Some strains of the malaria parasite can take on another form that allows them to hide in the liver. So, if the main thrust of an anti-malaria campaign is targeting the blood stage of the parasite, then it could be undermined by relapses caused by the parasites in the liver.
Now, a new study suggests this could be happening in the Asia-Pacific. Reporting in the journal PLOS Medicine, the international team proposes that most childhood infections in endemic areas of this region arise from relapsed and not new infections.
The researchers came to this conclusion after running a clinical trial in a group of children living in an area of Papua New Guinea (PNG), where malaria is endemic.
Malaria is a disease that results from the bite of a female mosquito carrying a Plasmodium parasite. Of the five species of Plasmodium that cause malaria, P. vivax and P. ovale have the added complication of a dormant liver stage, which can be reactivated without the need for a mosquito bite.
The new study shows that four out of five children aged 5-10 years in PNG were susceptible to recurring infection with P. vivax.
The researchers note that the finding has significant implications for malaria control programs not only in Asia-Pacific, but also in Central and South America, South and Southeast Asia and the Middle East, where P. vivax is also a significant cause of malaria.
Lead author Dr. Leanne Robinson, of the Walter and Eliza Hall Institute and Papua New Guinea Institute of Medical Research, says:
“Our research has shown that one of the biggest problems in realizing malaria eradication is relapsing P. vivax infections, which are critical for sustained transmission in the region.”
The study recruited around 500 children aged 5-10 years living in a PNG region where malaria is endemic. They were randomly assigned to receive malaria drugs that either targeted the liver and blood stage of infection or only the blood stage.
The results showed that the children who received drugs that targeted the liver and blood stages of malaria infection had 80% fewer infections than those treated with drugs that only targeted the blood stage.
Using mathematical models, the researchers also showed that anti-malaria programs are unlikely to eradicate malaria if they cannot identify and treat children with dormant liver infections.
Dr. Robinson concludes:
“Mass drug administration that includes a drug that kills parasites in the liver is likely to be a highly effective strategy for eliminating malaria in PNG.”
The researchers are planning to work – with other groups – on developing biomarkers for P. vivax malaria. These could help develop new tools to identify and treat people with chronic malaria infections, which they believe will be critical for reaching the goal of eradicating malaria in PNG and the Asia-Pacific.
Meanwhile, Medical News Today recently learned that Africa is at higher risk of drug-resistant malaria than previously thought. New research published in Nature Communications shows it is possible for drug-resistant forms of the malaria parasite – currently confined to mosquitoes in Southeast Asia – to infect African mosquitoes.