A horse in the New South Wales Hunter region has died and more across the state have been infected with West Nile virus in numbers not seen since the outbreak of 2011.
Cases of the illness, including its Kunjin strain, have been diagnosed recently in northern and southern parts of NSW amid good breeding conditions for mosquitoes.
Scone vet Lucy Cudmore described the virus as "shocking" and said symptoms could vary, but it often presented in similar ways to the Hendra virus.
"It can be quite distressing to find your horse presenting with these neurological abnormalities," she said.
"They can look like they have a headache or look quite dull and depressed … sometimes they'll have a fever."
Dr Cudmore encouraged horse owners who noticed symptoms such as weakness of limbs, loss of appetite and difficulty swallowing to act with caution, especially if the horse was not vaccinated against Hendra virus.
"Fortunately the horse in itself is a dead-end host, so they can't pass the virus on to humans, which is different to Hendra," she said.
While horse-to-human infection does not occur, mosquitoes can infect humans and in serious cases the virus can cause hospitalisation.
What's the cure?
Dr Cudmore said horses usually began to recover within days, but each case was different and factors such as age and general immunity could have an impact.
Two of the recent cases in the Hunter had to be hospitalised and one passed away.
"There's no specific treatment … it's really about supportive care," Dr Cudmore said.
"Some anti-inflammatories, some corticosteroids in some cases might be helpful, and then just making sure that they have good access to water, that they're able to drink and continue to eat."
She said some horses could need "a little more TLC", including intravenous fluids.
Without a cure, vets advise owners to keep mosquitoes away from their horses where possible and use animal-friendly insect repellent.
"Try to keep them out of them out of the paddocks as much as you can in the dawn and dusk periods when the mozzies are most active," Dr Cudmore said.
Low fatality rates
The last time NSW and Victoria saw an outbreak was in 2011, when about 100 horses died from the virus.
Dr Cudmore said until weather conditions cooled down horse owners needed to remain vigilant.
Fortunately the Australian strain of West Nile virus is not as severe as it is in other countries.
"Compared to our US counterparts, this disease tends to be relatively more mild than what they see, and certainly we have a lower mortality rate in Australia," Dr Cudmore said.
"The last outbreak was 2011 and we saw about 1,000 horses between NSW and Victoria test positive to the virus and there was only about a 10 per cent fatality rate."
