The woman who cooked a mushroom meal that resulted in the deaths of three of her husband’s relatives has been arrested, a major breakthrough in the case that has gripped Australia.

Police were on Thursday morning using specialist sniffer dogs to search the home of Erin Patterson, who prepared the beef wellington suspected of containing deadly ‘death cap’ fungi.

Gail Patterson and Don Patterson, both 70, died in hospital after experiencing severe gastrointestinal upset hours after dining at their daughter-in-law’s home on July 29. Gail’s sister, Heather Wilkinson, also died. Mrs Wilkinson’s husband, Ian, survived after receiving a liver transplant.

Ms Patterson had welcomed the four guests to her home in Leongatha, in south-east Victoria, as the family attempted to remain amicable throughout her separation from her husband, Simon.

A “devastated” Ms Patterson has previously paid tribute to the victims, saying she had a “deep love” for her in-laws and did not deliberately add the poisonous ingredient.

In the most significant development in the case, Victoria Police confirmed on Thursday that a 49-year-old woman was arrested at her home and that detector dogs from the Australian Federal Police were searching the property.

“The woman will now be interviewed by police and the investigation remains ongoing,” read a statement from police.

Detectives have previously seized a food dehydrator found at a rubbish tip.

Ms Patterson told police that, in a state of panic, she had dumped the cooking equipment after her estranged husband asked if she had used the dehydrator to “poison” his parents.  

She told police she had bought button mushrooms from a local supermarket as well as dried mushrooms from an Asian grocery in Melbourne.

Ms Patterson was first interviewed in the days after her relatives died but was released without charge.

Death caps, which can appear similar to edible varieties, are responsible for about 90 per cent of mushroom-related deaths worldwide. Ingesting even a small piece of the mushroom can be enough to cause serious liver and kidney damage.