Key points
- Harmful algal blooms in oceans and other bodies of salt water can make toxins.
- Signs and symptoms caused by these harmful algal blooms vary based on toxin and exposure.
- Illnesses can be mild to life-threatening.
Exposure and symptoms
Skin contact
Karenia brevis red tides in the Gulf of Mexico (a specific type of harmful algal bloom) can make brevetoxins. Having skin contact with brevetoxins can cause skin and mucous membrane irritation. People may have skin contact while swimming, wading, or doing other activities in water during a Karenia brevis red tide.
Inhalation
Brevetoxins
People who go in or near the water during Karenia brevis red tides can breathe in brevetoxins in seaspray.
Inhaling brevetoxin can lead to serious health effects including:
- Shortness of breath
- Asthma exacerbation
- Bronchoconstriction
- Bronchitis
- Pneumonia
Palytoxins
Palythoa and Zoanthus corals produce respiratory irritants called palytoxins. Exposures are primarily limited to those in the aquarium trade and people with saltwater aquariums containing these corals. Palytoxins can cause severe respiratory irritation when inhaled. These patients may require hospitalization.
Foodborne exposure
Eating seafood contaminated with harmful algal bloom toxins can affect different organ systems, causing a variety of signs and symptoms. Keep reading for more information about specific seafood poisoning diseases and conditions caused by harmful algal blooms in salt water.
Neurotoxic shellfish poisoning
Eating bivalve shellfish (scallops, clams, mussels, or oysters) contaminated with brevetoxins can cause gastrointestinal, cardiovascular, neurologic, or other health effects. Signs and symptoms usually appear 30 minutes to 3 hours after eating contaminated shellfish.
Gastrointestinal effects
- Nausea
- Vomiting
- Diarrhea
Cardiovascular effects
- Hypotension
- Hypertension
- Arrhythmia
Neurological effects
- Enhanced hot and cold sensations
- Paresthesia of the lips, tongue, or throat
- Dizziness
Other effects
- Muscle aches
- Skin rash
Ciguatera poisoning
Eating reef fish or seafood contaminated with ciguatoxins can cause gastrointestinal, neurologic, respiratory, or other health effects. Reef fish include barracuda, grouper, red snapper, and amberjack.
The effects vary based on the time since the food was eaten and the geographic location where the seafood was harvested. Reports suggest that Caribbean ciguatera poisoning presents with gastrointestinal symptoms first, followed by neurologic effects. In contrast, Pacific ciguatera poisoning presents with neurologic symptoms first, with or without subsequent gastrointestinal symptoms.
1–6 hours after exposure
Gastrointestinal effects
- Nausea
- Diarrhea
- Abdominal pain
- Vomiting
Neurologic effects
- Metallic taste
- Weakness
- Paresthesia of palms of hands and feet, lips, and mouth
- Enhanced hot and cold sensations
- Tooth pain
- Sensation of loose teeth
Respiratory effects
- Shortness of breath
- Respiratory depression
Other symptoms
- Blurry vision
- Arthralgia
- Myalgia
Severe signs
Seizures and respiratory paralysis are rare but have occurred in people who ate a whole fish, including viscera.
1–5 days after exposure
Cardiovascular effects
- T-wave abnormalities
- Bradycardia
- Hypotension
Months to years after exposure
- Persistent fatigue and paresthesia
- Recurring symptoms when patients eat certain foods, such as fish or nuts, or drink alcohol
Amnesic shellfish poisoning
Eating bivalve shellfish or Dungeness crab viscera contaminated with domoic acid can cause gastrointestinal, cardiovascular, neurologic, or respiratory health effects. Bivalve shellfish include scallops, mussels, razor clams (Siliqua patula), and oysters. Signs and symptoms usually occur within 24 hours of eating the contaminated shellfish.
Gastrointestinal effects
- Nausea
- Abdominal cramps
- Diarrhea
- Vomiting
Cardiovascular effects
- Hypertension
- Hypotension
- Arrhythmias
Neurological effects
- Paresthesias
- Enhanced hot and cold sensations
- Burning in the teeth or extremities
- Confusion
- Disorientation
- Memory loss (potentially chronic amnesia)
- Rarely, seizures or coma in severe cases
Respiratory effects
- Excessive secretions
- Shortness of breath
- Pulmonary edema
- Possibly paralysis
Diarrhetic shellfish poisoning
Eating bivalve shellfish (scallops, mussels, clams, or oysters) contaminated with okadaic acid, dinophysistoxins, or pectenotoxins can cause gastrointestinal and other health effects. Signs and symptoms are usually mild and occur within 2 hours after exposure. Onset and severity of illness are based on the amount of toxin ingested. Signs and symptoms are self-limited and resolve in 3 to 4 days.
Signs and symptoms
- Chills
- Headache
- Nausea
- Abdominal pain
- Diarrhea
- Vomiting
- Fever
Paralytic shellfish poisoning
Eating seafood contaminated with saxitoxin, neosaxitoxins, or tetrodotoxin can cause gastrointestinal, cardiovascular, neurologic, or respiratory health effects. Signs and symptoms usually occur within minutes to less than 24 hours after eating contaminated food. Signs and symptoms can last days to weeks.
Gastrointestinal effects
Patients may have nausea and vomiting, mainly resulting from pufferfish poisoning.
Cardiovascular effects
- Hypertension
- Hypotension
- Arrhythmias
- Chest pain
Neurological effects
- Headache
- Dizziness
- Paresthesia
- Numbness of the lips, tongue, neck, face, or extremities
- Ataxia
- Dysphagia
- Dysphonia
- Tongue immobilization
- Loss of gag reflex
- Nystagmus
- Temporary blindness
- Iridoplegia
- Jaw and facial muscle incoordination
- Flaccid paralysis
Muscle weakness and muscle incoordination can be chronic.
Respiratory effects
- Shortness of breath
- Respiratory failure
Respiratory paralysis
In severe cases, patients can experience respiratory paralysis within the first 12 hours after exposure.
Azaspiracid shellfish poisoning
Eating bivalve shellfish (scallops, mussels, clams, or oysters) contaminated with azaspiracid toxins can cause gastrointestinal and other health effects. Signs and symptoms usually start within 24 hours after exposure and last for days.
Signs and symptoms
- Chills
- Headache
- Nausea
- Abdominal pain
- Diarrhea
- Vomiting
- Fever
Poisoning from palytoxins
Eating fish or crustaceans (such as xanthid crabs from the Philippines or sardines from Madagascar) contaminated with palytoxins has been reported to cause gastrointestinal illness and other health effects.
Signs and symptoms
Signs and symptoms reported from isolated poisoning events:
- Muscle cramps
- Numbness of extremities
- Abdominal pain
- Vomiting
- Azziz-Baumgartner E, Luber G, Conklin L, Tosteson TR, Grenade HR, Dickey RW, Backer LC. Environ Health Perspect. 2012;120(4):526-9.
- Backer LC. Impacts of Florida red tides on coastal communities. Harmful Algae. 2009;8(4):618-22.
- Backer L, McGillicuddy DJ Jr. Oceanography. 2006;19(2):94-106.
- Backer LC, Kirkpatrick B, Fleming LE, Cheng YS, Pierce R, Bean JA, Clark R, Johnson D, Wanner A, Tamer R, Baden D. Environ Health Perspect. 2005;113-5:644-9.
- Berdaleti E; Fleming LE, Gowen R, Davidson K, Hess P, Backer LC, Moore SK, Hoagland P, Enevoldsen H. J Mar Biol Assoc U.K. 2015;2015. doi:10/1017/S0025315415001733.
- Bienfang PK, DeFelice SV, Laws EA, Brand LE, Bidigare RR, Christensen S, Trapido-Rosenthal H, Hemscheidt TK, McGillicuddy DJ, Anderson DM, Solo-Gabriele HM, Boehm AB, Backer LC. Int J Microbiol. 2011;2011:152815.
- Cheng YS, Zhou Y, Irvin CM, Pierce RH, Naar J, Backer LC, Fleming LE, Kirkpatrick B, Baden DG. 2005. Environ Health Perspect. 113-5:638.
- Deeds JR & Schwartz MD. . Toxicon. 2010;56(2):150-162
- Fleming LE, Backer LC, Baden DG. Environ Health Perspect. 2005;113(5):618-20.
- Fleming LE, Bean JA, Kirkpatrick B, Cheng YS, Pierce R, Naar J, Nierenberg K, Backer LC, Wanner A, Reich A, Zhou Y, Watkins S, Henry M, Zaias J, Abraham WM, Benson J, Cassedy A, Hollenbeck J, Kirkpatrick G, Clarke T, Baden DG. Environ Health Perspect. 2009;117(7):1095-1100.
- Kirkpatrick B, Fleming LE, Bean JA, Nierenberg K, Backer LC, Cheng YS, Pierce R, Reich A, Naar J, Wanner A, Abraham WM, Zhou Y, Hollenbeck J, Baden DG. Harmful algae. 2011;10(2):138-43.
- Kirkpatrick B, Fleming LE, Squicciarini D, Backer LC, Clark R, Abraham W, Benson J, Cheng YS, Johnson D, Pierce R, Zaias J, Bossart GD, Baden DG. Harmful Algae. 2004;3(2):99-115.
- Milian A, Nierenberg K, Fleming LE, Bean JA, Wanner A, Reich A, Backer LC, Jayroe D, Kirkpatrick B. J Asthma. 2007;44(7):583-87.
- Penotti R, Scallan E, Backer L, Thomas J, Angulo FJ. Foodborne Pathog Dis. 2013;10(12):1059-66.
- Pierce RH, Henry MS, Blum PC, Hamel SL, Kirkpatrick B, Cheng Y-S, Zhou Y, Irvin CM, Naar J, Weidner A, Fleming LE, Backer LC, Baden DG. Harmful Algae. 2005;4:965-972.
- Shoemaker RC, Hudnell HK. Environ Health Perspect. 2001;109(5):539-45.
- Swinker M, Tester P, Koltai Attix D, Schmechel D. Microbes Infect. 2002;4(7):751-62.