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.

Researchers Discover Microbe That Could Help Fight Malaria

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Researchers have discovered a bacterium in the gut of the Anopheles mosquito which may someday be used to destroy and, therefore, prevent the spread of the disease-causing parasite.

The World Health Organization estimates 800,000 people die of malaria each year. The parasite that causes the disease is transmitted by the Anopheles mosquito. After the mosquito feeds on the blood of an infected individual, the parasite matures into an infectious stage in the insect’s gut.  From there, the parasite, known as Plasmodium falciparum, takes up residence in the mosquito’s salivary glands so it can infect the next person that’s bitten.

Researchers at Johns Hopkins School of Public Health in Baltimore, Maryland found the bacterium in the gut of the Anopheles mosquito among hundreds of so-called microbial flora that live harmlessly in the stomach of a group of Anopheles mosquitoes collected in an area of southern Zambia where malaria is rampant.

The microbe, which was in the guts of a small percentage of the mosquitoes, protected those insects against infection with the parasite.

Lead researcher George Dimopoulos says the protection seems to be a side-effect of the bacterium’s normal bodily function, adding that scientists would like to figure out a way to use the microbe as a weapon against malaria.

“Our study has shown that this bacterium produces free radicals, molecules that contain oxygen and that can cause damage to cells.  So, we believe that’s how this bacterium is killing the malaria parasite in the mosquito gut.  But we need to understand that mechanism in greater detail.”

To demonstrate the beneficial effect, the researchers used antibiotics to kill the bacterium in mosquitoes that contained it, and were then able to infect those mosquitoes more easily with the Plasmodium parasite.

They also introduced the bacterium into the guts of mosquitoes that didn’t have it. When they fed this group infected blood, the parasite was destroyed in nearly all of the insects.

Dimopoulos says researchers’ goal now is to figure out a way to introduce the microbe into large populations of Anopheles mosquitoes – perhaps through bait laced with their favorite snack.

“Mosquitoes need to feed on sugar every day.  And one can potentially expose mosquitoes in the field to these bacteria through sugar bait.”

The researchers noted that mosquitoes with the bacterium in their guts die sooner than those without it – when both groups are infected with the parasite. Since the malaria parasite lives in mosquitoes for about two weeks before maturing to an infectious stage, Dimopoulos says it’s good news that the stomach bacterium seems to shorten the insect’s lifespan, before it could potentially transmit the parasite to humans.

Source: VOA News

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.

Malaria Countries and Map

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Geographic Distribution of Malaria Around the World

Where malaria is found depends mainly on climatic factors such as temperature, humidity, and rainfalls. Malaria is transmitted in tropical and subtropical areas, where:

  • Anopheles mosquitoes can survive and multiply
  • Malaria parasites can complete their growth cycle in the mosquitoes (“extrinsic incubation period”).

Temperature is particularly critical. For example, at temperatures below 20°C (68°F), Plasmodium falciparum (which causes severe malaria) cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted. [Read more…]