High temperatures and reduced salinity in Sambhar Lake have created conditions that may have contributed to an outbreak of avian botulism, leading to the mass deaths of migratory birds in Rajasthan. The Centre for Avian Research Institute reported at least 600 bird deaths earlier this month. The deaths began on October 26, 2024, and continued for about two weeks.
What is Avian Botulism?
Avian botulism is caused by the ingestion of a toxin produced by the bacterium Clostridium botulinum. This toxin leads to paralysis in birds and can be fatal. The bacterium is commonly found in wetland sediments and is present in many wetland habitats, including invertebrates like insects, mollusks, crustaceans, and vertebrates such as healthy birds.
Contributing Environmental Conditions
- High Temperatures: The India Meteorological Department (IMD) reported above-average temperatures in Jaipur district, which is about 70 km from Sambhar Lake. The maximum temperatures in the region were 1 to 5.1 degrees Celsius higher than normal throughout October.
- Reduced Oxygen Levels: As a salt lake, Sambhar Lake may have experienced low oxygen levels due to a lack of rainfall in October. The expected 13.7 mm of rainfall did not occur, exacerbating the issue.
- Changes in Water Quality: P Sathiyaselvam, deputy director of the Bombay Natural History Society (BNHS), noted that a sudden influx of fresh water into the lake could have altered its salinity, potentially triggering the outbreak. Fresh water reduces the salinity of the lake, making it more conducive to bacterial growth.
How the Disease Spreads
Migratory birds arriving at the lake, exhausted from their long journey, are more vulnerable to diseases like avian botulism. Once infected, the birds die and decay, attracting maggots that further contaminate the water, spreading the disease to other birds and animals that consume the infected carcasses.
Previous Outbreaks and Challenges in Prediction
The disease was also reported at Sambhar Lake in 2019, when nearly 18,000 birds died in a similar mass die-off. Predicting outbreaks of avian botulism is challenging because they require specific environmental conditions, such as the alignment of temperature, salinity, and oxygen levels, which favor the growth of the bacteria.
Preventive Measures and Treatment
There is currently no treatment for avian botulism. However, experts recommend that affected birds should be immediately removed and disposed of to prevent further spread of the disease.
Global Incidence and Expert Opinion
Similar outbreaks of avian botulism have been reported in countries like Australia and the United States, often when salinity levels drop in wetland areas. Sathiyaselvam also highlighted that there are about 57 different diseases reported among wild birds worldwide.
Multiple-Choice Questions (MCQs) with Answers:
- What is the primary cause of avian botulism in birds?
- A) High temperatures
- B) Toxin produced by Clostridium botulinum bacterium
- C) Lack of food
- D) Low oxygen levels
- Answer: B) Toxin produced by Clostridium botulinum bacterium
- When did the mass deaths of migratory birds in Sambhar Lake begin?
- A) October 1, 2024
- B) October 26, 2024
- C) November 1, 2024
- D) November 10, 2024
- Answer: B) October 26, 2024
- What environmental condition contributed to the outbreak of avian botulism in Sambhar Lake?
- A) Heavy rainfall
- B) High temperatures and reduced salinity
- C) Increased oxygen levels
- D) Decreased water pollution
- Answer: B) High temperatures and reduced salinity
- What is one recommended preventive measure for avian botulism outbreaks?
- A) Increase water salinity
- B) Immediately remove and dispose of affected birds
- C) Add more food for migratory birds
- D) Introduce more fresh water into the lake
- Answer: B) Immediately remove and dispose of affected birds
- In which year was avian botulism also reported in Sambhar Lake, causing the deaths of nearly 18,000 birds?
- A) 2018
- B) 2019
- C) 2020
- D) 2021
- Answer: B) 2019
- What is the role of maggots in the spread of avian botulism?
- A) They help to neutralize the bacteria
- B) They spread contamination as they decay
- C) They consume the infected birds without spreading the disease
- D) They serve as a food source for the birds
- Answer: B) They spread contamination as they decay