4.5 months for CJD). As of April 2002, 117 cases of vCJD had been reported in the United Kingdom, 6 in France, and 1 each in the Republic of Ireland and Italy (CDC, 2002w).
The nature of the causal agent for vCJD, and TSEs in general, is still a matter of debate. According to a leading theory, the disease agent is composed largely, if not entirely, of a self-replicating protein known as a prion, so that the TSEs are now sometimes referred to as prion diseases. Prions are transmissible protein particles that are devoid of nucleic acid and consist only of modified protein. According to the prion theory, the brain and other organs of mammals (at least those examined thus far) contain a normal version (PrPC) of the pathological protein form (PrPsc) that makes up a prion. When an animal or human becomes infected with PrP, the invading protein somehow converts normal protein molecules into toxic ones by causing the proteins to change shape. Despite strong evidence in support of the prion theory (Prusiner, 1995), a few scientists still believe that the ability of the TSE agent to form multiple strains is better explained by a DNA-containing, virus-like agent. To date, no such agent has been found.
Many scientists are keeping a watchful eye on chronic wasting disease (CWD), a fatal neurological illness of farmed and wild deer and elk (Animal and Plant Health Inspection Service, 2002). It was first identified in 1967, although researchers did not determine it to be a TSE until 1978. The first case was diagnosed in Colorado in 1981. By 2001, CWD had been detected in deer and elk in Wyoming, Nebraska, South Dakota, Canada, Wisconsin, New Mexico, Oklahoma, Montana, Kansas, and Illinois (Animal and Plant Health Inspection Service, 2002). Although the most obvious and consistent clinical sign of CWD is weight loss over time, many infected animals also show behavioral changes, including decreased interaction with other animals, listlessness, lowering of the head, blank facial expression, and repetitive walking in set patterns. No evidence linking CWD to any disease in humans or domestic animals had been detected as of 2002, although studies seeking such evidence have been limited.
volcanic nature of the soil in the area which made digging latrines almost impossible (GOMA Epidemiology Group, 1995). Bathing in the river, long distances to a water source, and consumption of dried fish were significantly associated with the risk of cholera during the 1997 epidemic in southern Tanzania (Acosta et al., 2001).
Cases of cholera are rare in industrialized nations, where modern sewage and water treatment systems exist. In the United States, cholera was prevalent in the 1800s but has now been virtually eliminated. Between 1965 and 1991, just 136 cases were reported to CDC. From 1992 through 1994, the number jumped to 160; half of these were among airline passengers traveling from Latin America (75) and cruise ship passengers from Southeast Asia (5) (Mahon et al., 1996). Although all regions of the world reported a reduction in the total number of cholera cases between 1999 and 2000, in 2000 WHO received reports of 137,071 cases from 56 countries,