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, state health department epidemiologist.
Deer, elk and moose pass the deadly disease through normal interaction, said CSU professor Edward A. 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.
Surveys show the disease is fairly well-established in Colorado, particularly in the north-central part.
CWD was first found in captive deer in state 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.
A separate study released last month looked at Colorado deaths from Creutzfeldt-Jakob from 1979 to 2001 and whether more people died in counties with a high prevalence of CWD. It showed no connection.
In the CSU study, 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.”
Proving that saliva spreads CWD is important so that scientists next can determine exactly how that happens in the wild, said Richard T. Johnson, a Johns Hopkins University neurology professor who headed a major report on prion science.
“You can move deer out of a pasture, put other deer into the pasture, and they’ll come down with the disease. It’s not even casual contact; it’s contact with the pasture,” he said.
Is CWD spread through shared salt licks? Or by drooling onto grass or into streams? Studying environmental contamination by prions is among Hoover’s next steps.
The Associated Press contributed to this report.
Staff writer Jeremy P. Meyer can be reached at 303-954-1367 or jpmeyer@denverpost.com.
