Science News, The Need-To-Know of Science

New Malaria Drug gets the Green Light

Although the heatwave has fooled us into believing that we could be living in Sub-Saharan Africa, we are fortunate enough not to be at a great risk of contracting Malaria. Malaria is one of the biggest killers in the world, with 216 million cases and 445,000 deaths in 2016, and primarily affects tropic and sub-tropical regions by the equator.

It comes with exciting potential that the drug Tafenoquine has recently been approved by the Food and Drug Administration (FDA) in the United States to treat recurring malaria.

Primaquine is the currently administered to those with recurring malaria, but has the disadvantage of its requirement to be taken for 14 days at a time. In contrast, only a single dose of Tafenoquine is necessary to have the same effect. There are still concerns associated with whether the drug could cause neurotoxicity, with suggestions that a more vigorous risk assessment should be conducted before its approval.

The symptoms of malaria include shaking chills, fever, nausea and diarrhoea, among others. In a healthy individual or one that is treated on time, malaria can be cleared within a few weeks. Some forms of malaria, on the other hand, are reoccurring. Despite the person affected not exhibiting any symptoms, it is possible that the parasite is dormant and that a signal could trigger the parasite to be active again.

This is may seem easy enough to understand, until you try to picture what is happening inside the body of a person who has malaria, and how taking Tafenoquine can help. How do we get malaria, what is it that causes the disease, and what is it that triggers the associated symptoms? Scientists have spent decades researching these questions (including my own Mamma Farr), so I will have to do my best with the word limit provided by WordPress to answer these questions as concisely as possible…

Mosquitoes, most commonly the Anopheles genus, transmit malaria. They bite the human, feed on the blood which contains malaria, then bite another human to pass it on. They are, however, simply a vector for the disease; the vehicle that the parasite uses to get from one host to the other. It is in fact the Plasmodium parasite that is the bad boy causing all the commotion;

Image result for plasmodium
A blood smear containing Plasmodium falciparum macro- and microgametocytes. Image from Wikipedia/Phys.org.

The two most common species of Plasmodium are P.falciparum and P.vivax. Whilst P.falciparum is most prevalent in Africa and responsible for the greatest number of global deaths, P.vivax is the more common form in other countries.

Both parasites follow a very similar life cycle. After being carried by the mosquito and then entering the bloodstream of a human, the Plasmodium enters the liver as sporozoites, develops into merozoites and then moves into the red blood cells (RBCs). It is the rupture of the RBCs when there are too many merozoites in the cell that causes the fever-like symptoms associated with malaria. Merozoites then develop into male or female gametocytes, and wait for the next mosquito to take a bite.

Life cycle stages of Plasmodium also occur in the mosquito. Gametocytes of opposite genders can fertilise to create a zygote, which then develops into an ookinete. Many ookinetes form an oocyst within the mosquito midgut. When the oocyst bursts, the parasites enter the salivary glands, ready to be transmitted into a host again.

Fig. 1.
The epidemiology and infectivity of Plasmodium. Image from Clinical Microbiology Reviews.

Not as happy and colourful as ‘The Lion King’, but that is the Circle of Life!

Tafenoquine acts on the liver stage, where the parasites have developed into hypnozoites (a sub-stage common to P.vivax). It is impossible to detect P.vivax using blood tests when it is present in this form because no symptoms are shown, and the parasite is capable of remaining dormant in the liver for many years. If this drug is administered, effectively destroying the hypnozoites before they develop into merozoites, then there is the potential to prevent the 8.5 million cases of malaria caused by P.vivax each year.

The highest prevalence of malaria is found in Sub-Saharan Africa, Asia and Latin America. Unfortunately, the occurrence of malaria in developing regions decreases the available incentive to treat such a disease than if it affected more affluent areas like Western Europe or the United States. Malaria remains an endemic, but charities such as the Bill & Melissa Gates Foundation has been beneficial in improving research and prevention in affected areas and are taking a step further towards a world without malaria.

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