Viral Infections


PAPILLOMAVIRUSES Essentials of Diagnosis Causes warts and genital lesions; latter may be premalignant or malignant. Hyperplasia of prickle cells and excess keratin in skin biopsy, vacuolated squamous epithelial cells. Human papillomavirus (HPV) antigen detected in clinical samples by immunofluorescence assay (IFA), immunoperoxidase. HPV DNA detected in biopsies, cervical smears. General Considerations Epidemiology Papillomaviruses (HPVs) cause skin warts, most commonly in children and young adults, which may reflect acquired immunity in older age groups (Box 1). Laryngeal papillomas are found most commonly in young children and middle-aged adults. Genital warts (condylomas) are most common among sexually active patients and are sexually transmitted. Recent studies suggest that genital HPV infections may occur in […]

Miscellaneous Systemic Viral Syndromes

This SITE includes a variety of viral infections that produce severe systemic syndromes (Table 1). In some cases, these infections are transmitted by arthropod vectors; in others, they are acquired by direct contact with the reservoir animal or its excreta. The illnesses may be hemorrhagic fever (eg, dengue, Marburg, Ebola, or Lassa fevers), generalized fever (yellow fever or Colorado tick fever), or pneumonia (caused by hantavirus infection). Only two of these are endemic in the United States, hantavirus infection and Colorado tick fever. All of these viruses are RNA viruses, and vaccine has been developed for one (yellow fever). Dengue & Yellow Fever Marburg & Ebola Virus Hantaviruses Colorado Tick Fever […]

Colorado Tick Fever

Colorado tick fever, an acute disease characterized by fever, headache, and severe myalgia, was originally described in the nineteenth century and is now believed to be one of the most common tick-borne viral diseases in the United States. Although hundreds of infections occur annually, the exact number is not known because it is not a reportable disease. It is caused by a coltvirus, a member of the reovirus family. This family also includes the rotaviruses, which are discussed in site. Epidemiology Colorado tick fever has occurred in western and northwestern areas of the United States and western Canada, where the wood tick Dermacentor andersoni is distributed. Ticks acquire the virus by […]


Essentials of Diagnosis Acute severe respiratory infection in a young adult. Exposure to deer mice, eg, in a remote cabin. Occurrence of disease in far western United States, especially Four Corners states. Diagnosis by serology. Can detect viral RNA by PCR of respiratory samples. General Considerations Hantaviruses are members of the bunyavirus group, which is the largest family of viruses and contains several human pathogens including California encephalitis virus (see site). The hantavirus group was first recognized as causing hemorrhagic fevers with renal failure in Asia and Eastern Europe but became much more prominent in the United States when the hantavirus pulmonary syndrome was described in the United States. Epidemiology Unlike […]

Marburg & Ebola Virus

General Considerations Two unique RNA viruses, the Marburg and Ebola viruses, are members of a new family known as filoviruses. These agents can cause severe or fatal hemorrhagic fevers and are endemic in Africa. Laboratory workers have been exposed to the Marburg agent while working with tissue cultures from African green monkeys. Travelers in or residents of central Africa (eg, Zaire or the Sudan) may be infected by the Ebola virus. Epidemiology Marburg virus infection was first detected among laboratory workers in Marburg, Germany, who had been exposed to tissues from apparently healthy African green monkeys. However, it is not clear that these monkeys were, or are, the reservoir for this […]

Dengue & Yellow Fever

General Considerations Dengue and yellow fever are both caused by flaviviruses, and each is spread by an arthropod vector. The etiologic agents of dengue are the dengue virus types 1-4, whereas yellow fever is caused by the yellow fever virus. Flaviviruses produce a wide range of diseases including hemorrhagic fevers, arthritis, encephalitis, and hepatitis. Hepatitis C is caused by a flavivirus and is discussed in site. Until recently the flaviviruses were included in the Togaviridae family, but differences in size, morphology, gene sequence, and replication strategy have made it necessary to classify them as an independent virus family. Epidemiology The flaviviruses are also classified as arboviruses (see site) because they are […]

Viral Infection of the Central Nervous System

Many viruses causing infection of the central nervous system (CNS) are covered in chapters devoted to each type of virus. For example, enteroviruses, the agents most frequently causing meningitis and occasionally encephalitis, are covered in site. The herpes viruses that cause meningitis, encephalitis, or both, especially herpes simplex virus (HSV), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV), are discussed in site. This SITEconsiders viruses that cause CNS diseases (Box 1) as their primary manifestations. Arthropod-Borne Viral Encephalitis LYMPHOCYTIC CHORIOMENINGITIS (LCM) Lymphocytic choriomeningitis (LCM) virus is an arenavirus, the same family as Lassa virus. All arenaviruses have a common reservoir in animals, especially small rodents. The infected animals may be asymptomatic or […]

Creutzfeldt-Jakob Disease

Essentials of Diagnosis Progressive mentation abnormalities leading to disorders of gait and myoclonus. Occurs in sixth and seventh decades in previously normal patients. May be history of corneal transplant, neurosurgical procedures, or use of human growth hormone. Characteristic brain biopsy abnormalities of spongiform degeneration, neuron loss, and astrogliosis. General Considerations Creutzfeldt-Jakob disease is a progressive, fatal illness of the central nervous system that is seen most frequently in the sixth and seventh decades of life. The disease is sporadic and found worldwide, with an incidence of disease of 1 case/million people per year. The mode of acquisition is unknown, but a higher incidence of the disease among Israelis of Libyan origin […]


Essentials of Diagnosis Subacute onset of neurologic abnormalities including hallucinations, combativeness, muscle spasms, seizures, and focal paralysis. Detection of negri bodies or rabies antigen in animal or human brain tissue (70-90%). Rabies-neutralizing antibody in serum or CSF diagnostic in an unimmunized patient. General Considerations Rabies is an acute fatal viral illness of the CNS. It can affect all mammals and is transmitted between them by infected secretions, most often by bite. It was first recognized more than 3000 years ago and has been among the most feared of infectious diseases. It is said that Aristotle recognized that rabies could be spread by a rabid dog. Epidemiology Rabies exists in two epizooic […]

Arthropod-Borne Viral Encephalitis

Essentials of Diagnosis Summer and fall cases, especially if in a cluster or outbreak, suggest arboviruses or enteroviruses. History of exposure to mosquitoes suggests arbovirus infection, especially in geographic areas of high endemicity (eg, swamps of Florida). Maculopapular rash suggests enterovirus disease. Lymphocytic pleocytosis in cerebrospinal fluid (CSF) with normal glucose and protein concentrations suggests viral meningitis. General Considerations Arthropod-borne (arbo) viruses causing encephalitis are members of the toga-, flavi-, and bunyavirus families. The medically important togaviruses include rubella virus, which is discussed in site, and the equine encephalitis viruses. The flavivirus family, which includes St. Louis encephalitis (SLE) and West Nile viruses, also includes dengue and yellow fever viruses; the […]