April 01, 2006


 CDC on the offensive to stamp out rodent virus

Pest pathogen linked to deaths, birth defects

Posted March 15, 2006

Three deaths linked to a rodent borne virus have the Centers for Disease Control and Prevention working to raise awareness about the zoonotic threat.

Last May, the national public health agency concluded that four organ transplant recipients in New England had contracted lymphocytic choriomeningitis virus from a common organ donor infected by a pet hamster. Three of the four patients died as a result.

This is a new development for a virus believed to have been circulating in North America since the region's colonization. As a result, the CDC is asking veterinary practitioners to inform the pet-owning public about the risks of owning hamsters, guinea pigs, gerbils, and other rodents.

"For example, we'd prefer if pregnant women and immunocompromised people do not own pet rodents," said Abbigail Tumpey with the CDC Special Pathogens Branch.

Lymphocytic choriomeningitis virus infection during pregnancy has been associated with spontaneous abortion. In addition, a human fetus infected by its mother during the early stages of pregnancy could suffer permanent developmental disabilities.

The virus is found throughout the world in wild rodents but especially in the common house mouse, Mus musculus. Approximately five percent of mice in the United States carry LCMV, according to the CDC.

Although the disease is rarely fatal in healthy people, the CDC says the disease is underreported. Numerous serologic surveys conducted in urban areas reveal an infection rate between two percent and five percent. Anyone exposed to an infected rodent is at risk of contracting LCMV. The virus is shed in urine, droppings, saliva, and nesting materials.

"Everybody has house mice in their dwellings, and that's where most of the infections come from," explained Dr. Thomas G. Ksiazek, chief of the CDC Special Pathogens Branch. "So if the numbers of mice get high and the animals are infected, that creates a risk."

While house mice are the most likely vectors for the virus, infections from pet rodents are not unknown. After the organ transplant patients died this past year, health officials traced the virus to a pet hamster purchased by the donor from a pet store in Rhode Island. Two hamsters and a guinea pig at the store were also infected with LCMV. A single distributor in Ohio was found to have supplied all four rodents.

The animals came from a breeding facility in Arkansas from which this particular viral outbreak is believed to have originated. Infected pet rodents were shipped to stores in some 22 states. "(The virus) was introduced at some point into the population and as the population continued to breed, the virus was spread to other animals," Tumpey said. "If it were wider spread, we would've seen other viral strains."

The most likely scenario is the breeding colonies at the facility were exposed to a wild mouse infected with LCMV. Rodents are attracted to large sources of food, and if proper biosecurity precautions aren't in place, the rodents can spread the virus as they crawl around the cage tops, according to Dr. Ksiazek.

Lymphocytic choriomeningitis virus is not fatal in mice, and signs of illness are unlikely because of the well-adapted host-parasite relationship between the mouse and virus, Dr. Ksiazek said.

"You can get infection of animals in utero, and those animals are persistently infected, with little outward sign," he explained. "Those animals will, in turn, infect their progeny and so on. And the virus is shed for the life of the animal. The virus can cause die-off in pet rodents—especially adults—when introduced into a colony until the virus establishes itself."

If a veterinarian is presented with a pet rodent having signs of CNS illness, it may be a case of LCMV, Dr. Ksiazek said. Although there's little research in this area, dogs and cats are likely susceptible to LCMV, since the virus is known to infect a broad spectrum of mammals, including primates and pigs, he added.

The CDC and pet industry are now working toward ways of educating consumers to the risks of owning pet rodents and also developing guidelines to prevent additional infections at breeding facilities and pet retailers.

"The main thing we wanted to get out of these partnerships is to have recommendations and guidelines in place for breeding and distribution facilities to prevent wild rodent infestations and other biosecurity measures that could be put into place to prevent some of these outbreaks in the future," Tumpey said.

Information about LCMV, including fact sheets for pet owners and pregnant women, is posted on the CDC Web site.