Cyanobacteria are photosynthetic microorganisms found in various aquatic environments, such as lakes, rivers and ponds. Some can cause gastrointestinal, skin and pulmonary symptoms.
In summer, rising temperatures and summer sunshine lead to an increase in the proliferation of cyanobacteria in many bodies of water, lakes and rivers in France. Faced with the appearance of these greenish “water blooms” and the risk of the release of cyanotoxins harmful to humans and fatal for pets, several Regional Health Agencies (ARS) and municipalities have strengthened health surveillance and issued orders temporarily prohibiting swimming or water activities on the affected sites.
What is the definition of a cyanobacteria?
“Cyanobacteria, or Cyanobacteriota, are bphotosynthetic acteria, to be distinguished from algae which are eukaryoticdetails Dr Valentin Wehrle, medical biologist. They can take on different colors (green, red, purple or yellow) due to their pigments (Chlorophyll-a, Phycocyanin, Phycoerythrin, etc.) which vary depending on the spectral quality of the light.“. These bacteria are part of oldest living beings identified and fix carbon from carbon dioxide then release oxygen which contributed to the enrichment of oxygen in the Earth’s atmosphere. “They live almost everywhere on earth and develop in certain water polluted by human activities (eutrophication, dystrophication) forming colored “water flowers”. They then represent a natural reaction to pollution already present. It is essential to monitor water quality to prevent their proliferation too high, particularly in bathing waters. Indeed, cyanobacteria can be presentr a danger for animals and humans due to the release of cyanotoxins that they produce (microcystins, cylindrospermopsin, saxitin, anatoxin-a). “They may be responsible for gastrointestinal, skin and pulmonary symptoms, loss of kidney and liver functions, neurotoxic syndromes, liver cancer and mortality“. Around forty cases of chronic or acute poisoning have been recorded around the world in recent decades. “However, these data are underestimated due to the lack of information in certain regions of the world.”
“The main routes of transmission to humans are the ingestion of more or less well-treated drinking water, recreational activities in bathing water at low flow (lakes, rivers, etc.) via inhalation or accidental ingestion of cyanobacteria and/or their toxins”, continues the biologist. “Transmission can also be observed in case of consumption of plant foods or fish contaminated by irrigation water“. Rare cases have been reported through intravenous transmission in people on dialysis.
There is no specific treatment for poisoning caused by cyanobacteria.
What are the symptoms?
The symptoms can be classified into two categories depending on the intoxication. “In case of acute poisoning, the symptoms are mainly digestive (gastroenteritis, abdominal pain, vomiting, diarrhea), headaches, fever, and dermatological (skin rash)”, underlines our interlocutor. “And in the case of chronic intoxication, we observe an increase in risk of colorectal and stomach cancers. There is also an increase in liver enzyme levels in exposed populations.
Is it mortal?
“Only 6 cases of death attributable to cyanobacteria are listed in the bibliography in recent decades (Svircev et al., 2016)”, calls back the doctor. Which is a far cry from bacterial infections which constitute the second cause of death in the world with 7.7 million deaths per year.“.
Diagnosis of exposure to cyanobacteria is very difficult to make. “It is mainly based on questioning the patient (ingestion of contaminated water? Activity in recreational water? …) and on the presence of a possible epidemic“, recognizes Dr. Wehrle. “The detection and quantification of cyanobacteria is based on direct visual observation, on in situ biological indicators (Chlorophyll-a, Phycocyanin, use of fluorometric probes) and complementary indicators such as physical parameters, transparency or turbidity of water“. If exposure is related to drinking contaminated water, public health authorities may test the water for the presence of cyanobacteria and cyanotoxins.
Is it contagious?
Cyanobacteria are not pathogenic organisms that can be transmitted from one person to another by direct contact or by air, as are most bacteria or viruses encountered in human health. “To date, human-to-human contagiousness of cyanobacteria has not been demonstrated.which is logical since their dangerousness comes only through their toxins.
What treatment to treat an infection?
There is no specific treatment for poisoning caused by cyanobacteria. “The main treatment is therefore based on avoiding the source of exposure to cyanotoxins implicated as well as the reduction of the proliferation phases (blooms) of cyanobacteria“, concludes our interlocutor. algal bloom management in aquatic ecosystems is a constantly evolving area of research and environmental intervention, aimed at minimizing risks to human and animal health, as well as impacts on ecosystems. Local authorities generally monitor cyanobacteria levels in water and issue warnings when high concentrations are detected to protect public health.
Thanks to Dr Valentin Wehrle, medical biologist at the BIO-LBS Laboratory in Lillebonne (76), and member of the Les Biologistes Indépendants network.
