Scientists probe new ways to control malaria | Science News for Students

Scientists probe new ways to control malaria

From jungles to mountains, researchers hunt new approaches to tackling this mosquito-borne killer
Feb 6, 2018 — 6:45 am EST
mosquito feeding

A hungry Anopheles merus mosquito sucks blood from a human hand. This is one of the mosquito species that can spread malaria.

James Gathany/CDC

CHICAGO, Ill. — Science detectives are following new clues in their quest to stop a killer — malaria. The disease claimed the lives of roughly 429,000 people in 2015 alone, according to the World Health Organization. And kids face the biggest risk. More than seven in every 10 of malaria’s victims are children.

The disease is caused by a parasite that spends part of its life cycle in mosquitoes and part in blood-making animals. Once it gets into people, it attacks liver and blood cells. Mild cases cause fever, headaches and chills. Severe cases leave the blood with too few healthy cells to carry oxygen. Sometimes, the disease also affects the lungs and brain.

Some medicines can cure malaria. But those drugs don’t always work. So scientists are exploring new ways to thwart this killer. Last summer, they described two of them at a meeting here in Chicago, Ill.

malaria parasite
This false-color image shows a malaria parasite (in blue) attaching to a human red blood cell. The inset is a close-up of the point of attachment.
NIAID

“Malaria doesn't just affect humans,” explains Holly Lutz. She works in Chicago at the Field Museum and the University of Chicago. Bats, other mammals, birds and lizards also can develop the disease. “In fact, nearly all terrestrial vertebrates can be infected with their own species of malaria,” she says.

Lutz calls herself “both an evolutionary biologist and a microbial ecologist. But first and foremost, I am an explorer,” she says. By exploring animals and their parasites, Lutz hopes to learn more about how to thwart malaria in people.  

A microscopic parasite called Plasmodium (Plaz-MO-dee-um) is behind the illness. Mosquitoes pick up the microbe when they feed on infected blood. It grows in their gut. Then it gets into the insects’ saliva. When a mosquito takes its next bite, it can now share some of these parasites with a new host. In many cases, that host may be a human.

There is some good news. Malaria killed only about half as many people in 2015 as it did 15 years earlier. Bed nets helped. People drape these mesh curtains, treated with mosquito-killing poison, over their beds at night. Medical care is better in some areas, too.

Story continues below video

Half of all people on Earth are at risk of contracting malaria. This video is an introduction to the disease, its symptoms and treatments.
World Health Organization/YouTube

But here’s the bad news. Like other organisms, the parasites that cause malaria evolve. As a result, more of them can now resist the microbe-killing action of various drugs. Mosquitoes also evolve. Some can now resist common insecticides. That means they can survive to infect more people — and reproduce. And climate change is altering weather patterns around the globe. In the future, malaria-carrying mosquitoes will likely survive in more places.

Holly Lutz and colleague
Holly Lutz (left) works with a colleague in Uganda to collect malaria parasites from birds.
Courtesy of Holly Lutz

Here in Chicago, two researchers are taking very different approaches to dealing with the problem. Lutz looks at malaria in wildlife. University of Chicago ecologist Mercedes Pascual asks how things like climate change or human sprawl might affect malaria’s spread.

For the birds?

Lutz’s research has taken her to remote parts of Africa, Central America and South America. She wants to know how wildlife deal with malaria. She hopes that what she learns will offer “insights into our own human struggle with this devastating parasite.”

For example, in the East African nation of Malawi, her team collected blood from 152 bird species. Those blood samples showed links between malaria infection rates and the behaviors of different types of birds. For example, they showed two years ago, malaria parasites were more likely to infect bird species that built closed-cup nests.

In her lab, Lutz studies the malaria parasites. These single-celled microbes live inside blood cells. To study the parasites, she has to get them out. Her team recently developed a way to do that. They use a laser to cut a single parasite cell away from the rest of a host’s blood cell.

With the microbes now freed, the researchers can study the genes in the parasites’ DNA.

For one project, Lutz looked at DNA from about 250 Plasmodium species. They included every species known at that time to cause malaria. Many had been discovered in African birds and bats. “Using the DNA from these parasites,” she explains, “I was able to build a ‘family tree’ of malaria to see which parasites were more closely related to each other.” Such closely related species had more similarities in their genes — the codes that instruct cells on what they are to do.

The results offered new clues to where the parasites came from. “This [family] tree,” Lutz reports, “now shows us that the very first mammals to be infected by malaria parasites appear to be bats.” And the types that today infect rodents and other non-human mammals seem to have evolved from those bat-hosted parasites.

malaria blood
In this image, tiny knobs cover a human red blood cell that is infected with malaria. Uninfected blood cells surround it.
Rick Fairhurst and Jordan Zuspann/NIAID/NIH

More questions remain. For example, in some bird species, up to eight in every 10 individuals may become infected with malaria. Still, many of these animals appear healthy, Lutz says. Why don’t those birds get sick? She hopes to find out.

Lutz also wants to know which plasmodium genes show up in the species that infect people and birds. The answer could point to traits that the parasite needs for survival. And those features could become targets for new malaria medicines, Lutz explains.

On the edges

Mercedes Pascual studies how organisms relate to one another and to their surroundings. In particular, she looks at how changes in the environment can affect the spread of malaria and other diseases.

Malaria thrives in warm areas where rainy seasons make it easy for mosquitoes to breed. As the world continues to warm, more regions will host such conditions. Pascual therefore wondered how climate change might affect outbreaks of malaria in people.

To find out, her team analyzed data on malaria infections from highland areas of Ethiopia and Colombia.

In those areas, not everyone carries the disease. Instead, outbreaks happen from time to time. During an outbreak, lots of people get the disease around the same time. Later, illness rates drop back down. That’s different from many warm places closer to sea level. Although many people have the disease in those places, it’s rare to have huge swings in malaria rates. Instead, the parasites hang out and continually infect a large number of people.

In early 2014, Pascual’s team used a computer to probe how malaria infection relates to climate cycles. They used a computer model to study one cycle known as El Niño (Neen-yo). Every few years, there is a warming of tropical surface waters in parts of the eastern and central Pacific. In later years, those waters cool again off the coast of South America, and warmer water shifts westward. This whole cycle affects weather patterns across the globe. And, Pascual’s team showed, it also affects malaria rates in people. Malaria rates rose as El Niños emerged. Then infection rates fell as that an El Niño ended.

After each El Niño cycle, however, rates of malaria infections generally did not fall all the way back to the earlier background low. The reason, researchers now suspect, is climate change. Higher average temperatures mean parasites have a better chance to survive in high-altitude areas (which are normally cooler regions). If more malaria parasites survive, they can infect more people.

Another one of Pascual’s studies looked at malaria in areas into which people were starting to migrate. People often change the landscape as they settle some new area. They cut down forests. They build roads. Often they divert stream water to irrigate their farms. All of these things can create more spots for water to collect. And that means more places for mosquitoes to breed.

What’s more, as people open new frontiers, they often have few doctors or clinics nearby to treat malaria.

Pascual’s group got data on malaria rates and the new settlements of people in two areas. One was in Brazil. The other was in India. And as people made changes to the land, rates of malaria also varied. The team used math to model what happened as people altered the ways land was used. As rates of land-use changes went up, so did rates of disease.

This work suggests how people might better attack malaria in developing countries. Spraying insecticides and taking other steps to control mosquitoes could prevent many malaria cases as people first move in. As an area becomes more developed, other improvements — such as better medical treatment and housing — could help fight a spread of the disease. The team described its findings in the March 20, 2017, Nature Ecology & Evolution.   

A clearer picture

Holly Lutz with machete
Evolutionary biologist Holly Lutz sometimes needs a machete to hack through dense forests while collecting samples of malaria parasites.
Courtesy of Holly Lutz

Rickard Ignell is an ecologist at the Swedish University of Agricultural Sciences in Uppsala. He did not work on the projects led by Lutz and Pascual. He thinks Lutz’s work will likely uncover features that are shared by malaria parasites that infect both people and other animals. For example, some genes keep showing up in lots of parasite species. If so, whatever they tell the cells to do might be something the parasites find really, really important. A medicine that targets that feature might kill the parasites.

Pascual’s research is helping to show how malaria spreads, Ignell points out. “With ongoing climate change, we are likely going to see a spread of malaria into regions previously not affected by the disease.” And that can only worsen as people continue to change landscapes, Ignell adds.

S. Noushin Emami is a biologist at Stockholm University in Sweden. She sees some limitations to all of this work. For example, Pascual’s studies don’t deal with all factors that affect the spread of malaria. As for Lutz’s work, she notes that the biology of parasite species can differ from host to host. So findings from one species might not apply to all others.

Still, the work by both teams could give important clues to the mysteries of a major infectious killer, she says. “Malaria is a disease that was and still is very important to a lot of people around the world,” she notes. So each new piece of evidence could give scientists a better picture of how the parasites live and cause disease. Ultimately, that work could help slow — or even stop — this global killer.

This video features Holly Lutz talking about her decision to study birds and emerging pathogens.
Field Museum of Natural History/YouTube

Reporting for this piece was made possible by an MBL Logan Science Journalism Fellowship in Chicago arranged by the Marine Biological Laboratory in Woods Hole, Mass., and the University of Chicago. 

Power Words

(for more about Power Words, click here)

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

bat     A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.

biology     The study of living things. The scientists who study them are known as biologists.

breed     (noun) Animals within the same species that are so genetically similar that they produce reliable and characteristic traits. German shepherds and dachshunds, for instance, are examples of dog breeds. (verb) To produce offspring through reproduction.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

develop      (as with towns) The conversion of wildland to host communities of people. This development can include the building of roads, homes, stores, schools and more. Usually, trees and grasslands are cut down and replaced with structures or landscaped yards and parks.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

El Niño     Extended periods when the surface water around the equator in the eastern and central Pacific warms. Scientists declare the arrival of an El Niño when that water warms by at least 0.4 degree Celsius (0.72 degree Fahrenheit) above average for five or more months in a row. El Niños can bring heavy rainfall and flooding to the West Coast of South America. Meanwhile, Australia and Southeast Asia may face a drought and high risk of wildfires. In North America, scientists have linked the arrival of El Niños to unusual weather events — including ice storms, droughts and mudslides.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).

evolutionary biologist     Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).

evolve     (adj. evolving) To change gradually over generations, or a long period of time. In living organisms, such an evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs).

factor     Something that plays a role in a particular condition or event; a contributor.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

irrigation    (v. irrigate) The supply of water to land or crops to help growth.

insight     The ability to gain an accurate and deep understanding of a situation just by thinking about it, instead of working out a solution through experimentation.

laser     A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.

link     A connection between two people or things.

lizard     A type of reptile that typically walks on four legs, has a scaly body and a long tapering tail. Unlike most reptiles, lizards also typically have movable eyelids. Examples of lizards include the tuatara, chameleons, Komodo dragon, and Gila monster.

malaria     A disease caused by a parasite that invades the red blood cells. The parasite is transmitted by mosquitoes, largely in tropical and subtropical regions.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microscopic     An adjective for things too small to be seen by the unaided eye. It takes a microscope to view objects this small, such as bacteria or other one-celled organisms.

migrate     To move long distances (often across many countries) in search of a new home. (in biology) To travel from one place to another at regular times of the year to find food or more hospitable conditions (such as better weather). Species that migrate each year are referred to as being migratory.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

outbreak     The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.

Pacific     The largest of the world’s five oceans. It separates Asia and Australia to the west from North and South America to the east.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

plasmodium     A form within the life cycle of some simple organisms such as slime molds, typically consisting of a mass of naked protoplasm containing many nuclei. (in medicine) It also refers to a genus of protozoa that cause the disease malaria. The Plasmodium genus includes more than 100 species; just five are responsible for most malaria in humans.

rodent     A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

terrestrial     Having to do with planet Earth, especially its land. Terra is Latin for Earth.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

tropics     The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.

vertebrate     The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

World Health Organization     An agency of the United Nations, established in 1948, to promote health and to control communicable diseases. It is based in Geneva, Switzerland. The United Nations relies on the WHO for providing international leadership on global health matters. This organization also helps shape the research agenda for health issues and sets standards for pollutants and other things that could pose a risk to health. WHO also regularly reviews data to set policies for maintaining health and a healthy environment.

Citation

Journal: K. Day et al. “Evidence of strain structure in Plasmodium falciparum var gene repertoires in children from Gabon, West Africa.” Proceedings of the National Academy of Sciences. Vol. 114, May 16, 2017, p. E4103.  doi: 10.1073/pnas.1613018114.

Journal: A. Baeza et al. “The rise and fall of malaria under land-use change in frontier regions.” Nature Ecology & Evolution. Vol. 1, March 20, 2017. doi: 10.1038/s41559-017-0108.

Journal: H. Lutz et al. “Laser capture microdissection microscopy and genome sequencing of the avian malaria parasite, Plasmodium relictum.” Parisitology Research. Vol. 115, December 2016, p. 4503. doi: 10.1007/s00436-016-5237-5.

Journal: H. Lutz et al. “Diverse sampling of East African haemosporidians reveals chiropteran origin of malaria parasites in primates and rodents.” Molecular Phylogenetics and Evolution. Vol. 99, June 2016, p. 7. doi: 10.1016/j.ympev.2016.03.004.

Journal: H. Lutz et al. “Parasite Prevalence Corresponds to Host Life History in a Diverse Assemblage of Afrotropical Birds and Haemosporidian Parasites.” PLOS One. Vol. 10, April 8, 2015, (as corrected May 18, 2015). doi: 10.1371/journal.pone.0121254 (and doi: 10.1371/journal.pone.0128851).

Journal: A. Siraj et al. “Altitudinal Changes in Malaria Incidence in Highlands of Ethiopia and Colombia.” Science. Vol. 343, March 7, 2014, p. 1154. doi: 10.1126/science.1244325.