Chronic wasting disease passes between animals through saliva and blood - most likely when they nuzzle or groom one another - according to results of a Colorado State University-led study published Thursday in the journal Science.
Previously, researchers thought the fatal disease spread through urine or feces on grasses that animals ate.
"The study suggests we were looking at the wrong end of the animal," said John Pape, a Colorado health department epidemiologist.
Deer, elk and moose pass the deadly disease through normal interaction, said Colorado State professor Edward Hoover, who led the 18-month study.
The CSU research indicates blood-sucking insects, such as mosquitoes and ticks, could carry the disease. It also confirms that people who come in contact with animals' blood must be careful, Pape said.
"That reinforces our recommendation to hunters that you should be using gloves when you are dressing your animals," he said. "You should also have your animal tested when you are harvesting animals in affected areas."
The study supports the theory that no tissue from an infected animal can be considered safe from the disease.
CWD was first found in captive deer in Colorado in the 1960s and in wild elk in the 1980s. It's now found in 14 states and two Canadian provinces.
In parts of Colorado, Wyoming and Nebraska, about 1 percent of wild elk are infected with CWD. It has infected about 5 percent of wild mule deer and between 10 percent and 12 percent of white-tailed deer, according to the National Wildlife Federation.
Last year, a male moose in north-central Colorado was diagnosed with the disease. CWD slowly destroys the brains of infected animals and is in the same family of prion diseases as mad cow in cattle or the fatal variant Creutzfeldt-Jakob disease in humans.
Research also has shown that people who eat venison could swallow the proteins that cause CWD. But there has been no evidence humans have contracted a prion disease from CWD exposure.
Colorado State researchers biopsied tonsils of animals exposed to CWD-infected urine, blood, feces and saliva. Findings showed animals could be infected as early as three months after being exposed to CWD-tainted blood and saliva.
"It helps explain how CWD can be transmitted so readily," Hoover said. "That gives us better steps to diagnose it."
CWD was first documented in a Utah deer in 2002
Chronic wasting disease first was discovered in Utah in 2002 in a buck shot near Vernal. The Utah Division of Wildlife Resources confirmed a second case in the state in early 2003, when a dead mule deer doe found in an agricultural field near Moab also tested positive. A third area of Utah was found to have CWD in late 2003 when officers clearing an agricultural area near Fountain Green of mule deer recorded a positive test result.
Eight of 2,494 samples tested in 2005 came back as CWD positive, according to DWR's Web site.
To date, 26 mule deer and no elk have tested positive for CWD in Utah. The highest prevalence rate (2 percent in the buck population) in Utah is found on state Wildlife Management Unit 13, in the La Sal Mountains, where 18 of the 26 cases have been found. Prevalence rates are less than 1 percent in the other two areas where the disease has been found.
DWR says Utah researchers are studying migration patterns and reproductive behavior of mule deer on the La Sal Mountains and how this behavior may be related to prevalence and spread of CWD.
The study, which began in early 2005, will take at least three years to complete, and the agency asks hunters not to shoot mule deer with radio collars.
- Brett Prettyman