Gametocyte production and transmission fitness of African and Asian isolates with differential susceptibility to artemisinins.

The emergence of parasites partially resistant to artemisinins (ART-R) poses a significant threat to recent gains in malaria control. ART-R has been associated with PfKelch13 (K13) mutations, which differ in fitness costs. This study investigates the gametocyte production and transmission fitness of African and Asian isolates with different K13 genotypes across multiple mosquito species.

Safety and Efficacy of Immunization with a Late-Liver-Stage Attenuated Malaria Parasite.

Background: Currently licensed and approved malaria subunit vaccines provide modest, short-lived protection against malaria. Immunization with live-attenuated malaria parasites is an alternative vaccination strategy that has potential to improve protection.

Methods: We conducted a double-blind, controlled clinical trial to evaluate the safety, side-effect profile, and efficacy of immunization, by means of mosquito bites, with a second-generation genetically attenuated parasite (GA2) - a single knockout NF54 parasite (sporozoite form) with extended development into the liver stage.

Plasmodium falciparum gametocyte production correlates with genetic markers of parasite replication but is not influenced by experimental exposure to mosquito biting.

Background: Plasmodium blood-stage parasites balance asexual multiplication with gametocyte development. Few studies link these dynamics with parasite genetic markers in vivo; even fewer in longitudinally monitored infections. Environmental influences on gametocyte formation, such as mosquito exposure, may influence the parasite's investment in gametocyte production.

AlbuMAX supplemented media induces the formation of transmission-competent P. falciparum gametocytes.

Asexual blood stage culture of Plasmodium falciparum is routinely performed but reproducibly inducing commitment to and maturation of viable gametocytes remains difficult. Culture media can be supplemented with human serum substitutes to induce commitment but these generally only allow for long-term culture of asexual parasites and not transmission-competent gametocytes due to their different lipid composition. Recent insights demonstrated the important roles lipids play in sexual commitment; elaborating on this we exposed ring stage parasites (20-24 hours hpi) for one day to AlbuMAX supplemented media to trigger induction to gametocytogenesis.

Quantification of sporozoite expelling by mosquitoes infected with laboratory and naturally circulating gametocytes.

It is currently unknown whether all -infected mosquitoes are equally infectious. We assessed sporogonic development using cultured gametocytes in the Netherlands and naturally circulating strains in Burkina Faso. We quantified the number of sporozoites expelled into artificial skin in relation to intact oocysts, ruptured oocysts, and residual salivary gland sporozoites.

Comparative analysis of glass and Hemotek membrane feeding systems for malaria transmission research.

Background: Glass membrane feeders are used in malaria research for artificial blood feeding. This study investigates the use of Hemotek membrane feeders as a standardized alternative feeding system.

Methods: Hemotek feeders were compared with glass feeders by assessing mosquito feeding rate, imbibed blood meal volume and Plasmodium falciparum infection intensity on mosquito guts.

Estimating female malaria mosquito age by quantifying Y-linked genes in stored male spermatozoa.

Vector control strategies are among the most effective measures to combat mosquito-borne diseases, such as malaria. These strategies work by altering the mosquito age structure through increased mortality of the older female mosquitoes that transmit pathogens. However, methods to monitor changes to mosquito age structure are currently inadequate for programmatic implementation.

No time to die: An in-depth analysis of James Bond's exposure to infectious agents.

Global travelers, whether tourists or secret agents, are exposed to a smörgåsbord of infectious agents. We hypothesized that agents pre-occupied with espionage and counterterrorism may, at their peril, fail to correctly prioritize travel medicine. To examine our hypothesis, we examined adherence to international travel advice during the 86 international journeys that James Bond was observed to undertake in feature films spanning 1962-2021.

A portfolio of geographically distinct laboratory-adapted Plasmodium falciparum clones with consistent infection rates in Anopheles mosquitoes.

Background: The ability to culture Plasmodium falciparum continuously in vitro has enabled stable access to asexual and sexual parasites for malaria research. The portfolio of isolates has remained limited and research is still largely based on NF54 and its derived clone 3D7. Since 1978, isolates were collected and cryopreserved at Radboudumc from patients presenting at the hospital.

The effect of anticoagulants in blood collection tubes on Plasmodium falciparum transmission in direct membrane feeding assays.

Background: Direct membrane feeding assays assess the transmission potential of malaria-infected individuals using whole blood collected in anticoagulant vacutainers.

Methods: The potential inhibitory effect of four commonly used anticoagulants on gametocyte infectivity to mosquitoes was assessed in standard membrane feeding assays with cultured Plasmodium falciparum.

Results: Infection burden in mosquitoes was significantly reduced when blood was collected in sodium citrate and EDTA.

Zonal human hepatocytes are differentially permissive to Plasmodium falciparum malaria parasites.

Plasmodium falciparum (Pf) is a major cause of human malaria and is transmitted by infected Anopheles mosquitoes. The initial asymptomatic infection is characterized by parasite invasion of hepatocytes, followed by massive replication generating schizonts with blood-infective merozoites. Hepatocytes can be categorized by their zonal location and metabolic functions within a liver lobule.

Persistence of mRNA indicative of Plasmodium falciparum ring-stage parasites 42 days after artemisinin and non-artemisinin combination therapy in naturally infected Malians.

Background: Malaria control in sub-Saharan Africa relies upon prompt case management with artemisinin-based combination therapy (ACT). Ring-stage parasite mRNA, measured by sbp1 quantitative reverse-transcriptase PCR (qRT-PCR), was previously reported to persist after ACT treatment and hypothesized to reflect temporary arrest of the growth of ring-stage parasites (dormancy) following exposure to artemisinins. Here, the persistence of ring-stage parasitaemia following ACT and non-ACT treatment was examined.

A mosquito feeding assay to examine Plasmodium transmission to mosquitoes using small blood volumes in 3D printed nano-feeders.

Background: To understand the dynamics of malaria transmission, membrane feeding assays with glass feeders are used to assess the transmission potential of malaria infected individuals to mosquitoes. However, in some circumstances, use of these assays is hindered by both the blood volume requirement and the availability of fragile, specially crafted glass feeders. 3D printed plastic feeders that require very small volumes of blood would thus expand the utility of membrane feeding assays.

When Is a Plasmodium-Infected Mosquito an Infectious Mosquito?

Plasmodium parasites experience significant bottlenecks as they transit through the mosquito and are transmitted to their mammalian host. Oocyst prevalence on mosquito midguts and sporozoite prevalence in salivary glands are nevertheless commonly used to confirm successful malaria transmission, assuming that these are reliable indicators of the mosquito's capacity to give rise to secondary infections. Here we discuss recent insights in sporogonic development and transmission bottlenecks for Plasmodium.

An open-label phase 1/2a trial of a genetically modified rodent malaria parasite for immunization against malaria.

For some diseases, successful vaccines have been developed using a nonpathogenic counterpart of the causative microorganism of choice. The nonpathogenicity of the rodent () parasite in humans prompted us to evaluate its potential as a platform for vaccination against human infection by (), a causative agent of malaria. We hypothesized that the genetic insertion of a leading protein target for clinical development of a malaria vaccine, circumsporozoite protein (CSP), in its natural pre-erythrocytic environment, would enhance 's capacity to induce protective immunity against infection.

s230 and s48/45 Fusion Proteins Elicit Strong Transmission-Blocking Antibody Responses Against .

The s230 and s48/45 proteins are expressed during transmission from man to mosquito and are leading candidates for a malaria transmission blocking vaccine. Individually they generate transmission blocking (TB) antibodies in rodent models. Whether the single protein vaccines are suitable to use in field settings will primarily depend on their potency to elicit functional antibodies.

Outcomes of controlled human malaria infection after BCG vaccination.

Recent evidence suggests that certain vaccines, including Bacillus-Calmette Guérin (BCG), can induce changes in the innate immune system with non-specific memory characteristics, termed 'trained immunity'. Here we present the results of a randomised, controlled phase 1 clinical trial in 20 healthy male and female volunteers to evaluate the induction of immunity and protective efficacy of the anti-tuberculosis BCG vaccine against a controlled human malaria infection. After malaria challenge infection, BCG vaccinated volunteers present with earlier and more severe clinical adverse events, and have significantly earlier expression of NK cell activation markers and a trend towards earlier phenotypic monocyte activation.

Gametocyte Enrichment in Peripheral Blood Samples by Magnetic Fractionation: Gametocyte Yields and Possibilities to Reuse Columns.

Gametocytes are sexual stage malaria parasites responsible for transmission to mosquitoes. Multiple gametocyte-producing clones may be present in natural infections, but the molecular characterization of gametocytes is challenging. Because of their magnetic properties, gametocyte enrichment can be achieved by magnetic fractionation.

Controlled Human Malaria Infection with Graded Numbers of NF135.C10- or NF166.C8-Infected Mosquitoes.

Controlled human malaria infections (CHMIs) with () parasites are well established. Exposure to five (NF54)-infected mosquitoes results in 100% infection rates in malaria-naïve volunteers. Recently clones NF135.

Predicting the likelihood and intensity of mosquito infection from sex specific gametocyte density.

Understanding the importance of gametocyte density on human-to-mosquito transmission is of immediate relevance to malaria control. Previous work (Churcher et al., 2013) indicated a complex relationship between gametocyte density and mosquito infection.

The Complement System Contributes to Functional Antibody-Mediated Responses Induced by Immunization with Plasmodium falciparum Malaria Sporozoites.

Long-lasting and sterile homologous protection against malaria can be achieved by the exposure of malaria-naive volunteers under chemoprophylaxis to -infected mosquitoes (chemoprophylaxis and sporozoite [CPS] immunization). While CPS-induced antibodies neutralize sporozoite infectivity and , antibody-mediated effector mechanisms are still poorly understood. Here, we investigated whether complement contributes to CPS-induced preerythrocytic immunity.

Mosquito Infectivity and Parasitemia after Controlled Human Malaria Infection.

Controlled Human Malaria Infection (CHMI) has become an increasingly important tool for the evaluation of drugs and vaccines. Controlled Human Malaria Infection has been demonstrated to be a reproducible model; however, there is some variability in time to onset of parasitemia between volunteers and studies. At our center, mosquitoes infected with by membrane feeding have variable and high salivary gland sporozoite load (mean 78,415; range 26,500-160,500).

Publisher Correction: Unravelling the immune signature of Plasmodium falciparum transmission-reducing immunity.

The original version of this Article contained errors in Fig. 3. In panel a, bars from a chart depicting the percentage of antibody-positive individuals in non-infectious and infectious groups were inadvertently included in place of bars depicting the percentage of infectious individuals, as described in the Article and figure legend.

A randomized feasibility trial comparing four antimalarial drug regimens to induce gametocytemia in the controlled human malaria infection model.

Background: Malaria elimination strategies require a thorough understanding of parasite transmission from human to mosquito. A clinical model to induce gametocytes to understand their dynamics and evaluate transmission-blocking interventions (TBI) is currently unavailable. Here, we explore the use of the well-established Controlled Human Malaria Infection model (CHMI) to induce gametocyte carriage with different antimalarial drug regimens.