Malaria Infectious?

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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.

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!

Malaria in Hong Kong and China

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QUESTION

Is malaria a risk in Hong Kong and Southern China?

ANSWER

There is no reported malaria transmission in Hong Kong, nor in the provinces directly bordering it in southern China. However, there is some risk of malaria in other parts of southern and central China, notably in the provinces of Anhui, Guizhou, Hainan, Henan, Hubei, and Yunnan, though rare cases may also be observed in other rural parts of the country between December and May below <1,500 m (4,921 ft).

Other Causes of Malaria

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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.

Discovery of Malaria

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QUESTION

How was malaria discovered?

ANSWER

Malaria has long been known to human populations from across the world. In fact, the first mention of the symptoms of malaria comes from an ancient Chinese manuscript from 2700 BCE! However, the actual cause and mechanism of transmission of the disease was only discovered in the 19th century.

It was Charles Louis Alphonse Laveran, a French physician working in Algeria, who first observed the parasites that cause malaria in 1880, by looking at the blood of a patient that had recently died of malaria. However, at this point, it still wasn’t understood how malaria was transmitted. That was not discovered until 1897, when Ronald Ross, a British physician dedicated to curing malaria, observed malaria parasites in a mosquito that had been experimentally fed the blood of a patient infected with malaria. Working in India, Ross also later showed that mosquitoes could also transmit malaria to birds, if they had previously fed on the blood of birds which had malaria. In this way, he showed that mosquitoes of the genus Anopheles are responsible for transmitting malaria between hosts.

Malaria in Southern Africa

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QUESTION

Which areas in southern africa harbour malaria?

ANSWER

Most of Namibia, Botswana and South Africa does not harbor malaria, either because it is too cold, too dry, or control measures have successfully eliminated transmission. However, malaria transmission is found in virtually all parts of Zimbabwe and southern Mozambique.

In addition, pockets of malaria transmission can be found in parts of the other countries of southern Africa, namely in northern Namibia (provinces of Kunene, Ohangwena, Okavango, Omaheke, Omusati, Oshana, Oshikoto, and Otjozondjupa and in the Caprivi Strip), in northern Botswana (Central, Chobe, Ghanzi, Northeast, and Northwest provinces) and also in the north-eastern corner of South Africa (north-eastern KwaZulu-Natal, with the southern-most limit of transmission corresponding with the Tugela River, Limpopo (Northern) Province, and Mpumalanga Province). Malaria is also transmitted in Kruger National Park.

First Malaria Outbreak

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QUESTION

When was the first ever outbreak of malaria?

ANSWER

Malaria has actually been known in human populations for thousands of years, so the first ever outbreak occurred long before any records were kept. The ancient Chinese recorded the symptoms of malaria in a medical manuscript which dates back to 2700 BCE, so almost 5000 years ago!

The symptoms of malaria were also known to the ancient Romans, Greeks, Egyptians and native peoples of the Americas, though none of them fully understood the cause of the disease or how it was transmitted. That information was discovered in the late 19th century, by Charles Louis Alphonse Laveran, who first observed malaria parasites in the blood of a patient and attributed them to the disease, and by Ronald Ross, who demonstrated that the malaria parasite was transmitted by mosquitoes.

Malaria in Kitwe Zambia

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QUESTION

Is it dangerous for my children two years old in Kitwe?

ANSWER

Kitwe has been part of the Roll Back Malaria campaign to control malaria in Zambia—the program has been very successful, reducing deaths by malaria by over 65% nationwide. However, there still is a risk of contracting malaria in most parts of the country, and so preventative measures should be taken when visiting or living in Kitwe, such as sleeping under a long-lasting insecticide treated bednet, wearing long-sleeved clothing in the evening and at night and screening doors and windows to prevent mosquitoes from entering.

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.

Is Malaria Contagious?

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QUESTION

Is malaria contagious?

ANSWER

Malaria cannot be transmitted directly between people via normal circumstances, so it is not contagious in the same way flu or the common cold is contagious. It also cannot be sexually transmitted.

In most cases, malaria can only be transmitted via the bite of an infected mosquito, so unless those mosquitoes are present, it cannot be transmitted. Because infectious stages of the parasite are present in the blood, in some cases malaria can be transmitted via blood transfusion (if the blood is not properly treated or screened), via organ transfer, or from a mother to her foetus, either via the placenta or during childbirth (this is called “congenital malaria”). However, compared to the amount of transmission which occurs via mosquito, these cases are relatively rare, and the vast majority of the time, malaria is not directly transmitted between people.