P pungens and P brasiliana. Botavara et al.

MANILA (UPDATED) — Researchers from the Philippines and Malaysia have confirmed the presence in Luzon of a type of microscopic algae called diatoms that can cause vomiting, diarrhea, abdominal cramps, and short-term memory loss that may be permanent.

Scientists from the Ateneo de Manila University Department of Biology and Universiti Malaysia Sarawak found the presence of two species of Pseudo-nitzschia diatoms — P pungens and P brasiliana — in water samples from shellfish farms in Bacoor Bay in Cavite and Pagbilao Bay in Quezon. For the first time, P brasiliana was found in Luzon, they said.

Diatoms are mostly harmless and serve as food for many marine animals, including shellfish. But about half of the known species of the diatom Pseudo-nitzschia are "notorious" for producing domoic acid, a biotoxin that can cause gastrointestinal symptoms and, in rare cases, permanent short-term memory loss, a condition known as amnesic shellfish poisoning, the researchers said.

The last documented case of amnesic shellfish poisoning was in 1987 in Prince Edward Island, Canada where four victims died after consuming toxic mussels.

According to the Washington State Department of Health, the toxin that causes amnesic shellfish poisoning is not destroyed by cooking or freezing and there is no antidote for it. 

"The only treatment for severe cases [of amnesic shellfish poisoning] is the use of life support systems until the toxin passes from the victim's system," it said.

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NO CAUSE FOR ALARM

According to the Washington State Department of Health, it is normal for the biotoxin-producing algae to be present in marine water. They are usually at "very low concentrations and pose no problems for most people who eat moderate amounts of shellfish."

However, toxic domoic acid can accumulate in filter-feeding shellfish such as mussels and clams during algal blooms or red tide when algae become a greater food source for shellfish, it said.

"Biotoxins don't harm shellfish, so the level in their tissue will rise until the bloom subsides. When the number of toxin-producing algal cells returns to normal low levels, the shellfish eventually flush the toxin from their bodies," the US health agency said. "It can be several days to several months or longer before they're safe to eat again."

The researchers also noted that Pseudo-nitzschia and other diatoms "naturally exist in the water in very small numbers that are generally no cause for alarm or concern. Side effects can only happen under very specific conditions such as a harmful algal bloom."

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The paper on diatoms by researchers Lorenzo A. Botavara, Janice A. Ragaza, Hong Chang Lim, and Sing Tung Teng was published by the academic publisher Taylor and Francis in October 2024.

What prompted the researchers to study the microscopic organisms was that "little is known" about the extent of proliferation of diatom Pseudo-nitzschia in the Philippines, adding that the molecular taxonomy or genetic classification system of Pseudo-nitzschia in the country was "virtually nonexistent."

"It is important to be aware of the toxic potential of these diatoms and to monitor them accordingly, but such efforts must begin by establishing their presence in our waters," the researchers said.

They noted that confirming the presence of diatom Pseudo-nitzschia was "essential" to harmful algal blooms or red tide monitoring in the Philippines, where many coastal communities consume shellfish regularly.

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