.O. Oyewole

Papers

Distribution of the molecular forms of Anopheles gambiae and pyrethroid knock down resistance gene in Nigeria.

Physico-chemical characteristics of Anopheles breeding sites: Impact on fecundity and progeny development

Anti-malarial and repellent activities of Tithonia diversifolia (Hemsl.) leaf extracts

Behaviour and population dynamics of the major anopheline vectors in a malaria endemic area in southern Nigeria.

Dynamics of knockdown pyrethroid insecticide resistance alleles in a field population of Anopheles gambiae s.s. in southwestern Nigeria.