Onset is within 15 minutes but may occur as late as 18 hours with a mean time of 3 hours. Symptoms may persist for several days. NSP is unique in that it aerosolizes in conditions of heavy surf or spray. Symptoms in this setting resemble an upper respiratory tract infection. Onset is within 30 minutes and may persist for 1 day.
Symptoms are self-limited and mild.
No cases of death from DSP have been reported. Diatoms produce domoic acid, which is the causative agent and exhibits glutamatelike activity. Exposure to domoic acid has been demonstrated to cause cellular death in the hippocampus. Symptoms of ASP include nausea, vomiting, diarrhea, loss of cognitive ability, coma, and seizures. A 1987 outbreak of ASP in Canada's eastern province of Prince Edward Island affected more than 100 people.