Recently, Business Mirror carried a news report stating that the shellfish harvested from Hinatuan Bay in Surigao del Sur are already safe for eating.  The lifting of the ban was issued by the Bureau of Fisheries and Aquatic Resources (BFAR).

However, BFAR said that people should still not eat shellfish collected from Lianga Bay in Surigao del Sur and those coming from Matarinao Bay in Eastern Samar; the coastal waters of Dauis and Tagbilaran City in Bohol; and Puerto Princesa and Honda Bays in Palawan.

Based on the laboratory tests conducted on the water sample from the aforementioned areas, the shellfish “remain positive for paralytic shellfish poison that is beyond the regulatory limit.”

Aside from Hinatuan Bay, the coastal waters of Cavite, Las Piñas, Parañaque, Navotas, Bulacan and Bataan in Manila Bay are also free from red tide, according to BFAR.  But for how long, no one knows.

Red tide is layman’s term for paralytic shellfish poisoning (PSP).  It does not occur only in the Philippines in other parts of the world as well.  Even in developed countries, red tide occurs in the United States, Canada, Japan, France, Spain, and New Zealand.

Despite several studies being done, no one still knows when and where red tide started. But some people believe that the first occurrence was recorded in the Holy Bible. In Exodus 7:20-21, these words were written: “Moses raised his staff in the presence of Pharaoh and his officials and struck the water of the Nile, and all the water was changed into blood. The fish in the Nile died, and the river smelled so bad that the Egyptians could not drink its water.”

Although red tide phenomenon has been reported since time immemorial, scientists still could not predict its occurrence.   However, current researchers are investigating the possibility.

Dr. Rafael D. Guerrero III, a fishery expert and academician at the National Academy of Science and Technology, said red tide is a natural phenomenon brought about by the bloom or predominance of a floating microscopic organism known as dinoflagellates. These “single-celled organisms can swim at the maximum rate of one meter per hour, by means of two whip-like flagella.”

The University of the Philippines at Los Baños said the name “red tide” was coined by some scientists due to the sea water discoloration which ranges from amber, red, brown, yellow orange to purple caused by the highly-dense population of dinoflagellates. To make it short, its present name was given. In science, it is called harmful algal blooms.

Experts say red tides occur in warm seas and in calm coastal waters, usually between the end of warm months and the onset of the rainy season. They may last from a few hours to several months, depending on the prevailing conditions in the area.

“Some red tides are considered harmless when there is no harmful impact on the environment, living organism and humans as well,” the BFAR said, adding that swimming is safe for most people during a red tide event.

“However, red tide can cause some people to suffer from skin irritation and burning eyes,” the BFAR said.  “If you are particularly susceptible to irritation from plant products, avoid red tide water.  If you experience irritation, get out of the water and wash thoroughly.”

Of the 2,000 dinoflagellates known, only 20 species can produce toxins or poisonous substances that kill humans. In the Philippines, the red tide organism that caused deaths has been identified as Pyrodinium bahanse var. compressum.

The P. bahamense, according to Dr. Guerrero, is capable of horizontal and vertical movements in the water. Being attracted to sunlight, it rises up to the surface during daytime and settles at the bottom in the dark hours.

The organism multiplies rapidly through asexual means (without sex cells) during its productive stage which results in bloom. For its resting or dormant stage, the organism reproduces sexually and form cysts which “hibernate” in the sediment until activated by favorable conditions in the next outbreak.

Marine scientist Howard Seliger said that red tide is triggered by the increased nutrients in coastal currents. In his book, Biology, Epidemiology and Management of Pyrodinium Red Tide, he wrote that in the past there was not enough food in the currents to allow them to be carried over long distances.

But now, Seliger believes that more nutrients may be entering coastal waters “due to increased discharges of industrial and human wastes into waterways and decreased natural filtering due to deforestation.”

This finding has been bolstered by Dr. Teresita M. Espino, a scientist with the National Institute of Molecular Biology and Biotechnology. “When there is so much waste, it becomes conducive to the growth of microorganisms that deplete the oxygen. The oxygen is eaten by the shellfishes which may cause the red tide incidence,” she explained.

The red tide organism that beset the Philippine waters, Seliger said, thrives only in coastal waters and lagoons under conditions of high salinity. It does not survive in freshwater bodies, he added.

During a red tide phenomenon, people are advised not to eat filter-feeding shellfish which include clams, cockles, mussels, oysters, and scallops.  These shellfish are particularly prone to toxin contamination as they feed by filtering microscopic food out of the water along with other nontoxic foods.  Alamang harvested from red tide affected areas are also not safe for human consumption.

According to BFAR, among those that can be eaten taken from red tide infested waters because the edible tissues of these don’t absorbed the toxin are the following: fish, squids, crabs, seaweeds and shrimps.  However, the gills, viscera and internal organs must be removed first and thoroughly washed before cooking them, it advised.

Even if the shellfish are cooked thoroughly, people still get poisoned because the toxin is not destroyed by heat, Dr. Guerrero said. The poison in the red tide organism is known as saxitoxin, a water-soluble salt that affects the nervous system.

The potency of saxitoxin has been reported to increase by acidic chemicals like vinegar used in preparing common Filipino dishes like adobo and paksiw, and the hydrochloric acid present in the human stomach.

Saxitoxin is detrimental to the nervous system. “Saxitoxin blocks the sodium channels of excitable membranes of the nervous system and associated muscles resulting in death by respiratory paralysis in extreme cases,” said Dr. Eric A. Tayag, one of the country’s noted epidemiologists.

Health officials said PSP victims have symptoms of tingling or burning sensation on the lips, tongue and face within 30 minutes after eating shellfishes with red tide organisms. The gastrointestinal symptoms are vomiting, abdominal pain, water diarrhea, nausea, and hypersalivation.

PSP-affected persons experience sensory abnormalities, numbness, dizziness, headache, lightheadedness, and short-tongue sensation. In severe cases, they cannot walk, and they breathe, swallow, and speak with difficulty. Some die from inability to breathe spontaneously.

“There is no specific treatment for shellfish poisoning,” wrote Dr. Charles Patrick Davis for emedicinehealth.com “However, some health care professionals may induce vomiting or use a stomach pump to remove food if the patient is seen within three hours of ingesting the shellfish. These actions may reduce the amount of poison that is absorbed through the gastrointestinal tract.

“In addition, patients are often given intravenous (IV) fluids as they may become dehydrated from vomiting. The use of oral charcoal may be used in some patients that are seen early after ingestion of large amounts of food likely containing large amounts of shellfish poison. Some health care professionals advise the stomach should be pumped to remove foods before charcoal is administered.”

Since there is still no known antidote to red tide poison, Dr. Guerrero said the best way to prevent PSP is to avoid the consumption of contaminated shellfishes during the ban imposed by the government authorities.

Levels exceeding 80 micrograms of toxin per 100 grams of shellfish meat warrant a ban on the harvest, sales, and ingestion of implicated shellfishes, according to the World Health Organization.

In the Philippines, a ban is issued by BFAR when the toxic levels have exceeded 40 micrograms of toxin per 100 grams of shellfish meat.

“Individuals should pay close attention to Red Tide Advisory and under no circumstances should individuals harvest, market and consume shellfish from any areas under shellfish ban due to red tides,” the BFAR reminded. – ###

Note: The red time piosoning chart is taken from the net.