Red tide, or harmful algal bloom (HAB), involves the rapid multiplication of microscopic algae in ocean waters, causing negative impacts on marine life and human health. In many regions, particularly along Florida’s Gulf Coast, the specific organism responsible for these blooms is Karenia brevis, a type of dinoflagellate.
While natural, environmental factors like nutrient pollution, temperature changes, and altered ocean currents can intensify blooms. The Karenia brevis algae produce potent neurotoxins known as brevetoxins, which can affect various organisms in the marine ecosystem.
How Toxins Reach Humans
Red tide toxins can enter the human body through several pathways. One common route is inhalation, where wave action breaks open algal cells, releasing brevetoxins into the air as fine aerosols. These airborne toxins are carried by winds along beaches and inhaled.
Direct contact with contaminated water is another pathway. Toxins can affect skin and eyes during recreational activities like swimming, especially when immersed or splashed.
Consumption of contaminated seafood is another exposure route. Filter-feeding shellfish, such as oysters, clams, and mussels, accumulate brevetoxins in their tissues. Consuming these shellfish transfers the toxins to humans, potentially causing illness. Finfish generally do not accumulate brevetoxins in their flesh, though toxins may be present in their guts, which are typically removed during preparation.
Airborne and Contact Effects
Exposure to airborne red tide toxins primarily affects the respiratory system, leading to irritation. Common respiratory effects include coughing, sneezing, and throat irritation. Nasal discharge and shortness of breath may also occur. These symptoms are generally temporary, resolving within a few hours of leaving the affected area.
Individuals with pre-existing respiratory conditions, such as asthma, may experience more severe symptoms. They should avoid areas with active red tide blooms. The severity of respiratory effects can vary based on factors like wind direction, proximity to the coast, and the concentration of the bloom.
Direct contact with contaminated water can cause localized irritation, including itchy, watery eyes and skin rashes. If irritation occurs while swimming, leave the water and rinse thoroughly.
Illnesses from Contaminated Seafood
The most serious human illness from consuming Karenia brevis contaminated seafood is Neurotoxic Shellfish Poisoning (NSP). NSP occurs when individuals eat shellfish, such as oysters, clams, or mussels, that have accumulated brevetoxins.
Symptoms of NSP can manifest as both gastrointestinal and neurological issues. Gastrointestinal symptoms include nausea, vomiting, diarrhea, and abdominal pain. Neurological symptoms can involve tingling sensations in the fingers and toes, a reversal of hot and cold sensations, dizziness, muscle aches, dilated pupils, and difficulty with coordination.
Symptoms typically appear within a few hours of consuming contaminated shellfish. The duration of symptoms can range from a few days to several weeks, depending on the amount of toxins ingested. While NSP is rarely fatal, symptoms can be debilitating and usually require medical attention.
Preventing NSP requires checking local shellfish harvesting warnings and consuming seafood only from reputable, regulated sources. Cooking or freezing does not destroy brevetoxins.
Safeguarding Human Health
Staying informed about red tide conditions is important. Individuals should regularly check local beach advisories, news reports, and public health websites for updates to make informed decisions about coastal activities.
Avoiding affected areas is advisable, especially for individuals with respiratory issues. Stay away from beaches and waters with active red tide blooms. When near a bloom, limit airborne toxin exposure by closing windows and using air conditioning with recirculated air.
For seafood safety, avoid consuming locally harvested shellfish during red tide events. While finfish generally do not accumulate toxins in their flesh, consume them only from reputable sources and ensure they are properly cleaned with guts removed.
If individuals experience severe or persistent symptoms after potential red tide exposure, seek medical attention. This applies to symptoms from inhaling airborne toxins or consuming contaminated seafood. Prompt medical evaluation can help manage symptoms and ensure proper care.