‘Manipulation’ without the parasite: altered feeding behaviour of mosquitoes is not dependent on infection with malaria parasites

Previous studies have suggested that Plasmodium parasites can manipulate mosquito feeding behaviours such as probing, persistence and engorgement rate in order to enhance transmission success. Here, we broaden analysis of this ‘manipulation phenotype’ to consider proximate foraging behaviours, including responsiveness to host odours and host location. Using Anopheles stephensi and Plasmodium yoelii as a model system, we demonstrate that mosquitoes with early stage infections (i.e. non-infectious oocysts) exhibit reduced attraction to a human host, whereas those with late-stage infections (i.e. infectious sporozoites) exhibit increased attraction. These stage-specific changes in behaviour were paralleled by changes in the responsiveness of mosquito odourant receptors, providing a possible neurophysiological mechanism for the responses. However, we also found that both the behavioural and neurophysiological changes could be generated by immune challenge with heat-killed Escherichia coli and were thus not tied explicitly to the presence of malaria parasites. Our results support the hypothesis that the feeding behaviour of female mosquitoes is altered by Plasmodium, but question the extent to which this is owing to active manipulation by malaria parasites of host behaviour.     

Activation of Akt Signaling Reduces the Prevalence and Intensity of Malaria Parasite Infection and Lifespan in Anopheles stephensi Mosquitoes

Malaria (Plasmodium spp.) kills nearly one million people annually and this number will likely increase as drug and insecticide resistance reduces the effectiveness of current control strategies. The most important human malaria parasite, Plasmodium falciparum, undergoes a complex developmental cycle in the mosquito that takes approximately two weeks and begins with the invasion of the mosquito midgut. Here, we demonstrate that increased Akt signaling in the mosquito midgut disrupts parasite development and concurrently reduces the duration that mosquitoes are infective to humans. Specifically, we found that increased Akt signaling in the midgut of heterozygous Anopheles stephensi reduced the number of infected mosquitoes by 60–99%. Of those mosquitoes that were infected, we observed a 75–99% reduction in parasite load. In homozygous mosquitoes with increased Akt signaling parasite infection was completely blocked. The increase in midgut-specific Akt signaling also led to an 18–20% reduction in the average mosquito lifespan. Thus, activation of Akt signaling reduced the number of infected mosquitoes, the number of malaria parasites per infected mosquito, and the duration of mosquito infectivity.     

Identification of four evolutionarily related G protein-coupled receptors from the malaria mosquito Anopheles gambiae

The mosquito Anopheles gambiae is an important vector for malaria, which is one of the most serious human parasitic diseases in the world, causing up to 2.7 million deaths yearly. To contribute to our understanding of A. gambiae and to the transmission of malaria, we have now cloned four evolutionarily related G protein-coupled receptors (GPCRs) from this mosquito and expressed them in Chinese hamster ovary cells. After screening of a library of thirty-three insect or other invertebrate neuropeptides and eight biogenic amines, we could identify (de-orphanize) three of these GPCRs as: an adipokinetic hormone (AKH) receptor (EC₅₀ for A. gambiae AKH, 3 × 10⁻⁹ M), a corazonin receptor (EC₅₀ for A. gambiae corazonin, 4 × 10⁻⁹ M), and a crustacean cardioactive peptide (CCAP) receptor (EC₅₀ for A. gambiae CCAP, 1 × 10⁻⁹ M). The fourth GPCR remained an orphan, although its close evolutionary relationship to the A. gambiae and other insect AKH receptors suggested that it is a receptor for an AKH-like peptide. This is the first published report on evolutionarily related AKH, corazonin, and CCAP receptors in mosquitoes.     

A putative kinase-related protein (PKRP) from Plasmodium berghei mediates infection in the midgut and salivary glands of the mosquito

The completion of the Plasmodium (malaria) life cycle in the mosquito requires the parasite to traverse first the midgut and later the salivary gland epithelium. We have identified a putative kinase-related protein (PKRP) that is predicted to be an atypical protein kinase, which is conserved across many species of Plasmodium. The pkrp gene encodes a RNA of about 5300 nucleotides that is expressed as a 90 kDa protein in sporozoites. Targeted disruption of the pkrp gene in Plasmodium berghei, a rodent model of malaria, compromises the ability of parasites to infect different tissues within the mosquito host. Early infection of mosquito midgut is reduced by 58-71%, midgut oocyst production is reduced by 50-90% and those sporozoites that are produced are defective in their ability to invade mosquito salivary glands. Midgut sporozoites are not morphologically different from wild-type parasites by electron microscopy. Some sporozoites that emerged from oocysts were attached to the salivary glands but most were found circulating in the mosquito hemocoel. Our findings indicate that a signalling pathway involving PbPKRP regulates the level of Plasmodium infection in the mosquito midgut and salivary glands.     

Wolbachia increases susceptibility to Plasmodium infection in a natural system

Current views about the impact of Wolbachia on Plasmodium infections are almost entirely based on data regarding artificially transfected mosquitoes. This work has shown that Wolbachia reduces the intensity of Plasmodium infections in mosquitoes, raising the exciting possibility of using Wolbachia to control or limit the spread of malaria. Whether natural Wolbachia infections have the same parasite-inhibiting properties is not yet clear. Wolbachia–mosquito combinations with a long evolutionary history are, however, key for understanding what may happen with Wolbachia-transfected mosquitoes after several generations of coevolution. We investigate this issue using an entirely natural mosquito–Wolbachia–Plasmodium combination. In contrast to most previous studies, which have been centred on the quantification of the midgut stages of Plasmodium, we obtain a measurement of parasitaemia that relates directly to transmission by following infections to the salivary gland stages. We show that Wolbachia increases the susceptibility of Culex pipiens mosquitoes to Plasmodium relictum, significantly increasing the prevalence of salivary gland stage infections. This effect is independent of the density of Wolbachia in the mosquito. These results suggest that naturally Wolbachia-infected mosquitoes may, in fact, be better vectors of malaria than Wolbachia-free ones.     

Midgut Microbiota of the Malaria Mosquito Vector Anopheles gambiae and Interactions with Plasmodium falciparum Infection

The susceptibility of Anopheles mosquitoes to Plasmodium infections relies on complex interactions between the insect vector and the malaria parasite. A number of studies have shown that the mosquito innate immune responses play an important role in controlling the malaria infection and that the strength of parasite clearance is under genetic control, but little is known about the influence of environmental factors on the transmission success. We present here evidence that the composition of the vector gut microbiota is one of the major components that determine the outcome of mosquito infections. A. gambiae mosquitoes collected in natural breeding sites from Cameroon were experimentally challenged with a wild P. falciparum isolate, and their gut bacterial content was submitted for pyrosequencing analysis. The meta-taxogenomic approach revealed a broader richness of the midgut bacterial flora than previously described. Unexpectedly, the majority of bacterial species were found in only a small proportion of mosquitoes, and only 20 genera were shared by 80% of individuals. We show that observed differences in gut bacterial flora of adult mosquitoes is a result of breeding in distinct sites, suggesting that the native aquatic source where larvae were grown determines the composition of the midgut microbiota. Importantly, the abundance of Enterobacteriaceae in the mosquito midgut correlates significantly with the Plasmodium infection status. This striking relationship highlights the role of natural gut environment in parasite transmission. Deciphering microbe-pathogen interactions offers new perspectives to control disease transmission.     

Transgenic Mosquitoes Expressing a Phospholipase A2 Gene Have a Fitness Advantage When Fed Plasmodium falciparum-Infected Blood

Background

Genetically modified mosquitoes have been proposed as an alternative strategy to reduce the heavy burden of malaria. In recent years, several proof-of-principle experiments have been performed that validate the idea that mosquitoes can be genetically modified to become refractory to malaria parasite development.

Results

We have created two transgenic lines of Anopheles stephensi , a natural vector of Plasmodium falciparum, which constitutively secrete a catalytically inactive phospholipase A₂ (mPLA₂) into the midgut lumen to interfere with Plasmodium ookinete invasion. Our experiments show that both transgenic lines expressing mPLA₂ significantly impair the development of rodent malaria parasites, but only one line impairs the development of human malaria parasites. In addition, when fed on malaria-infected blood, mosquitoes from both transgenic lines are more fecund than non-transgenic mosquitoes. Consistent with these observations, cage experiments with mixed populations of transgenic and non-transgenic mosquitoes show that the percentage of transgenic mosquitoes increases when maintained on Plasmodium -infected blood.

Conclusions

Our results suggest that the expression of an anti-Plasmodium effector gene gives transgenic mosquitoes a fitness advantage when fed malaria-infected blood. These findings have important implications for future applications of transgenic mosquito technology in malaria control.     

Loop-mediated isothermal amplification assays for identification of antiseptic- and methicillin-resistant Staphylococcus aureus

A method for rapid identification of antiseptic- and methicillin-resistant Staphylococcus aureus (MRSA) based on 3 loop-mediated isothermal amplification (LAMP) assays was developed. LAMP targeting the femB gene identified S. aureus with 100% specificity, and LAMP targeting the mecA gene associated with methicillin resistance identified methicillin-resistant staphylococci with 100% specificity. LAMP targeting the qacA/B gene encoding an efflux pump responsible for antiseptic resistance identified high-acriflavine-resistant (MIC ≥ 100 mg/L) MRSA (92.5% positive) and acriflavine-susceptible (MIC < 25 mg/L) MRSA (100% negative). They were performed under the same reaction conditions within 60 min at 63 °C. The combined LAMP assays will be useful for rapid identification of S. aureus isolates and determination of their antibiotic and antiseptic resistance patterns with regard to methicillin and organic cationic substrates.     

A novel nested polymerase chain reaction assay targeting Plasmodium mitochondrial DNA in field‐collected Anopheles mosquitoes

Sensitive techniques for the detection of Plasmodium (Aconoidasida: Plasmodiidae) sporozoites in field‐collected malaria vectors are essential for the correct assessment of risk for malaria transmission. A real‐time polymerase chain reaction (RT‐PCR) protocol targeting Plasmodium mtDNA proved to be much more sensitive in detecting sporozoites in mosquitoes than the widely used enzyme‐linked immunosorbent assay targeting Plasmodium circumsporozoite protein (CSP‐ELISA). However, because of the relatively high costs associated with equipment and reagents, RT‐PCRs are mostly used to assess the outcomes of experimental infections in the frame of research experiments, rather than in routine monitoring of mosquito infection in the field. The present authors developed a novel mtDNA‐based nested PCR protocol, modified from a loop‐mediated isothermal amplification (LAMP) assay for Plasmodium recognition in human blood samples, and compared its performance with that of routinely used CSP‐ELISAs in field‐collected Anopheles coluzzii (Diptera: Culicidae) samples. The nested PCR showed 1.4‐fold higher sensitivity than the CSP‐ELISA. However, nested PCR results obtained in two laboratories and in different replicates within the same laboratory were not 100% consistent, probably because the copy number of amplifiable Plasmodium mtDNA was close in some specimens to the threshold of nested PCR sensitivity. This implies that Plasmodium‐positive specimens should be confirmed by a second nested PCR to avoid false positives. Overall, the results emphasize the need to use molecular approaches to obtain accurate estimates of the actual level of Plasmodium circulation within malaria vector populations.     

The Plasmodium bottleneck: malaria parasite losses in the mosquito vector

Nearly one million people are killed every year by the malaria parasite Plasmodium. Although the disease-causing forms of the parasite exist only in the human blood, mosquitoes of the genus Anopheles are the obligate vector for transmission. Here, we review the parasite life cycle in the vector and highlight the human and mosquito contributions that limit malaria parasite development in the mosquito host. We address parasite killing in its mosquito host and bottlenecks in parasite numbers that might guide intervention strategies to prevent transmission.     

Avian Plasmodium in Culex and Ochlerotatus Mosquitoes from Southern Spain: Effects of Season and Host-Feeding Source on Parasite Dynamics

Haemosporidians, a group of vector-borne parasites that include Plasmodium, infect vertebrates including birds. Although mosquitoes are crucial elements in the transmission of avian malaria parasites, little is known of their ecology as vectors. We examined the presence of Plasmodium and Haemoproteus lineages in five mosquito species belonging to the genera Culex and Ochlerotatus to test for the effect of vector species, season and host-feeding source on the transmission dynamics of these pathogens. We analyzed 166 blood-fed individually and 5,579 unfed mosquitoes (grouped in 197 pools) from a locality in southern Spain. In all, 15 Plasmodium and two Haemoproteus lineages were identified on the basis of a fragment of 478 bp of the mitochondrial cytochrome b gene. Infection prevalence of blood parasites in unfed mosquitoes varied between species (range: 0–3.2%) and seasons. The feeding source was identified in 91 mosquitoes where 78% were identified as bird. We found that i) several Plasmodium lineages are shared among different Culex species and one Plasmodium lineage is shared between Culex and Ochlerotatus genera; ii) mosquitoes harboured Haemoproteus parasites; iii) pools of unfed females of mostly ornithophilic Culex species had a higher Plasmodium prevalence than the only mammophylic Culex species studied. However, the mammophylic Ochlerotatus caspius had in pool samples the greatest Plasmodium prevalence. This relative high prevalence may be determined by inter-specific differences in vector survival, susceptibility to infection but also the possibility that this species feeds on birds more frequently than previously thought. Finally, iv) infection rate of mosquitoes varies between seasons and reaches its maximum prevalence during autumn and minimum prevalence in spring.     

Optimized Pan-species and Speciation Duplex Real-time PCR Assays for Plasmodium Parasites Detection in Malaria Vectors

Background

An accurate method for detecting malaria parasites in the mosquito’s vector remains an essential component in the vector control. The Enzyme linked immunosorbent assay specific for circumsporozoite protein (ELISA-CSP) is the gold standard method for the detection of malaria parasites in the vector even if it presents some limitations. Here, we optimized multiplex real-time PCR assays to accurately detect minor populations in mixed infection with multiple Plasmodium species in the African malaria vectors Anopheles gambiae and Anopheles funestus.

Methods

Complementary TaqMan-based real-time PCR assays that detect Plasmodium species using specific primers and probes were first evaluated on artificial mixtures of different targets inserted in plasmid constructs. The assays were further validated in comparison with the ELISA-CSP on 200 field caught Anopheles gambiae and Anopheles funestus mosquitoes collected in two localities in southern Benin.

Results

The validation of the duplex real-time PCR assays on the plasmid mixtures demonstrated robust specificity and sensitivity for detecting distinct targets. Using a panel of mosquito specimen, the real-time PCR showed a relatively high sensitivity (88.6%) and specificity (98%), compared to ELISA-CSP as the referent standard. The agreement between both methods was “excellent” (κ = 0.8, P<0.05). The relative quantification of Plasmodium DNA between the two Anopheles species analyzed showed no significant difference (P = 0, 2). All infected mosquito samples contained Plasmodium falciparum DNA and mixed infections with P. malariae and/or P. ovale were observed in 18.6% and 13.6% of An. gambiae and An. funestus respectively. Plasmodium vivax was found in none of the mosquito samples analyzed.

Conclusion

This study presents an optimized method for detecting the four Plasmodium species in the African malaria vectors. The study highlights substantial discordance with traditional ELISA-CSP pointing out the utility of employing an accurate molecular diagnostic tool for detecting malaria parasites in field mosquito populations.     

Malaria vectors of Papua New Guinea

Understanding malaria transmission in Papua New Guinea (PNG) requires exact knowledge of which Anopheles species are transmitting malaria and is complicated by the cryptic species status of many of these mosquitoes. To identify the malaria vectors in PNG we studied Anopheles specimens from 232 collection localities around human habitation throughout PNG (using CO₂ baited light traps and human bait collections). A total of 22,970 mosquitoes were individually assessed using a Plasmodium sporozoite enzyme-linked immunosorbent assay to identify Plasmodiumfalciparum, Plasmodiumvivax and Plasmodiummalariae circumsporozoite proteins. All mosquitoes were identified to species by morphology and/or PCR. Based on distribution, abundance and their ability to develop sporozoites, we identified five species as major vectors of malaria in PNG. These included: Anophelesfarauti, Anopheleshinesorum (incriminated here, to our knowledge, for the first time), Anophelesfarauti 4, Anopheleskoliensis and Anophelespunctulatus. Anopheleslongirostris and Anophelesbancroftii were also incriminated in this study. Surprisingly, An. longirostris showed a high incidence of infections in some areas. A newly identified taxon within the Punctulatus Group, tentatively called An. farauti 8, was also found positive for circumsporozoite protein. These latter three species, together with Anopheleskarwari and Anophelessubpictus, incriminated in other studies, appear to be only minor vectors, while Anophelesfarauti 6 appears to be the major vector in the highland river valleys (>1500 m above sea level). The nine remaining Anopheles species found in PNG have been little studied and their bionomics are unknown; most appear to be uncommon with limited distribution and their possible role in malaria transmission has yet to be determined.     

Blood-meal preferences and avian malaria detection in mosquitoes (Diptera: Culicidae) captured at different land use types within a neotropical montane cloud forest matrix

Human activities modify environmental conditions, altering ecological interactions that can contribute to the increasing number of vector-borne pathogens affecting both human and wildlife populations. There is a dearth of knowledge about mosquitoes feeding preferences and their role as potential vectors of haemosporidian parasites, particularly in modified habitats. During 2013–2014 we sampled mosquitoes in five different land use types within a cloud forest matrix. From a total of 4107 adult mosquitoes, 90 were engorged. We extracted DNA from mosquito blood-meals, abdomens, and thoraxes, which belonged to seven different species. Seventeen specimens were positive for avian Plasmodium parasites. We were able to identify the blood-meal source of 10 mosquitoes, the identified vertebrate species were: Homo sapiens (Human), Sturnira hondurensis (Bat), and Bos taurus (Cow). Our results show that Culex restuans is positive for avian malaria and it is feeding on both humans and domestic animals at urban and peri-urban habitat types, where it is also an abundant species throughout the year. Furthermore, Aedes quadrivittatus, also positive for avian malaria, is feeding on humans in the well-preserved cloud forest, where this mosquito species is highly abundant. This study is the first in Mexico to provide reference data showing generalist mosquito feeding preferences and presence of avian Plasmodium at locations with different land use types.     

A dehydrochlorinase-based pH change assay for determination of DDT in sprayed surfaces

A glutathione S-transferase (GST) from the mosquito Aedes aegypti (aagste2), selected in the field as a major metabolic resistance enzyme for this parasite vector, was employed to produce a highly specific assay for the determination of DDT [1,1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene]. Detection is based on the pH change occurring in an appropriate buffer system by the concomitant release of H⁺ during the aagste2-catalyzed dehydrochlorination reaction and is monitored potentiometrically or colorimetrically in the presence of a pH marker. The theoretical limit of detection (LOD) of the assay is 3.8 μg/ml, and the linear range of quantification is 12 to 250 μg/ml. The method does not recognize biologically inactive DDT analogues or major DDT photodegradants and breakdown molecules, and it is highly specific for the insecticidal p.p’DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane]. The biosensor was validated with a number of insecticide swabs from DDT-sprayed surfaces and found to be reproducible and reliable as compared with high-performance liquid chromatography (HPLC) (correlation coefficient R² = 0.98). Given the current expansion of DDT residual sprayings in many regions of Africa as a key strategic intervention for malaria vector control, this simple assay to monitor DDT levels for vector control spraying programs could have an important impact on malaria control.     

Malaria's Missing Number: Calculating the Human Component of R0 by a Within-Host Mechanistic Model of Plasmodium falciparum Infection and Transmission

Human infection by malarial parasites of the genus Plasmodium begins with the bite of an infected Anopheles mosquito. Current estimates place malaria mortality at over 650,000 individuals each year, mostly in African children. Efforts to reduce disease burden can benefit from the development of mathematical models of disease transmission. To date, however, comprehensive modeling of the parameters defining human infectivity to mosquitoes has remained elusive. Here, we describe a mechanistic within-host model of Plasmodium falciparum infection in humans and pathogen transmission to the mosquito vector. Our model incorporates the entire parasite lifecycle, including the intra-erythrocytic asexual forms responsible for disease, the onset of symptoms, the development and maturation of intra-erythrocytic gametocytes that are transmissible to Anopheles mosquitoes, and human-to-mosquito infectivity. These model components were parameterized from malaria therapy data and other studies to simulate individual infections, and the ensemble of outputs was found to reproduce the full range of patient responses to infection. Using this model, we assessed human infectivity over the course of untreated infections and examined the effects in relation to transmission intensity, expressed by the basic reproduction number R₀ (defined as the number of secondary cases produced by a single typical infection in a completely susceptible population). Our studies predict that net human-to-mosquito infectivity from a single non-immune individual is on average equal to 32 fully infectious days. This estimate of mean infectivity is equivalent to calculating the human component of malarial R₀. We also predict that mean daily infectivity exceeds five percent for approximately 138 days. The mechanistic framework described herein, made available as stand-alone software, will enable investigators to conduct detailed studies into theories of malaria control, including the effects of drug treatment and drug resistance on transmission.     

The Puf-family RNA-binding protein Puf2 controls sporozoite conversion to liver stages in the malaria parasite

Malaria is a vector-borne infectious disease caused by unicellular, obligate intracellular parasites of the genus Plasmodium. During host switch the malaria parasite employs specialized latent stages that colonize the new host environment. Previous work has established that gametocytes, sexually differentiated stages that are taken up by the mosquito vector, control expression of genes required for mosquito colonization by translational repression. Sexual parasite development is controlled by a DEAD-box RNA helicase of the DDX6 family, termed DOZI. Latency of sporozoites, the transmission stage injected during an infectious blood meal, is controlled by the eIF2alpha kinase IK2, a general inhibitor of protein synthesis. Whether RNA-binding proteins participate in translational regulation in sporozoites remains to be studied. Here, we investigated the roles of two RNA-binding proteins of the Puf-family, Plasmodium Puf1 and Puf2, during sporozoite stage conversion. Our data reveal that, in the rodent malaria parasite P. berghei, Puf2 participates in the regulation of IK2 and inhibits premature sporozoite transformation. Inside mosquito salivary glands puf2(-) sporozoites transform over time to round forms resembling early intra-hepatic stages. As a result, mutant parasites display strong defects in initiating a malaria infection. In contrast, Puf1 is dispensable in vivo throughout the entire Plasmodium life cycle. Our findings support the notion of a central role for Puf2 in parasite latency during switch between the insect and mammalian hosts.     

Multiple blood feeding in mosquitoes shortens the Plasmodium falciparum incubation period and increases malaria transmission potential

Many mosquito species, including the major malaria vector Anopheles gambiae, naturally undergo multiple reproductive cycles of blood feeding, egg development and egg laying in their lifespan. Such complex mosquito behavior is regularly overlooked when mosquitoes are experimentally infected with malaria parasites, limiting our ability to accurately describe potential effects on transmission. Here, we examine how Plasmodium falciparum development and transmission potential is impacted when infected mosquitoes feed an additional time. We measured P. falciparum oocyst size and performed sporozoite time course analyses to determine the parasite’s extrinsic incubation period (EIP), i.e. the time required by parasites to reach infectious sporozoite stages, in An. gambiae females blood fed either once or twice. An additional blood feed at 3 days post infection drastically accelerates oocyst growth rates, causing earlier sporozoite accumulation in the salivary glands, thereby shortening the EIP (reduction of 2.3 ± 0.4 days). Moreover, parasite growth is further accelerated in transgenic mosquitoes with reduced reproductive capacity, which mimic genetic modifications currently proposed in population suppression gene drives. We incorporate our shortened EIP values into a measure of transmission potential, the basic reproduction number R₀, and find the average R₀ is higher (range: 10.1%–12.1% increase) across sub-Saharan Africa than when using traditional EIP measurements. These data suggest that malaria elimination may be substantially more challenging and that younger mosquitoes or those with reduced reproductive ability may provide a larger contribution to infection than currently believed. Our findings have profound implications for current and future mosquito control interventions.     

A mathematical model for zoonotic transmission of malaria in the Atlantic Forest: Exploring the effects of variations in vector abundance and acrodendrophily

Transmission foci of autochthonous malaria caused by Plasmodium vivax-like parasites have frequently been reported in the Atlantic Forest in Southeastern and Southern Brazil. Evidence suggests that malaria is a zoonosis in these areas as human infections by simian Plasmodium species have been detected, and the main vector of malaria in the Atlantic Forest, Anopheles (Kerteszia) cruzii, can blood feed on human and simian hosts. In view of the lack of models that seek to predict the dynamics of zoonotic transmission in this part of the Atlantic Forest, the present study proposes a new deterministic mathematical model that includes a transmission compartment for non-human primates and parameters that take into account vector displacement between the upper and lower forest strata. The effects of variations in the abundance and acrodendrophily of An. cruzii on the prevalence of infected humans in the study area and the basic reproduction number (R₀) for malaria were analyzed. The model parameters are based on the literature and fitting of the empirical data. Simulations performed with the model indicate that (1) an increase in the abundance of the vector in relation to the total number of blood-seeking mosquitoes leads to an asymptotic increase in both the proportion of infected individuals at steady state and R₀; (2) the proportion of infected humans at steady state is higher when displacement of the vector mosquito between the forest strata increases; and (3) in most scenarios, Plasmodium transmission cannot be sustained only between mosquitoes and humans, which implies that non-human primates play an important role in maintaining the transmission cycle. The proposed model contributes to a better understanding of the dynamics of malaria transmission in the Atlantic Forest.     

The Major Yolk Protein Vitellogenin Interferes with the Anti-Plasmodium Response in the Malaria Mosquito Anopheles gambiae

When taking a blood meal on a person infected with malaria, female Anopheles gambiae mosquitoes, the major vector of human malaria, acquire nutrients that will activate egg development (oogenesis) in their ovaries. Simultaneously, they infect themselves with the malaria parasite. On traversing the mosquito midgut epithelium, invading Plasmodium ookinetes are met with a potent innate immune response predominantly controlled by mosquito blood cells. Whether the concomitant processes of mosquito reproduction and immunity affect each other remains controversial. Here, we show that proteins that deliver nutrients to maturing mosquito oocytes interfere with the antiparasitic response. Lipophorin (Lp) and vitellogenin (Vg), two nutrient transport proteins, reduce the parasite-killing efficiency of the antiparasitic factor TEP1. In the absence of either nutrient transport protein, TEP1 binding to the ookinete surface becomes more efficient. We also show that Lp is required for the normal expression of Vg, and for later Plasmodium development at the oocyst stage. Furthermore, our results uncover an inhibitory role of the Cactus/REL1/REL2 signaling cassette in the expression of Vg, but not of Lp. We reveal molecular links that connect reproduction and immunity at several levels and provide a molecular basis for a long-suspected trade-off between these two processes.