Sambhar bird deaths due to botulism, confirms IVRI
CAUSE The report blames heavy rain in July and August that led to growth of bacterium
JAIPUR: Eleven days after bird deaths were reported at Sambhar, the Bareilly-based Indian Veterinary Research Institute (IVRI) confirmed on Thursday that the cause of mortality of around 18,500 migratory birds at India’s biggest inland salt water wetland is botulism.
In Bareilly, IVRI director Dr Raj Kumar Singh said: “We carried out lab tests on the samples we received from Rajasthan authorities. The tests confirmed that the deaths were due to avian botulism.” The illness is caused by a toxin that is produced by the bacterium clostridium botulinum, said scientists.
The IVRI director said there were several factors, which could lead to the outbreak of the toxinproducing bacteria, which occurs when there are large amounts of decaying plant or animal materials. “These bacteria are harmless initially until the environmental factors and anaerobic conditions prompt them to germinate and begin the vegetative growth of the toxin-producing bacterial cells,” he said.
Earlier, experts at the National Institute of High Security Animal Diseases in Bhopal had suspected avian botulism as the reason behind the deaths.
The institute’s report sent to animal husbandry directorate on Thursday said, “Heavy rains in the month of July and August resulted in filing of lake and there was formation of new marshy areas after 20 years.”
The report signed by VK Gupta, joint director of Centre for Animal Disease Research and Diagnosis (CADRAD) at IVRI, said, “Based on epidemiological and laboratory investigations, the cause of mortality in migration birds is Avian Botulism caused by Clostridium botulinum.”
So far, carcasses of around 18,500 birds have been recovered in the area.
The IVRI report said the initial dead bird that were recovered on November 10 were infested with maggots, “which clearly indicates that the birds must have died 10-14 days earlier”.
“The fresh birds that fed on these maggots have also succumbed to botulism thus establishing a maggot-carcass vicious cycle,” the report said.
The report said the presence of botulinum toxin from the samples was demonstrated by mouse lethality assay.
It said the salinity of water must have been less due to downpour which would be conducive environment for the proliferation of planktons, a bunch of mirco or small organisms which harbour C. botulinum in their body. “Upon receding of water levels, there must be mild increase in the salinity levels, which must have led to the death of planktons,” the IVRI report said.
The report said there was death in the insectivorous and
omnivorous birds only; there was no death in the herbivorous ones. “The carcasses were infested with maggots, which are known to accumulate botulinum toxins,” it added.
HT had earlier reported that fall in oxygen level in lake water gave rise to anaerobic condition that lead to bacterial proliferation. The IVRI report has confirmed what HT wrote.