Key points
- Harmful algal blooms of cyanobacteria are most commonly found in fresh water such as lakes, rivers, and streams.
- Signs and symptoms caused by these harmful algal blooms vary based on toxin and exposure.
- Illnesses can be mild to life-threatening.
Ingestion
People may ingest cyanobacteria or their toxins by:
- Swallowing water contaminated with cyanobacteria or their toxins
- Eating fish contaminated with toxins
- Swallowing blue-green algae supplements contaminated with toxins
Toxins and symptoms
Hepatotoxins and nephrotoxins
Microcystins and nodularins are hepatotoxins and nephrotoxins made by cyanobacteria. Ingesting these toxins can cause:
- Bad taste in mouth
- Loss of appetite
- Malaise or lethargy
- Headache or fever
- Nausea, vomiting, or diarrhea
- Blood in urine or dark urine
- Acute hepatitis or jaundice
Cylindrospermopsin is also a hepatotoxin and nephrotoxin made by cyanobacteria. Ingesting cylindrospermopsin can cause:
- Headache
- Fever
- Vomiting
- Bloody diarrhea
Neurotoxins
Anatoxins, guanitoxin (formerly known as anatoxin-a(S)), and saxitoxins are neurotoxins made by cyanobacteria. All three of these toxins can cause progression of muscle twitches when ingested. High doses of saxitoxin may cause progressive muscle paralysis.
Anatoxin-a can cause additional neurologic symptoms including:
- Tingling
- Numbness
- Burning sensation
- Drowsiness
- Salivation
- Speech disturbances
Skin or eye contact
People can have direct skin contact with water contaminated with cyanobacteria or their toxins during activities like swimming or boating. Their eyes may be exposed from contact with contaminated water or aerosols.
Contact with dermal toxins can cause:
- Allergic dermatitis, including rash, itching, or blisters
- Conjunctivitis
Inhalation
People can be exposed when they breathe in aerosols contaminated with cyanobacteria or their toxins.
Inhaling microcystins and other toxins can cause upper respiratory symptoms including:
- Coughing
- Wheezing
- Chest tightness
- Shortness of breath
Dialysis
Rarely, dialysis patients have been exposed to the hepatotoxin microcystin through contaminated dialysis water.
Exposure to microcystin through dialysis water can cause:
- Liver damage
- Liver failure
- Death
Health effects research
Information about human health effects from exposure to cyanobacteria and their toxins is primarily derived from:
- A few epidemiology studies of recreational exposures
- Studies with laboratory animals
- Reports of extreme human exposure events, such as exposure to contaminated dialysis water
- Animal (cattle and dog) exposures
The long-term health effects of harmful algal blooms of cyanobacteria are being studied but remain unclear.
Resources
- Cyanobacterial Blooms and Associated Illnesses: A Clinician Training Module for Physicians and Healthcare Providers | ASTHO
- Health Effects from Cyanotoxins | U.S. EPA
- Blue-Green Algae Products and Microcystins | FDA
Physician Reference for Cyanobacterial Blooms
Facts about Cyanobacterial Blooms for Poison Center Professionals
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