Senegal: a toxic marine microalgae discovered on


In Dakar, a marine microalgae was discovered that releases a toxin that affects human health on the coast. Its presence explains why the inhabitants of the sea suffer from symptoms similar to seasonal flu, every year during the warm season until the trade winds and the cold season resume. This strange phenomenon, observed for years, was hitherto inexplicable. A similar epidemic was observed in the Basque Country in France this summer. A report by Théa Ollivier.

From our Dakar correspondent,

Surfers and users of the coast regularly flee the waves of the Corniche des Almadies. The cause: flu-like symptoms that take them to the throat every year during the hot season, explains Oumar Sèye, business manager in the surfing industry a few meters from the sea: “The symptoms are sore throat, cold, fever, you lie down. As soon as a southerly wind blows, at certain times, there is. Afterwards it disappears. It is something that has moved us for 20 years, but we did not know where it came from “.

Researchers from the Research Institute for Development (IRD) and the Senegalese Institute for Agricultural Research (ISRA) finally found in early September that these symptoms were caused by a toxic marine microalgae. A result expected by Babacar Thiaw, President of the Surfrider Foundation in Senegal: “Before, we had many ideas. We told ourselves that it was the boats that cleaned their bunkers or the chemical industry in Senegal. Afterwards, researchers began to talk about this algae. But at the same time, it is not clear what causes its toxicity. Is it the pollution? We need to find out and see what can be done to solve it. “

Researchers have suspected such microalgae since 2016. In July last year, residents warned them as soon as the characteristic symptoms began to appear. They immediately mobilized to take samples, explains Waly Ndiaye, an aquaculture researcher at ISRA: “We did 18 dives, then we took some samples of water near places where he used water. It was then validated that it was a toxic microalgae that gave it, of the genus ostreopsis. It is a species that produces a toxin that produces the symptoms that populations have reported to us ”.

The poison is released into the water and rises when it swells, then the winds carry it to the beach. The microalgae at the origin of this toxin develop two or three meters deep when the water is warm, but other reasons explain their blowout, states Patrice Brehmer from IRD: “Wastewater is untreated wastewater, can be an aggravating factor. The first observation of this type of phenomenon, about fifteen years ago, corresponds well to the massive urbanization of the Almadies peninsula, with undersized sanitary capacity. It is absolutely necessary, in the city plans, to put sufficient sanitation capacity in future subdivisions ”.

Although the exact species is not yet known, researchers assure that there is no lethal risk to human populations.


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