OUTLINE #33
TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES
Submitted by: Jane Hatashita RN
(519)883-2006 ext 5286
DEFINITION
· Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases of humans and animals. They share a characteristic brain pathology which has the appearance of “spongy” holes in the brain; a long incubation period – sometimes decades long; and the probable causative agent proteinaceous infectious particles, known as prions.
· Animal TSEs include bovine spongiform encephalopathy, known as BSE or “mad cow disease”, scrapie in sheep and varying forms which occur in cats, mink, elk, deer, and exotic zoo animals.
· Creutzfeldt-Jacob disease, known as CJD, is the most common human TSE; other lesser known and rarer TSEs include Fatal Familial Insomnia and Kuru. A new distinct variant form of CJD – vCJD has been recognized since 1996.
· Since 1996 there has been evidence pointing towards a causal relationship between ongoing outbreaks in Europe of BSE in cattle and vCJD
.
EPIDEMIOLOGY CJD/vCJD
· In the early stages of the disease, CJD patients may have failing memory, behavior changes, impaired coordination and visual disturbances. With progression of the illness, mental deterioration becomes pronounced, and involuntary movements, blindness, weakness of extremities and coma may occur. CJD is usually diagnosed later in life and disease typically leads to death within one year following symptom onset. The mean age at death is 67 years.
· vCJD is also fatal, but is clinically distinct from CJD. With vCJD, onset of symptoms occurs at an earlier age with mean age at death: 29 years. Presentation is usually due to behavioral changes, loss of ability to coordinate muscular movements, and peripheral sensory disturbances such as loss of sensation, rather than changes in mental activity and thinking ability. Duration of illness from onset of symptoms to death is around 14 months. Currently, the diagnosis of vCJD can only be confirmed following pathological examination of the brain.
· To date, according to the UK Department of Health, there have been 122 deaths from probable or confirmed vCJD. The global total of definite or probable vCJD cases is 141, with cases also reported from France, Canada, Hong Kong, Ireland, Italy and the United States.
· CJD has been reported from countries all over the world. It is still very rare, afflicting only about 1 in 1 million people per year.
MODE OF TRANSMISSION
· The mode of transmission for most cases of CJD is unknown. Iatrogenic cases have been recognized: these involve corneal transplantation, human dura mater grafts, injections of growth or gonadotropic hormones prepared from human pituitary glands, and use of cortical electrodes previously used on known CJD patients.
· The concern that it may be possible to transmit CJD through blood and related blood products such as plasma is theoretical. Some animal studies suggest that contaminated blood and related products may transmit the disease, although this has never been shown in humans.
· Health Canada, when making recommendations for the use of FSME-IMMUN (tick-borne encephalitis) vaccine which is manufactured from plasma collected from European donors makes the following statement:
‘It is well known and recognized that, to date, the risk of transmission of vCJD by blood and blood products, is strictly theoretical, as no case of CJD or vCJD has been shown to be related to the administration of blood or blood products to a patient. The theoretical risk of vCJD to the Canadian population for vaccines manufactured with human albumin has been estimated by the Population and Public Health Branch of Health Canada to be 1 in 100-million per treatment per subject vaccinated’
· Transmission of vCJD is believed to be through consumption of beef from cattle with BSE.
RISK TO TRAVELERS
· The current risk of acquiring vCJD from eating beef and beef products produced from cattle in Europe cannot be precisely determined, and this risk in specific countries might not reflect the fact that cattle products from one country might be distributed and consumed in others.
· In the UK, the current risk appears to be extremely small, perhaps about 1 case per 10 billion servings.
PREVENTIVE MEASURES
· Public health control measures, such as BSE surveillance, the culling of sick animals, or banning specified risk materials, or a combination of these, have been instituted in Europe to prevent potentially BSE infected tissues from entering the human food chain.
· Travelers to Europe should be advised to consider either: (1) avoiding beef and beef products altogether or (2) selecting beef or beef products without attached spinal bone, such as solid pieces of muscle meat (versus brains or beef products such as burgers, sausages and pate), that might have a reduced opportunity for contamination with tissues that might harbor the BSE agent.
References:
The Control of Communicable Diseases Manual 17th Edition
CDC Health Information for International Travel, 2001-2002
National Institute of Neurological Disorders and Stroke, web page fact sheets
Health Canada drug safety update, July, 2002