Birds found dead at the Zoo Lake, at different locations, were killed by avian botulism.
Johannesburg City Parks and Zoo (JCPZ) said test results sent to the Onderstepoort Veterinary Hospital, tested positive for botulism.
Dr Dewald Keet, Manager of Veterinary Services at Johannesburg Zoo, said however, tests for avian influenza, came back negative.
He also said this assessment, is based on the birds’ clinical signs, history of similar outbreaks and environmental conditions at the lake.
“The history, clinical signs and environmental conditions at Zoo Lake, however, point to avian botulism as the likely cause of these deaths. Prompt carcass removal is the most effective, immediate intervention to break the carcass–maggot cycle and limit further losses. Sustained attention to water quality and accumulated organic matter is also essential” said Keet.
Avian botulism occurs when birds ingest a toxin produced by Clostridium botulinum bacteria.
Warm to hot weather can exacerbate conditions by increasing water temperatures, accelerating the decomposition of organic material and reducing dissolved oxygen.
The outbreak is most active when there is stagnant water and accumulated organic matter.
The toxins from this water, affect the nerves and causes muscle of water birds to weaken.
Affected birds may become unable to fly, feed or hold their heads above water, placing them at risk of drowning.
Rapid detection and carcass removal is essential.
Most carcasses were removed from the shoreline and island and transported to the Johannesburg Zoo for incineration, on Wednesday this week.
Teams collected about seventy four (74) carcasses.
The JCPZ continues to investigate the effects of sewer spills and other sources of pollution and links to bird deaths.
Thanduxolo Mendrew, Managing Director of the JCPZ, has urged residents to avoid feeding birds, keep pets on a leash at all times and to stay a safe distance away from the water.
Picture: BirdLife SA