The St. Louis Type

Every summer and fall, parts of the U.S. are stricken by outbreaks of encephalitis, or inflammation of the brain, caused by insect-borne viruses. But this year's outbreak may prove to be the worst in a decade. Hundreds of suspected cases of St. Louis encephalitis (SLE)* have been reported by health officials in Alabama, Louisiana, Texas, Arkansas, Indiana, Missouri, North Dakota, Kentucky, Tennessee, Ohio and New Jersey. The disease has reached epidemic proportions in two other states. In Mississippi, encephalitis has afflicted some 200 people and killed more than 30. In Illinois, the disease has struck more than 100, and is suspected in three deaths.

Elderly Ailment. Inflammation of the brain -which leads to fever, convulsions and, in some cases, death -can be caused by any of a large variety of viruses or bacteria or can follow a wide range of other illnesses. But the bugs responsible for the current outbreak of encephalitis are unique. They are "arboviruses," a contraction for arthropod-borne viruses. The arthropod that carries the virus is, in this case, an insect with jointed feet -the common mosquito -that has been particularly numerous and active in large areas of the U.S. this year. Mosquitoes pick up the arboviruses when they bite birds, which usually carry the viruses without being ill themselves, and transmit them when they feast on the blood of their next victim.

Until improved insecticides destroyed many of the mosquitoes that transmit encephalitis, the disease often hit thousands each year. Despite improvements in mosquito-control methods, encephalitis still persists, particularly in humid, swampy areas. Of the 100-odd victims in the hardest-hit Mississippi town of Greenville (pop. 40,000), many live in the poorest part of town. Of those infected in Illinois, most live near cemeteries, where mosquito larvae have been flourishing in water-filled flower vases.

For reasons that are still not understood, this year's St. Louis encephalitis seems to have bypassed the young and hit hardest at the elderly. In Mississippi, for example, the median age for SLE victims is 70, and there have been relatively few cases in people under 40. SLE's younger victims usually suffer nothing worse than a moderate fever, stiff neck, severe headaches and some lassitude. The aged are more likely to run high fevers, have convulsions and, especially if already debilitated, die.

The situation is reversed for those who contract another form of the disease called Western Equine Encephalitis (WEE) -a variation that is largely confined to horses but can also hit humans. Adults usually recover from a WEE infection, but in infants and children, it can produce high fever, convulsions and coma; those under one year of age who survive an infection are likely to have permanent brain damage. So far this year WEE has struck hundreds of horses and killed six of its 9 human victims in the Red River Valley of North Dakota and Minnesota.

Doctors have tried for years to prevent, or at least reduce, the ravages of St. Louis and other forms of insect-borne encephalitis. But the disease is difficult to treat or eradicate. No effective way has been developed to immunize people against it. Health officials are concentrating on spraying and swamp-drainage programs aimed at cutting down the number of mosquitoes, for the only known way to prevent encephalitis is to eliminate the pesky insects that transmit it.

* So-called because the virus was first isolated from brain-tissue specimens in a St. Louis laboratory in 1933.

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