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In February 2004, British investigators published a study in The Lancet titled "Possible transmission of variant Creutzfeldt-Jakob disease by blood transfusion."[76] This report came on the heels of the first documented case of
TSEs have been transmitted from animal to animal, animal to human, and human to human. Until the mid-1990s, transmission among humans was thought to be dependent on the transmission of neurologic tissue, either by transplantation or by contaminated surgical instruments. In 1995, mad cow disease was linked to a new variant of Creutzfeldt-Jakob disease (CJD) in England and Europe.[80] The new variant (vCJD) is thought to be the result of transmission of bovine spongiform encephalopathy from cattle to humans by the ingestion of infected beef products. Unlike CJD, vCJD is found in lymphoreticular tissue and can theoretically be transmitted by the transfusion of blood or blood products. This section focuses on the possibility of blood-borne transmission of this devastating disease.
Pruisner coined the term prion in 1982 to describe the proteinaceous infectious agent responsible for the transmission of scrapie in sheep.[81] The equivalent disease in humans, CJD, was first described in the 1920s as a rapidly progressive dementia followed by ataxia and myoclonus.[82] Subsequent epidemiologic studies have shown that CJD can be sporadic, inherited, or acquired. Kuru is the most exotic example of the acquired form because of its transmission by ritualistic cannibalism among the natives of New Guinea.[82] The first iatrogenic transmission of CJD was documented in 1974. It was the first of three cases of CJD to result from corneal transplantation. Since then, over 300 cases of iatrogenic transmission have been documented in the literature. Most are the result of cadaveric pituitary-derived growth hormone used to treat children of short stature (162 cases). However, transmission by dura mater grafts (136 cases), human gonadotropin (5), stereotactic electrodes (2), and neurosurgical instruments (4) has been reported.[83]
Although transmission of CJD is extremely rare, a number of factors combine to make the disease particularly threatening to health care personnel. TSEs result in rapidly progressive and devastating neurologic deterioration and are uniformly fatal. The time from infection to clinical symptoms is a matter of years, during which time the disease may be unknowingly transmitted to others. To date, there is no reliable method to screen blood from an infected patient. Moreover, prions are resistant to the conventional means used to decontaminate medical devices.
A number of studies have demonstrated hematologic transmission of TSEs from animal to animal, and several studies have demonstrated transmission of CJD from humans to animals in the laboratory.[78] Whereas CJD is confined to neurologic tissue, the new variant is found in lymphatic tissue, including the tonsils, spleen, thymus, lymph nodes, and appendix.[77] [84] [85] [86] vCJD resides in lymphatic tissue early in the incubation phase of the disease when the patient is asymtomatic.[77] [87] [88]
Despite reports of possible transmission of vCJD by blood products, to date there has been no definitive proof of transfusion-related transmission in humans. Even the most recent epidemiologic data are not conclusive.[76] In fact, reassuring evidence suggests that the disease is not transmitted by blood. Such evidence includes four epidemiologic case-control studies in the United States, Japan, and the United Kingdom in which it was found that the percentage of patients with CJD who had received blood transfusions was no higher than the percentage in matched controls.[78] Another study conducted by the CDC and the Red Cross monitored 178 recipeints of transfusions from patients in whom CJD later developed; in no recipient did clinical disease develop up to 24 years after transfusion (although many died of other causes early on).[89] Additionally, no increase in the incidence of CJD has been reported in patients whose disease requires numerous transfusions of whole blood or blood products.[78] [89]
In 2003, tonsillar biopsy was identified as a way to reliably diagnose vCJD antemortem.[84] The presence of vCJD in tonsillar tissue potentially puts anesthesia caregivers and ear, nose, and throat surgeons at increased risk of occupational exposure when performing routine tonsillectomies. Because of the prolonged incubation period during which infected patients remain asymptomatic, all adenotonsillectomies in the United Kingdom are performed with single-use disposable surgical and anesthesia equipment.[90]
Routine decontamination protocols do not inactivate prions. The proteins are resistant to proteases, and autoclaving alone is not effective. Attempts to clean instruments before autoclaving can result in further fixation of the protein to the instruments. Once the protein is allowed to dry, it becomes even more resistant to decontamination methods. As a result, the World Health Organization has developed guidelines for infection control when caring for patients with suspected CJD:
By spring 2003, 135 cases of vCJD had been verified in the United Kingdom and 1 in the United States.[83] Because of the lack of an effective screen to identify vCJD in asymptomatic persons, the blood donor policy in the United States currently excludes donations from anyone who lived in or visited the United Kingdom for a cumulative period of more than 6 months between 1980 and 1996.[92] The United Kingdom currently imports all plasma for transfusion. All whole blood from U.K. donors is filtered to eliminate white blood cells.[93]
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