Microcystin is a toxin that is released by blue-green algae or cyanobacteria. Cyanobacterial blooms occur when algae that are normally present grow exuberantly. Within a few days, a bloom can cause clear water to become cloudy. The blooms usually float to the surface and can be many inches thick, especially near the shoreline. Cyanobacterial blooms can form in warm, slow-moving waters that are rich in nutrients such as fertilizer runoff or septic tank overflows. Blooms can occur at any time, but most often occur in late summer or early fall. Exposure to microcystin at significant levels through ingestion, inhalation, and dermal exposure can lead to microcystin poisoning.
A. Clinical Description
Both humans and animals can get microcystin poisoning from exposure to contaminated water. People can get microcystin poisoning from being exposed to contaminated waters, either by intentionally or accidentally swallowing water, by having direct skin contact (as when swimming, wading, or showering), or by breathing airborne droplets containing microcystins, such as during boating or waterskiing. Microcystin poisoning cannot be spread from one person to another, or from an animal to a person.
Symptoms may take hours or days to show up in people, but normally show up within one week after exposure.
Symptoms of microcystin exposure/poisoning include:
- Rash, hives, or skin blisters (especially on the lips and under swimsuits).
- Gastrointestinal symptoms such as stomach pain, nausea, vomiting, diarrhea, severe headaches, and fever.
- Runny eyes and nose, cough, and sore throat, pleuritic pain, asthma-like symptoms, or allergic reactions.
- Exposure to large amount of microcystin can cause liver damage (elevated gamma glutamyl transpeptidase).
B. Sources of Exposure
Microcystin poisoning is most likely to occur from exposure to surface water where cyanobacteria blooms are currently occurring or have occurred in the recent past. Exposure can occur from intentionally or accidentally swallowing water, by having direct skin contact, or by breathing airborne droplets. Another potential route of exposure could be from drinking water from a public water source that obtains its water from a surface water body that has elevated levels of microcystin toxin.
C. Population at Risk
People at greater risk are those who use recreational waters during and immediately after a cyanobacteria bloom is present. Populations whose drinking water supply is surface water that has experienced cyanobacteria blooms are also at risk. One of the populations to experience the greatest risk of adverse health impacts has been dialysis patients who were exposed to microcystin within the water used for dialysis and experienced liver and kidney damage and even death in some cases.
D. Diagnosis, Treatment, and Prognosis
Diagnosis of microcystin poisoning involves observation of the symptoms and exposure to water that is suspected of or tested to show evidence of elevated microcystin levels. Symptoms normally begin within 24 hours of exposure.
Treatment for both humans and animals is supportive. Patients are advised to not drink alcohol, not to use acetaminophen, or to use blue-green algal dietary supplements.
People exposed to small amounts of microcystin toxin experiencing gastrointestinal discomfort or headaches from oral exposure usually recover fully within 2 days of exposure. Symptoms including rash, skin irritation, or blisters from dermal exposure usually subside within 1 to 2 weeks after exposure.
E. Prevention of Exposure
People are advised to avoid contact with and exposure to recreational water where cyanobacteria blooms are currently occurring or have occurred in the recent past.