How is cjd spread

Consequently, a negative finding of risk attributable to blood in these studies may simply reflect an absence of exposure to the disease. Study design will have to account not only for a rare disease, but possibly for a rare exposure as well.

In addition, when hospitalized persons are used as controls, the design must consider Berkson's bias, a selection bias that occurs when the selection method for controls affects the rate of exposure to the agent studied The study design must then show that hospitalized controls do not have a different rate of potential exposure to blood transfusion from the general population.

The use of population controls may be more appropriate for studying blood exposure. Another weakness in the existing studies was the use of a reporter, most often a relative, to collect information about exposure to blood or blood products. Oral history of blood exposure tends to underestimate the rate of exposure to blood. Kennealy, Pers. King, Pers. The hemophilia centers in the United States have been asked to report deaths of persons with neurologic symptoms for neurologic confirmation of cause of death; no CJD cases have been reported in persons with hemophilia B.

Evatt and L. Schonberger, Pers. Wong-Reiger, Pers. In Canada, a combined active surveillance system and case control study will begin in to identify the risk for CJD as a result of transfusion with blood from a person with CJD. Many of the methodologic problems in other studies have been addressed in the design of this study.

The investigation of a patient with CJD who donated 35 units of blood in 20 years identified 27 persons who definitely received his blood and eight who probably received blood; for 20 units, the recipients could not be identified None of the recipients had exhibited neurologic disease, although some were observed only briefly; only eight were observed for longer than 5 years.

By linking the names of persons who received blood from CJD patients with the national death records, the cause of death for each person will be determined. Of the recipients identified, 80 have died; for 65, the cause of death is known but no cases of CJD have been found M. Sullivan, Pers. Cohort studies are unlikely to accumulate enough cases of exposure to allow a reasonably precise estimate of risk.

However, if pooled product confers uniform risk to each recipient, data from a large number of exposed recipients can be collected. The cohort studies under way may be able to identify higher than expected rates of disease, thus indicating transmission through blood transfusion without quantifying the rate of transmission.

Many health professionals are concerned that CJD may be transmissible through blood. As noted by Brown, "iatrogenic disease from this source would dwarf in importance all other sources by virtue of the sheer number of people who theoretically have been or could be at risk" Animal studies indicate that the infective agent of CJD is present in blood but in low titer, and sufficient evidence of animal transmission suggests that the disease has the potential to be transmitted through blood However, human epidemiologic evidence only indicates that if blood transmission occurs, it is likely rare.

Some researchers suspect that the agent of CJD is ubiquitous, therefore, we are commonly exposed to it; perhaps, another, as yet unidentified factor, "turns on" the disease. If so, is there any part of the human population that is not exposed? Most people are exposed to some components of blood products through vaccines. Some people may be protected by strain variation through exposure to nonvirulent forms, so only subgroups are susceptible to a virulent form Polymorphism at codon may restrict susceptibility to a small portion of the population, or most transfusions may not contain a dose large enough to cause infection.

Can experimental studies answer these questions? Sufficiently large numbers of study animals could overcome problems such as the species barrier and low transmission rates due to a low dose or peripheral route of inoculation. The studies would require strict adherence to proper laboratory technique and replication in at least one other laboratory. Unanswered questions include the following: Can the transmissible spongiform encephalopathies of animals be transmitted, by transfusion, within the species when spiked blood is used?

Within species from "naturally infected" blood? From humans to animals with spiked blood? From humans to animals with "naturally infected" blood? Does transmission by blood become more efficient after passage?

Can human blood cells carry the agent? What are the routes for infection of the brain if infection is peripheral? Can epidemiologic methods detect blood transmission of CJD if it is rare? Epidemiologic tools such as outbreak investigations, case-control studies, and cohort studies are limited in their ability to detect rare events.

In addition, during the long incubation period, patients often move away from the location where they received the transfusion; forget their exposure; and essentially lose their membership in a recognizable cohort. The absence of a test for exposure, such as an antibody test or gene sequencing of an agent as used in investigating HIV-related out-breaks, makes the investigation of iatrogenic CJD extremely difficult, hence the importance of vigilance, in the form of case reports from alert and informed clinicians, followed by critical field investigation.

Surveillance systems provide the core resources for identifying and investigating unique or unexplained events. Followup case-control studies allow the observation and recording of the actual chain of exposure to blood. Her research interests include the CJD surveillance system in Canada, a collaborative international study on the incidence and risk factors for CJD, and policy and infection control guidelines for CJD and other prion diseases.

The authors thank Drs. Table of Contents — Volume 3, Number 2—June Please use the form below to submit correspondence to the authors or contact them at the following address:. Maura N. Highlight and copy the desired format. Data is collected weekly and does not include downloads and attachments. View data is from. The Altmetric Attention Score for a research output provides an indicator of the amount of attention that it has received. The score is derived from an automated algorithm, and represents a weighted count of the amount of attention Altmetric picked up for a research output.

Section Navigation. Facebook Twitter LinkedIn Syndicate. On This Page. Table 1 Table 2. Article Metrics. Abstract Creutzfeldt-Jakob disease CJD has been considered infectious since the mids, but its transmissibility through the transfusion of blood or blood products is controversial.

Iatrogenic CJD. Animal Experimentation Data Human CJD has been reported to be transmitted to mice by injecting blood from human patients directly into mouse brain 39 , Evidence from Studies of Humans.

Surveillance Population surveys or surveillance systems of the worldwide epidemiology of CJD indicate that CJD occurs in the population at a rate of 0. Cohort Studies The investigation of a patient with CJD who donated 35 units of blood in 20 years identified 27 persons who definitely received his blood and eight who probably received blood; for 20 units, the recipients could not be identified Creutzfeldt-Jakob disease: patterns of worldwide occurrence and the significance of familial and sporadic clustering.

Ann Neurol. The epidemiology of Creutzfeldt-Jakob disease: conclusion of a 15 year investigation in France and review of the world literature. PubMed Google Scholar. Will RG. Incidence of Creutzfeldt-Jakob disease in the European Community. In: Gibbs CJ Jr, editor. New York: Springer-Verlag Geneva: WHO, Creutzfeldt-Jakob disease in Australia: first annual report. Creutzfeldt-Jakob disease in Canada.

Kovanen J , Haltia M. Descriptive epidemiology of Creutzfeldt-Jakob disease in Finland. Acta Neurol Scand. DOI Google Scholar. Epidemiology of Creutzfeldt-Jakob disease in the United States, analysis of national mortality data. Human spongiform encephalopathy: clinical presentation and diagnostic tests. Methods in molecular medicine: prion diseases. Diagnostic criteria for sporadic Creutzfeldt-Jakob disease. Arch Neurol.

Ironside JW. Neuropathological diagnosis of human prion disease. Molecular analysis of prion strain variation and the aetiology of "new variant" CJD. The brain protein in cerebrospinal fluid as a marker for transmissible spongiform encephalopathies. N Engl J Med. Manuelidis L. The dimensions of Creutzfeldt-Jakob disease.

Ozel M , Diringer H. Small virus-like structure in fractions from scrapie hamster brain. Genetic pre-disposition to iatrogenic Creutzfeldt-Jakob disease. Brown P , Gajdusek DC. In: Chesebro BW, editor. Current topics in microbiology and immunology, vol New York: Springer-Verlag, Experimental transmission of a kuru-like syndrome to chimpanzees.

The normal prion protein is found throughout the body but is most abundant in the nervous system. Its overall role is not fully understood. It is believed that the harmless to infectious protein conformational change is common to the all major forms of human prion disease, including CJD. In the acquired form of the disease, the PrP Sc comes from the outside the body, for example, through contaminated meat as is seen in vCJD.

It then clings to and changes the conformation of the normal prion protein of the host and progressively spreads in domino-like fashion toward the brain where it causes lesions. As the mutated PrP C replicates itself, it spontaneously changes shape into the infectious form. Prions themselves do not contain genetic information and do not require genes to reproduce themselves. Several different mutations in the prion gene have been identified. The particular mutation found in each family affects how frequently the disease appears and what symptoms are most noticeable.

However, not all people with mutations in the prion protein gene develop CJD. In the sporadic form, the infectious prions are believed to be made by an error of the cell machinery that makes proteins and controls their quality.

These errors are more likely to occur with aging, which explains the general advanced age at onset of CJD and other prion diseases. Once they are formed, abnormal prion proteins aggregate, or clump together. Investigators think these protein aggregates lead to the nerve cell loss and other brain damage seen in CJD.

However, they do not know exactly how this damage occurs. CJD cannot be transmitted through the air or through touching or most other forms of casual contact.

Spouses and other household members of people with sporadic CJD have no higher risk of contracting the disease than the general population. However, exposure to brain tissue and spinal cord fluid from infected persons should be avoided to prevent transmission of the disease through these materials. In some cases, CJD has spread to other people from grafts of dura mater a tissue that covers the brain , transplanted corneas, implantation of inadequately sterilized electrodes in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers.

Doctors call these cases that are linked to medical procedures iatrogenic cases. Since , all human growth hormone used in the United States has been synthesized by recombinant DNA procedures, which eliminates the risk of transmitting CJD by this route. Many people are concerned that it may be possible to transmit CJD through blood and related blood products such as plasma. Some animal studies suggest that contaminated blood and related products may transmit the disease, although this has never been shown in humans.

Recent studies suggest that while there may be prions in the blood of individuals with vCJD, this is not the case in individuals with sporadic CJD. Scientists do not know how many abnormal prions a person must receive before he or she develops CJD, so they do not know whether these fluids are potentially infectious or not. They do know that, even though millions of people receive blood transfusions each year, there are no reported cases of someone contracting sporadic CJD from a transfusion.

Even among people with hemophilia a rare bleeding disorder in which the blood does not clot normally , who sometimes receive blood plasma concentrated from thousands of donors, there are no reported cases of CJD. While there is no evidence that blood from people with sporadic CJD is infectious, studies have found that infectious prions from BSE and vCJD accumulate in the lymph nodes which produce white blood cells , the spleen, and the tonsils.

At present, four cases of vCJD infection have been identified following transfusion of red blood cells from asymptomatic donors who subsequently died from vCJD. Recently, one case of likely transmission of vCJD infection by concentrates of blood-clotting protein has been reported in an elderly individual with hemophilia in the United Kingdom.

The possibility that blood from people with vCJD may be infectious has led to a policy preventing individuals in the United States from donating blood if they have resided for more than three months in a country or countries where BSE is common. Both brain biopsy and autopsy pose a small, but definite, risk that the surgeon or others who handle the brain tissue may become accidentally infected by self-inoculation.

Special surgical and disinfection procedures can markedly reduce this risk. A small number of people have also developed the disease from eating contaminated beef. Variant CJD is linked primarily to eating beef infected with mad cow disease bovine spongiform encephalopathy, or BSE. In an autosomal dominant disorder, the mutated gene is a dominant gene located on one of the nonsex chromosomes autosomes.

You need only one mutated gene to be affected by this type of disorder. Most cases of Creutzfeldt-Jakob disease occur for unknown reasons, and no risk factors can be identified. However, a few factors seem to be associated with different kinds of CJD :. Exposure to contaminated tissue. People who've received infected manufactured human growth hormone, or who've had transplants of the infected tissues that cover the brain dura mater , may be at risk of iatrogenic CJD.

The risk of getting vCJD from eating contaminated beef is very low. In general, if countries are effectively implementing public health measures, the risk is virtually nonexistent. Chronic wasting disease CWD is a prion disease that affects deer, elk, reindeer and moose. It has been found in some areas of North America.

To date, no documented cases of CWD have caused disease in humans. Creutzfeldt-Jakob disease greatly affects the brain and body. CJD usually progresses quickly. Over time, people with CJD withdraw from friends and family and eventually lose the ability to recognize or relate to them. They also lose the ability to care for themselves and many eventually slip into a coma. The disease is always fatal. If you have a family history of neurological disease, you may benefit from talking with a genetics counselor.

He or she can help you sort through the risks associated with your situation. Hospitals and other medical institutions follow clear policies to prevent iatrogenic CJD. These measures have included:. This includes people who:. The U. Only four cases have been reported in the U. According to the U. Centers for Disease Control and Prevention CDC , strong evidence suggests that these cases were acquired in other countries outside of the U.

In the United Kingdom, where the majority of vCJD cases have occurred, fewer than cases have been reported. CJD incidence peaked in the U. A very small number of other vCJD cases also have been reported in other countries worldwide.