How Infectious Diseases Emerge
AIDS is not the first disease that just appeared as if from nowhere. The classic example is syphilis. We often hear of the syphilization of Europe being attributed to Columbus’s sailors bringing the disease back from the New World. However, since the disease was a major problem in the armies of both France and Naples in a war that broke out four months after the return of the explorer’s ships to Spain, it is unlikely that a handful of sailors can be responsible. A spirochetal disease similar to yaws had been well known in northern Africa for centuries. It is probable that syphilis was a mutation of this disease. For the first 40 years that the disease existed, it was much more severe than syphilis is today. Secondary syphilis had a mortality rate of 20% to 40 % during this early time. The virulence of the disease then decreased to the level we know today.
Changing virulence is a common phenomenon in infectious diseases. The great plagues of the Middle Ages came and went in waves that had little to do with medical care, hygiene, or immunity in the general population. Today plague is endemic in Asia and the western United States. We have the necessary insect vectors, the animal reservoir of infection, and the potential human exposure yet there are only sporadic cases instead of epidemics. At the beginning of this century, streptococcal disease was dreaded. Even well-nourished and well- cared-for children died of strep throat and rheumatic fever. The severity of this disease has decreased so much that many states have removed it from the list of reportable diseases. Although this has been attributed to penicillin, the change occurred before the era of antibiotics and extends to children who have not received treatment. The cycle now is reversing as the severity of strep and the incidence of rheumatic fever increase. [ Med World News. 1990;31:20.]