New TB Guidelines Call for TB Screening and Treatment for All HIV-Infected Individuals

Copies of the recommendations can be obtained from the NCHSTP Office of Communications by calling (404)639-8063, or you can download the document from the Division of TB Elimination Web site at http://www.cdc.gov/nchstp/tb.

Transmissible Spongiform Encephalopathies: What Do We Know?

The Basics: Transmissible spongiform encephalopathies (TSE) are degenerative diseases that destroy the brain. While the exact mode of transmission of these diseases is unknown, research indicates that these diseases may be caused by a protein-like infective material (prion). TSE tend to have very long incubation periods and have been described in many types of animals, including man. TSE are incurable and inevitably fatal. Although some of these conditions have been clinically recognized for years, we still have much to learn about these diseases.

What is "mad cow disease"? Bovine Spongiform Encephalopathy (BSE) is popularly known as "mad cow disease". This is a TSE that affects cattle. Affected cattle behave abnormally, have difficulty moving, lose weight in spite of eating well, and die within six months after their onset of symptoms. BSE was first recognized in Great Britain in 1986, and it is believed that the disease was transmitted to cattle by feeding them meal made from meat and bone of sheep infected with scrapie (see Scrapie on next page). Great Britain has prohibited feeding practices that are believed to be associated with the transmission of BSE and their number of new cases continues to decline. Unfortunately, cattle in other countries have been diagnosed with BSE and control efforts are ongoing.

Do we have BSE in the United States? According to the United States Department of Agriculture (USDA), BSE has not been detected in the U.S., despite active surveillance that include three components. First, cattle that were imported into the U.S. from Great Britain before those imports were banned in 1989 were traced. As of September 1997, none of these showed any signs of BSE. Second, the USDA is conducting surveillance within the U.S. to look for BSE. USDA and State veterinarians routinely conduct field investigations of cattle with neurological disease. Third, USDA officials identify cattle that are showing signs of neurological disease in slaughterhouses. The brains from these cattle, as well as the brains of rabies-negative cattle from veterinary diagnostic labs, are examined for signs of BSE. No evidence of BSE in U.S. cattle has been seen.

What is Creutzfeldt-Jakob Disease (CJD)? CJD is a TSE that affects humans. No cause for most cases of CJD (80-85%) is ever identified. There is an inherited form of CJD associated with a specific chromosome pattern that accounts for 5-10% of cases. Fewer than 1% of CJD cases are associated with medical procedures. Such procedures include neurosurgical procedures that were conducted using contaminated instruments, and transfer of contaminated central nervous system tissue (including optic nerves from corneal transplants) and extracts (i.e., growth hormone). CJD has been recognized since the 1920’s, and typically affects individuals between the ages of 60 and 75. People diagnosed with CJD usually die within a year of their onset of symptoms.

What is the New Variant of CJD? A New Variant of CJD (nv-CJD) has been described. In 1995, five young people (<29 years old) died in the U.K. from CJD. However, these cases of CJD were different from the "classical" CJD that had been previously recognized. The patients were younger, they experienced an unusual clinical course with a longer duration of illness, and at autopsy they were found to have brain lesions that were different from those in most CJD patients. As of September 1998, 26 cases of nv-CJD have been identified in persons from the U.K. and one from France.

Do we know that nv-CJD is related to BSE? While a definitive answer is not available yet, there is strong epidemiologic and laboratory evidence to support a link between nv-CJD and BSE. First, cases of nv-CJD have appeared only in geographical areas where there was also BSE. Second, the time interval from when people would have first been exposed to BSE (1984-1986) to the time when cases began to appear (1994-1996) is consistent with known incubation periods for CJD. Finally, laboratory studies have shown that inoculation of BSE-infected brain tissue into mice or monkeys can result in these animals developing illnesses similar to nv-CJD. It is likely that people were exposed to BSE by eating infected cattle.

What is being done about CJD in the U.S.? The Centers for Disease Control and Prevention (CDC) monitors the occurrence of CJD in the U.S. by analyzing death certificate information. The rate of CJD in the U.S. has remained relatively stable from 1979 through 1995, with a low of 0.8 cases per million in 1980 and a high of 1.1 cases per million in 1987. CJD deaths in persons who are less than 30 years of age remain extremely rare in the U.S, with fewer than five cases per billion per year. (In contrast, in the U.K., at least 13 of the 23 patients who died with nv-CJD were younger than 30.)

Do we have nv-CJD in the U.S.? The CDC is looking for nv-CJD through active surveillance in five areas: Minnesota, Oregon, Connecticut, the San Francisco Bay area of California, and metropolitan Atlanta, Georgia. The CDC also has an ongoing national project where medical records of any CJD victims younger than 55 years of age are thoroughly reviewed. Such a review was recently conducted on a 29-year-old Utah resident who had been diagnosed with CJD. While there had been concern that this patient might have had nv-CJD (because of the young age or onset), molecular and biochemical testing have confirmed that the patient has "classical" CJD, and not nv-CJD. The CDCs surveillance efforts have not found any evidence that nv-CJD is occurring in the U.S..

Are there other TSE’s in animals or humans? Scrapie is a TSE that affects sheep, and rarely goats. This condition has been recognized for over 200 years. Affected sheep become nervous and tremble, or they develop an intense itch over their entire body. They will rub or bite their wool off in an attempt to relieve the itch, are unable to feed or rest properly, and will die within six months of onset of their illness. The disease may be spread from mothers to their offspring, or from one sheep to another via respiratory secretions. As mentioned previously, some experts believe that the feeding of meal made from meat and bone of scrapie-infected sheep to cattle may have resulted in the development of BSE.

Another TSE of concern in the U.S. is Chronic Wasting Disease of Deer and Elk (CWD). This was first recognized in 1967 in deer in Colorado. It has been found in elk and other wild and domestic ruminants, primarily in Colorado and Wyoming, and in other parts of the U.S., Canada and Great Britain. The symptoms are similar to those of BSE, and affected animals generally die within six months of their onset of illness.

There are other TSE that occur in animals, such as Feline Spongiform Encephalopathy and Transmissible Mink Encephalopathy.

TSE that occur in humans also include Kuru,Gerstmann-Straussler Sheinkers Syndrome, and Fatal Familial Insomnia. These are extremely rare diseases.

Can TSE be spread from one kind of animal to another? Much remains unknown about TSE, but experts believe that this is possible. The scenario that may have occurred with scrapie, BSE and nv-CJD would support this possibility.

What can be done to prevent the spread of TSE’s? Our best understanding of these diseases is that they are difficult to transmit from one person to another. While everything is not known about the transmission of these diseases, there are some common sense things to do to avoid possible exposure.

Recommendations on how to prevent TSE will undoubtedly change as we gain a better understanding of these diseases.

The Epidemiology Newsletter is published monthly by the Utah Department of Health, Division of Epidemiology and Laboratory Services, Bureau of Epidemiology, to disseminate epidemiologic information to the health care professional and the general public.