Antihistamines, including H 2 -receptor blocking agents, and bronchodilators are effective. Fatalities have not been reported. These planktonic flagellates are abundant in latitudes above 30 N and below 30 S, but cases have been recorded from warmer regions, including the tropics. In the Northern Hemisphere, most outbreaks occur between May and October, when large numbers of these dinoflagellates bloom, causing a red discoloration of the sea. Toxic conditions may prevail, however, in the absence of this so-called red tide, and not all red tides are contaminated.
Symptoms usually begin one-half hour to two hours after ingestion.
Paresthesias involve the head and the extremities, frequently accompanied by nausea, vomiting, and diarrhea. Low back pain may be a prominent complaint. In severe cases, ataxia and muscle paralysis develop and lead to dysphonia, dysphagia, and ventilatory impairment. Neurologic symptoms usually abate within six to 24 hours, but death caused by respiratory paralysis may occur within the first 12 hours. The prognosis is favorable for those who survive beyond 12 to 18 hours.