The ripples of fear spread across Nicaragua and far beyond. The poor, normally placid town of Achuapa had suddenly become the epicenter of a mysterious infection that was felling victims right and left. In the face of 2,168 cases and 16 known deaths, health authorities were on full alert. Could this be the emergence of a previously unknown and lethal virus?

Tissue samples from the victims were flown to the U.S. Centers for Disease Control and Prevention in Atlanta for identification of the mystery fever, an essential first step in halting the outbreak. Epidemiologists tested for many of the deadliest infectious agents, including plague and the Ebola virus, which swept the Zairian region of Kikwit earlier this year, but found no matches with the Nicaraguan specimens. When the puzzle was finally solved last week, the verdict provided a measure of relief to Latin Americans. The diagnosis was leptospirosis, a nasty but well-known and easily cured bacterial disease spread by contact with the urine of rats and other animals.

Nicaraguan officials set about at once organizing airlifts of penicillin to Achuapa for containment of the illness, which in all events is only rarely communicated from one person to another. "When we found out it was leptospirosis, we relaxed again," said Dr. Francisco Araujo of Brazil's National Epidemiology Center, explaining, "We deal with it all year long." At the same time, however, health ministries across the tropical New World could hardly afford to sit still. For every mopped brow of relief about Achuapa syndrome, thousands of febrile brows in Latin America this year are reflecting a large number of infectious outbreaks, driving people to maddening dizziness, internal bleeding and death.

Dengue fever and its more evil strain, hemorrhagic dengue, have mushroomed during the 1995 rainy season beyond any epidemic of the virus in recent years. Also fatal have been the incidences of equine encephalitis, which has ravaged remote parts of Venezuela and Colombia and is still rising in the region. Add to that mixture some similarly dramatic upsurges of better-known sicknesses like cholera, the most deadly of the current epidemics, and the result is a witch's brew of microbes spelling a health emergency of a very high order. Last month the Venezuelan Congress, in an uproar over how readily some unusual epidemics had spread unchecked, took the unprecedented step of ousting the country's Health Minister.

What in the world could be causing all this communicable grief? The answer seems to be weather, in its immediate role at least. Many parts of Latin America and the Caribbean have experienced record rainfalls this year, including downpours from disastrous storms such as hurricanes Opal and Roxanne. One result is that Achuapa alone has received 5.2 m of rainfall, about four times its average. Flooding not only contaminates drinking-water supplies but also flushes disease-carrying rats and other animals from their habitats in the wild and provides plentiful new breeding grounds for mosquitoes that carry dengue and equine encephalitis. Poor villagers and tribal families have little protection against such a triple whammy. Once livestock or household animals are infected, opportunities for human infection become great.

The stricken town of Achuapa was clearly vulnerable to a health catastrophe. Lying about 105 km northwest of Managua, the town has more horses and mules than cars, and its roads are muddy ruts. During the rains this year, peasants could only too easily come in contact with animal waste, from which leptospirosis can invade the body through lesions or mucous membranes. The consequences: fever, severe headaches, jaundice and the breakdown of functions in lungs, liver and kidneys. At Achuapa's tiny government-run clinic, victims crowded together after being hauled down mountain slopes in hammocks or on mules. "It's just terrible--you feel like you're going to die," moaned Luz Bonilla, 54, as she sat on a wooden bench in a long queue outside the clinic. Inside, Dr. Maria Rojas reported, "People arrive walking and talking like normal, when suddenly they start bleeding in the lungs or hemorrhaging. They die within eight or 10 hours."

From the nearby village of La Calera, Ines Galeano Hernandez suddenly found himself the foster father of an infant girl after a neighbor took ill. As Galeano Hernandez and his wife cuddled the baby at the Achuapa clinic, he sketched the neighbor's descent. "On Monday she caught a fever," he explained. "On Wednesday they took her to the hospital. By dawn on Thursday she was dead." The disease is especially dangerous to the young, the old and the infirm, though malnourishment as a result of crop flooding has made most people around Achuapa more vulnerable.

Still, Achuapa may have been lucky in one respect. The "mystery fever" caught so many headlines that the government could not ignore it. Now Managua has earmarked about $500,000 for control of the disease. Victim Bonilla suspected that might not have come about had Achuapa come down with cholera or malaria.

In truth, health budgets have been so slashed around Latin America in recent years, in keeping with belt-tightening regimes, that disease-control campaigns have languished. For example, spraying pools of stagnant water to kill off the Aedes mosquito, carrier of dengue fever as well as equine encephalitis, used to be widespread in the region. And now? Said Rosario Altamirano, who lives in a Managua shantytown: "We ask for fumigation trucks, and they say there are neither trucks nor gasoline." What outraged Venezuelan legislators against evicted Health Minister Carlos Walter was his failure to handle the epidemics, including equine encephalitis, which spread to the isolated Guajira peninsula early this year. The disease has produced 11,371 victims in Venezuela, 15 of whom have died, to go with almost 30,000 dengue fever casualties after Aedes mosquitoes had a breeding spurt. Some Colombians are indignant that their neighbor did not serve notice about the encephalitis outbreak. The equine strain ran riot among Wayuu Indians on Colombia's side of the border.

Scares make headlines and sometimes stir welcome action, but they are a poor defense in the long run. When leptospirosis appeared in a remote Honduran village, a Tegucigalpa daily splashed large photos of rats on Page One under the headline, ENORMOUS ARMY OF RATS OVERTAKES THE CAPITAL! But panic is a bad substitute for realistic public-awareness programs, which Brazil has used effectively to contain hemorrhagic dengue. Said Dr. Cesar Hernida of the Pan American Health Organization in Honduras: "It's not that these diseases are going to return; they're here already." Wherever poor sanitation and poverty prevail, doom can always come from the nearest mosquito, mule or, yes, rat.

--Reported by John Otis/Managua, with other bureaus