The pigs are destroying native vegetation, farming crops and the Nepean River corridor.

Their presence also increases the possibility of transferring diseases to humans.

Feral pigs are a pest under the Rural Lands Protection Act. The authority has implemented control programs using trapping, poisoning or shooting.

Mr Parker alleges that illegal pig hunters are undoing the authority's work by transporting and releasing the pests into the area.

It is possible that they are also interfering with the authority's traps, releasing feral pigs and removing surveillance cameras.

Over the past year the authority has captured and eradicated about 60 feral pigs in Penrith.

Mr Parker said tested pigs showed positive results for zoonotic diseases. These are diseases that can be transmitted from animals to humans. They included Q fever and leptospirosis. In other areas brucellosis has also been detected. Feral pigs also have a high risk of carrying other exotic and serious diseases such as foot and mouth disease, Menangle virus and Nipah virus.

Mr Parker said the Menangle and Nipah viruses are a potential risk as Penrith has a large bat population. Feral pigs can become infected with these viruses if they eat infected dead bats and bat droppings.

Menangle virus was discovered near Campbelltown, and caused pigs to abort. This virus is also transmissible to humans. The Nipah virus devastated Malaysia in 1999, causing human deaths and destroying the country's $400 million pork industry.

``We want to avoid any similar situations, hence our efforts with these eradication programs,'' he said.

``Under the Rural Lands Protection Act it is an offence to transport and release feral pigs or keep them in captivity, with penalties of up to $22,000.

``We don't want to tarnish the reputation of law-abiding pig hunters but there are minority groups that have an attraction to illegal hunting.''

Mr Parker is urging anyone with any information about local illegal pig hunting to contact the NSW Police.