Palytoxin: a potent but poorly understood marine toxin found on aquarium coral
Palytoxin (PLTX) is a potent but poorly understood marine toxin that periodically attracts media attention when poisonings occur. Some recent incidents included:
- In August 2019, a family of five from Shropshire, England was poisoned and hospitalized after cleaning a tropical aquarium.
- In 2018 and 2019, two poisonings involving the handling of corals were reported in Quebec.
- In 2017, seven family members and their dog were treated for breathing difficulties after their saltwater aquarium was cleaned in Adelaide, Australia.
In the cases above, the source of PLTX was traced to soft marine corals belonging to the Zoantharian (zoanthids) genera known as Palythoa growing in home, saltwater aquariums. This toxin has been found in other environments as well, including fish and seafood in tropical regions, during Ostreopsis phytoplankton blooms in the Mediterranean Sea, and in certain marine bacteria. All confirmed PTLX poisonings reported in Canada were related to the handling of Palythoas from home aquariums.
Routes of exposure and poisoning reports
PLTX is released by Palythoas when they are stressed and the toxin can be rapidly aerosolised. Exposure can be through dermal, inhalation, or ocular routes and symptoms appear within minutes to hours following exposure. Reactions range from localized, transient irritation to longer-term disability. The U.S. Poison Data System recorded 171 cases between 2000 and 2014. Most involved minor symptoms and full recovery, but 10 required ICU care. Consultation with Canadian poison centres revealed 32 confirmed and several suspected cases between 2011 and 2019.
Mode of Action, Symptoms and Treatment of PLTX Poisoning
PLTX disrupts the electrochemical equilibria needed for normal cell functioning by impairing the activity of the enzyme (Na+,K+-ATPase) responsible for regulating the flow of potassium and sodium across cellular membranes. Case reports based on aquarium-related incidents reveal that initial symptoms of acute toxicity depend on the exposure route. Inhaling aerosolized spores can cause nasal congestion, coughs, shortness of breath or other signs of respiratory distress. Dermal and ocular exposures are associated with local inflammation and numbness in the affected area. A metallic taste and fever are common in all exposure routes. Multiple systems may become adversely affected and if untreated, effects can be severe especially if the muscles of the cardiac, respiratory and skeletal systems are impaired. Progressive symptoms include fatigue, chills, gastrointestinal distress, muscle pain, stiffness and spasm, speech disturbance, and loss of consciousness. Blood analyses often show elevated lactate dehydrogenase (LDH), creatine phosphokinase (CPK), white blood cells and leukocytes. Studies of chronic toxicity and its symptoms are lacking.
There is no antidote to PLTX but early intervention with supportive treatments, such as oxygen supplementation and administration of inhaled corticosteroids to relieve respiratory symptoms, appear to have been effective. Prompt identification of poisoning is thus important.
Avoiding the use of Palythoas as a decorative element in aquariums in homes and businesses is recommended but may be challenging as it can be difficult to distinguish between toxic and non-toxic zoanthids. Often they have similar appearances and common names. PLTX may also persist on hard substrates such as dried coral even in the absence of live Palythoa. In addition, many aquarium enthusiasts are unaware of the risks. Several health authorities and a professional aquarium organization have recognized the popularity of soft corals and the challenges inherent in avoiding poisonous varieties and have created primers that include safety guidelines such as:
- Zoanthids should be handled by professionals or persons experienced with saltwater aquariums containing corals (also known as reef aquariums). Advice and training should be sought from the same types of qualified people.
- Protective gloves, masks (P100 level), coveralls and eyewear should be used when handling corals and during aquarium maintenance by all persons (whether they are carrying out the work or not) in the vicinity. All equipment should be cleaned or safely disposed of after use.
- Work on aquariums should take place in well-ventilated areas.
- Do not break, brush or scrub hard corals; or expose them to steam or pressurised, hot or boiling water, especially if encrusted with zoanthids. These activities will rapidly aerosolize any toxins present.
- Reef aquariums should not be accessible to children or in proximity to places where food is prepared and consumed.
The documents also include additional cautions and directions for recognizing and responding to poisonings:
- PLTX has no distinct odour or colour to signal the presence of a hazard.
- Recognize the first signs of poisoning in humans and pets and seek immediate medical attention, especially for children as they can be more vulnerable.
- PLTX is toxic to dogs and cats.
- If aerosol contamination is suspected, emergency services must be contacted as the area will need to be decontaminated.
PLTX poisonings may be under-reported because symptoms are variable and tracing incidents to their origins can be difficult. Minimising risks and successfully dealing with poisonings should they occur requires the involvement of several stakeholder groups, including aquarium owners, public health professionals, medical practitioners and emergency responders. Anyone living or working where there is a saltwater aquarium on the premises should understand and follow recommended practices. These premises include homes, businesses and workplaces, institutions such as child care facilities and schools, and commercial aquarium establishments.
In the context of environmental public health protection, environmental health officers can communicate the risks of PTLX with operators of businesses with onsite aquariums (e.g., food establishments; spa and other personal service facilities). Procedures for communicating, quarantining and decontaminating sites following an event must be in place. Medical professionals need to recognize and respond to the signs of poisoning and protocols must be in place for treatment and follow-up.
Useful Guidance Documents:
- Palytoxin and marine aquarium safety webpage from Government of South Australia Health.
- Measures to prevent palytoxin poisoning from the Ornamental Aquatic Trade Association Ltd.
- Recommended clean-up procedures following palytoxin incidents from Health Protection Scotland.
Photo credit: Brian Gratwicke, FLIKR