Professor Ralph Robinson, Contributor

Over the last few weeks, several very useful media releases about the resurgence of malaria in Jamaica have facilitated the public with understanding malaria, and provided timely updates on the nature and spread of infections and measures taken to control them. As a reference for the interested reader, I have prepared an article that takes the form of a question and answer session, and speaks to the main features of malaria from a scientific perspective.

What is malaria?

Malaria is a disease caused by infection with one or more of five species of protists (single celled organisms) called Plasmodium, and marked by recurring fevers, prostration, and sometimes death. The protists live in the liver and red blood cells of man and some other animals, and are spread from one infected person to another mainly by female Anopheles mosquitoes.

How many people are infected with malarial parasites?

Of the 2.4 billion persons at risk of malaria worldwide (about ¹/4 of the global population), there are about 350 million clinical cases, which results in as many as 1.5 million deaths each year. Most deaths occur in children under 5 years, and pregnant females. Malaria is therefore one of the most important infectious diseases in the world.

How is malaria transmitted?

Up until the end of the 19th century, it was commonly concluded that malaria was contracted by breathing bad air (mal-aria) associated with swamps. Today, almost everyone knows that malaria is transmitted by mosquitoes, but empirical evidence of this appears only fairly recently in biomedical literature.

The discovery that the mosquito was the vector of malaria was made in 1897, and involved several persons but principally tropical disease experts Dr. Charles Laveran, Dr. Patrick Manson, and Surgeon-Major Ronald Ross. The greatly experienced Dr. Manson knew that mosquitoes were involved in the transmission of other infections (e.g. worms that caused the dreaded 'elephantiasis'), and he convinced Major Ross to continue with research in India that involved dissecting thousands of mosquitoes in a painstaking search for malarial parasites in these flies.

On the evening of Ross' historical find of malarial parasites associated with the stomach of a female mosquito of the genus Anopheles, he penned the following in his research notebook:

"This day, relenting God hath placed within my hand a wondrous thing, and god be praised. At his command, seeking His secret deeds with tears and toiling breath, I find thy cunning seeds, Oh million-murdering death."

Although having made the discovery of the century, Major Ross never completed the final experiment - that was to demonstrate transmission of malaria from mosquito to man. He was transferred by the army to a non-malarious zone of India; by then his eyes were failing him; and it is said his microscope had rusted from his sweat! While several persons in history claimed credit for various discoveries involving malaria parasites, it is generally agreed that credit for demonstrating experimentally that malarial parasites really were transmitted from infected mosquitoes to humans should go to two Italians, Dr. Amigo Bigami and Dr. Giovanni Grassi working in 1898.

There are about 390 recognised species of Anopheles, 65 of which are capable of transmitting malaria. Once infected, a female mosquito remains infective to man for the rest of her life.

Malaria can be transmitted by means other than mosquitoes: by blood transfusions; by 'contaminated syringe' infection among drug addicts; by accidental infection in laboratory technicians; or rarely by congenital infection (of an unborn baby in the womb).

Source: http://www.nidcd.nih.gov/staticresources/images/malaria.jpg