Nine persons in the United States and Canada were infected with salmonella in 2004 and 2005 after handling pet treats made with beef or seafood, according to the CDC.

Six cases of salmonellosis occurred among people who became ill after handling pet treats produced by manufacturing plants in Washington state or British Columbia. Two other cases involved victims who handled pet dogs that were carriers of the salmonella bacteria.

The manufacturing plants that produced the salmonella-tainted pet snacks received frozen, raw beef parts from slaughterhouses in the United States and Canada. The Washington plant also received frozen, raw salmon.

“Animal-derived pet treats are often contaminated with salmonellae, and the dehydration procedure used to make pet treats might not be effective" at eliminating the potentially deadly bacteria, wrote Dr. Larry Crowe of the Calgary Health Region in Alberta, the study’s lead investigator. In these cases, the authors said, the dehydration temperatures were not high enough to destroy bacteria that were present.

Stool cultures from the nine victims all showed evidence of infection with the Thompson strain of salmonella, which exactly matched bacteria from pet treats, pets and the manufacturing plants.

Although most Americans have no idea that handling pet snacks made of meat or seafood can make them vulnerable to salmonellosis, the issue has concerned public health officials since 1999. In that year, contaminated pig ear pet treats were confirmed as the source of salmonella infections in several Canadian provinces.

The CDC and the Public Health Agency of Canada advise pet owners to wash their hands with soap and water after handling animal-derived pet treats. They encourage people at high risk for salmonella infection, such as the elderly, the very young and the immune-compromised, not to touch pet treats.

In addition, they say manufacturers of pet snacks should thoroughly treat animal products to kill bacteria and should add pertinent product information to their labels.