The American Plague - Molly Caldwell Crosby [106]
Though many doctors were still searching for bacteria in the blood that could be linked to yellow fever, Theiler began to have ideas of his own. For decades a long list of skilled bacteriologists that included names like Sternberg, Sanarelli and more recently Noguchi had been searching for the bacteria that caused yellow fever—this, in spite of the fact that James Carroll had shown that yellow fever blood passes through a filter without catching any known bacteria. Theiler began to wonder if there wasn’t something even smaller, something that could pass through a filter, something incapable of living in dead cells.
During the summer of 1929, Max Theiler’s boss at the lab in Boston went on vacation, and Theiler decided to try his own experiment. Since monkeys were costly at fifteen dollars each, he opted for mice, which cost only a few cents. First, Theiler injected bits of yellow fever-tainted liver into the brains of mice.
They did not develop yellow fever, but died nonetheless, developing a sort of encephalitis. Next, he tried injecting the same blood into the abdominal cavity of the mice—they lived. Each time, he drew new blood from the mouse. He purchased three rhesus monkeys and injected each with the mice blood. The first monkey died of yellow fever, the second developed a fever but survived, the third developed nothing at all. The yellow fever virus, it seemed, had been turned upside down and inside out—it was killing mice that were not supposed to be able to contract yellow fever, and it was not killing the monkeys that were highly susceptible to it. In Theiler’s hands, the virus could become more deadly in one animal and less so in another. What Theiler had was a vaccine in the making.
Theiler cannot be credited with this line of thinking. After all, Edward Jenner is considered the first to have achieved this with cowpox at the end of the eighteenth century. Jenner named the process vaccine from the Latin word for cow—vacca. But the basic premise was the same: a virus can be manipulated, taking something harmful, and creating out of it something protective. As the virus is passed into another animal it adapts to its new host, it mutates into a less harmful form. The scientist becomes God and the virus his subject. The danger comes in the fact that a virus, ever mindful of evolution and its survival, has its own methods of defense. If man can manipulate the virus, the virus can manipulate man.
Aside from its brute force in taking over cells, the other major weapon in a virus’s assault on the body is the ability to mutate. Complex creatures, like humans, store their genetic material in DNA, which is more stable and less likely to change. Viruses are often made of RNA, an unstable store of genetic material, which can produce errors when it replicates known as mutations. The mutations can work against the virus, hindering it or even killing it; in other cases, they enable the virus to kill more efficiently.
HIV is a prime example of a virus’s skill at changing forms and mutating easily. Just when the body produces the right antibodies to fight a viral strain, the virus alters its outer coating just slightly. The key will no longer fit into the lock. That is why a flu vaccine, made up of several different influenza strains, is a yearly vaccine and not one that produces lifelong immunity. That is also why an influenza pandemic would prove so deadly. In the six months it would take to isolate the virus, grow it in chicken eggs and create the vaccine, the virus may have spread through the population decimating millions of people.
In spite of carrying a single, simple strand of RNA, yellow fever does not mutate easily. Instead, flaviviruses like yellow fever somehow disable the body’s immune response—a process that continues to elude science. When the body encounters the virus, it mounts a mass campaign against the foreign invader on two fronts. White blood