A second release of infected carrots will take place in May as part of the program to control the city's wild rabbit population.
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The carrots, chopped and laced with Rabbit Haemorrhagic Disease Virus, were first distributed by Greater Sydney Local Land Services to more than 30 councils and other government bodies and released in council-owned parks, school grounds, national parks and other public spaces after dusk on March 12.
A smaller second release of the virus across about 10 areas where dense rabbit populations are still being observed was likely to occur in early May, at the same time as a release in the Central Coast, according to Local Land Services manager of biosecurity and emergency services Graham Wilson.
The program aims to address environmental, agricultural and urban damage caused by wild rabbits, including damage to gardens and parklands, threatened ecosystems, underground cables and water pipes. Damage related to rabbit populations is estimated to cost between $600 million and $1 billion nationally every year.
Infected rabbits generally die within 48 hours of ingesting the virus, which is approved by the Department of Primary Industries as a humane method of pest control.
"It doesn't affect anything else - people, cats, dogs, or any of the other wildlife," said Mr Wilson.
"The method will kill a reasonable number of rabbits. It won't kill them all, but more than other methods."
The program includes testing the immunity of wild rabbits to the virus ahead of its release. It has been running annually since 2009, with the exception of 2011 when it was cancelled after a high level of RHDV antibodies were found in rabbit populations.
"This year, immunity was about 20 per cent so we thought it would work well," Mr Wilson said.
There is no firm information on rabbit numbers before or after the program is implemented, but anecdotal evidence suggests a "substantial population reduction" following the release of the virus, according to Aziz Chowdhury, the officer managing the program.
However, there are concerns about increasing levels of resistance to the virus through the exposure of young rabbits, which are less susceptible to its effects and could develop life-long immunity.
The virus entered the wild rabbit population in Australia two decades ago and spreads naturally in many parts of the country, but appears to be less effective in urban areas.
"The problem with somewhere like Sydney with lots of urban development is that you get the fragmentation of rabbit populations," Mr Wilson said.
"We figured we'd get the same [control effect] by using the virus as you see naturally in the rest of NSW.
"There's no perfect method to control an introduced pest. This is the best we've got."
