Does malaria spread from a person to another?

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QUESTION:

Can malaria spread from one person to another?

ANSWER:

Usually, no. In most cases, the malaria parasite has to first pass from a human host into a mosquito as the mosquito takes a blood meal, and then from the mosquito into another human via the mosquito’s saliva. This severely limits the amount of person-to-person transmission that exists. In fact, the only mechanisms for direct transmission between humans are when malaria parasites are passed between a mother and her unborn child via the placenta (congenital transmission) and through unscreened blood transfusions.

Congenital malaria is the more common type of human-to-human transmission; across various surveys of newborns in West Africa, between 8-24% were found to be infected with malaria parasites.

All four main species of human malaria (P. falciparum, P. vivax, P. ovale and P. malariae) have been implicated in congenital transmission. Infection with malaria during pregnancy not only puts the mother at greater risk of severe disease episodes (probably through reduced immunocompetence during pregnancy) but may also negatively impact the baby; although in endemic areas it is rare for babies to be symptomatic for malaria when acquired congenitally, even if they have parasitaemia, they have been shown to have a higher mortality rate than non-infected newborns. In non-endemic areas, babies with congenital malaria often display symptoms, which usually manifest themselves between 2 and 8 weeks after birth. Both quinine and artemisinin-based therapies have been successfully used to treat congenital malaria.

Malaria infection as a result of blood transfusion was first identified in 1911 and is one of the most common illness transmitted via transfusion, although the risk of being infected, particularly in non-endemic countries, is very low.

As it is difficult to screen blood directly for malaria infection, a number of standards have been put in place by blood-collection services to reduce the risk of obtaining blood containing malaria parasites. For example, in many places, you will not be allowed to donate whole blood if you have visited an endemic malarial region in the last three months, nor should you donate if you have previously had malaria unless you have been symptom-free for at least three years.

Due to the longevity of Plasmodium malariae in the blood, you are unlikely to be able to donate blood if you have ever been confirmed as positive for P. malariae. Serological screening of blood for malaria antibodies has recently been shown to be a sensitive method for testing for malaria in blood, although it is expensive and therefore not cost-effective for screening every sample, especially in non-endemic countries. However, it can be effective and efficient to avoid wastage when employed together with a travel-based questionnaire to ascertain donors who are high-risk for malaria.

It is worth mentioning that transmission of malaria via plasma only is very uncommon, and so frequent travellers or residents in malarial areas, who may be denied the right to donate whole blood, should ask about the possibility of donating plasma instead.

What is malaria?

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QUESTION:

What is malaria?

ANSWER:

Malaria is a disease caused by parasites of the genus Plasmodium. Transmitted by mosquitoes, there are several different kinds of malaria distributed throughout the tropical and sub-tropical regions of the world, causing somewhere between 300-500 million cases of disease each year, and as many as 1 million deaths. In fact, malaria is one of the biggest killers of children under the age of five in sub-Saharan Africa, one of the regions of the world where the burden from malaria is the highest. Malaria is usually an acute disease, manifesting itself with severe fever, chills, headache and often nausea as well. Some types of malaria can have relapsing episodes over a time period of many years.

Having said this, malaria is easily preventable, through avoiding mosquito bites by wearing appropriate clothing and sleeping under insecticide-treated bednets, or through taking preventative medication (called prophylaxis). Malaria is also treatable once symptoms appear, through ingesting safe, effective and relatively cheap drugs. With such control measures at hand, you may ask why malaria is still such a huge problem in our world; the answer is that delivering control strategies and treatment to populations most at risk is difficult, and often countries with high malaria burdens don’t have efficient and effective health systems in place to coordinate control efforts.

International non-governmental organisations such as the World Health Organisation, as well as a multitude of non-profit organisations such as the Malaria Consortium and Malaria No More, work tirelessly to bring malaria control and treatment to the places that need it most, with the aim to eradicate malaria as a disease of public health importance.

 

Which doctor first linked Anopheles to cases of malaria?

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QUESTION:

Which doctor first found that Anopheles mosquitoes transmitted malaria?

ANSWER:

The first person to show conclusively that malaria could be transmitted by Anopheles mosquitoes was Ronald Ross (later knighted in 1911 for his services to medicine).

Working in the Presidency General Hospital in Calcutta (Sir Ronald was born in India and joined the Indian Medical Services in 1881 after studying medicine in London), he observed malaria parasites in the salivary glands of mosquitoes that had been fed on infected birds. This was in 1898, and he was awarded the Nobel Prize for Medicine and Physiology in 1902 based on this discovery. A medical board in 1900 later confirmed his findings, and provided recommendations for the control of malaria, some of which were instrumental in limiting the impact of the disease on workers employed to construct the Panama Canal.

The parasite that causes malaria, of the genus Plasmodium, had been identified in 1880 by the French doctor Charles Louis Alphonse Laveran, who had observed the parasites in the red blood cells of infected patients in Algeria.

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.