Over the next few days another neurological equine case is seen in your clinic and you hear of a horse in the next town with neurological signs similar to Smoky and the other case. You realise that these cases may constitute a cluster and are relieved to see Smoky’s additional lab results are consistent with a diagnosis of Kunjin virus exposure and infection (see report, access a PDF version here).
Here Roche and colleagues (2013) provide a descriptive review of a cluster of Kunjin cases that occurred in 2011. This reported cluster was similar to the cluster presented in this case.
Kunjin is an arboviral disease that is spread by mosquitoes, with birds acting as reservoir and amplifying hosts. Like Murray Valley Encephalitis (MVE) Virus, Kunjin virus is a Flavivirus. Weather events such as warm, wet conditions are favourable for amplifying hosts and vectors of Flaviviruses, resulting in increased risk of spillover events in other species, including horses. Equine infection with Kunjin or MVE may or may not result in clinical disease, as a result of diffuse myeloencephalopathy. Signs include ataxia, paresis, muscle fasciculations, hyper responsiveness, changes in mentation and/or behaviour and occasionally cranial nerve deficits. Horses are dead-end hosts for both Kunjin virus and MVE virus, however people may contract either virus through the bite of an infected mosquito. In the Australian context, clinical infection in horses with either Kunjin virus or MVE virus often resolves with appropriate supportive therapy, but is associated with approximately 10% mortality.