‘Malaria research is an ongoing arms race’

The work begins with colleagues Ivonne and Anne-Marie, sitting side by side behind the microscope, says researcher Annemarie van der Wel. In front of them lie dozens of dead mosquitoes on their sides. “One by one we decapitate them with a tiny needle. Then we gently press on the thorax so the salivary glands come out. That is where the malaria parasites are. It is delicate work, but an important step in understanding malaria better.”

Malaria research looks very different today than it did in the past. In the 1980s, many monkeys were still infected to test new medicines. Now, a large part of the research takes place in the laboratory, using cultured liver cells in which researchers track and test the parasite.

“That is a world of difference,” says Annemarie, who works closely with fellow researcher Anne-Marie and analyst Ivonne. “We can now study what happens in a much more targeted way and we need far fewer animals to do so.”

At BPRC, researchers work with Plasmodium cynomolgi, a malaria parasite found in monkeys that closely resembles the human variant Plasmodium vivax. “This human parasite is common in parts of Southeast Asia and South America and poses a risk to one third of the world’s population. Until the 1970s, it even occurred in the Netherlands.”

Parasites hiding in the liver

Every year, millions of people worldwide contract vivax-type malaria. This form can keep coming back.

What makes this type of malaria so persistent happens deep in the liver. After infection, the parasite travels through the bloodstream to the liver, where it settles in liver cells. There it can remain in a dormant form known as a hypnozoite.

“Such a parasite can remain hidden in the liver for weeks, months, or even years and then become active again,” Annemarie explains. “As a result, people can fall ill again long after they were first infected.”

Difficult to combat

These dormant parasites are particularly difficult to eliminate. Currently, there is only one type of drug that works against them. This drug cannot be used everywhere because it can cause serious side effects, such as severe anemia.

“That is why researchers are looking for new medicines that can specifically target these dormant parasites.” It is also important to have multiple drugs available to prevent parasites from becoming resistant. “Malaria research is an ongoing arms race.”

At BPRC, research is conducted using malaria parasites stored in ultra-cold freezers so they remain viable for years without dividing.

From mosquito to microscope

When Annemarie and her colleagues need malaria parasites, they thaw a small amount and use it to infect a monkey. This is necessary because it has not yet been possible to reliably feed mosquitoes with blood from a malaria blood culture. “We are investigating how this could be done in the future.”

In the monkey, the parasites multiply in red blood cells. The infected blood is then fed to mosquitoes, which BPRC obtains from a mosquito laboratory in Nijmegen. “Inside the mosquito, the parasite develops further and eventually moves to the salivary glands. That is exactly where we need them.”

Next comes the dissection work. Annemarie and her colleagues collect the salivary glands and break them down. The material is then placed on a special slide with a grid and examined under the microscope. “Using a calculation model, we determine how many parasites we have.”

‘Some remain dormant, others become active again’

The parasites are then added to culture dishes containing liver cells. There, they enter the cells and continue to develop. “Some remain dormant, while others become active again.” The researcher continues, “At that point, we can add a potential drug. After a few days, we check whether the parasites are still alive and whether the liver cells remain healthy. This is how we test whether a compound has potential as a new malaria drug.”

Around 2008, liver cell culture techniques began to emerge, Annemarie explains. “Anne-Marie went to a laboratory in Paris to learn this technique. Since then, we have been cultivating liver cells ourselves and can carry out much of the research in the lab.”

Three-dimensional liver models

As a result, the research has become largely animal-sparing. Most of the work now takes place in the laboratory. Only for specific steps, such as obtaining infected blood or testing promising compounds in a complete organism, are animals still needed. “You cannot do that in humans.”

At the same time, efforts continue to refine, reduce, and replace animal use in malaria research. “The techniques we use have improved significantly in recent years. For example, we now work with parasite lines developed in a specialized laboratory in Singapore that can be cultured directly in dishes. We are also trying to infect mosquitoes with these, but that is still difficult. We are continuing to investigate this.”

Research is also being conducted on three-dimensional liver models that more closely resemble a real liver. “These are complex steps. The parasite requires a very specific environment to survive and grow. That is precisely why developing good laboratory models is difficult and time-consuming.”

‘We can now carry out some experiments without animals’

Step by step, the research is progressing, Annemarie says. “It is difficult to predict when research will be entirely animal-free. What we do know is that experiments in culture dishes already allow us to quickly test the effectiveness of large numbers of compounds. And that is important, because new medicines are urgently needed in the ongoing fight against malaria.”