Botulism identified as the primary cause of a paralyzing disease in birds

Barcelona (Spain), May 12 (EFE).- An international scientific team, including the RIAS (Wildlife Rehabilitation and Research Center of Ria Formosa) and the Pasteur Institute of the University of Paris, among others, has identified botulism as the most likely cause of paralytic syndrome, a disease that causes severe paralysis in seagulls and other aquatic birds.

Specifically, in addition to the aforementioned institutions, the Center for Environment Fisheries and Aquaculture Science (Cefas), the Spanish Institute of Oceanography (IEO-CSIC), and the Institute for Research in Game Resources (IREC) collaborated.

Botulism was detected in these birds through a study published in two articles in the journal Toxins , in which the Spanish Institute for Environmental Diagnosis and Water Studies (IDAEA-CSIC) also participated.

The study identifies botulinum toxin as the cause of paretic syndrome, which has been depleting seagull populations for years, and maintains that "removing carcasses and controlling water quality are key to curbing the disease and preventing damage to biodiversity."

571 samples from 377 birds

During the investigation, 571 samples from 377 birds, both healthy and with symptoms of paralysis, taken off the southern coast of Portugal were analyzed.

The results show that 100% of the 22 sick birds tested positive for botulinum neurotoxin, while none of the asymptomatic birds had this toxin.

Paretic syndrome manifests with symptoms such as flaccid paralysis of the limbs, respiratory distress, and diarrhea, preventing birds from feeding, swimming, or escaping predators.

The RIAS center treats hundreds of birds with this condition each year, and has successfully recovered more than half of them, although its cause was previously unknown.

A bacterium that thrives in aquatic environments

According to Rafael Mateo, a researcher at IDAEA-CSIC and one of the authors of the study, "avian botulism is a poisoning caused by the toxin produced by the bacterium Clostridium botulinum , which thrives in aquatic environments with high temperatures and excess organic matter."

Birds usually become infected by consuming fly larvae that develop in decomposing carcasses contaminated by the bacteria, although in the specific case of seagulls it is not clear whether it is the water or the food.

Rapid removal of corpses

For this reason, prompt removal of carcasses "is a good way to stop the cycle," and failure to do so "can lead to outbreaks that kill thousands of birds," the study's author noted.

During the course of the investigation, the presence of other environmental toxins was detected, such as paralytic shellfish toxins and microcystins (produced by microalgae).

The levels detected, however, would not be sufficient on their own to cause severe paralysis, so researchers suggest that they could contribute to the birds' general weakening and worsen the effects of botulism.

Two positive cases of avian influenza were also identified among apparently healthy birds, highlighting the need to consider multiple possible causes in cases of wild bird mortality. EFE

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