A salmonella threat which prompted a national egg recall may have been caused by wild birds' droppings falling on a Victorian farm.

Droppings from passing migratory wild birds may be responsible for spreading salmonella bacteria, prompting a national recall of eggs and possible cull of hundreds of thousands of hens.

Some brands of free-range and barn-laid eggs with particular used-by dates have been recalled across NSW, Victoria, Tasmania and South Australia after a food poisoning outbreak.

The source of the infection was traced back to Victoria's Bridgewater Poultry, which has been put in quarantine as authorities investigate.

Egg Farmers of Australia spokesman John Coward speculated that the farm may have contracted the bacteria from birds flying overhead.

"It may have come from a migrating wild bird that can bring in this strain and infect the flock," he suggested to AAP on Friday.

"You can't stop bird flying over with this type of salmonella."

Authorities are investigating the link between the latest Victorian outbreak and another in NSW last year.

Mr Coward said even if the hens needed to be killed, it would not have a significant impact on the national egg supply chain as it could be readily absorbed by other producers.

"You do not need to rush out and buy eggs tomorrow," he said, warning consumers against panic buying.

Symptoms of salmonella enteritidis include fever, headache, diarrhoea, abdominal pain and nausea, and usually start six to 72 hours after eating the contaminated food and can last up to a week.

The company's free-range and barn-laid eggs are packaged as Woolworths brand, Victorian Fresh, and Loddon Valley, with best-before dates ranging from March 20 to April 29.

These eggs should be destroyed.