Prions can be transmitted through feces

NEW YORK (Reuters Health) - Prions, the tiny agents that cause untreatable and fatal brain infections, such as "mad cow disease," can be detected in and transmitted through the feces of Syrian hamsters, which have been used to study prion disease, according to a report in The Journal of Infectious Diseases.

Scrapie in sheep and chronic wasting disease in deer and similar animals, two neurodegenerative diseases caused by prions, spread naturally from animal to animal in their flocks and herds, the authors explain, but how this occurs not known.

Dr. Stanley B. Prusiner and colleagues from the University of California, San Francisco, used Syrian hamsters orally infected with prions to look for the presence of prions in feces.

Cohabitation of uninfected hamsters with hamsters that were fed prion-infected brains in the previous 2 days resulted in a transmission rate of 100%, the authors report.

In a separate experiment, hamsters exposed to infected bedding developed prion disease with average incubation times ranging from 140 to 148 days.

Prion protein was detected in the feces of hamsters fed prion-infected brain, peaking 2 days after infection, gradually decreasing over the next 15 days, then increasing again and remaining detectable until the animals began to show symptoms 116 days after infection.

Feces from orally infected hamsters spread the infection, especially feces collected in the early days after infection, the report indicates.

Similarly, fecal material collected 42 days after inoculation of prions into the resulted in infection 362 days after being injected intracerebrally into mice.

"The data presented in the current study clearly demonstrate that laboratory prions are transmissible by cohabitation with orally infected Syrian hamsters and that the source of infection is prion-infected feces," the authors conclude.

"Considering the long-term survival of prions in soil, the data presented in the current study have raised imperative questions about the safe disposal of excrement from BSE-infected cattle and animals with chronic wasting disease and scrapie, especially during the early, asymptomatic stage of disease," the researchers add. "The methods of disposal of excrement from patients with variant CJD and sporadic CJD in a hospital or home setting also should be reexamined."

However, an editorial advises, "One must be careful before concluding that fecal contamination of the environment is the mode by which lateral transfer of prions occurs under natural conditions in deer and sheep herds."

Dr. P. J. Bosque and Dr. K. L. Tyler from University of Colorado Health Sciences Center, Denver, Colorado write: The oral prion concentration given to the hamsters was "enormous" and the high levels of prions found in the stool of these animals, at least early after infection, are probably the direct excretion of this high concentration of prions.

Given the differences in the way prions are distributed in the infected animal, the researchers continue, the current investigations don't prove that feces are responsible for the transmission from sheep and deer "but, rather, merely suggest that such transmission is plausible."

SOURCE: The Journal of Infectious Diseases, July 1, 2008.