The two Pseudo-nitzschia species found in Luzon produce a dangerous neurotoxin that can cause severe sickness and permanent short-term memory loss.

Over half of the Philippines’ population lives on the densely populated island of Luzon, where many people regularly consume shellfish. The international team of scientists has just confirmed the presence there of two species of Pseudo-nitzschia diatoms capable of producing a dangerous neurotoxin that can cause severe sickness and memory loss. 

Poetically described as “algae that live in glass houses,” diatoms are microscopic aquatic organisms that cover themselves in protective milk-colored silica shells. While most diatom species are harmless, half of the 64 known species from the genus Pseudo-nitzschia are notorious for producing domoic acid (DA). A person who has eaten DA-infected shellfish may experience vomiting, nausea, diarrhea, and abdominal cramps.

In some cases, DA has even caused the permanent loss of short-term memory in a condition known as “amnesic shellfish poisoning” (ASP). However, ASP is rare: the last documented case was in Canada in 1987.

Despite their toxin-producing potential, little is known about the extent of Pseudo-nitzschia proliferation in the Philippines. This prompted scientists from the Ateneo de Manila University Department of Biology and Universiti Malaysia Sarawak to study the physical and genetic characteristics of the diatoms in water samples from shellfish farms in Bacoor Bay and Pagbilao Bay in Luzon.

“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. To our knowledge, the molecular taxonomy of Pseudo-nitzschia in the Philippines is virtually nonexistent,” said researchers Lorenzo A. Botavara, Janice A. Ragaza, Hong Chang Lim, and Sing Tung Teng.

They confirmed the presence of the DA-producing diatoms Pseudo-nitzschia pungens and Pseudo-nitzschia brasiliana in the samples. They also noted that this is the first time that P. brasiliana has ever been found in Luzon.

During excessive growth called harmful algal blooms (HABs) or “red tide,” DA can accumulate large amounts in filter-feeding shellfish such as mussels and clams. Thus, “Confirming species identities of a genus with half of its constituents known to produce DA is essential to HAB monitoring (in the Philippines),” the scientists underscored.