Plasmodium Vivax

Vivax malaria, often overlooked

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Malaria doesn't get the respect it should. It has caused a lot of damage around the world and throughout history. Roughly, it infects 200 million a year and leaves 500,000 dead. One type of malaria, Vivax, is often overlooked. It causes about 40% of these 200 million infections, though it does not kill as many.

1. There are different types of malaria

There are 100 malaria species. 5 species infect humans - Falciparium, MalariaeOvaleKnowlesi, and Vivax.

 A case of Falciparum is the deadliest, but Vivax is more common in many parts of the world. 

There's not just one type of malaria. One of these types is often overshadowed. It has spread the most widely around the world. According to the CDC, it is "probably the most prevalent human malaria parasite".

This is Plasmodium Vivax.

2. Vivax is found in more places than any other.

Vivax is found more widely around the world than any other type. It is found in the Americas, Asia, and some parts of Africa. It is the most common type in Asia.

It usually does not kill, but it can. It is usually not directly fatal, but it can indirectly - coupled with other medical issues - lead to death. It causes 70-80 million cases/year. The disease also impacts pregnant women.

It causes about 1 in 10 to 1 in 5 cases of malaria in Africa. It causes only <1% cases in western and central Africa. Most cases outside of Africa are due to P vivax - in the Middle East, Asia, Western Pacific, and Central and South America.

3. Some people tend not to get Vivax

P vivax invades red blood cells through a receptor called Duffy. Some people don't have this Duffy receptor. Those who are Duffy-negative tend to not get sick with Vivax.

Those who are Duffy-negative can get Vivax. They're not entirely immune. But it also means that in areas where many people are Duffy negative, Vivax tends not to be found.

Duffy protects a lot of people. Most people of African descent - from 68% of African-Americans to 90% of West Africans are Duffy negative. Many others around the world have the Duffy negative. Some in Iran, Papua New Guinea, islands off of India (Andaman islands), parts of the Americas, and many other areas around the world

4. Vivax can return long after a mosquito bite

P vivax (as well as P ovale) can hide out in the liver, asleep. P vivax may reactivate - months or years later - resulting in illness a long time after that first mosquito bite. When the parasite is in this sleeping hypnotized state, it's referred to as "hypnozoites". The longest time recorded it ever spent asleep before reactivating was 

5. The treatment for Vivax is risky for some people

One of the treatments, Primaquine, used for Vivax, clears the hypnotized state of Vivax. However, in some people, this drug can cause red blood cells to break down (not that differently from what malaria does). This occurs in those who have a particular gene, G6PD.

 Primaquine causes varying degrees of red blood cell breakdown depending on what mutation of G6PD someone has, which generally depends on ethnic background. G6PD is found in 400 million people worldwide, particularly in those of African, Mediterranean, and Asian descent, though the precise mutations vary. Unfortunately, this means that where Vivax is common, G6PD is also common, which can affect treatment.

6. Can infect others before getting sick

P vivax unfortunately can spread from one person to the next mosquito before someone even has symptoms. This is because malaria goes through stages and not all stages can be picked up by mosquitoes. For vivax, the parasite stage that can lead to transmission can be in the blood before there are symptoms. 

7. Vivax used to be common in the US

The CDC was founded in Atlanta to combat malaria - which was Vivax. Multiple past US presidents likely were infected - including George Washington, Abraham Lincoln, and Ulysses S Grant. The Revolutionary War and the Civil War were affected by it.

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