Altered body odor indicates malaria even if microscope doesn't

May 14, 2018, Pennsylvania State University
An Anopheles stephensi mosquito is obtaining a blood meal from a human host through its pointed proboscis. Note the droplet of blood being expelled from the abdomen after having engorged itself on its host's blood. This mosquito is a known malarial vector with a distribution that ranges from Egypt all the way to China. Credit: Jim Gathany / CDC

Typhoid Mary may have infected a hundred or more people, but asymptomatic carriers of malaria infect far more people every year. An international team of researchers is working toward a way to identify malaria patients including infected individuals who show no malaria symptoms.

People who have malaria but are not symptomatic abound in the heaviest areas of malaria infestation. Even blood tests do not necessarily pick up infection with the plasmodium parasite, especially at low parasite densities. DNA tests for the parasite usually show infection, but they are far from rapid.

"Our previous work in a mouse model found that malaria infection altered the odors of infected mice in ways that made them more attractive to mosquitoes, particularly at a stage of infection where the transmissible stage of the parasite was present at high levels," said Consuelo De Moraes, adjunct professor of biology, Penn State, and professor of environmental systems science, ETH Zurich. "We also found long-term changes in the odor profiles of infected mice."

The researchers wanted to see if they could identify changes in human odors associated with that might be useful for diagnosing infected individuals. They were particularly interested in identifying those who were infected, but had no symptoms. The researchers initially used microscopy and an SD Bioline Rapid Diagnostic Test to identify patients with malaria. Because these methods have limited sensitivity, particularly when parasite loads are low, infections were confirmed by DNA tests. They identified 333 people who unambiguously were either infected with malaria or were not infected with malaria.

Only if both microscopy and DNA studies were negative were subjects considered malaria-free. Infected patients for the initial studies were both microscopy and DNA positive for malaria. In some later analyses, the researchers included 77 people who were positive for malaria according to DNA, but showed no in the microscopic tests.Malaria infection does not create new volatile chemicals in the body, but alters the amounts—up or down—of volatile chemicals that are already present in the odors of healthy people.

"It is interesting that the symptomatic and asymptomatic infections were different from each other as well as from healthy people," said Mark C. Mescher, adjunct professor of biology, Penn State, and professor of environmental systems science, ETH Zurich.

This difference among infected, infected asymptomatic, and healthy individuals may eventually lead to tests capable of rapidly and accurately identifying , even those without symptoms.

The researchers report in today's (May 14) issue of Proceedings of the National Academy of Sciences that predictive models using machine learning reliably identify status based on volatile biomarkers. They state "our models identified asymptomatic infections with 100 percent sensitivity, even in the case of low-level infections not detectable by microscopy." These results far exceed any currently available rapid diagnostic tests.

"But, we should emphasize that we are a long way away from developing a practical diagnostic assay based on odor cues," said De Moraes.

For a to succeed it would need to be rapidly and cheaply deployable under field conditions, but still detect infections with high sensitivity.

"In the near term, our goal is to refine the current findings to find the most reliable and effective biomarkers we can," said Mescher. "This is really basic science to identify the biomarkers of . There is still a lot more work to be done to develop a practical diagnostic assay."

Explore further: Researchers describe the dynamics of P. falciparum infections in adults without fever

More information: Consuelo M. De Moraes el al., "Volatile biomarkers of symptomatic and asymptomatic malaria infection in humans," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1801512115

Related Stories

Researchers describe the dynamics of P. falciparum infections in adults without fever

March 30, 2018
Asymptomatic malaria occurs when parasites are present in an individual's blood, but do not cause fever or other symptoms. These "afebrile" infections can be detected either by classical diagnostic tests (if there are enough ...

Study explores new strategy to develop a malaria vaccine

April 11, 2018
A serum developed by Yale researchers reduces infection from malaria in mice, according to a new study. It works by attacking a protein in the saliva of the mosquitos infected with the malaria parasite rather than the parasite ...

Human antibodies undermine parasite sex

February 8, 2018
Some people develop an immune response following a malaria infection that stops them from infecting other mosquitoes. The antibodies that these people produce are ingested by the mosquito and destroy the malaria parasite ...

Recommended for you

Researchers find infectious prions throughout eyes of patients with deadly sporadic Creutzfeldt-Jakob disease

November 20, 2018
By the time symptoms of sporadic Creutzfeldt-Jakob disease (sCJD) are typically discovered, death is looming and inevitable. But, in a new study, researchers at University of California San Diego School of Medicine with colleagues ...

Researchers a step closer to understanding how deadly bird flu virus takes hold in humans

November 19, 2018
New research has taken a step towards understanding how highly pathogenic influenza viruses such as deadly bird flu infect humans.

Infants born to obese mothers risk developing liver disease, obesity

November 16, 2018
Infant gut microbes altered by their mother's obesity can cause inflammation and other major changes within the baby, increasing the risk of obesity and non-alcoholic fatty liver disease later in life, according to researchers ...

New study shows NKT cell subsets play a large role in the advancement of NAFLD

November 16, 2018
Since 2015 it has been known that the gut microbiota could have a direct impact on nonalcoholic fatty liver disease (NAFLD), which affects up to 12% of adults and is a leading cause of chronic liver disease. In the November ...

Antibiotic prescribing influenced by team dynamics within hospitals

November 15, 2018
Antibiotic prescribing by doctors is influenced by team dynamics and cultures within hospitals.

Discovery suggests new route to fight infection, disease

November 14, 2018
New research reveals how a single protein interferes with the immune system when exposed to the bacterium that causes Legionnaires' disease, findings that could have broad implications for development of medicines to fight ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.