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Pathobiology of Human Immunodeficiency Viruses

Human immunodeficiency viruses (HIV-1, HIV-2) cause progressive immune deficiency and death from opportunistic infections or neoplastic diseases. Increased understanding of HIV pathobiology has led to significant advances in diagnosis ( Chapter 355 ), prevention ( Chapter 356 ), and treatment ( Chapter 357 ) that have reduced morbidity and mortality, and tipped the balance toward control of the epidemic worldwide. The Pathogen HIV is a member…

Epidemiology and Diagnosis of Human Immunodeficiency Virus Infection and Acquired Immunodeficiency Syndrome

Four decades after the initial recognition of acquired immunodeficiency syndrome (AIDS) in 1980 and the subsequent identification of the human immunodeficiency virus (HIV; which exists in two types: HIV-1, which is the predominant circulating type, and HIV-2), the HIV pandemic remains one of the leading causes of death worldwide. Early efforts at prevention and treatment with antiretroviral drugs tempered the spread and decreased the fatality rate…

Arboviruses Causing Fever, Rash, and Neurologic Syndromes

Common Features of Arboviruses Definition Zoonotic viruses ( Chapter 303 ) in animal populations infect humans. An extremely large reservoir of known and unknown viruses represents important causes of described and emerging human infectious diseases. Modes of transmission include human contact with animal bodily fluids or excrement, bite wounds, and direct exposure to an animal carcass. However, many arthropods have evolved to utilize animal blood as…

Viral Hemorrhagic Fevers

Definition Viral hemorrhagic fever is an acute systemic illness classically involving fever, a constellation of initially nonspecific signs and symptoms, and a propensity for bleeding and shock. The Pathogens Viral hemorrhagic fever may be caused by more than 30 different viruses from four taxonomic families, Filoviridae, Arenaviridae, Bunyaviridae, and Flaviviridae ( Table 351-1 ), but not every virus in these families causes the syndrome. Recently discovered…

Rotaviruses, Noroviruses, and Other Gastrointestinal Viruses

Definition Viruses are a principal cause of acute infectious gastroenteritis, a syndrome of vomiting, watery diarrhea, or both that begins abruptly in otherwise healthy persons. Two distinct viruses account for much of these cases. Before rotavirus vaccines were widely introduced over the last 15 years, rotaviruses accounted for over 400,000 deaths annually. Rotaviruses remain the most frequent cause of sporadic, severe gastroenteritis in young children worldwide,…

Enteroviruses

Definition The enteroviruses belong to the genus Enterovirus in the family Picornaviridae. With the advent of molecular virology, the more than 110 recognized strains are classified on the basis of phylogenetic analysis of the nucleic acid sequence of VP1, which is the major enteroviral capsid protein ( Table 349-1 ). TABLE 349-1 CLASSIFICATION OF ENTEROVIRUSES SPECIES SEROTYPES Enterovirus A 25 (sero)types CV- A2-A8, A10, A12, A14,…

Epstein-Barr Virus Infection

Definition Epstein-Barr virus (EBV), a member of the gamma human herpesvirus family, is the etiologic agent of infectious mononucleosis and of a diverse assortment of neoplastic and lymphoproliferative syndromes. Epidemiology Ubiquitous in the human population, EBV is found in 90 to 95% of adults throughout the world. As in the case of other herpesviruses, infection with EBV is lifelong. The virus resides in B lymphocytes and…

Cytomegalovirus

Definition Cytomegalovirus (CMV) is a member of the herpesvirus family and shares, with the other members, the ability to establish a long-lived latent infection. Most of the clinical diseases caused by this virus result from reactivation of latent virus in immune-impaired patients, although primary infection in such patients can also lead to significant disease. The Pathogen CMV has a linear, double-stranded DNA genome with about 236,000…

Varicella-Zoster Virus (Chickenpox, Shingles)

Definition Primary infection with varicella-zoster virus results in the rash of varicella (chickenpox). The varicella-zoster virus establishes a latent infection in the nervous system and can reactivate later in life to cause zoster (shingles). The Pathogen Varicella-zoster virus is a member of the alpha herpesvirus family and has a DNA core surrounded by a nucleocapsid, which is in turn surrounded by a viral envelope that is…

Herpes Simplex Virus Infections

Definition The Pathogen Among the herpesviruses, HSV-1 and HSV-2 are most closely related, with approximately 60% genomic homology. Historically, HSV-1 was more frequently associated with nongenital (especially orolabial) disease and HSV-2 with genital disease, but that distinction has become blurred with the recognition that HSV-1 causes more than half of initial genital herpes infections in some populations. These two viruses can be distinguished most reliably by…

Papillomavirus

Definition Human papillomaviruses (HPVs) are a group of small DNA viruses that cause a variety of benign and malignant lesions of the skin and mucous membranes. The most commonly recognized HPV-associated diseases include warts ( Chapter 407 ) at anogenital sites (condyloma acuminatum), other skin surfaces (common wart or verruca vulgaris, as well as flat wart or verruca plana), and the plantar surface of the foot…

Smallpox, Monkeypox, and Other Poxvirus Infections

Definition Human illness caused by a poxvirus is characterized by a cutaneous manifestation; illness may be localized or systemic, depending on the particular poxvirus and the route of introduction. DNA-based assays, including polymerase chain reaction (PCR) and DNA sequencing, are the most precise methods for identification and differentiation of poxvirus genera, species, strains, and variants. The guanosine plus cytosine content of orthopoxviruses, yatapoxviruses, molluscum contagiosum virus,…

Parvovirus

Definition B19 parvovirus, which was discovered in the mid-1970s by electron microscopy of an anomalous precipitin reaction of a blood donor’s serum (occupying position 19 in plate B), was first linked to human disease by the observation of virus-specific immunoglobulin M (IgM) antibody or the virus itself in the sera of sickle cell disease patients suffering transient aplastic crisis ( Chapter 149 ). The common illness…

Polyomaviruses

Human Polyomavirus Definition Human polyomaviruses comprise at least 14 species, denoted human polyomavirus 1 to 14, and five of these are associated with human diseases ( Table 341-1 ). Of the types of polyomaviruses that infect humans, the principal causes of human disease are BK polyomavirus, JC polyomavirus, Merkel cell polyomavirus, human polyomavirus 7, and Trichodysplasia spinulosa polyomavirus. TABLE 341-1 HUMAN POLYOMAVIRUSES, THEIR DISEASE, AND POPULATION…

Mumps

Definition Mumps is an acute viral infection characterized by inflammation of the parotid and other salivary glands. Prior to the introduction of vaccination in the United States, mumps was a common childhood illness. The incidence of mumps declined dramatically after the introduction of the vaccine, but mumps remains endemic. Cases and even outbreaks can occur in previously vaccinated children and adults. The Pathogen The mumps virus…

Rubella (German Measles)

Definition Although most cases of rubella infection lead to a mild viral illness, significant morbidity occurs when rubella virus infects the fetus, particularly during the first trimester of pregnancy, when it causes miscarriage and the congenital rubella syndrome in up to 90% of cases. Humans are the only known host, so this disease is eradicable. The Pathogen Rubella is a single-stranded, positive-sense RNA virus that is…

Measles

Definition The term measles is applied most appropriately to “rubeola” (also known as “morbilli”), an extremely contagious, prolonged respiratory and systemic viral illness characterized by high fever, an erythematous maculopapular rash, cough, coryza, and conjunctivitis. A member of the family Paramyxoviridae, within the genus Morbillivirus , the measles virus exhibits at least 24 distinct genotypes but behaves as a single serotype because natural infection or adequate…

COVID-19 Treatment and Vaccination

Treatment of Infected Persons General Principles The approach to treating coronavirus-2019 disease (COVID-19) must first consider the severity of the patient’s disease, which can range from mild to moderate respiratory or systemic symptoms, to severe disease (i.e., dyspnea, tachypnea, and hypoxia), to critical illness (i.e., respiratory failure, shock, and/or multiorgan failure; see Fig. 336-1 ). The second consideration is the phase of illness. The third consideration…

COVID-19: Epidemiology, Clinical Manifestations, Diagnosis, Community Prevention, and Prognosis

Epidemiology On December 31, 2019, the World Health Organization (WHO) was informed of a cluster of cases of pneumonia of unknown cause in Wuhan City, Hubei Province, China. On January 9, 2020, a novel coronavirus (named severe acute respiratory syndrome coronavirus-2 [SARS-CoV-2]) was identified in samples obtained from these patients, whose disease is now called coronavirus 2019 (COVID-19). Although the precise source of the COVID-19 pandemic…

COVID-19: Virology and Pathology

In December 2019, a cluster of patients with pneumonia of unknown etiology were identified in Wuhan, a city of 11 million residents in South Central China. RNA extracted from bronchoalveolar fluid provided the complete genome of a novel betacoronavirus named SARS-CoV-2 (for severe acute respiratory syndrome coronavirus-2). The disease caused by this virus is called COVID-19 (for COronaVirus Infectious Disease). SARS-CoV-2: The Virus and the Genome…