Is Malaria Transmitted by Female Mosquitoes?

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QUESTION

Is malaria caused by only female mosquitoes?

ANSWER

Malaria is only transmitted by female mosquitoes, yes. This is because only female mosquitoes of the genus Anopheles (the genus that transmits malaria in mammals, including humans) feed on blood, and the parasite that causes malaria (called Plasmodium) spends part of its life cycle in the blood. Therefore, when a female mosquito feeds on an infected person, when she sucks up their blood, she also takes up some of the Plasmodium parasites. These parasites mature inside the mosquito, and then, when the mosquito goes to bite another person, she passes some of the mature Plasmodium parasites into that new person’s blood while she feeds. The Plasmodium parasites may then be able to undergo further development in the new host, which may lead to the person experiencing a malaria infection. So, while technically female mosquitoes don’t cause malaria (since the disease is caused by the Plasmodium parasite), female mosquitoes are required to pass it between one person and another.

Ingestion of Malaria Blood

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QUESTION

If someone were to eat/ingest the blood of an infected individual would they become infected with malaria? If an infected person’s blood was on their hands and they handled food, would eating the food put others at risk for malaria?

ANSWER

No, you would not get infected with malaria, as the malaria parasites must be transmitted into a person’s blood directly in order for them to be infected. As such, most transmission only occurs via mosquitoes: when a mosquito bites a person infected with malaria, it may pick up some of the malaria parasites while it feeds on the person’s blood. When it then goes to bite another person, after the parasite has replicated and changed inside the mosquito, it can pass the malaria on to the next person, again when it bites them and drinks the person’s blood.

Additionally, in some cases malaria can be transmitted by blood transfusion or organ donation, or from a mother to her unborn baby via the placenta, or through blood passed in childbirth. If you ate/drank malaria-infected blood, the parasites would be broken down and destroyed by your stomach acid.

Structure and Size of Malaria Mosquito

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QUESTION

What is the structure and size of the mosquito?

ANSWER

The mosquitoes that transmit human malaria belong to the genus Anopheles. As such, they follow the general body plan structure of a flying insect—three segments (head, thorax and abdomen), three pairs of legs and two pairs of wings. Anopheles females have modified mouthparts that allow them to feed on blood, by inserting a specialized proboscis into the skin; male Anopheles feed on nectar and so do not possess the same type of mouthparts.

The size of the adult mosquito varies on factors such as the exact species, the larval environment and food availability, but the length of the body is rarely greater than 16mm and the total weight is usually less than 2.5 milligrams.

Malaria Hosts

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QUESTION

Which are malaria hosts and how does malaria have an effect on one of them?

ANSWER

The parasite which causes malaria (called Plasmodium) requires two different hosts—a vertebrate intermediate host, such as a human, and an insect definitive host, also known as the vector. For the types of malaria which infect humans and other mammals, the vector is always a mosquito of the genus Anopheles.

However, there are other types of malaria which infect birds and reptiles, and these can use other genera of mosquito as their vectors, and some parasites closely related to Plasmodium can even use sandflies and other types of insects as their vectors too.

In humans, malaria usually causes disease, characterized by high fever, chills, aches and nausea. However, the presentation of symptoms and their severity depends on a number of factors, such as the type of Plasmodium (P. falciparum is the most dangerous to humans), the immune status of the host and the infective dose received from the vector.

Many mammals are also susceptible to malaria, such as macaque monkeys, and with them as well the effect of the parasite depends on a number of factors. For example, for macaques in south-east Asia, many will be co-infected with several different types of malaria simultaneously, though none appear to cause disease. However, if macaques from other parts of tje world, such as the Himalayas, are experimentally infected with these same types of malaria, they will get sick and possibly even die. As such, evolutionary history also plays a part in terms of how severe malaria will be in a particular host.

For the insect vector, infection with malaria parasites does not appear to have a strong deleterious effect, though some studies have shown reduced survival in mosquitoes infected with malaria. Also, changes in behavior have been observed. For example, some studies have shown that mosquitoes which are infected with malaria are more likely to continue seeking for food (i.e. through biting a host) even if they have recently fed than mosquitoes which are uninfected, or infected with non-transmissable life stages of malaria. This suggests that in some way the malaria parasite is manipulating the vector’s behavior in order to increase its own chances of being passed on to a new host.

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.

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 Transmission

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QUESTION

How is malaria transmitted?

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 Effect on Host

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QUESTION

What is the effect of malaria on host?

ANSWER

In the human host, malaria can often make a person very sick, though the exact symptoms and severity of the disease depends on the type of malaria (five different kinds of malaria infect humans). Many people will have a high fever, chills, nausea and body aches. In a symptom very typical of malaria, a patient will experience cyclical fever, with periods of no fever in between, lasting between one and two days. In infections with Plasmodium falciparum, the most dangerous kind of malaria, patients may experience impaired consciousness, a sign of “cerebral malaria”, which can lead to loss of consciousness, coma and even death.

In terms of the mosquito host (more commonly called the vector), the insect does not experience “illness” in the same way as the human host, and the parasite does not seem to have a particularly negative effect on the mosquito. However, some research has shown that infection with malaria may cause a mosquito to seek out blood meals more frequently, which scientists argue is an adaptation of the malaria parasite to ensure that its life cycle is continued.

Is Malaria a Mosquito STD?

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QUESTION

Is Malaria a type of STD for mosquitoes?

ANSWER

No. Mosquitoes pick up the malaria parasite from feeding on the blood of infected humans. Since only female mosquitoes feed on blood (the males feed on nectar), male mosquitoes never get infected with the malaria parasite. The life cycle of malaria in the mosquito is also completely different than in humans, and mosquitoes have a completely different physiology and immune system to humans, so it cannot be said that they get the same disease as we observe when people get infected with malaria.

Life Cycle of Malaria

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QUESTION

Why does the malaria parasite first enter the liver?

ANSWER

The malaria parasite enters the liver in order to transform from a sporozoite (which can infect liver cells) to a merozoite, which is capable of infecting red blood cells. Both stages also include a proliferation step, but in the blood, the merozoites are also able to differentiate into gametocytes, which are then taken back up by a mosquito during a blood meal, allowing the malaria parasite to continue its life cycle. If the red blood cell stage were first, followed by the liver, then it would be much harder for the gametocytes to be able to reach a new mosquito host, unless they were to enter the blood a third time.

The blood is also a difficult place for a parasite to survive, since it is the highway of the immune system, whereas the parasite is less easily destroyed when it is hiding out in the hepatocyte cells in the liver. It is also important to note that Plasmodium has a long evolutionary history, and may in some parts of its life cycle be constrained by physiological or life history characteristics of its evolutionary forebears, which may also contribute to our perception of the life cycle as being very complex!

Anopheles Mosquito

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QUESTION

Why is it only the female anopheles mosquito alone can cause malaria but not the male anopheles mosquito or any other mosquitoes?

ANSWER

Malaria is actually caused by a single-celled parasite called Plasmodium—it is transmitted via the bite of a female mosquito, of the genus Anopheles, as she takes a blood meal from a human (or other mammal) host. Male mosquitoes do not feed on blood (they only feed on nectar), whereas females need the nutrients from blood in order to produce their eggs; as such, only female Anopheles transmit mosquito.

Why only Anopheles are able to transmit malaria to humans is interesting—birds and reptiles also can get Plasmodium (though different species than those that infect humans and other mammals), and these kinds of malaria can also be transmitted by other kinds of mosquitoes, such as Aedes and Culex. Other closely related blood parasites can even be transmitted by other flying insects, such as sand flies and black flies. However, it is true that only Anopheles can transmit human malaria.