Introduction of malaria

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QUESTION:

What is the introduction of malaria?

ANSWER:

Malaria is introduced into the human host via mosquitoes, who pass the parasite into the human blood stream through their mouthparts as they take a blood meal. Since the development of both the mosquito and the parasite are temperature-dependent, and tend to favour warm, humid conditions (mosquito larvae require pools of still water to develop into adults), the distribution of malaria is limited to parts of the world where these temperature and humidity conditions are met.

However, cases of malaria can also be introduced into other parts of the world by travellers coming from malarial regions or by mosquitoes, already infected with malaria, being accidentally transported into non-malarial countries in aeroplanes or in ships. These kinds of introductions resulted in about 1500 cases of malaria reported in the United States in 2007, a country which is usually free of malarial transmission. These introductions are rare, and also short lived, as the conditions do not favour the continued survival of the transmission cycle. However, this is one of the worries regarding climate change; it may make some areas of the world, which currently do not have malaria, more climatically suited to transmission of the disease, thus allowing for introductions of the mosquitoes and the parasite in the future.

How does malaria spread?

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QUESTION:

How does malaria spread?

ANSWER:

Malaria is a vector-borne disease; this means that it has to be spread through a “vector” species, which in this case are female mosquitoes of the genus Anopheles. The female mosquito needs to feed on blood in order to produce eggs; most species lay eggs every 2-3 days, which means each female mosquito needs to take very regular blood meals.

Around 20 species of Anopheles mosquito have been implicated in the transmission of malaria; some species are better than others at acting as a vector. The most important group in Africa is the Anopheles gambiae complex; these mosquitoes are also relatively long-lived, which is important for transmission since it means that whole portions of the malaria parasite’s life cycle can be completed inside the vector mosquito.

When the female mosquito takes a blood meal, she inserts her slender mouth part (called a ‘proboscis’) into a tiny cut she makes uses specialized slicing parts of her mouth. She probes until she finds a small surface blood vessel, from which she feeds. The proboscis contains two narrow tubes – one delivers her own saliva into the wound (containing chemicals to stop the blood coagulating as well as a slight pain-killer, to stop you feeling the bite) while the other sucks up blood.

The mosquito’s saliva also contains the malaria parasite; this is how the parasite is delivered into the human body. Similarly, the parasite passes back into the mosquito through the blood she ingests, once the human portion of the life cycle has been completed. As mosquitoes pass between human to human, and indeed also between other animals, they spread the malaria parasite through the delivery of saliva and the uptake of blood.

What is malaria? What Causes Malaria?

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QUESTIONS:

What is malaria?
What causes malaria?

ANSWER:

I have copied below the text from an earlier question, also asking about the causes of malaria and explaining what it is:

Malaria is a disease caused by a parasitic single-celled animal known as Plasmodium. There are different species of Plasmodium, which cause different kinds of malaria. The main types which infect humans are P. falciparum, P. vivax, P. ovale and P. malariae. The parasite is transmitted by certain species of mosquito; the parasite lives in the human blood stream and so goes in to the mosquito when the insect feeds. When the same individual mosquito then feeds on another person, it transmits parasites into a new host.

The symptoms of malaria are caused by the actions that the parasite undertakes while in the human host. For example, part of its reproductive cycle involves invading and then multiplying inside red blood cells. Once several cycles of reproduction have occurred, the new parasites burst out of the red blood cell, destroying it. The cycles are times so that all the new parasites burst out of the red blood cells at the same time; this coordinated destruction of the red blood cells, either every 24, 48 or 72 hours, depending on the malaria species, causes the one day, two day or three day cycles of fevers and chills that characterize malaria infection episodes.


How does malaria infect the body?

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QUESTION:

How does malaria infect the body?

ANSWER:

Malaria is transmitted to humans via certain species of mosquito. The parasite that causes malaria, called Plasmodium (there are several species, which cause slightly different forms of the disease), lives in the saliva of the mosquito and is introduced into the human blood when the mosquito bites through the skin. It is interesting to note that only female mosquitoes transmit malaria; male mosquitoes don’t feed on blood, only on nectar and other plant juices, and their mouth parts are too soft to break human skin!

Once the parasite is in the human bloodstream, it undergoes several different life stages. Throughout, it must evade the human immune system, and it has a number of clever ways to do this. One method is by producing a protein which it attaches to its surface; this acts as a “cloak” against the human immune system and hides the parasite. The parasite also uses other proteins to complete its life cycle, for example several are used to enter red blood cells, where part of the reproductive cycle of the parasite is carried out. Finally, after several transformations and cycles of reproduction, the malaria parasites are released again into the bloodstream, where they can be picked up by another female mosquito, and transported to a different human.

For more information about some of the mechanisms for evading the immune system, check out this article from the BBC website, which summarises some recent findings about Plasmodium falciparum, the malaria parasite which causes some of the most debilitating and deadly malaria cases worldwide.