Transmission of Malaria

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QUESTION

Why can the malaria parasite be transmitted from mosquito to human, but not from human to human (via blood)?

ANSWER

This is a very good question, and actually, malaria can be transmitted via human blood directly to another person, but this occurs relatively rarely!

It has to do with the life cycle of the malaria parasite. When a mosquito bites a human host, it injects sporozoites from its salivary glands into the blood. This life stage first migrates to the liver, where it undergoes a cycle of multiplication, before entering the blood stream. Here, in the so-called “erythrocytic” portion of the life cycle, the parasite reproduces a series of times in red blood blood, before finally forming gametocytes, which are required to be ingested by a mosquito vector during another blood meal for the life cycle to be continued. As such, when blood is passed between people, they would have to pass infected red blood cells, and not gametocytes (which are not infective to humans, only to mosquitoes) in order for the other person to become infected.

As such, when a person who is infected with malaria donates blood, there is a chance that they might pass on some red blood cells which are infected with mature trophozoites or schizonts; these could then go on to infect more red blood cells in the person who received the blood. However, in most countries, blood is screened for malaria, and in fact, in many places, people who might have been exposed to malaria are not allowed to donate whole blood, only plasma (in which the red blood cells have been removed, and therefore there is no risk of transmission). Given the high levels of malaria prevalence in some endemic countries, however, preventing people from donating blood who are positive for malaria may result in too little blood being collected; in these cases, other strategies, such as treating donors or closely monitoring patients post-transfusion, may prove to be a better strategy.

malaria life cycle schematic CDC

Schematic of the malaria life cycle, courtesy of CDC (www.cdc.gov)

Malaria Transmission

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QUESTION

Can one get malaria through contact with the infected person or is it airborne?

ANSWER

Malaria cannot be transmitted through direct contact with an infected person, nor is it airborne! It is actually transmitted directly via the bite of an infected mosquito. Only certain female mosquitoes, of the genus Anopheles, can carry malaria. The mosquito picks up the malaria parasite (there are five different types of malaria that infect humans, though all are transmitted in exactly the same way) when it feeds on the blood of an infected person. The parasite then undergoes a cycle of reproduction in the mosquito, before new parasites migrate once again to the mosquitoes salivary glands. From here, they are able to escape into the blood of a new human host when the mosquito takes another blood meal by biting the person.

Since malaria is transmitted by blood, there have been a some reports of malaria transmission via organ donor or blood transfusion, though most countries now screen for malaria before using donated blood or organs. Additionally, if a pregnant woman gets malaria, the parasite can be passed to her baby either across the placenta or during delivery; this is called “congenital malaria”, and can be quite harmful to the baby. As such, and also because pregnant women themselves are especially vulnerable to malaria, many campaigns have dedicated themselves to providing pregnant women with long-lasting insecticide treated bednets and other measures to prevent and treat malaria.

Malaria Transmission Through Sexual Contact

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QUESTION

Can i get malaria if i have sex with someone that has malaria?

ANSWER

No. Malaria cannot be sexually transmitted. In virtually all cases, malaria is transmitted through the bite of an infected mosquito, of the genus Anopheles. The mosquito passes the malaria parasite (there are several species which cause malaria in humans, all of the genus Plasmodium) through its saliva when it feeds on blood. Only female mosquitoes feed on blood, and so only females transmit malaria. The mosquito picks up malaria also by feeding on blood, this time from someone who already has the infection.

The only other ways to get infected with malaria are through blood transfusion, organ transplant and via the placenta during pregnancy (“congenital” malaria), and these are all very rare, particularly as blood and organ donors are now usually screened for malaria infection prior to transfusion or transplant.

If you have taken medications for malaria, please help Malaria.com by taking our Malaria Medication Side-effects Survey: Treatment and Prophylaxis. Thank you!

Causes of Malaria

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QUESTION

What are the causes of malaria?

ANSWER

Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells. Usually, people get malaria by being bitten by an infective female Anopheles mosquito.

Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the person being bitten.

Following the infective bite by the Anopheles mosquito, a period of time (the “incubation period”) goes by before the first symptoms appear. The incubation period in most cases varies from 7 to 30 days. The shorter periods are observed most frequently with P. falciparum and the longer ones with P. malariae.

Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery (“congenital” malaria).


How to get malaria?

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QUESTION

How do we get malaria?

ANSWER

Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells. Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the person being bitten.

Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery (“congenital” malaria).

Causes of Malaria

by

QUESTION

What causes malaria?

ANSWER

Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells.

Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the person being bitten.

Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery (“congenital” malaria).

 


 

Malaria After Blood Transfusion

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QUESTION:

How many days does it take to become symptomatic after a blood transfusion of malaria infected blood to patient?

ANSWER:

This depends on the strain and burden of malaria parasites in the blood being transfused. Onset of malaria symptoms can be very rapid if infected red blood cells begin to rupture immediately, say within 24-48 hours, or conversely symptoms can be very delayed (days/weeks/months) if only a few parasites are transfused. Depending on strain, the malaria parasites may need to cycle through the liver to mature before they infect the red cells (such as in the case of Plasmodium vivax or P. ovale).  Then, depending on the strain (P. vivax most commonly), the infected red cell “burden” often needs to approach 0.5 to 1% before synchronized rupture of red cells and release of the parasites is sufficient to produce acute fever and symptoms.