A mysterious illness that's driving some indigenous Nicaraguans to hysteria has authorities scrambling to find answers.

No one is entirely sure why the so-called grisi siknis -- the Miskito term for ''crazy sickness'' -- has returned to this port town on Nicaragua's northern Caribbean coast, but it has residents on edge.

More than 80 cases have been reported here in the past two months, including eight more girls who were afflicted at school April 21. The outbreaks are becoming a daily occurrence in schools, according to regional government authorities.

''We were scared,'' said 11-year-old Ana Stefani, whose Morava J.A.C. school in Bilwi was closed for three days last month after 35 of her classmates were afflicted in the schoolyard. ''The girls were yelling like they were possessed and they were calling out names of other students. Their eyes were closed and their fists were clenched.''

Grisi siknis is a powerful and puzzling cultural-bound syndrome that afflicts Nicaragua's indigenous and ethnic communities, mostly young adolescent Miskito women. Outbreaks have been reported as far back as the early 1800s. Some health experts say the illness is more mental than physical. However, it behaves similar to other viral outbreaks in that it's contagious and can last for months or years.

'The end of times'

Residents say it's related to the supernatural: An evangelical reverend says the phenomenon is a sign of ''the end of times'' while a Catholic priest conducts ''preventive exorcisms'' and urges his faithful to pray for protection against demonic forces. And witch doctors are giving children charms to protect them from witchcraft and dwarfs.

Authorities have had to close four schools in recent weeks to prevent widespread panic among students.

''There is more devil than God in the city right now,'' said Rev. Kenneth Bushey, of the Moravian Renovation Evangelical Church, where seven women took ill with grisi siknis during a youth group event last month. ''God is testing our faith.''

While most outbreaks have occurred in remote villages, in the past month there have been some 50 new cases reported in the relatively populous regional capital of Bilwi, and dozens more cases have been reported in neighboring municipalities. Residents here fear the area is on the brink of an epidemic.

José Manzanares, a head of the regional government's department of traditional medicine, said he has asked the central government to take grisi siknis seriously. So far, however, the issue has been regarded by Managua as one of ''Indian craziness,'' Miskito leaders say.

The Sandinista government has not issued a formal response.

''The people feel unprotected,'' Manzanares said. ''The epidemic is getting worse and the government is not prepared to respond to the situation.''

Katie Booton, a nursing student from Nebraska working for a missionary group in the rural Miskito community of Francia Sirpi, said she was recently asked by villagers to transport a young woman with grisi siknis to a nearby health clinic.

''At first she seemed scared, but by the end of the trip she was raging,'' Booton said. ''Three men were struggling to hold her down in the back of the truck, as she tore their shirts. She was screaming and digging her fingernails into her palms.''

Symptoms

Grisi siknis sufferers often experience alternate states of a coma-like trance and indomitable mania, according to witnesses. In the manic stage, victims usually keep their eyes closed and fists clenched with their thumbs tucked underneath their other four fingers, which many interpret as a sign of the dwarf -- evil spirits thought to inhabit the earth, an important part in the indigenous view of the cosmos.

''The dwarf only has four fingers, so he can't stand to see a fifth,'' explained Serafina Espinoza, head of the department of traditional medicine for URRACAN, the university of Nicaragua's autonomous regions.

Those who are afflicted sometimes yell out the names of people nearby, who reportedly fall into a similar trance. Others yell at invisible assailants and swing machetes, sticks, or other weapons in attempts at self defense as they flee into the bush.

It is up to the other villagers to catch and restrain the grisi victims to prevent them from hurting themselves, drowning in a river, or disappearing into the mountains for days, weeks or -- in some reported cases -- even years.

Though little is known about the causes of grisi siknis, some scientists -- in and outside of Nicaragua -- have tried to explain the phenomenon in recent years by hypothesizing that it is caused by a poisoning of water or food sources. Others have speculated that it's caused by ergot, the fungi that grows on wheat and has been linked to other historical cases of collective madness, such as the outbreak of ''Saint Anthony's Fire'' in the Middle Ages.

Testing of food and water supplies in areas suffering outbreaks of grisi siknis have all proven inconclusive.

U.S. anthropologist Philip Dennis, professor emeritus at Texas Tech University, lived among the Miskito population in the community of Awastara in 1978-79 and studied the tail end of another major outbreak in the early 1970s.

Dennis concluded that grisi siknis is related to stress, fear and anxiety, but that it also appeared to be a ''flood of repressed libidinal feelings pouring out at once -- a wild, orgiastic rite of sex and violence.''

Another theory

In recent years, however, the collective hallucination has taken on a different form. One theory of grisi siknis is that it might represent a sort of cultural reenactment of traumatic experiences in the Miskito culture -- first the arrival of the white man and then violent relocation by the Sandinista military, which forced entire indigenous communities to move inland in the 1980s to prevent them from becoming recruitment camps for Contra rebels.

''The phantoms or demons that show up during the attacks definitely represent lived reality -- the British, the Creole people, the Sandinistas,'' Dennis told The Miami Herald.

Grisi siknis attacks are also becoming more violent.

During a 2003 outbreak in the rural indigenous Mayangna village of Santo Tomás de Umra, 26 grisi siknis victims terrorized the population and destroyed the entire village. José Manzanares, a traditional healer sent to Santo Tomás to cure the grisi siknis victims, said the afflicted chased other villagers around with machetes.

''They had their eyes closed and their faces turned up toward the sky, but they still chased people around,'' Manzanares said. ''The only way people could escape from them was to hide under a porch or a house.''