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

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 Anopheles 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.

Paralytic activity of lysophosphatidylcholine from saliva of the waterbug Belostoma anurum.

Lysophosphatidylcholine (LPC) is a major bioactive lipid that is enzymatically generated by phospholipase A(2) (PLA(2)). Previously, we showed that LPC is present in the saliva of the blood-sucking hemipteran Rhodnius prolixus and modulates cell-signaling pathways involved in vascular biology, which aids blood feeding. Here, we show that the saliva of the predator insect Belostoma anurum contains a large number of lipids with LPC accounting for 25% of the total phospholipids. A PLA(2) enzyme likely to be involved in LPC generation was characterized. The activity of this enzyme is 5-fold higher in Belostoma saliva than in other studied hemipterans, suggesting a close association with the predator feeding habits of this insect. Belostoma employs extra-oral digestion, which allows for ingestion of larger prey than itself, including small vertebrates such as amphibians and fish. Therefore, prey immobilization during digestion is essential, and we show here that Belostoma saliva and B. anurum saliva purified LPC have paralytic activity in zebrafish. This is the first evidence that lysophospholipids might play an important role in prey immobilization, in addition to contributing to blood feeding, and might have been an evolutionary acquisition that occurred long before the appearance of hematophagy in this animal group.

An epithelial serine protease, AgESP, is required for Plasmodium invasion in the mosquito Anopheles gambiae.

BACKGROUND: Plasmodium parasites need to cross the midgut and salivary gland epithelia to complete their life cycle in the mosquito. However, our understanding of the molecular mechanism and the mosquito genes that participate in this process is still very limited. METHODOLOGY/PRINCIPAL FINDINGS: We identified an Anopheles gambiae epithelial serine protease (AgESP) that is constitutively expressed in the submicrovillar region of mosquito midgut epithelial cells and in the basal side of the salivary glands that is critical for Plasmodium parasites to cross these two epithelial barriers. AgESP silencing greatly reduces Plasmodium berghei and Plasmodium falciparum midgut invasion and prevents the transcriptional activation of gelsolin, a key regulator of actin remodeling and a reported Plasmodium agonist. AgESP expression is highly induced in midgut cells invaded by Plasmodium, suggesting that this protease also participates in the apoptotic response to invasion. In salivary gland epithelial cells, AgESP is localized on the basal side--the surface with which sporozoites interact. AgESP expression in the salivary gland is also induced in response to P. berghei and P. falciparum sporozoite invasion, and AgESP silencing significantly reduces the number of sporozoites that invade this organ. CONCLUSION: Our findings indicate that AgESP is required for Plasmodium parasites to effectively traverse the midgut and salivary gland epithelial barriers. Plasmodium parasites need to modify the actin cytoskeleton of mosquito epithelial cells to successfully complete their life cycle in the mosquito and AgESP appears to be a major player in the regulation of this process.

Mitochondrial reactive oxygen species modulate mosquito susceptibility to Plasmodium infection.

BACKGROUND: Mitochondria perform multiple roles in cell biology, acting as the site of aerobic energy-transducing pathways and as an important source of reactive oxygen species (ROS) that modulate redox metabolism. METHODOLOGY/PRINCIPAL FINDINGS: We demonstrate that a novel member of the mitochondrial transporter protein family, Anopheles gambiae mitochondrial carrier 1 (AgMC1), is required to maintain mitochondrial membrane potential in mosquito midgut cells and modulates epithelial responses to Plasmodium infection. AgMC1 silencing reduces mitochondrial membrane potential, resulting in increased proton-leak and uncoupling of oxidative phosphorylation. These metabolic changes reduce midgut ROS generation and increase A. gambiae susceptibility to Plasmodium infection. CONCLUSION: We provide direct experimental evidence indicating that ROS derived from mitochondria can modulate mosquito epithelial responses to Plasmodium infection.

Energy metabolism affects susceptibility of Anopheles gambiae mosquitoes to Plasmodium infection.

Previous studies showed that Anopheles gambiae L3-5 females, which are refractory (R) to Plasmodium infection, express higher levels of genes involved in redox-metabolism and mitochondrial respiration than susceptible (S) G3 females. Our studies revealed that R females have reduced longevity, faster utilization of lipid reserves, impaired mitochondrial state-3 respiration, increased rate of mitochondrial electron leak and higher expression levels of several glycolytic enzyme genes. Furthermore, when state-3 respiration was reduced in S females by silencing expression of the adenine nucleotide translocator (ANT), hydrogen peroxide generation was higher and the mRNA levels of lactate dehydrogenase increased in the midgut, while the prevalence and intensity of Plasmodium berghei infection were significantly reduced. We conclude that there are broad metabolic differences between R and S An. gambiae mosquitoes that influence their susceptibility to Plasmodium infection.

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

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.

Flight-oogenesis syndrome in a blood-sucking bug: biochemical aspects of lipid metabolism.

Lipophorin (Lp), either labeled in diacylglycerol moiety with [(3)H]-Palmitic acid or in phospholipid moiety with (32)Pi, was injected into Rhodnius prolixus females. Insects were induced to flight for different times. In just a few minutes of flight, the transfer of radioactivity to ovaries decreased, accompanied by its increase to flight muscles. After one hour of flight, Lp density was higher (1.132 g/mL) than before flight (1.116 g/mL). Lp purified from insects after flight was analyzed by gel filtration chromatography and a polyacrylamide gel pore limit electrophoresis. Both analyses demonstrated a decrease in Lp molecular mass after flight but no changes in apoLp-III amounts were observed. Time-course experiments showed that only 30 min of flight are required for the detection of changes in Lp density and molecular mass. About the same time of rest is necessary for Lp density and molecular mass to return to the baseline value. The lipid content from Lp particles, determined by high-performance thin-layer chromatography (HPTLC), showed a decrease in total lipids after flight. At the same time, an increase of many classes of lipids was observed in flight muscles except for triacylglycerol, which was reduced. The increase of flight muscle lipids was accompanied by a decrease of the ovaries lipid content. The insects subjected to daily exhaustive flight showed a significant decrease in total number of eggs produced. But insects subjected to a single exhaustive flight showed only a small reduction in total number of eggs. Lp density variation during the flight activity of Rhodnius prolixus females is discussed in association with physiological events such as oogenesis.