Environmentally sick: our poisoned planet is losing the battle with infectious diseases.

Environmentalists urging us to "Save the Whales" or "Save the Spotted Owl" may soon take up a new plea - "Save the Humans." After decades of decline, deaths from infectious diseases in the United States are on the rise, and many scientists are pointing their fingers at our poisoned planet.

"Wildlife diversity helps control pathogens," explains Dr. Paul Epstein of the Harvard School of Public Health. "This is what Rachel Carson was writing about [in her 1962 classic Silent Spring] - no birds in the spring to eat the bugs. People are just starting to take notice."

A hint of the plagued future some scientists foresee came in January, when the Centers for Disease Control (CDC) reported a 58 percent rise in deaths from infectious diseases between 1980 and 1992. Although AIDS accounts for most of the increase, deaths from all other infectious diseases rose a frightening 22 percent.

Environmental changes are being linked to a broad range of illnesses, from the cholera epidemic that in 1991 struck more than 336,000 Latin Americans, to the 20-year-old outbreak of Lyme disease in the suburbs of New England and New York. However diverse, these diseases share the ability to flourish when man upsets the ecosystem's delicate balance.

Consider the case of Lyme disease, named for the Connecticut seaside town where it emerged in the 1970s. The arthritis-like ailment is caused by a bacterium carried by a tick. This particular tick thrives on the blood of deer. Scientists believe now that the ticks may have carried the bacterium for years without transferring it to man. But suburban sprawl brought people farther into the deer's habitat. Coyotes, cougars and wolves that once kept deer populations in check had long ago been killed off. Hungry deer took their search for food into suburban back-yards.

The number of Lyme disease cases reported in the Northeast doubled each year between 1982 and 1990. By 1992, it had spread to all 50 states and became the most common animal-borne disease in the country. "As people are pushed into areas that were not open to human incursion, there's the risk of exposure," explains Stephen S. Morse, a microbiologist at Rockefeller University. He cites the epidemic of Argentine hemorrhagic fever, which erupted in the 1950s when that country was clearing the pampas for agriculture. "That activity favored one mouse which carried this infection," Morse says.

By the year 2050, the World Bank predicts the Earth's population will approximately double from its current size, to between 11 and 14.5 billion. Development in the United States alone each year claims an area the size of Delaware, according to Zero Population Growth.

Another critical factor shaping the spread of infectious diseases will be the Earth's climate. The World Health Organization (WHO) predicts the temperature of the planet will rise 2.7 to eight degrees Fahrenheit by the year 2030, profoundly affecting human health.

One of the most predictable results will be an expansion of mosquito-borne disease from the tropics into temperate zones, possibly as far north as New York. Among the diseases are malaria, dengue (a painful disease commonly called breakbone fever) and yellow fever, which kills 50 percent of its victims.

WHO in 1990 warned that global warming would enlarge the territories of disease-carrying insects. Approximately two million people are now at risk of these potentially lethal mosquito-borne diseases. If predictions of global warming are accurate, that population will climb to 620 million by the year 2050, claims Jonathan Patz of the Johns Hopkins School of Hygiene and Public Health in Baltimore.

Epstein suspects that the mosquitoes' migration has already begun, specifically referring to two people who contracted malaria in New Jersey in 1991, and others who developed it in 1993 in Queens, New York in 1993. "These were hot, humid periods," he says.

Anyone who's eaten spoiled chicken salad knows that heat makes bacteria multiply like crazy. That same effect may have lead to a deadly 1991 cholera outbreak in Latin America. Dr. Rita Colwell in the 1970s found that cholera can live dormant inside algae for months, even years.

The next generation may face not only a greater threat from infectious diseases, but fewer defenses against them. In addition to greater UV-B radiation exposure because of ozone layer damage, we are susceptible to immune suppression from chemicals that are pervasive in the environment, like dioxin, pesticides, and PCBs.

When Newsday reporter Laurie Garrett was researching her 1994 bestseller, The. Coming Plague, she worried about the battle between man and microbe. Since her book was published, she has seen change. The CDC, WHO and the Environmental Protection Agency (EPA) suddenly began focusing attention on emerging infectious diseases. Now, she says, it's our turn. "Change will require serious political and social commitment," says Garrett.

CONTACT: Harvard School of Public Health, 665 Huntington Avenue, Cambridge, MA 02115/[phone].