Is Malaria Contagious Between Humans?

QUESTION

If someone has malaria, is it contagious?

ANSWER

No. Malaria cannot be transmitted via touching or saliva or air. In virtually all cases, it is only transmitted by the bite of an infected mosquito, and so cannot be passed from one person to another. There are a few exception—because the parasite lives in certain organs and in the blood, it can sometimes be transmitted via blood transfusion or organ transplant. It can also pass via the placenta from a mother to her unborn child, or to the child during childbirth.

Malaria: Mode of Transmission

QUESTION

What is the mode of transmission of Malaria?

ANSWER

Malaria is transmitted normally via the bite of an infected mosquito. These mosquitoes, always female and of the genus Anopheles, carry malaria parasites in their salivary glands. The parasites, at this part of their life cycle known as sporozoites, are introduced into the host’s blood when the mosquito takes a blood meal. From there, the sporozoites travel to the liver, reproduce (this process may take several weeks), then finally re-enter the blood stream. At this point, the patient will begin to experience symptoms. Eventually, the malaria parasites change again, into gametocytes, which are picked up by another mosquito, again when it bites the infected person. In this way, the life cycle of the malaria parasite continues.

Because malaria reproduces in the blood and in the liver, in some cases malaria can be transferred via organ transplant or blood transfusion. In addition, malaria parasites can cross the placenta, and so can be transmitted from a mother to her unborn child, either in the womb or during childbirth. This is known as congenital malaria.

Causes of Malaria

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.

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 Infectious?

QUESTION

Is malaria infectious?

ANSWER

Yes, malaria is considered an infectious disease, though it is very rarely transmitted directly between people, and virtually all of the time must be transmitted via the bite of a mosquito (of the genus Anopheles).

Because part of the life cycle of malaria occurs in red blood cells in the human host, if sufficient amounts of blood are shared between people, for example during a blood transfusion, malaria can also pass between them this way, though screening measures reduce the likelihood of this occurring. Similarly, an earlier part of the life cycle occurs in the liver, so transplant of this organ can also result in transmission.

Finally, malaria is able to pass through the placenta, and so can be transmitted from a mother to her unborn child in this way, or also via blood during childbirth. When a baby contracts malaria from each mother, either via the placenta or during childbirth, it is known as “congenital” malaria.

Other Causes of Malaria

QUESTION

Apart from mosquitoe bites, is there any other thing that can cause malaria or if not from mosquitoes, is there any other way someone can get malaria?

ANSWER

Since the malaria parasites reside and reproduce in the blood, in some cases it is possible to transmit malaria from person to person through transfer of a large volume of blood, for example during a blood transfusion.

Some life stages of the parasite are also present in the liver, so cases of malaria transmission via organ donation (particularly of the liver) have also been noted. Finally, it is possible for a mother to transmit malaria to her unborn child via the placenta, or sometimes during childbirth, via the blood. The observation of malaria in newborn babies, who have not been bitten by mosquitoes, is known as congenital malaria. Despite the above possibilities, the vast majority of malaria transmission occurs via the bite of infected mosquitoes, so it is very important to protect yourself from these insects when in malarial areas.

Can Child Be Affected by Mother’s Malaria

QUESTION
If the baby’s mother has malaria, can it affect the child?

ANSWER

If the mother is pregnant when she gets malaria, particularly if it is her first pregnancy and particularly if she has never had malaria before, the effects on both the mother and child can be very serious. For the mother, this is because her immune system changes when she gets pregnant. This leaves her more vulnerable to the effects of malaria, including anaemia.

The most dangerous type of malaria, P. falciparum, also seems very able to infect cells in the placenta, leading to a higher intensity infection, and also reducing oxygen delivery to the baby. This, combined with the mother’s illness and anaemia, can lead to low birth weight, anaemia and other complications in the child once it is born. Malaria can also pass through the placenta, or be transferred to the baby through blood during childbirth, resulting in “congenital malaria”; that is, malaria which has been passed from mother to infant. Since newborns have inexperienced immune systems, malaria in the first days or weeks of life, and especially if the child is already low birth weight, can be very dangerous.

As such, a lot of effort has gone to finding ways to prevent malaria in pregnancy and to treat women who do get malaria while pregnant to prevent negative effects both to her and her unborn child. These efforts mainly involve the distribution of long-lasting insecticide treated bednets, and in some places also include the administration of intermittent preventive therapy, where women are given periodic doses of anti-malarials during pregnancy to protect against the disease.

Malaria and Pregnancy

QUESTION

Can your baby become immune if you’re pregnant and you have malaria?

ANSWER

Some of the protective antibodies that the mother produces when she has malaria can pass to her baby via the placenta. There is also evidence for immune system “priming” in foetuses when their mothers have been infected my malaria during pregnancy. However, these potentially protective effects are usually far outweighed by the negative effects of malaria during pregnancy.

Due to changes to the mother’s immune system and also perhaps due to the creation and physiology of the placenta, pregnant women are very vulnerable to malaria. For reasons which are not fully understood, women experiencing their first pregnancy (primagravidae) are most susceptible to malaria and their foetuses are most likely to have severe effects. These effects vary depending on the immune status of the mother and whether she is from an endemic or low transmission malaria environment, but typical results include low birth weight, anaemia and spontaneous abortion—abortion rates due to malaria can vary between 15-70%.

There is also the risk (up to 33% in some studies) that malaria will pass directly from the mother to the baby, either through the placenta or in blood during childbirth—this is called “congenital malaria,” and can manifest as early as 1 day after delivery but a late as months after. The symptoms are similar to that of adult malaria, with fever, anaemia, lethargy, etc.

Given these negative effects, it is very important to protect pregnant women against malaria, and bednet distribution schemes in many places target these women. In high transmission settings, women may also be offered intermittent preventive therapy (IPT) which consists of at least two doses of anti-malarial medication, usually once during the second and once during the third trimester.

Pregnant Women and Malaria

QUESTION

Why are pregnant women and children at the highest risk of getting malaria?

ANSWER

The reason why pregnant women and children are at greater risk of contracting malaria is due to their reduced levels of immunity. Children living in malarial areas have less immunity than adults because they have had less exposure to malaria, and so their immune systems have not had a chance to develop antibodies to protect against the disease. Pregnant women, although they may normally have good immunity, witness changes in their immune systems during pregnancy in order for the woman to carry the child.

Given that a baby is genetically distinct from its mother, the mother’s immune system has to be modulated in order to ensure that the body’s defenses do not act against the baby, as they would some other foreign object such as an infection. While this immune modulation allows the mother to carry her foetus, it does leave her vulnerable to other infections, such as malaria. In areas of high malaria transmission, the mother may still retain enough immunity to not present with severe symptoms of malaria. In these cases, the dangers of malaria in pregnancy come from resulting anemia in the mother, as well as passage of malaria antigens or the parasite itself through the placenta and to the foetus, which can result in problems for the baby.

Interestingly, a study came out last year which showed evidence that using long-lasting insecticide treated bednets increased malaria prevalence in older children and adults, probably because the nets protected against even sub-clinical exposure to malaria and therefore the levels of natural immunity in people using the nets declined over time, leaving them more susceptible to infection. However, this result has been controversial, as in other studies community-wide coverage of bednets has reduced overall malaria incidence due to reduced transmission.

Malaria Transmission Through Sexual Contact

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.

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