But it has few easy-to-detect symptoms, complicating the issue for Gold Ace's trainer Steven Reid.
He was to have put his multiple group one winner on a plane to Melbourne yesterday to contest Saturday's A$100,000 Cranbourne Cup but pulled him off the flight.
"He is 90 per cent but that is not good enough to be going to a race like Cranbourne," Reid told the Herald.
"So I will let him miss that and give him a workout at Alexandra Park on Saturday.
"If he comes through that as well as I think he will, then he will be on the plane to Melbourne the following Wednesday."
Reid says Gold Ace has missed only two days' work and is eating now, but he is certain his team has been hit by the virus as they performed below their best at the workouts on Saturday.
Gold Ace is the fourth favourite for the Victoria Cup, which should host a sensational field headed by I'm Themightyquinn and Bitobliss as well as Reid's former stable rep Washakie.
Washakie won a record fourth Treuer Memorial at Bankstown on Saturday night, breaking Christian Cullen's track record and looks to be in career-best form.
The Victoria Cup will also contain warhorse Smoken Up, who won at Melton on Friday night, Mah Sish and Sushi Sushi, who contests Friday night's $40,000 Franklin Cup at Alexandra Park. That is also the target for Sir Lincoln, whose connections will make a decision on the Victoria Cup after that race.
He was struck by the virus just before New Zealand Cup Week and while he has won at the Alexandra Park workouts the last two Saturdays he hasn't looked his crushing best.
"We will know more after the Franklin Cup," said trainer Ray Green.
He was impressive enough on Saturday when leading throughout a tame 2200m workout and beat Easy On The Eye, with the run of the heat coming from Pembrook Benny, who also heads to the Franklin Cup.
Bettor Cover Lover finished hard held behind the placegetters and will contest mares races the next two Fridays.
The star of the workouts was last season's Woodlands Derby winner Ideal Scott, who was at his free-running best in his heat and looks ready for a return, probably next week.
Meanwhile, Dexter Dunn put a week of frustration behind him to drive his 1000th New Zealand winner with No Potato at Addington on Friday night.
He had gone winless at his previous two meetings but the 23-year-old gave a victory salute as he became the youngest driver to achieve the feat by a staggering six years.
