Infectious Disease: A Very Short Introduction by Marta Wayne & Benjamin Bolker

Author:Marta Wayne & Benjamin Bolker [Wayne, Marta & Bolker, Benjamin]
Language: eng
Format: epub
ISBN: 9780199688937
Publisher: OUP Oxford
Published: 2015-03-27T00:00:00+00:00

Chapter 6

Malaria

Malaria might be the most important infectious disease on the planet. Compared to the infectious diseases discussed in the previous chapters, it is less frightening to people in temperate, developed countries—not because it is less infectious or less virulent, but because in modern times it rarely reaches out of the tropics, being limited by the ecological niche of its mosquito vectors. Unlike cholera, malaria tends to be endemic—maintaining a relatively constant level in the population over time—rather than occurring in intense epidemic outbreaks. Typical of endemic disease, the most widespread strains of malaria are typically chronic and debilitating, rather than causing acute infection and death. The exception is falciparum malaria, most common in tropical sub-Saharan Africa. The malnutrition and anaemia associated with chronic malaria are associated with poorer educational outcomes in children, while acute malaria can lead to chronic neurological problems. Combining these non-lethal effects common to all malaria species with the lethal effects of falciparum, the cumulative impact of malaria on humanity is enormous.

Public health officials measure the impact of chronic diseases in terms of disability-adjusted life years (DALYs), which take into account both the loss of life and the loss of productivity and happiness due to a disease. Coming up with appropriate weights poses obvious ethical challenges. Is one year of life with a chronic, crippling disease equivalent to six months of healthy life? Three months? One month? How should one compare the impact of death or disability in an infant, a middle-aged person, or an elderly person? Nevertheless, DALY calculations account for the fact that the chronic effects of disease on people living with disease can be just as important, if not more important, than disease-induced deaths. In 2010, malaria accounted for more lost DALYs than any other infectious disease, narrowly edging out HIV/AIDS. Although hard evidence is difficult to come by—poor countries tend to be malarial while rich ones do not—researchers have suggested that eliminating malaria could increase economic growth rates by several percentage points, the difference between a struggling economy and a healthy one.

Although every infectious disease has its bizarre and intriguing quirks, malaria is more complex than the other diseases we have discussed so far. It is caused by a protozoan, a single-celled organism whose genetic material (unlike in bacteria) is confined within a nucleus. Its genome comprises about twenty-three million base pairs of DNA, thousands of times larger than the viral genomes of HIV and influenza and about five times larger than cholera’s genome.

Malaria’s complexity also stems from its vector-borne nature; it is transmitted from one human to another via various species of Anopheles mosquitoes. Cholera adjusts its biochemistry to function alternately as a free-living organism in the ocean and as a pathogen in the human gut. Malaria has an even more challenging problem; it adjusts its biochemistry to two different biological environments (the human host and mosquito vector), and to multiple organs within each host (human blood and liver; mosquito gut and salivary glands). Biological environments represent bigger challenges for parasitic organisms than physical environments.

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