Johannesburg City Parks and Zoo (JCPZ) has identified avian botulism as the likely cause of the recent deaths of waterbirds at Zoo Lake, while laboratory tests have ruled out avian influenza in the birds examined. In a media statement issued on Wednesday, 12 November, JCPZ said veterinary findings pointed to avian botulism based on the birds’ clinical signs, previous outbreak patterns and environmental conditions at the lake.
The assessment was compiled by Dr Dewald Keet, Manager of Veterinary Services at Johannesburg Zoo. He explained that the toxin responsible for the illness affects birds’ nervous systems, causing muscle weakness and paralysis. Affected birds may lose the ability to fly, feed or keep their heads above water, leaving them vulnerable to drowning.Avian botulism is associated with a toxin produced by Clostridium botulinum bacteria.
Warm temperatures, stagnant water, low oxygen levels and decomposing organic material can create favourable conditions for outbreaks. JCPZ teams are removing dead birds from the shoreline and island before transporting the carcasses to Johannesburg Zoo for incineration. On 11 November, officials, assisted by members of the boating club who provided access to the island, recovered an additional 74 carcasses.
Prompt removal is important to interrupt the cycle in which maggots feeding on decomposing birds carry the toxin and are subsequently eaten by other waterbirds.JCPZ has reassured residents that the type C botulinum toxin commonly associated with waterbird outbreaks poses a low risk to humans. However, the toxin type has not yet been confirmed through laboratory testing. The lake water is therefore considered unsafe for pets, swimming and angling.
The organisation is working with the City’s Environment and Infrastructure Services Department to investigate environmental conditions and identify measures to improve the lake’s health.Although sewer spills and other possible pollution sources are being investigated, the veterinary findings have not established a direct link between a particular spill and the bird deaths.
Johannesburg City Parks and Zoo Managing Director Thanduxolo Mendrew said the loss of birdlife was deeply concerning and appealed to visitors to help protect the remaining wildlife. Visitors are urged not to feed waterbirds, particularly bread, and to avoid touching or collecting sick and dead birds.
Children and pets should be kept away from carcasses and the affected water, while pets must remain on a leash. Sightings of sick or dead birds should be reported to emi@jhbcityparks.com, with the precise location provided.JCPZ says it will continue monitoring the situation and provide further updates as investigations progress.
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