b. Undecylenic acid is available as a 10 percent solution in 59-ml bottles; as an
ointment in 1-ounce (28.35-gram) containers; and as a 1 percent foot powder in 1-
ounce (28.35-gram) containers.
Section IV. ANTIMALARIAL DRUGS
a. Cause and Transmission. Malaria is caused by a microbe called the
plasmodium. There are four principal species of malaria-producing plasmodia--P.
falciparum, which caused about 84 percent of the cases of malaria contracted by
Americans in Vietnam; P. vivax, a more benign plasmodium which caused about 85
percent of the cases of malaria contracted in the United States in 1971; P. malariae,
which causes the form of malaria called quartan malaria; and P. ovale, a plasmodium
rarely seen except in certain parts of South America and East and West Africa. These
parasites are generally transmitted by the Anopheles mosquito, of which there are many
species. (An important method of defense against malaria, in addition to control of the
mosquito and its environment, is personal measures taken to avoid mosquito bites.) In
addition to transmission by mosquitos, malaria may also be transmitted in a blood
transfusion or in a contaminated needle used for an injection.
b. Progression of Malaria in Man. After a person has been infected with
malaria by a mosquito, there is a latent period called the tissue stage, when the
parasites, or schizonts, are multiplying in liver cells. This stage without overt effects
generally lasts from 10 days to 6 weeks, depending on the type of malaria, but may last
as long as several months. Eventually, however, the parasites, now called merozoites,
enter the red blood cells, where they develop into small, ring-shaped forms called
trophozoites. The trophozoites grow rapidly and fill the cells, and some of them develop
into still other forms, sexual forms called gametocytes. During this stage, called the
erythrocytic stage, many of the red blood cells burst and the typical symptoms of
malaria--a chill followed by a fever, profuse sweating, headache, and backache--ensue.
Meanwhile, some of the schizonts may remain in the liver, and, if not destroyed, cause
a relapse of the disease even when the parasites in the blood have been destroyed by
drugs. The details of the life cycle of the Plasmodium are illustrated in Figure 6-1.