Investigational Malaria Vaccine Gives Strong, Lasting Protection

Two U.S. Phase 1 clinical trials of a novel candidate malaria vaccine have found that the regimen conferred unprecedentedly high levels of durable protection when volunteers were later exposed to disease-causing malaria parasites.

The vaccine combines live parasites with either of two widely used antimalarial drugs—an approach termed chemoprophylaxis vaccination. A Phase 2 clinical trial of the vaccine is now underway in Mali, a malaria-endemic country. If the approach proves successful there, chemoprophylaxis vaccination, or CVac, potentially could help reverse the stalled decline of global malaria. Currently, there is no vaccine in widespread use for the mosquito-transmitted disease. 

The trials were conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, Maryland. They were led by Patrick E. Duffy, M.D., of the NIH National Institute of Allergy and Infectious Diseases (NIAID), and Stephen L. Hoffman, M.D., CEO of Sanaria Inc., Rockville, Maryland. 

The World Health Organization (WHO) report states that there were an estimated 229 million cases of malaria worldwide in 2019 with an estimated number of malaria deaths at 409 000, adding that children aged under 5 years are the most vulnerable group affected by malaria; in 2019, they accounted for 67% (274 000) of all malaria deaths worldwide. The report further states that total funding for malaria control and elimination reached an estimated US$ 3 billion in 2019 with contributions from governments of endemic countries amounted to US$ 900 million, representing 31% of total funding.

The Sanaria vaccine, called PfSPZ, is composed of sporozoites, the form of the malaria parasite transmitted to people by mosquito bites. Sporozoites travel through blood to the liver to initiate infection. In the CVac trials, healthy adult volunteers received PfSPZ along with either pyrimethamine, a drug that kills liver-stage parasites, or chloroquine, which kills blood-stage parasites.

Malaria sporozoites, the infectious form of the malaria parasite that is injected into people by mosquitoes.
Credit: NIAID

Three months later, under carefully controlled conditions, the volunteers were exposed to either an African malaria parasite strain that was the same as that in the vaccine (homologous challenge) or a variant South American parasite (heterologous challenge) that was more genetically distant from the vaccine strain than hundreds of African parasites. Exposure in both cases was via inoculation into venous blood, which infects all unvaccinated individuals. 

At the lowest PfSPZ dosage, the CVac approach conferred modest protection: only two of nine volunteers (22.2%) who received the pyrimethamine combination were protected from homologous challenge. In contrast, seven out of eight volunteers (87.5%) who received the highest PfSPZ dosage combined with pyrimethamine were protected from homologous challenge, and seven out of nine volunteers (77.8%) were protected from heterologous challenge.

In the case of the chloroquine combination, all six volunteers (100%) who received the higher PfSPZ dosage were completely protected from heterologous challenge. The high levels of cross-strain protection lasted at least three months (the time elapsed between vaccination and challenge) for both higher-dose regimens. One hundred percent protection for three months against heterologous variant parasites is unprecedented for any malaria vaccine in development, the authors note. These data suggest that CVac could be a promising approach for vaccination of travelers to and people living in malaria-endemic areas.

New research shows how the malaria parasite grows and multiplies

For the first time, scientists have shown how certain molecules play an essential role in the rapid reproduction of parasite cells, which cause this deadly disease.

This could be the next step towards being able to prevent the malaria parasite from reproducing.

The research, which is co-led by Rita Tewari, Professor of Parasite Cell Biology in the School of Life Sciences at the University of Nottingham and Professor Karine Le Roch at the University of California Riverside, USA, could pave the way in helping to eradicate the disease.

The study, which is published in Cell Reports, was a collaborative effort with scientists from the Universities of Dundee, and Warwick in the UK, the University of Bern, Switzerland, ICGEB, India and the Francis Crick Institute.

Malaria is one of the world’s biggest killer infections and is responsible for almost half a million deaths a year, mainly in tropical developing countries. The disease is caused by a one-celled parasite called Plasmodium. It is passed on from person to person as female Anopheles mosquitoes pick up the parasite from infected people when they bite to get the blood needed to nurture their eggs. Inside the mosquito the parasites reproduce, multiply and develop.

As part of their latest research, the team wanted to better understand how the parasite’s cell divides and multiplies especially within a mosquito.

Condensin in Male cell multiplication
Condensin in asexual cell multiplication

Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs. Each organism has DNA organised into a certain number of chromosomes and needs condensins in order to ‘split’ this DNA when they multiply. Condensins are large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis.

In the malaria parasite (Plasmodium), the role of condensins in multiplication and proliferation was unclear. The team looked at two of the crucial condensin subunits, called SMC2 and SMC4, which are required to maintain the structure of chromosomes in a cell of other organisms.

Professor Tewari said: “We have tried to understand how these molecules work in the unusual pattern of multiplication by the parasite. We found that these molecules are there at all the stages of multiplication and they are present only at a certain part of the chromosome, which is called the centromere.  We wanted to understand how does the parasite multiply? How do these molecules organise themselves and the DNA in those cells? It is fascinating how a single cell can carry out so many different modes of multiplication, and we need to understand how it does this.”

After analysing the parasite, the team found a very unusual type of cell division, showing that the malaria parasite has evolved ways to ensure its survival by way of its cell division.

Professor Tewari says: “This particular parasite is very adaptable. Even if you kill it in the human blood stream, it can move into the mosquito stage. Over time, it has adapted to survive and has a lot of genetic plasticity, which is why it is difficult to control the disease.

“We need to understand what gives the parasite this plasticity and what it needs at every stage to survive, so it is crucial to understand how the parasite cell divides. The aim of our research is not to develop a drug immediately, but to answer the fundamental question of how the parasite divides and survives and the machinery it uses. The parasite has diverse modes of multiplying, so even if a drug or an effective vaccine is created, they may be able to adapt and we need to understand how. This is a next step towards that goal.”

Professor Le Roch says: “By understanding the fundamental aspect of parasite biology, we are decrypting how the parasite divide, and how the different mechanisms regulating cell division can affect the ability of the parasite to thrive and replicate exponentially inside its hosts.  If we identify the molecular components that are essential for the replication of this parasite, we will be able to develop novel and long-lasting therapeutic strategies against this devastating disease.”

This research is funded by MRC and BBSRC to Professor Tewari’s group and by NIH grants to Prof Karine Le Roch’s group.

Published courtesy of NIAID

NIH-developed Zika vaccine improves fetal outcomes in animal model

A vial of the NIAID Zika virus investigational DNA vaccine, taken at the NIAID Vaccine Research Center’s Pilot Plant in Frederick, Maryland. NIAID

An experimental Zika vaccine lowered levels of virus in pregnant monkeys and improved fetal outcomes in a rhesus macaque model of congenital Zika virus infection, according to a new study in Science Translational Medicine. 

The research was conducted by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, and their collaborators from the University of California, Davis; Duke University, Durham, North Carolina; and the University of California, Los Angeles. NIAID scientists developed the experimental vaccine and currently are evaluating it in a Phase 2 human clinical trial. The vaccine uses a small circular piece of DNA, or plasmid, containing genes that encode Zika virus surface proteins to induce an immune response.

Zika virus is primarily transmitted to humans by Aedes mosquitoes; it also can be transmitted through sex. The virus can cause serious birth defects in babies born to mothers who become infected during pregnancy. Ideally, the authors note, a Zika vaccine would be given to adolescents and adults of childbearing age before pregnancy to prevent congenital Zika syndrome.

Large outbreaks of Zika virus in the Americas in 2015 and 2016 led to thousands of cases of congenital Zika syndrome, prompting NIAID scientists to quickly develop and begin clinical trials of the NIAID DNA Zika vaccine. While clinical trials can yield data on safety and how the vaccine performs in recipients, due to the diminished incidence of Zika, conducting a clinical trial that would determine the vaccine’s ability to prevent adverse fetal outcomes has been logistically difficult. Therefore, researchers developed a macaque model of congenital Zika syndrome to provide another way to evaluate the experimental vaccine.

Their study compared outcomes in 12 unvaccinated pregnant macaques and 13 macaques vaccinated before pregnancy. All macaques were exposed to Zika virus a total of three times during the first and second trimesters. Vaccinated animals had a significant reduction in the amount of Zika virus in the blood and in the length of time virus was detectable compared to unvaccinated animals. The vaccinated group was significantly less likely to transmit Zika virus to the fetus, whereas persistent Zika virus infection in unvaccinated macaques was associated with fetal infection. No cases of early fetal loss occurred in the vaccinated group, which also had no evidence of damage to either the placenta or the fetal brain.

The study suggests that sterilizing immunity — an immune response that prevents infection entirely, with no detectable virus — may not be required for significant protection against congenital Zika syndrome, according to the authors. They note that the ability of a vaccine to prevent persistent Zika virus infection may be an important consideration for future clinical research. Meanwhile, the animal model can be used to learn more about Zika virus transmission from mother to fetus and possible intervention strategies.

Graphene shield shows promise in blocking mosquito bites

NIH-funded project shows graphene could provide alternative to chemicals in insect repellant and protective clothing.

An innovative graphene-based film helps shield people from disease-carrying mosquitos, according to a new study funded by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health. The research, conducted by the Brown University Superfund Research Center, Providence, Rhode Island, is published in the Proceedings of the National Academy of Sciences.

Bite by an Aedes mosquito. This species can transmit diseases such as chikungunya, dengue, and Zika. NIAID

“These findings could lead to new protective methods against mosquitos, without the environmental or human health effects of other chemical-based repellants,” said Heather Henry, Ph.D., a health scientist administrator with the NIEHS Superfund Research Program.

Researchers found dry graphene film seemed to interfere with mosquitos’ ability to sense skin and sweat because they did not land and try to bite. When they looked closely at videos taken of the mosquitos in action, they noticed the insects landed much less frequently on graphene than on bare skin. The graphene film also provided a strong barrier that mosquitos could not bite through, although when wet it did not stop mosquitos from landing on skin.

“We set out imagining that graphene film would act as a mechanical barrier but after observing the mosquitos’ behavior, we began to suspect they were not interested in biting,” said Robert Hurt, Ph.D., director of the Superfund Research Program at Brown University. 

Mosquitos threaten public health by carrying infectious viruses such as Yellow Fever, West Nile, and Zika, leading to disability and death for millions of people every year.

Results show that graphene, a tight, honeycomb lattice of carbon, could be an alternative to chemicals now used in mosquito repellants and protective clothing. Until this study, insect-bite protection was an unexplored function of graphene-based materials.

Several years ago, Hurt began devising suits with graphene to protect workers against hazardous chemicals at environmental clean-up sites. He pointed out a wealth of literature demonstrates graphene’s impermeable qualities. Graphene is invisible to the unaided eye, yet harder than diamonds, stronger than steel, and more conductive than copper. Since its discovery in 2004, graphene has been used for a variety of barrier and filtration purposes.

“This innovation using graphene to repel mosquitos could help reduce the burden of ill health associated with a number of infectious diseases and might reduce the need for pesticides to eradicate the mosquitos that carry them,” said William Suk, Ph.D., director of the NIEHS Superfund Research Program. “New material such as this one should be assessed in the field to determine full public health implications.”

Researchers Discover How Mosquitoes Smell Human Sweat

For many of us, pesky mosquitoes are part of life outdoors during the summer months. While some people consistently find themselves covered in bites after an evening outside, others may rarely get bitten. This puzzling phenomenon—why mosquitoes choose to bite some people over others—is actually an important area of research for infectious disease experts.

Bite by an Aedes mosquito. This species can transmit diseases such as chikungunya, dengue, and Zika. Credit: NIAID

Mosquito bites can be more than just an itchy nuisance in certain parts of the world. Mosquitoes can carry parasites, viruses, and worms, and spread deadly infections. In select parts of the United States, mosquitoes have transmitted viruses such as chikungunya, dengue, West Nile, and Zika. Mosquitoes found in other parts of the world can spread filariasis and malaria—a disease that caused 435,000 deaths worldwide in 2017.

One element all mosquitoes have in common is their complex sense of smell. Mosquitoes must seek out blood meals (a mosquito “bite” to humans) to reproduce and water sources to lay eggs; however, they have poor vision and instead use scent to find their next meal.

Mosquitoes have exquisitely sensitive small hairs (known as sensillae) on their antennae and mouth parts. These hairs have scent receptors that help the mosquitoes distinguish among and select hosts. However, the scents that attract mosquitoes, and why they choose to bite some people over others, is still not well understood. Various NIAID-supported scientists hope to learn more through basic and translational research projects on mosquito olfaction (the sense of smell), host-seeking behavior, and host identification.

Researchers have long known that mosquitoes are attracted to the human scent of sweat, which includes the odor of lactic acid. The mechanisms behind this attraction remained a mystery, until recently. A NIAID-funded team of investigators have identified a unique odor receptor, known as Ionotropic Receptor 8a (IR8a), that is used by the Aedes aegypti mosquito to detect lactic acid. Led by Dr. Matthew DeGennaro of Florida International University, the research team mutated various receptors of Aedes aegypti, a mosquito that transmits diseases such as dengue and Zika, to study the effects on olfaction. When they mutated IR8a, which is located on the antennae, researchers discovered that the mosquitoes were incapable of sensing lactic acid and other acidic smells in human odor. The findings, published in Current Biology,(link is external) could lead to the development of new and improved mosquito attractants and repellents. If researchers know how mosquitoes find people, they can develop novel ways to target those mechanisms.

NIAID also is applying concepts from basic research on mosquito olfaction to support the development and testing of novel tools for mosquito control. These include traps that use attractants to lure mosquitoes searching for a meal or a site to lay eggs. Scientists also are working to develop repellents, including improved, environmentally friendly products for personal and spatial protection. Investigators hope that mosquito olfaction research will lead to new ways to prevent mosquitoes from finding and biting people, and, ultimately, reduce the transmission of mosquito-borne diseases.

Reference: JI Raji et al. Aedes aegypti mosquitoes detect acidic volatiles found in human odor using the IR8a pathway. Current Biology DOI: 10.1016/j.cub.2019.02.045 (2019)

Weapon made from spider toxin destroys mosquitoes

The National Institute of Allergy and Infectious Diseases (NIAID)-funded researchers who developed a genetically modified mosquito-killing fungus, a weapon made from spider toxin, that destroys blood-sucking enemies from the inside and helps save people from disease and death.

MosquitoSphere is designed to simulate a village setting and included plants, huts, small pools of water and a food source for mosquitoes.
Credit: Etienne Bilgo

The researchers tested it in the West African nation of Burkina Faso and have shown that it even works against mosquitoes that have become resistant to chemical insecticides.

Most of the 435,000 annual deaths from malaria occur in African countries and those who succumb are typically very young children or pregnant women. The mosquitoes that spread malaria-causing parasites are kept in check mainly by insecticide-impregnated bed nets and indoor spraying. However, mosquitoes have developed resistance to chemical insecticides and the insecticides may harm beneficial insects or cause other damage because their effects are non-specific.

Several years ago, NIAID grantee Raymond St. Leger, Ph.D., and colleagues including Ph.D. candidate Brian Lovett at the University of Maryland Department of Entomology, began laboratory studies on Metarhizium pingshaense, a fungus that naturally infects and kills mosquitoes, but does not infect people, other mammals or birds. The team amped up the killing power of Metarhizium by adding a gene that codes for a toxin made by the Australian Blue Mountains funnel-web spider. They also included a genetic “switch” from the fungus that turns the toxin gene on only after fungal spores have penetrated the mosquito exoskeleton. The modified fungus killed mosquitoes faster than wild-type fungus, suggesting that it might be capable of killing off the insects before they could spread malaria. The previous lab-based studies showed that the modified fungus killed only mosquitoes and did not harm non-target insects, like honeybees.

In a study published recently in Science, the investigators took the modified fungus out of the lab and into the field to test it in near-natural conditions. The “field” in this case was not fully outdoors, but rather was contained in a sort of mini-village built inside a domed, net-covered structure called a MosquitoSphere. NIAID funded the development of the MosquitoSphere in the malaria-endemic village of Soumousso, Burkina Faso, as a tool to study genetically modified organisms in semi-field conditions. The 6,500-square-foot space contained multiple screened-in areas with experimental huts, plants, pools of water where mosquitoes could breed, and calves that served as food sources for the adult female mosquitoes. The netting meant temperature and humidity in the experimental space represented the surrounding conditions.

The University of Maryland team collaborated with scientists from Burkina Faso’s Research Institute for Health Sciences to conduct the trial. They were aided by volunteers who collected larvae and pupae of insecticide-resistant Anopheles coluzzii mosquitoes from local water sources. These wild-caught mosquitoes matured into adults that were placed in the experimental compartments inside the MosquitoSphere. Each space had a black cloth—for the mosquitoes to rest on after blood-feeding—affixed to one wall. All the cloths were coated with sesame oil, which allowed the fungal spores to adhere. In one compartment, which served as a control, no spores were placed on the oil-coated cloth. A second space contained wild-type Metarhizium fungal spores, while the third contained the modified fungus. Populations of 1,000 male and 500 female mosquitoes were released into each space and allowed to mate.

Each day for the next 45 days (the time needed to produce two generations of mosquitoes), researchers counted the number of mosquitoes at every life stage in each contained space. In the fungus-free compartment, nearly 1,400 adult mosquitoes were collected in the second generation. In the compartment containing wild-type fungus, 455 mosquitoes were collected in the second generation—a reduction, but still numerous. From the compartment containing modified fungus, the team found 399 hatched mosquitoes in the first generation but a mere 13 adults in the second generation. Because male mosquitoes must form swarms of about 1,000 in order to breed, the fungus delivering the spider toxin essentially wiped out their capacity to reproduce and thus their ability to spread malaria. While both forms of fungus eventually killed roughly 75 percent of mosquitoes over two weeks, the genetically engineered form worked faster and killed more mosquitoes. The team repeated the experiment three times—with similar results—during the height of mosquito breeding season from June to October.

These findings have generated international excitement, but Lovett warns there is more to be done before application. “This study provides promising scientific results, but a technology cannot be developed with science alone,” he said. “From the start, we and our Burkinabe colleagues, Drs Abdoulaye Diabate and Lea Pare Toe, have worked hard on its regulatory and community engagement aspects. More work is needed to attain further regulatory approval and continued social acceptance for this biotechnology before testing it in an open-field setting. This process will take time, and the pace of development will be up to the local community and other stakeholders.”

Applying antimalarial drugs to bed nets could lead to drop in malaria transmission

Mosquitoes that landed on surfaces coated with the antimalarial compound atovaquone were completely blocked from developing Plasmodium falciparum (P. falciparum), the parasite that causes malaria, according to new research led by Harvard T.H. Chan School of Public Health.

The study showed that atovaquone—an active ingredient in medication that’s commonly used in humans to prevent and treat malaria—can be absorbed through mosquitoes’ tarsi (legs) and prevents the insects from developing and spreading the parasite. The findings indicate that treating bed nets with atovaquone or similar compounds would be an effective way to reduce the burden of malaria while significantly mitigating the growing problem of insecticide resistance.

“Mosquitoes are amazingly resilient organisms that have developed resistance against every insecticide that has been used to kill them. By eliminating malaria parasites within the mosquito rather than killing the mosquito itself, we can circumvent this resistance and effectively prevent malaria transmission,” said Flaminia Catteruccia, professor of immunology and infectious diseases. “Ultimately, the use of antimalarials on mosquito nets could help eliminate this devastating disease. It’s a simple but innovative idea that’s safe for people who use mosquito nets and friendly to the environment.”

The study was published online in Nature on February 27, 2019.

Malaria poses a risk to nearly half of the world’s population. Annually, more than 200 million people become sick with malaria and more than 400,000 people die from it. During the past 20 years, bed nets treated with long-lasting insecticides that kill mosquitoes have significantly reduced the global malaria burden. It’s estimated that such bed nets are responsible for 68% of all malaria cases averted since 2000. Recent years, however, have seen a surge in mosquitoes that are resistant to the most commonly used insecticides. In some malaria hot spots, there is near total resistance to pyrethroids, one of the key groups of insecticides currently in use. The waning effectiveness of insecticides is a public health emergency that threatens to undo decades of progress toward controlling malaria and highlights the urgent need to develop new approaches to stop the spread of the disease.

For this study, the researchers reasoned that they could introduce antimalarial compounds to Anopheles mosquitoes in a way that’s similar to a mosquito making contact with insecticides on a bed net. Rather than kill the mosquitoes, the aim was to give them a prophylactic treatment so that they could not develop and transmit the malaria-causing parasite.

To test the approach, they coated glass surfaces with atovaquone and covered them with a plastic cup. Female mosquitoes were then introduced into the cup. Prior to or immediately after the mosquitoes made contact with the atovaquone-coated glass, the researchers infected them with P. falciparum. Over the course of the study, mosquitoes were exposed to different concentrations of atovaquone and were kept in the cups for different amount of times.

The study found that P. falciparum development was completely blocked at relatively low concentrations of atovaquone (100 μmol per m2) and when mosquitoes were exposed for just 6 minutes, which is comparable to the time wild mosquitoes spend on insecticide-treated bed nets. The researchers had similar success when using other compounds similar to atovaquone. While atovaquone effectively killed parasites, it had no effects on mosquito lifespan or reproduction.

“When we put these data into a mathematical model using real-world data on insecticide resistance, bed net coverage and malaria prevalence, it showed that supplementing conventional bed nets with a compound like atovaquone could appreciably reduce malaria transmission under almost any conditions we had data for in Africa,” said Douglas Paton, research fellow and lead author of the paper. “What got us really excited is that it also showed that this new intervention would have the greatest impact in areas with the highest levels of mosquito insecticide resistance.”