The author of the best-selling novel "The Horse Whisperer" is recovering in a hospital after eating poisonous mushrooms during a vacation in Scotland, his agent said Tuesday.

Nicholas Evans' agent said the writer, his wife, her sister and the sister's husband became sick after cooking and eating mushrooms they had picked in the woods on Aug. 23.

The A.P. Watt literary agency said tests established that the mushrooms included the highly toxic Cortinarius speciosissimus, which attacks the kidneys.

There are an estimated 100 species of mushrooms that are poisonous to humans and about 15 - 20 of these are lethal when ingested, according to a report written by Dr. Rania Habal, an assistant professor at the Department of Emergency Medicine at New York Medical College.

Most poisonings, about 95 percent, occur as a result of misidentification, Habal noted in her report.

Cortinarius speciosissimus contains the toxin orellanine. When ingested it causes several symptoms that occur within 36 hours to 3 weeks and include:

-- Mild nausea

-- Vomiting

-- Diarrhea

Victims may also experience headaches, muscle cramps, loss of consciousness, and convulsions. As many as 50 percent of patients may require dialysis, and as many as 15 percent may die as a result of ingesting the toxin, Habal said in her report.

In a statement, the literary agency said that Evans and the others had received dialysis treatment at Aberdeen Royal Infirmary and responded well. A family friend who visited them said they were "walking about and were in a cheerful and positive frame of mind."

Evans' 1995 novel about a trainer's rapport with a wounded, traumatized horse has sold more than 15 million copies around the world. It was made into a critically acclaimed film by Robert Redford.

The Associated Press Contributed to this report.