Since 2012, we have been documenting and characterising a syndrome colloquially known as “CHiPS”: Cockatoo Hindlimb Paralysis Syndrome. Affected birds are unable to stand or walk, and rapidly lose condition due to their inability to feed. The syndrome only affects Carnaby’s Cockatoo, which migrates to metropolitan Perth in the summer from breeding grounds in the north. With intensive supportive care, many cases will improve over 7-10 days to full use of their legs.
Data collection to characterise this syndrome has become increasingly refined, allowing many common differential diagnoses for paresis and paralysis in birds to be ruled out. However full characterisation of the index case continues to be elusive due to the non-specific nature of the presentation, high incidence of secondary trauma and lack of histopathological changes at post mortem.
We are currently investigating the hypothesis that CHiPS is a result of exposure to organophosphate (OP) pesticides which are widely used on crops in northern breeding areas. Although tissue testing for pesticide residues has been consistently negative, some birds have demonstrated depression of acetylcholinesterase in plasma and brain, indicative of exposure to anti-cholinesterase compounds. The clinical presentation also has intriguing similarities to ‘OP-induced delayed neuropathy’ (OPIDN), a rare human condition in which OP molecules bind to neuropathy target esterase, initiating degeneration of distal axons and resulting in a peripheral, often reversible, neuropathy.
We have recently developed reference ranges for brain acetylcholinesterase and plasma total cholinesterase in Carnaby’s cockatoos, which may hold the key to reliable identification of CHiPS cases if OP pesticides are implicated in the condition.
Key factors in the progress of this investigation are:
• Buildup of a longitudinal database
• Revisiting differential diagnoses in the light of additional data and analysis
• Systematic testing of likely hypotheses
• Cooperative data collection and disease screening involving a number of stakeholders