NIAID Raises Awareness to Malaria-like Diseases in W. Africa

Dengue, Zika, Chikungunya Viruses in Mali; Disease Likely Misdiagnosed

NIAID scientists and colleagues have identified dengue, Zika and chikungunya viruses in the West African country of Mali, where health care providers likely misdiagnose patients with illness from those viruses due to unavailable diagnostic tools. Because malaria is the most common fever-causing illness in rural sub-Saharan Africa, most medical workers presume patients with a fever have malaria. The primary cause of all four infectious diseases is a mosquito bite.

Records from the Malian Health Information System show that about one-third of all patient visits to health care facilities are related to malaria, with 2.37 million clinical cases.

A new study from NIAID’s Rocky Mountain Laboratories and the University of Sciences, Techniques and Technologies in Mali aims to help spread information to medical workers about the existence of the additional viral diseases. Ideally, circulating the information will help them obtain the necessary diagnostics.

The study, published in The American Journal of Tropical Medicine and Hygiene, involved 600 residents, 200 from each of the southern Malian communities of Soromba, Bamba and Banzana. The scientists detected antibodies to dengue virus in the blood of 77.2% of the residents tested; to Zika virus in 31.2%, and to chikungunya virus in 25.8%. They detected at least one of the three viruses in 84.9% of participants, meaning just 15.1% tested negative to any of the three viruses.

Evidence of the parasites that cause malaria was found in 44.5% of those tested. Unlike malaria, however, where most cases are found in children under age 14, residents over age 50 were most likely to have been exposed to dengue, Zika or chikungunya viruses. 

“Despite the high exposure risk to dengue virus in southern Mali, dengue fever cases have rarely been reported,” the researchers write. “This is likely due to the lack of diagnostic testing and the biased clinical focus on malaria in the region. Awareness of dengue virus as a cause of febrile illness needs to be urgently established in medical communities as an important public health measure.”

The scientists are hoping data from a more in-depth clinical study that just ended will provide additional details about the prevalence of these viruses in Mali. They also are planning to examine patients who have undiagnosed fevers to establish infection rates.

NIAID scientists are investigating dengue, Zika and chikungunya viruses to try and develop preventive and therapeutic treatment options, none of which exist.

Reference: S Bane, et al. Seroprevalence of Arboviruses in a Malaria Hyperendemic Area in Southern Mali. The American Journal of Tropical Medicine and Hygiene DOI: 10.4269/ajtmh.23-0803 (2024).

For years, malaria vaccine developers have focused on thwarting a key moment in the malaria parasite’s life cycle: when two parasite proteins, AMA1 and RON2L, combine to form a complex that anchors the parasite to a red blood cell and eases its passage into the cell interior. Quite sensibly, researchers developed candidate vaccines that elicit antibodies capable of blocking the crucial attachment. However, because AMA1’s make-up varies widely among different parasite strains, any vaccine based on a single strain’s AMA1 cannot protect against other parasite strains and thus has limited usefulness in malaria-endemic countries. Experimental malaria vaccines have also been made by mixing AMA1 and RON2L proteins. While these do elicit more strain-transcending antibodies than AMA1-only vaccines, they are difficult to manufacture and simple mixtures of AMA1 and RON2L in vaccines do not form the kind of stable protein complex seen in nature.

Now, researchers in NIAID’s Laboratory of Malaria Immunology and Vaccinology have used structural information about the two parasite proteins along with mechanistic information about the interaction between AMA1 and RON2L to design and build an entirely novel immunogen (the component of a vaccine that elicits an immune response). When tested in rats, their “structure-based design 1” (SBD1) immunogen vaccine performed better than any AMA1 or AMA1-RON2L vaccine. It also upends the conventional wisdom that successful vaccines must elicit receptor-blocking antibodies, notes Niraj H. Tolia, Ph.D., who led the research team.

The SBD1 immunogen does not exist in nature, explains Dr. Tolia. Rather, it consists of AMA-1 that the team altered by rearranging its amino acid sequence in a way that they predicted would work well as a vaccine. Once altered, the scientists linked RON2L to a position in their immunogen to recreate the two protein AMA1-RON2L complex. The team analyzed the structure of the designed immunogen using X-ray crystallography and determined that it closely mimicked that of naturally occurring AMA1-RON2L complex. However, SBD1 has a number of advantages over a simple mixture of two component proteins, Dr. Tolia explains. For instance, it is highly stable once injected, is easy to manufacture in large quantities and consistently takes the desired, immune-stimulating shape.

In rats, SBD1 vaccine elicited significantly more potent strain-transcending antibodies than either AMA1 alone or an AMA1-RON2L complex vaccine. The ability to provide protection from multiple parasite strains is highly desirable for any malaria vaccine. Most surprisingly, Dr. Tolia says, the SBD1 vaccine provided this strain-transcending protection even though it generated no antibodies whatsoever that were aimed at blocking AMA1 from binding to RON2L and initiating attachment to the red blood cell. Instead, it appears SBD1 elicits high quality antibodies that inhibit parasite growth by targeting parts of the parasite’s proteins that lie outside of RON2L binding site and operate independently of receptor blockade, explains Dr. Tolia.

Together, the team’s observations about SBD1 make it an appealing candidate for further studies in animals and perhaps ultimately in human trials, he adds. Furthermore, other parasites, including those that cause the human diseases toxoplasmosis and babesiosis and one that causes disease in cattle and dogs, use their own forms of AMA1 protein to invade host cells. Thus, insights gained in this recent work may be applicable to the design of vaccines against those parasites as well.

Reference: PN Patel et al. Structure-based design of a strain transcending AMA1-RON2L malaria vaccine. Nature Communications. DOI: 10.1038/s41467-023-40878-7 (2023).

Malaria is one of the most widespread and devastating infectious diseases across the globe. This mosquito-borne parasitic disease killed approximately 619,000 people in 2021 alone, many of them children in Africa. In one of the deadliest forms of malaria, known as cerebral malaria, the patient experiences severe neurological symptoms, such as seizures and coma. Although only a small fraction of people who fall ill with malaria also experience cerebral malaria, the condition is lethal without treatment. Among hospitalized patients with the condition, death rates range between 15 and 20%. In a new paper, recently published in Science Translational Medicine, researchers from the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH, and their colleagues studied children with cerebral malaria in Malawi to better understand the underlying causes of these devastating symptoms in the hope of developing improved treatments.

Researchers know that the symptoms of cerebral malaria are caused when the brain swells within the confines of the skull, eventually impinging upon the brainstem, which causes breathing to stop. However, researchers have been unsure how malaria infection leads to brain swelling. Some researchers hypothesized that the main cause was a weakening of the blood-brain barrier, which would allow fluid to seep into the brain and cause it to swell. Others speculated that the primary driver behind the swelling was inside the blood vessels themselves. Red blood cells infected with P. falciparum, the parasite which causes malaria, can become “sticky,” adhering to the walls of blood vessels. Partial blockages inside the cerebral veins could slow the flow of blood leaving the brain, causing the blood vessels themselves to become engorged and expand the brain from within.

This illustration shows two different ways that cerebral malaria could cause brain swelling: fluid seeping into the brain (extravascular edema) or swollen blood vessels (venous congestion.)

Credit: Rose Perry-Gottschalk, NIAID Research Technologies Branch

To distinguish between these two hypotheses, NIAID researchers and their collaborators used non-invasive imaging techniques to study the flow of blood within the brains of 46 children who had been hospitalized for cerebral malaria at the Pediatric Research Ward of Queen Elizabeth Central Hospital in Blantyre, Malawi. As a comparison, they also studied 33 children with uncomplicated malaria and 26 healthy children from the local region. By using a light-based external monitoring tool (called near-infrared spectroscopy, or NIRS) the researchers were able to measure the amount of hemoglobin in the children’s brains. They reasoned that if excess fluid was the cause of brain swelling, then the hemoglobin concentration would be low, due to dilution. Alternatively, if the blood vessels were engorged with blood, then the hemoglobin concentration would be high.

The researchers found that children with cerebral malaria had significantly higher concentrations of hemoglobin inside their brains than children who had uncomplicated malaria, or healthy children—and among those with cerebral malaria, higher hemoglobin concentrations were correlated with greater brain swelling. In addition, hemoglobin concentrations fluctuated more unpredictably in children with cerebral malaria—suggesting that the normal mechanisms for controlling blood flow in the brain were disturbed. Together, these results support the hypothesis that obstruction to the outflow of blood from the brain, likely because the blood vessels themselves are clogged by red blood cells infected with P. falciparum adhering to the walls, is a main driver of brain swelling in patients with cerebral malaria.

The researchers say that these results may lead to a better understanding of why some treatments for cerebral malaria are not as effective as expected. For instance, steroids or osmotic agents are sometimes used to treat brain swelling by reducing the leakage of fluid from the blood vessels into the brain—but if the swelling is caused by the parasite-related effects within the blood vessels themselves, these treatments would not address the underlying problem. By pinpointing the exact mechanism by which cerebral malaria leads to brain damage, the researchers hope, we may improve treating it.

Reference: R L Smith et al. Increased brain microvascular hemoglobin concentrations in children with cerebral malaria. Science Translational Medicine DOI: 10.1126/scitranslmed.adh4293 (2023)