Anopheles Mosquitoes and Malaria Transmission

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QUESTION

How are the Anopheles mosquitoes able to transmit human Malaria and others are not? What makes them different from the other genus of mosquito?

ANSWER

This is a great question and in fact scientists are not really sure of the answer. The ability of female Anopheles to transmit malaria is a quirk of evolutionary history. Other species of Plasmodium (the Latin genus name of the group of parasites which cause malaria), for example those that infect birds and lizards, are transmitted by other mosquitoes, such as Culex. When the parasite switched hosts and started infecting mammals, this coincided with the parasite specializing in infecting Anopheles mosquitoes, and this relationship has remained ever since. It is a case of what scientists term “coevolution”, where a parasite and its vector have a tightly coupled and highly specialized relationship.

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.

Malaria Parasite

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QUESTION

Which parasite transmits malaria?

ANSWER

Malaria is caused by a parasite called Plasmodium, which is transmitted via the bite of an infected mosquito. The parasite passes into the blood of the human patient when the mosquito bites, via its saliva. There are five species of Plasmodium which normally infect humans: P. falciparum, P. malariae, P. ovale, P. vivax and P. knowlesi. 

Discovery of Malaria

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QUESTION

Who was the discoverer of malaria?

ANSWER

Malaria has been known to humans since ancient times, though what exactly caused it and how it was transmitted was not known. The parasite which causes malaria, from the genus Plasmodium, was first observed in the blood of a patient who had died from the disease by Charles Louis Alphonse Laveran, a French physician working in Algeria. This was in 1880; a few years later, in 1897-1898, a British army doctor called Ronald Ross showed that malaria could be transmitted via the bite of a mosquito. Both doctors eventually received the Nobel Prize for their discoveries.

Classification of Malaria Parasite

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QUESTION

What is the classification of malaria?

ANSWER

Malaria is caused by a single celled protist of the genus Plasmodium. This genus is part of a Phylum of single-celled protist organisms called Apicomplexa.

The Apicomplexans mostly posses an organ called an apicoplast, which is part of an apical structure designed to aid entry into a host cell. The Apicomplexa is split into two Classes, of which Plasmodium belongs to the Aconoidasida (lacking a structure called a conoid, which is like a set of microtubules), and then to the Order Haemosporidia, which contains parasites which invade red blood cells. Within this Order, Plasmodium belongs to the Family Plasmodiidae, which all share numerous characteristics, including asexual reproduction in a vertebrate host and sexual reproduction in a definitive host (a mosquito, in the case of the Plasmodium species that infect all mammals, including humans).

In the case of human malarias, the definitive host is often referred to as the vector. The family contains about twelve genera, of which one is Plasmodium, which itself is now often divided up into numerous sub-genera, and then again into hundreds of different species, of which five infect humans (P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi).

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).

Classification of Malaria

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QUESTION

Classification of malaria

ANSWER

Malaria is caused by a single celled protist of the genus Plasmodium. This genus is part of a Phylum of single-celled protist organisms called Apicomplexa.

The Apicomplexans mostly posses an organ called an apicoplast, which is part of an apical structure designed to aid entry into a host cell. The Apicomplexa is split into two Classes, of which Plasmodium belongs to the Aconoidasida (lacking a structure called a conoid, which is like a set of microtubules), and then to the Order Haemosporidia, which contains parasites which invade red blood cells. Within this Order, Plasmodium belongs to the Family Plasmodiidae, which all share numerous characteristics, including asexual reproduction in a vertebrate host and sexual reproduction in a definitive host (a mosquito, in the case of the Plasmodium species that infect all mammals, including humans).

In the case of human malarias, the definitive host is often referred to as the vector. The family contains about twelve genera, of which one is Plasmodium, which itself is now often divided up into numerous sub-genera, and then again into hundreds of different species, of which five infect humans (P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi).