The circumsporozoite (CS) protein of ma- lariaparasites(Plasmodium)coversthesurfaceofsporozoites that invade hepatocytes in mammalian hosts and macro- phagesinavianhosts.CSgeneshavebeencharacterizedfrom many Plasmodium that infect mammals; two domains of the corresponding proteins, identified initially by their conserva- tion (region I and region II), have been implicated in binding to hepatocytes. The CS gene from the avian parasitePlasmo- dium gallinaceum was characterized to compare these func- tionaldomainstothoseofmammalianPlasmodiumandforthe studyofPlasmodiumevolution.TheP.gallinaceumproteinhas thecharacteristicsofCSproteins,includingasecretorysignal sequence, central repeat region, regions of charged amino acids, and an anchor sequence. Comparison with CS signal sequences reveals four distinct groupings, withP. gallinaceum most closely related to the human malariaPlasmodium falci- parum. The 5-amino acid sequence designated region I, which isidenticalinallmammalianCSandimplicatedinhepatocyte invasion, is different in the avian protein. TheP. gallinaceum repeat region consists of 9-amino acid repeats with the consensus sequence QP(AyV)GGNGG(AyV). The conserved motif designated region II-plus, which is associated with targeting the invasion of liver cells, is also conserved in the avian protein. Phylogenetic analysis of the aligned Plasmo- diumCS sequences yields at ree with at opology similar to the one obtained using sequence data from the small subunit rRNA gene. The phylogeny using the CS gene supports the proposalthatthehumanmalariaP.falciparumissignificantly more related to avian parasites than to other parasites infect- ing mammals, although the biology of sporozoite invasion is different between the avian and mammalian species.

Comparison of circumsporozoite proteins from avian and mammalian malarias: Biological and phylogenetic implications (plasmodiumyapicomplexayevolutionysporozoite invasionycell adhesion motif)

The human malaria parasite Plasmodium vivax is more resistant to malaria control strategies than Plasmodium falciparum, and maintains high genetic diversity even when transmission is low. To investigate whether declining P. vivax transmission leads to increasing population structure that would facilitate elimination, we genotyped samples from across the Southwest Pacific region, which experiences an eastward decline in malaria transmission, as well as samples from two time points at one site (Tetere, Solomon Islands) during intensified malaria control. Analysis of 887 P. vivax microsatellite haplotypes from hyperendemic Papua New Guinea (PNG, n = 443), meso-hyperendemic Solomon Islands (n = 420), and hypoendemic Vanuatu (n = 24) revealed increasing population structure and multilocus linkage disequilibrium yet a modest decline in diversity as transmission decreases over space and time. In Solomon Islands, which has had sustained control efforts for 20 years, and Vanuatu, which has experienced sustained low transmission for many years, significant population structure was observed at different spatial scales. We conclude that control efforts will eventually impact P. vivax population structure and with sustained pressure, populations may eventually fragment into a limited number of clustered foci that could be targeted for elimination.

/pdf/increasingly-inbred-and-fragmented-populations-of-plasmodium-d5qklruh4a.pdf

Increasingly inbred and fragmented populations of Plasmodium vivax associated with the eastward decline in malaria transmission across the Southwest Pacific.

Strategies designed to advance towards malaria elimination rely on the detection and treatment of infections, rather than fever, and the interruption of malaria transmission between mosquitoes and humans. Mass drug administration with anti-malarials directed at eliminating parasites in blood, either to entire populations or targeting only those with malaria infections, are considered useful strategies to progress towards malaria elimination, but may be insufficient if applied on their own. These strategies assume a closer contact with populations, so incorporating a vector control intervention tool to those approaches could significantly enhance their efficacy. Ivermectin, an endectocide drug efficacious against a range of Anopheles species, could be added to other drug-based interventions. Interestingly, ivermectin could also be useful to target outdoor feeding and resting vectors, something not possible with current vector control tools, such as impregnated bed nets or indoor residual spraying (IRS). Anopheles aquasalis susceptibility to ivermectin was assessed. In vivo assessments were performed in six volunteers, being three men and three women. The effect of ivermectin on reproductive fitness and mosquito survivorship using membrane feeding assay (MFA) and direct feeding assay (DFA) was assessed and compared. The ivermectin lethal concentration (LC) values were LC50 = 47.03 ng/ml [44.68–49.40], LC25 = 31.92 ng/ml [28.60–34.57] and LC5 = 18.28 ng/ml [14.51–21.45]. Ivermectin significantly reduced the survivorship of An. aquasalis blood-fed 4 h post-ingestion (X
 2
 [N = 880] = 328.16, p < 0.001), 2 days post-ingestion (DPI 2) (X
 2
 [N = 983] = 156.75, p < 0.001), DPI 7 (X
 2
 [N = 935] = 31.17, p < 0.001) and DPI 14 (X
 2
 [N = 898] = 38.63, p < 0.001) compared to the blood fed on the untreated control. The average number of oviposited eggs per female was significantly lower in LC5 group (22.44 [SD = 3.38]) than in control (34.70 [SD = 12.09]) (X
 2
 [N = 199] = 10.52, p < 0.001) as well as the egg hatch rate (LC5 = 74.76 [SD = 5.48]) (Control = 81.91 [SD = 5.92]) (X
 2
 [N = 124] = 64.24, p < 0.001). However, no differences were observed on the number of pupae that developed from larvae (Control = 34.19 [SD = 10.42) and group (LC5 = 33.33 [SD = 11.97]) (X
 2
 [N = 124] = 0.96, p > 0.05). Ivermectin drug reduces mosquito survivorship when blood fed on volunteer blood from 4 h to 14 days post-ingestion controlling for volunteers’ gender. Ivermectin at mosquito sub-lethal concentrations (LC5) reduces fecundity and egg hatch rate but not the number of pupae that developed from larvae. DFA had significantly higher effects on mosquito survival compared to MFA. The findings are presented and discussed through the prism of malaria elimination in the Amazon region.

/pdf/filling-gaps-on-ivermectin-knowledge-effects-on-the-survival-4vlkwwchc5.pdf

Filling gaps on ivermectin knowledge: effects on the survival and reproduction of Anopheles aquasalis, a Latin American malaria vector.

Background 
The mosquito resistance to the insecticides threatens malaria control efforts, potentially becoming a major public health issue Alternative methods like ivermectin (IVM) administration to humans has been suggested as a possible vector control to reduce Plasmodium transmission Anopheles aquasalis and Anopheles darlingi are competent vectors for Plasmodium vivax, and they have been responsible for various malaria outbreaks in the coast of Brazil and the Amazon Region of South America


Methods 
To determine the IVM susceptibility against P vivax in An aquasalis and An darlingi, ivermectin were mixed in P vivax infected blood: (1) Powdered IVM at four concentrations (0, 5, 10, 20 or 40 ng/mL) (2) Plasma (0 hours, 4 hours, 1 day, 5, 10 and 14 days) was collected from healthy volunteers after to administer a single oral dose of IVM (200 μg/kg) (3) Mosquitoes infected with P vivax and after 4 days was provided with IVM plasma collected 4 hours post-treatment (4) P vivax-infected patients were treated with various combinations of IVM, chloroquine, and primaquine and plasma or whole blood was collected at 4 hours Seven days after the infective blood meal, mosquitoes were dissected to evaluate oocyst presence Additionally, the ex vivo effects of IVM against asexual blood-stage P vivax was evaluated


Results 
IVM significantly reduced the prevalence of An aquasalis that developed oocysts in 10 to 40 ng/mL pIVM concentrations and plasma 4 hours, 1 day and 5 days In An darlingi to 4 hours and 1 day The An aquasalis mortality was expressively increased in pIVM (40ng/mL) and plasma 4 hours, 1, 5 10 and 14 days post-intake drug and in An darlingi only to 4 hours and 1 day The double fed meal with mIVM by the mosquitoes has a considerable impact on the proportion of infected mosquitoes for 7 days post-feeding The oocyst infection prevalence and intensity were notably reduced when mosquitoes ingested blood from P vivax patients that ingested IVM+CQ, PQ+CQ and IVM+PQ+CQ P vivax asexual development was considerably inhibited by mIVM at four-fold dilutions


Conclusion 
In conclusion, whole blood spiked with IVM reduced the infection rate of P vivax in An aquasalis and An darlingi, and increased the mortality of mosquitoes Plasma from healthy volunteers after IVM administration affect asexual P vivax development These findings support that ivermectin may be used to decrease P vivax transmission

/pdf/promising-approach-to-reducing-malaria-transmission-by-59safoj2de.pdf

Promising approach to reducing Malaria transmission by ivermectin: Sporontocidal effect against Plasmodium vivax in the South American vectors Anopheles aquasalis and Anopheles darlingi

Malaria is transmitted when an infected mosquito delivers Plasmodium sporozoites into a vertebrate host. There are many species of Plasmodium and, in general, the infection is host-specific. For example, Plasmodium gallinaceum is an avian parasite, while Plasmodium berghei infects mice. These two parasites have been extensively used as experimental models of malaria transmission. Plasmodium falciparum and Plasmodium vivax are the most important agents of human malaria, a life-threatening disease of global importance. To complete their life cycle, Plasmodium parasites must traverse the mosquito midgut and form an oocyst that will divide continuously. Mature oocysts release thousands of sporozoites into the mosquito haemolymph that must reach the salivary gland to infect a new vertebrate host. The current understanding of the biology of oocyst formation and sporozoite release is mostly based on experimental infections with P. berghei, and the conclusions are generalized to other Plasmodium species that infect humans without further morphological analyses. Here, it is described the microanatomy of sporozoite escape from oocysts of four Plasmodium species: the two laboratory models, P. gallinaceum and P. berghei, and the two main species that cause malaria in humans, P. vivax and P. falciparum. It was found that sporozoites have species-specific mechanisms of escape from the oocyst. The two model species of Plasmodium had a common mechanism, in which the oocyst wall breaks down before sporozoites emerge. In contrast, P. vivax and P. falciparum sporozoites show a dynamic escape mechanism from the oocyst via polarized propulsion. This study demonstrated that Plasmodium species do not share a common mechanism of sporozoite escape, as previously thought, but show complex and species-specific mechanisms. In addition, the knowledge of this phenomenon in human Plasmodium can facilitate transmission-blocking studies and not those ones only based on the murine and avian models.

/pdf/species-specific-escape-of-plasmodium-sporozoites-from-4vwb1xmmgi.pdf

Species-specific escape of Plasmodium sporozoites from oocysts of avian, rodent, and human malarial parasites

In the Americas, areas with a high risk of malaria transmission are mainly located in the Amazon Forest, which extends across nine countries. One keystone step to understanding the Plasmodium life cycle in Anopheles species from the Amazon Region is to obtain experimentally infected mosquito vectors. Several attempts to colonise Ano- pheles species have been conducted, but with only short-lived success or no success at all. In this review, we review the literature on malaria transmission from the perspective of its Amazon vectors. Currently, it is possible to develop experimental Plasmodium vivax infection of the colonised and field-captured vectors in laboratories located close to Amazonian endemic areas. We are also reviewing studies related to the immune response to P. vivax infection of Anopheles aquasalis, a coastal mosquito species. Finally, we discuss the importance of the modulation of Plasmodium infection by the vector microbiota and also consider the anopheline genomes. The establishment of experimental mosquito infections with Plasmodium falciparum, Plasmodium yoelii and Plasmodium berghei parasites that could provide interesting models for studying malaria in the Amazonian scenario is important. Understanding the molecular mechanisms involved in the development of the parasites in New World vectors is crucial in order to better determine the interaction process and vectorial competence.

/pdf/an-overview-of-malaria-transmission-from-the-perspective-of-17xsclwoiu.pdf

Paulo F P. Pimenta

Papers

An overview of malaria transmission from the perspective of Amazon Anopheles vectors.

Use of ivermectin for transmission blocking of Plasmodium vivax in Anopheles aquasalis and Anopheles darlingi