CYCLE OF INFECTION
The cycle of infection of the malarial parasite is as follows. An uninfected
mosquito bites an infected human and becomes infected. Malarial parasites enter the
mosquito's body, and sexual reproduction takes place. The resultant cells move to the
mosquito's salivary glands. If this mosquito bites a human within two weeks, the human
will become infected. The mosquito bites, and sporozoites enter the human's
bloodstream and circulate for one half hour. The sporozoites then enter the human's
liver cells and reproduce asexually. Later, the parasites leave the liver cells and enter
the bloodstream. (The length of time before leaving depends on the species of malarial
parasite.) The parasites, now called merozoites, enter the circulating red blood cells
and multiply. Some 48 to 72 hours later, the red blood cells break open and release
other merozoites. These merozoites will infect other red blood cells. If an uninfected
mosquito bites this person, the cycle of transmission will begin again.
MALARIA WITHIN THE UNITED STATES.
As shown in the cycle of transmission, the malarial parasite needs two hosts to
survive and reproduce, man and the mosquito. In the parasite's two stages of
development, the asexual stage takes place in the human body, and the sexual stage
takes place in the mosquito. If the parasite cannot pass back and forth from the
mosquito to the human host and from the human host to the mosquito, the chain of
transmission is broken, and the disease ends. The disease has been almost eradicated
in the US. A glance at figure 4-2 shows world events which have caused
malaria to reenter the US.
Characteristically, there are three stages of malaria attacks.
a. Stage 1. A shaking chill. Parasites are rupturing the person's red blood cells
and escaping into the bloodstream.
b. Stage 2. Spiking fever,nausea, vomiting, and headache. The patient's
temperature rises to about 104F (40C), and the patient has a severe headache. This
takes place when the parasites are ready to invade red blood cells.
c. Stage 3. After several hours, the patient begins sweating profusely. The
headache disappears, and the temperature returns to normal. The patient falls asleep