The latest death, a 5-year-old girl, occurred Thursday, The Phnom Penh Post reported Monday.
The border between Cambodia and Vietnam is long and difficult for the countries to police, enabling free-range ducks that might carry the H5N1 virus to easily pass from village to village or from country to country, said Dr. Philippe Buchy, head of the virology unit at the Institut Pasteur du Cambodge.
Sonny Krishnan, communications officer for WHO Cambodia, added that not only are Cambodian authorities unable to inspect all birds transported around the country, farmers have no incentives to report sick birds.
Poultry owners often don't worry about sick birds until humans start dying from the virus, Krishnan said.
The killing and burning of poultry in Prey Lvea, the commune where the latest victim died, would not be required until ordered by government officials in Phnom Penh, said commune chief Yon Korn.