Six countries in Africa accounted for about half of all malaria deaths worldwide in 2019: Nigeria (23%), the Democratic Republic of the Congo (11%), Tanzania (5%), Burkina Faso (4%), Mozambique (4%) and Niger (4%).
The World Health Organization (WHO) has set an ambitious target of reducing the global malaria burden by 90% by 2030. This is important work, given that malaria remains one of the world's deadliest infectious diseases. The WHO estimates that 3.4 billion people in 92 countries are at high risk of being infected with malaria and 1.1 billion are at high risk of getting malaria in a year.
There has been some progress towards the 2030 goal, with both cases of and deaths from malaria dropping from about 400,000 in 2010 to about 260,000 in 2018. But efforts are being hampered by the parasites resisting antimalarial drugs that people take and by mosquitoes resisting insecticides. While the WHO has recommended a vaccine for malaria, it is not yet accessible to all.
Researchers, myself among them, are also exploring alternative strategies to manage and treat malaria. I am studying whether plant-based remedies drawn from traditional medicinal practices may be of use. Herbs are already used to treat diseases in many cultures. In Nigeria, as in other African countries and most parts of Asia, medicinal herbs are widely used to treat and prevent various ailments - including malaria.
Some current antimalarial drugs developed in laboratories, including amodiaquine and artemisinin, were either isolated from plants or were developed from chemical compounds found in plants. So it's logical to investigate more plants and other natural products as potential sources of novel antimalarial agents.
Our new study examined whether extracts from a variety of plants were able to counter the effects of a malaria-causing parasite in mice - in other words, whether the plants treated malaria symptoms. We made a drink from three plants and gave it to mice infected with the Plasmodium berghei parasite.
We found a mixture of the herbs suppressed and prevented the presence of parasites inside the mice. This was more effective than each herb on its own.
What we did
A large number of medicinal plants are used for treating malaria in Nigeria. This is common in the southern region of the country, where rainforests and a humid tropical climate create ideal conditions for malaria transmission all year round.
One of the many groups of herbal remedies used in Nigeria is the antimalarial decoction popularly called Agbo iba. The composition, method of preparation and dosage of these antimalarial decoctions vary from vendor to vendor, as earlier reported by my research group. These decoctions are often polyherbal (containing more than one herb) and prepared in water or alcohol.
For our experiment, we used Mangifera indica, (mango), Azadirachta indica (known in Nigeria as dongoyaro), Nauclea latifolia (African peach) and Morinda lucida (brimstone tree). They are all used traditionally in malaria treatment.
We bought the plants fresh from Mushin herbal market in Lagos and they were identified and authenticated at the herbarium of the Department of Botany, University of Lagos.
Mice are commonly used in preclinical trials because of biological similarities with humans. They can mimic malaria disease in humans and indicate how people might respond to the herbal mixture.
The study was conducted with approval from the Health Research Ethics Committee of the College of Medicine, University of Lagos. We inoculated the mice with chloroquine-sensitive Plasmodium berghei, obtained from the Nigerian Institute of Medical Research.
The animals were grouped and dosed to examine for three possible responses: preventing, suppressing and curing effects of the polyherbal mixture. Both prevention and suppression involve destroying the malaria parasite. Cure means the herbal mixtures eliminate the parasites.
The mixture preparations gave promising antimalarial results in the three investigations.
In the prophylactic (prevention) test, the herbal decoctions demonstrated significant chemosuppression. Chemosuppression is the use of chemicals to defeat parasites in an animal.
All the herbal decoctions showed chemosuppressive activities. They significantly reduced the parasite load 24 hours after administration to the end of the treatment - four to seven days.
All the herbal decoctions were also active in the curative test. They considerably reduced the parasite load from day 2 of treatment.
At the end of treatment, none of the decoctions had completely cleared the parasites, but they all produced substantial clearance. This shows their potential usefulness against established plasmodial infection.
Our findings showed that the combination of all the plants could be useful in suppressing malaria in its early stages. All the decoctions investigated in this study could be considered as active antimalarial candidates. They could help with eradication of malaria parasites.
Further studies will be needed to evaluate whether the polyherbal mixture we tested on mice is safe and effective in humans.
But this is a good starting point. The study shows that, with the right safety and clinical controls, the use of standardised herbal medicines could be a valid complementary approach for malaria management.
It's good to find new medicines for malaria treatment because the parasites and microbes get used to the existing ones and become resistant. Medicinal plants are potential sources of new medicines.
Author: Stephanie Alaribe - Lecturer, University of Lagos