...
From the mosquito's salivary glands to the host's liver cell: a quiet
trip. Everything seems fine. Even the liver itself, that reddish sack of
blood-filtering cells, shows no sign of trouble. It's only in those few rooms
whose locks have been picked by falciparum where all is
pandemonium. Inside these cells, the malaria parasites eat and multiply. They
do this nonstop for about a week, until the cell's original contents have been
entirely digested and it is bulging with parasites like a soup can gone
bad. Each falciparum that entered the body has now replicated itself
40,000 times.
The cells explode. A riot of parasites is set loose in the
bloodstream. Within 30 seconds, though, the parasites have again entered the
safe houses of cells -- this time, each has drilled into a red blood cell,
flowing through the circulatory system. Over the next two days, the parasites
continue to devour and proliferate stealthily. After they have consumed the
invaded cells, they burst out again, and once more there is bedlam in the
blood.
For the first time, the body realizes it has been
ambushed. Headache and muscle pains are a sign that the immune system has been
triggered. But if this is the victim's first bout of malaria, the immune
response is mostly ineffective. The alarm has sounded, but the thieves are
already under the bed: The parasites swiftly invade a new set of blood cells,
and the sequence of reproduction and release continues.
Now the internal
temperature begins to rise as the body attempts to cook away the
invaders. Shivering sets in -- muscle vibrations generate warmth. This is followed
by severe fever, then drenching sweat. Cold, hot, wet; the symptoms are a
hallmark of the disease. But the parasites' exponential growth continues, and
after a few more cycles there are billions of them tumbling about the
blood.
By this point, the fever has reached maximum intensity. The body
is practically boiling itself to death -- anything to halt the attack -- but to no
avail. The parasites can even commandeer blood cells to help aid their
survival. In some cases of falciparum, infected cells sprout Velcro-like
knobs on their surfaces, and as these cells pass through the capillaries of the
brain, they latch to the sides. The adhesion keeps them from washing into the
spleen, which cleans the blood by shredding damaged cells. Somehow -- no one is
quite sure how -- the adhesion also causes the brain to swell. The infection
has turned into cerebral malaria, the most feared manifestation of the
disease.
This is when the body starts to break down. The parasites have
destroyed so many oxygen-carrying red cells that too few are left to sustain
vital functions. The lungs fight for breath, and the heart struggles to
pump. The blood acidifies. Brain cells die. The child struggles and convulses
and finally falls into a coma.
Extracted from Bedlam in the Blood: Malaria, National Geographic, July 2007. (local copy)
For you mathematicians out there, note the use of the phrase "exponential growth". I've often noted the use of this phrase, and sometimes it's appropriate; sometimes it's not. One interesting question, then, is the extent to which it's appropriate in this context?