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20: Acellular Pathogens and Diseases

  • Page ID
    23722
    • 20.1: Viral Infections of the Skin and Eyes
      Papillomas (warts) are caused by human papillomaviruses. Herpes simplex virus (especially HSV-1) mainly causes oral herpes, but lesions can appear on other areas of the skin and mucous membranes. Roseola and fifth disease are common viral illnesses that cause skin rashes; roseola is caused by HHV-6 and HHV-7 while fifth disease is caused by parvovirus 19. Viral conjunctivitis is often caused by adenoviruses and may be associated with the common cold. Herpes keratitis is caused by herpesviruses.
    • 20.2: Viral Infections of the Respiratory Tract
      Viruses cause respiratory tract infections more frequently than bacteria, and most viral infections lead to mild symptoms. The common cold can be caused by more than 200 viruses, typically rhinoviruses, coronaviruses, and adenoviruses, transmitted by direct contact, aerosols, or environmental surfaces. Due to its ability to rapidly mutate through antigenic drift and antigenic shift, influenza remains an important threat to human health. Two new influenza vaccines are developed annually.
    • 20.3: Viral Infections of the Reproductive System
      Genital herpes is usually caused by HSV-2 (although HSV-1 can also be responsible) and may cause the development of infectious, potentially recurrent vesicles Neonatal herpes can occur in babies born to infected mothers and can cause symptoms that range from relatively mild (more common) to severe. Human papillomaviruses are the most common sexually transmitted viruses and include strains that cause genital warts as well as strains that cause cervical cancer.
    • 20.4: Viral Infections of the Gastrointestinal Tract
      Helminths are widespread intestinal parasites. These parasites can be divided into three common groups: round-bodied worms also described as nematodes, flat-bodied worms that are segmented (also described as cestodes), and flat-bodied worms that are non-segmented (also described as trematodes). The nematodes include roundworms, pinworms, hookworms, and whipworms. Many of these parasites are so well adapted to the human host that there is little obvious disease.
    • 20.5: Viral Infections of the Circulatory and Lymphatic Systems
      Viral pathogens of the circulatory system vary tremendously both in their virulence and distribution worldwide. Some of these pathogens are practically global in their distribution. Fortunately, the most ubiquitous viruses tend to produce the mildest forms of disease. In the majority of cases, those infected remain asymptomatic. On the other hand, other viruses are associated with life-threatening diseases that have impacted human history.
    • 20.6: Acellular Pathogenic Diseases of the Nervous System
      A number of different viruses and subviral particles can cause diseases that affect the nervous system. Viral diseases tend to be more common than bacterial infections of the nervous system today. Fortunately, viral infections are generally milder than their bacterial counterparts and often spontaneously resolve. Some of the more important acellular pathogens of the nervous system are described in this section.