The War Against Disease. Insects

Bacteria need not be the only causative agents of an infectious disease and that is why Pasteur's discovery is called the "germ theory," "germ" signifying microorganisms generally and not bacteria only. In 1880, for instance, a French physician, Charles Louis Alphonse Laveran (1845-1922), while stationed in Algeria, found the causative agent of malaria. This was particularly exciting in itself since malaria is a widespread disease over most of the tropical and subtropical world, killing more human beings all told than any other. What made the discovery particularly interesting, however, was that the agent was not a bacterium, but a protozoon, a one-celled animal.

Indeed, an illness might not even be caused by a microorganism. In the 1860s, a German zoologist, Karl Georg Friedrich Rudolph Leuckart (1822-98), in his studies of invertebrates, found himself particularly interested in those which lived parasitically within the bodies of other organisms; thus founding the science of parasitology. He found that all the invertebrate phyla had their parasitic representatives. A number of these infest men, and such creatures as flukes, hookworms, and tapeworms—far from microscopic—can produce serious illness.

What's more, a multicellular animal, even if not the direct causative agent of a disease, may nevertheless be the earner of infection, which is just as bad. Malaria was the first disease in which this aspect of infection became important. An English physician, Ronald Ross (1857-1932), investigated suggestions that perhaps mosquitoes spread malaria from person to person. He collected and dissected mosquitoes and, in 1897, finally located the malarial parasite in the anopheles’ mosquito.

This was a most useful discovery, since the mosquito represented a weak point in the chain of infection. It could be easily shown that malaria did not spread by direct contact (the parasite, it seems, must pass through a life stage in the mosquito before it can enter man again), so why not simply do away with the mosquito? Why not sleep under mosquito netting? Why not drain swamps in which mosquitoes breed? This worked, and where such methods were used, the incidence of malaria declined.

Another deadly disease, one that during the eighteenth and nineteenth centuries periodically ravaged the east coast of the United States, was yellow fever. During the Spanish-American War, the American Government grew particularly disease-conscious, since germs killed far more American soldiers in Cuba than Spanish guns did. In 1899, after the war, an American military surgeon, Walter Reed (1851-1902), was sent to Cuba to see what could be done.

He found that yellow fever was not spread by direct contact and, in view of Ross's work, he suspected mosquitoes, this time another species, the Aedes mosquito. Doctors working with Reed allowed themselves to be bitten by mosquitoes that had been biting infected men, and some of them got the disease. One young doctor, Jesse William Lazear (1866-1900), died as a result, a true martyr to the cause of humanity. The case was proved.

Another American army surgeon, William Crawford Gorgas (1854-1920), used mosquito-fighting methods to wipe out yellow fever in Havana, and was then assigned to Panama. The United States was trying to build a canal there, although France had failed in a previous attempt. The engineering difficulties were great, to be sure, but it was the high death rate from yellow fever that really blunted all efforts. Gorgas brought the mosquito under control, stopped the disease cold, and in 1914, the Panama Canal was opened.

Nor was the mosquito the only insect that played the role of villain. In 1902, a French physician, Charles Jean Henri Nicolle (1866-1936), was appointed director of the Pasteur Institute in Tunis, North Africa. There, he had occasion to study the dangerous and highly infectious disease, typhus fever.

Nicolle noticed that while outside the hospital the disease was extremely contagious; it was not contagious at all within the hospital. Patients in the hospital were stripped of their clothes and scrubbed down with soap and water on admission, and it occurred to Nicolle that the infective agent must be something in the clothing, something that could be removed from the body by washing. His suspicion fell on the body louse, and, through animal experiments, he proved his case by showing that only through the bite of the louse could the disease be transmitted. Similarly, in 1906, the American pathologist, Howard Taylor Ricketts (1871-1911), showed that Rocky Mountain spotted fever was transmitted by the bite of cattle ticks.