Avian Botulism

On November 10, visitors at Sambhar Lake, India’s largest inland saltwater lake located about 80 km southwest of Jaipur, spotted a very large number of dead birds.

Why and how did these birds die?

• Nearly 10 days into the tragedy, the government is yet to determine the cause of the deaths.
• The investigation so far points to Avian Botulism — a paralytic, frequently fatal disease caused by the ingestion of toxins — as a possible cause.
• This has not, however, been officially confirmed.
• After studying bird samples and on the basis of history, epidemiological observations, classical clinical symptoms and post-mortem findings, the most probable diagnosis is avian botulism.
• The clinical signs exhibited by affected birds included dullness, depression, anorexia, flaccid paralysis in legs and wings, and neck touching the ground.
• The birds were unable to walk, swim, or take flight. There was no rise of body temperature, no nasal discharge, no respiratory distress or any other sign.

Other possible reasons

• After a Division Bench of the Rajasthan High Court took cognizance of the bird deaths, the Rajasthan government listed four likely reasons.

1. Viral infection
2. Toxicity, as new area has been filled up after almost 20 years, and there could be higher concentration of salts along the edges
3. Bacteriological infection
4. Higher temperature and high water levels due to good monsoon might have led to an increase in intra-species and inter-species competition for resources.

• The weaker individuals, exhausted from the long journey, perhaps were unable to compete, and may have succumbed to stress emanating from the shortage of food, susceptibility to disease/pollutants/toxins and other habitat-related factors in the wintering grounds.
• In such an eventuality, it is expected that with fall of temperature and lowering of water levels, the incidence of such mortality will go down.