Foreign Sources of Infection

1. Foreign Sources of Infection To−Vi Nguyen

2. Foreign Infection • Preventable environmental source of infection • Remove infectious material, epidemic outbreaks disappear • Ex. BSE & Kuru

4. Infectious Forms of Prion Diseases in Humans • Kuru • Iatrogenic CJD • ddVariant CJD

5. Kuru • Fore tribe from Papua New Guinea transmitted kuru through ritualistic cannibalism • Ate dead relatives • Only exposed to infectious agent if they consumed or came in contact with brain tissue or spinal fluid

6. Iatrogenic • Prion tainted human growth hormone and gonadotropin • Dura mater grafts • Transplants of corneas obtained from people who died of CJD • Neurosurgical procedures in which ineffectively sterilized depth electrodes or instruments were used

7. vCJD • Results from prions being transmitted from cattle with BSE to humans through consumption of contaminated beef products • All vCJD individuals were identified to express methioninemethioninehomozygously at codon 129 • Except a single case of vCJD in a patient who was heterozygous at codon 129 • Raised possibility of a second wave of BSE related deaths

8. Spread of BSE • Late 1970s, hydrocarbon solvent extraction method used in rendering offal was abandoned • Resulted in meat and bone meal with a much higher fat content • Fed to cattle, sheep, pigs, and chickens • Allowed scrapie prions from sheep or low levels of bovine prions generated sporadically to survive the rendering process • Resulted in widespread infection of cattle

9. CWD • White tailed deer and elk have developed CWD • Only prion disease known in free ranging animals

16. Genetics vs. Environment • 1930 High incidence of familial CJD in some families was known • 60 more years would pass before significance was appreciated • Once shown to be an infectious disease, little attention was paid to the familial form of the disease • How do you think the course of scientific investigation might have proceeded had transmission studies not been performed until after the molecular genetic lesion was discovered?

17. If we discovered the molecular genetic lesion before the transmission studies were performed, the prion concept may have been more readily accepted • Prion concept explains how a single disease can have a genetic or infectious etiology • Because the transmissibility was discovered first, there was more skepticism as to whether prions were a whole new infectious agent