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Emerging Infections: Microbial Threats to Health in the United States
CMV, as well as HSV-1 and HSV-2 in human atherosclerotic disease (Benditt et al., 1983; Yamashiroya et al., 1988; Hendrix et al., 1989, 1990).
Recently, a bacterium, Chlamydia pneumoniae, was reported to play a potential role in the pathogenesis of atherosclerotic disease. The investigators examined the consequences of human infection with C. pneumoniae and found evidence, in the form of persistently elevated levels of anti-C. pneumoniae antibodies and immune complexes containing chlamydial lipopolysaccharide, that chronic infection with this bacterium was associated with increased risk for coronary heart disease. This risk was shown to be independent of those factors—age, smoking, total cholesterol to high-density-lipoprotein-cholesterol ratios, and hypertension—most often associated with atherosclerosis (Saikku et al., 1992). Because C. pneumoniae infection is fairly common and can be treated with antibiotics, a proven association of this organism with atherosclerosis and subsequent myocardial infarction could have a significant public health impact.
Papillomaviruses were described and associated with disease in the early to mid-1900s. Research on these viruses, however, suffered from the inability to grow them in cells in the laboratory. It was not until the 1980s that techniques to identify and characterize human papillomavirus (HPV) became readily available (deVilliers, 1989). In the past 10 years, more than 67 HPV types have been defined; the molecular biology of the virus has been developed in exquisite detail; and knowledge concerning molecular mechanisms of infection and disease has emerged (Reeves et al., 1989).
Epidemiological studies have shown that HPV infection (with HPV types 16 and 18) is the major risk factor for cervical cancer (Reeves et al., 1989), an important public health problem in the United States and the developing world. The American Cancer Society estimated that 13,000 new cases would occur in the United States in 1991, resulting in about 4,500 deaths (American Cancer Society, 1991). Most of these cases and deaths could have been prevented by appropriate screening and control programs. Cervical cancer is uniquely amenable to secondary prevention by screening and early treatment since it evolves through surgically curable premalignant stages to invasive disease over a 10- to 20-year period (Tabbara et al., 1992).
Other factors besides HPV infection, however, play a role in the development of cervical cancer. For example, a woman's risk of cervical cancer is directly related to the number of sexual partners she has had (the greater the number of partners the greater her risk) and inversely related to age at first intercourse (the younger her age, the greater the risk). It has only recently been recognized that male sexual behavior also influences cervical cancer risk. Spouses of women with cervical cancer are more likely to