Botkin Environmental Science Earth as Living Planet 8th txtbk

8.3 Biological Evolution 151
A CLOSER LOOK 8.1
Natural Selection: Mosquitoes and the Malaria Parasite
Malaria poses a great threat to 2.4 billion people—over onethird
of the world’s population—living in more than 90 countries,
most of them in the tropics. In the United States, in 2003,
Palm Beach County, Florida, experienced a small but serious
malaria outbreak, and of particular concern is that the malaria
was the result of bites from local mosquitoes, not brought in
by travelers from nations where malaria is a continual problem.
Worldwide, an estimated 300–400 million people are infected
each year, and 1.1 million of them die (Figure 8.7). 6 It is the
fourth largest cause of death of children in developing nations—
in Africa alone, more than 3,000 children die daily from this
disease. 7 Once thought to be caused by filth or bad air (hence
the name malaria, from the Latin for “bad air”), malaria is actually
caused by parasitic microbes (four species of the protozoon
Plasmodium). These microbes affect and are carried by Anopheles
mosquitoes, which then transfer the protozoa to people. One
solution to the malaria problem, then, would be the eradication
of Anopheles mosquitoes.
By the end of World War II, scientists had discovered that
the pesticide DDT was extremely effective against Anopheles
mosquitoes. They had also found chloroquine highly effective
in killing Plasmodium parasites. (Chloroquine is an artificial
derivative of quinine, a chemical from the bark of the quinine
tree that was an early treatment for malaria.) In 1957 the
World Health Organization (WHO) began a $6 billion campaign
to rid the world of malaria using a combination of DDT
and chloroquine.
(a)
FIGURE 8.7 (a) A child with malaria and (b) where malaria primarily
occurs today. [Source: (b) U.S. Centers for Disease Control,
http://www.cdc.gov/Malaria/distribution_epi/distribution.htm.]
(b)
Malaria transmission
occurs throughout
Malaria transmission
occurs in some parts
Malaria transmission
is not known to occur