New Colorado State University-led research shows for the first time that chronic wasting disease may spread through saliva and blood of infected deer, which poses new possibilities that the disease may spread by blood-sucking insects or social contact between animals. The study also reinforces that no tissue from an infected animal can be considered free of prions, the disease-causing agent.
The study suggest that chronic wasting disease, called CWD, may spread by social contact such as grooming among deer in nature and environmental contact. The study, led by Edward A. Hoover, a Colorado State University Distinguished Professor in the Department of Microbiology, Immunology and Pathology, also was spearheaded by Colorado State researcher Candace Mathiason.
The research, released in the Oct. 6 edition of the journal Science, tested the blood, saliva, feces and urine of deer infected with CWD to determine ways the disease may be transmitted from animal to animal, which has remained a mystery to scientists.
"This study shows for the first time that CWD can be passed to deer that come into contact with the blood and saliva of infected deer," said Hoover.
"Although no instance of CWD transmission to humans has been detected, these results prompt caution regarding exposure to body fluids in prion infections such as CWD. This study also causes us to reconsider a potential role for blood-feeding insects such as mosquitoes and ticks in the transmission of CWD or other prion infections."
While this 18-month study focused on deer, CWD also affects elk and moose.
"Interactions among deer and elk, especially in high density situations, intensifies cross-contact among animals. This contact includes salivary exchange, which provides potential for CWD transmission," Hoover said. "Such things as grooming, licking and nuzzling are important in the social interactions of deer."
CWD was first discovered in deer in northeastern Colorado and southeastern Wyoming by Colorado State scientists in the 1960s. Related diseases belong to the family of diseases called transmissible spongiform encephalopathies and include scrapie, which affects sheep, and bovine spongiform encephalopathy. Scrapie has existed in sheep populations for centuries.
Many mysteries continue to surround how TSEs spread from animal to animal or animal to human. CWD now has been detected in deer in 14 states and two Canadian provinces. CWD is contagious to a higher degree among deer, elk and moose than other TSEs.
Researchers biopsied tonsils to detect infectious CWD prions, showing that CWD infection could be detected as early as three months after exposure to saliva or blood from an infected deer – a surprising and important finding, Hoover said.
A seven-year, $8 million grant from the National Institutes of Health’s National Institute of Allergy and Infectious Disease supported the research.
The study represented a collaboration between scientists from several agencies and universities. Additional researchers within the Colorado State University College of Veterinary Medicine and Biomedical Sciences were Gary Mason, Sheila Hays, Jeanette Hayes-Klug and Davis Seelig, and Terry Spraker, a scientist at the Colorado State Veterinary Diagnostic Laboratory. Other collaborators were David Osborn, Karl Miller and Robert Warren from the University of Georgia; Sallies Dahmes of WASCO Inc.; Michael Miller and Lisa Wolfe at the Colorado Division of Wildlife; Jennifer Powers and Margaret Wild of the U. S. National Park Service; Glenn Telling at the University of Kentucky; and Christina Sigurdson at the University of Zurich.