Parasites found in human blood samples showed a high prevalence for pyrimethamine-resistance, which was consistent with the class of drugs widely used to treat malaria in the region.
However, parasites taken from mosquitoes themselves had very low prevalence of pyrimethamine-resistance and a high prevalence of cycloguanil-resistant mutants indicating resistance to a newer class of antimalaria drug not widely used in Zambia. The findings are published November 7 in the online edition of the journal PNAS and will be discussed at the November 16 seminar, "The Forever War: Malaria versus the World," held in New York City by the Johns Hopkins Bloomberg School of Public Health and the New York Academy of Sciences.
Surveillance for drug-resistant parasites in human blood is a major effort in malaria control. Malaria in humans is caused by the parasite Plasmodium falciparum, which is spread from person to person through the feeding of the Anopheles mosquito. Over time, through repeated exposure to medications, the parasites can become less susceptible to drugs used to treat malaria infection, limiting their effectiveness.
"This contrast in resistance factors was a big surprise to us," said Peter Agre, MD, an author of the study and director of the Johns Hopkins Malaria Institute. "The contrast raises many questions, but we suspect that the malaria parasite can bear highly host-specific drug-resistant polymorphisms, most likely reflecting very different selection preferences between humans and mosquitos."
For the study, Sungano Mharakurwa, PhD, lead author and senior research associate with the Johns Hopkins Malaria Research Institute in Macha, Zambia, conducted a DNA analysis of P. falciparum found in human blood samples to those found in mosquitoes collected inside homes in rural Zambia. In samples taken from human blood, pyrimethamine-resistant mutations were greater than 90 percent and between 30 percent to 80 percent for other polymorphisms. Mutations of cycloguanil-resistance were 13 percent.
For parasites found in the mosquito midgut, cycloguanil-resistant mutants were at 90 percent while pyrimethamine-resistant mutants were detected between 2 percent and 12 percent.
"Our study indicates that mosquitoes exert an independent selection on drug resistant parasites—a finding that has not previously been noticed. If confirmed in other malaria endemic regions, it suggests an explanation for why drug resistance may appear so rapidly," said Mharakurwa.
Worldwide, malaria afflicts more than 225 million people. Each year, the disease kills approximately 800,000, many of whom are children living in Africa.
Authors of "Malaria antifolate resistance with contrasting Plasmodium falciparum dihydrofolate reductase (DHFR) polymorphisms in humans and Anopheles mosquitoes" are Sungano Mharakurwa, Taida Kumwenda, Mtawa A. P. Mkulama, Mulenga Musapa, Sandra Chishimba, Clive J. Shiff, David J. Sullivan, Philip E. Thuma, Kun Liu and Peter Agre.
The Johns Hopkins Malaria Research Institute is a state-of-the-art research facility at the Johns Hopkins Bloomberg School of Public Health. It focuses on a broad program of basic science research to treat and control malaria, develop a vaccine and find new drug targets to prevent and cure this deadly disease.
Funding was provided by the Johns Hopkins Malaria Research Institute, the Bill & Melinda Gates Foundation and the National Institutes of Health.
Tim Parsons | EurekAlert!
Self-organising system enables motile cells to form complex search pattern
07.05.2019 | Westfälische Wilhelms-Universität Münster
Mouse studies show minimally invasive route can accurately administer drugs to brain
02.05.2019 | Johns Hopkins Medicine
The well-known representation of chemical elements is just one example of how objects can be arranged and classified
The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...
Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.
Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...
Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.
The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...
Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.
The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....
Researchers at Chalmers University of Technology, Sweden, have discovered a completely new way of capturing, amplifying and linking light to matter at the nanolevel. Using a tiny box, built from stacked atomically thin material, they have succeeded in creating a type of feedback loop in which light and matter become one. The discovery, which was recently published in Nature Nanotechnology, opens up new possibilities in the world of nanophotonics.
Photonics is concerned with various means of using light. Fibre-optic communication is an example of photonics, as is the technology behind photodetectors and...
29.04.2019 | Event News
17.04.2019 | Event News
15.04.2019 | Event News
17.06.2019 | Information Technology
17.06.2019 | Earth Sciences
17.06.2019 | Ecology, The Environment and Conservation