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Cryptococcosis

Definition Cryptococcosis occurs most often in persons who are immunosuppressed, especially individuals who are infected with human immunodeficiency virus (HIV; see Chapter 358 ). Meningoencephalitis is the most common clinical manifestation, but the lungs and other organs can be involved as well. The Pathogen Cryptococcus neoformans and, much less often, Cryptococcus gattii are the predominant Cryptococcus species that cause infection in humans. In the environment, Cryptococcus…

Endemic Mycoses

Blastomycosis Definition Blastomycosis (North American blastomycosis) is an endemic mycosis that primarily causes infection of the lungs and skin and, less commonly, infection of the osteoarticular and genitourinary systems ( Table 308-1 ). TABLE 308-1 BLASTOMYCOSIS: CLINICAL CHARACTERISTICS AND TREATMENT CHARACTERISTIC DESCRIPTON Causative fungi Blastomyces dermatitidis and other Blastomyces spp. Primary geographic distribution South central and north central regions of the United States and Canadian provinces…

Systemic Antifungal Agents

Methods for in vitro testing of antifungal susceptibility are available as standardized tools. A variety of assays also are available for therapeutic monitoring of drug levels in the serum and other bodily fluids. The increasing prevalence of drug resistance requires careful antifungal stewardship programs. Drug-drug interactions are a particular prescribing challenge for triazole antifungal agents. Azole Antifungal Agents Mechanisms of Action The azole ring confers antifungal activity…

Nocardiosis

Definition Nocardiosis refers to infections caused by Nocardia spp. Nocardia most commonly causes pneumonia but also can infect the central nervous system (CNS) and the skin. Less commonly, this organism can disseminate throughout the body. These infections usually occur in immunosuppressed patients. The Pathogen Nocardia spp are thin, aerobic, gram-positive bacilli that form branching filaments. The bacteria stain irregularly and appear beaded on Gram stain and…

Whipple Disease

Definition Whipple disease is a rare chronic systemic infection that is caused by Tropheryma whipplei and is characterized by a wide range of symptoms including fever, diarrhea, malabsorption, weight loss, arthralgias, arthritis, central nervous system involvement, lymphadenopathy, and serositis. T. whipplei can also cause asymptomatic infection, acute transient infections, and isolated endocarditis or pneumonia. The Pathogen T. whipplei is a gram-positive, slowly replicating, rod-shaped bacterium, 0.25…

Actinomycosis

Definition Actinomycosis is an uncommon, subacute to chronic bacterial infection that induces both suppurative and granulomatous inflammation. Localized swelling with suppuration, abscess formation, tissue fibrosis, and draining sinuses characterize this disease. The infection spreads contiguously and often forms draining sinuses that extrude characteristic, but not pathognomonic, “sulfur granules.” Infections of the oral and cervicofacial regions are the most common, but any site in the body can…

Zoonoses

Definition Zoonoses, derived from the Greek words zōio (animal) and nósos (disease), are infectious diseases transmitted from animals, both wild and domestic, to humans or from humans to animals. Among emerging or reemerging infectious diseases, 60 to 75% are zoonoses. Most recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; Chapters 335 , 336 , and 337 ) has shown the devastating effects of zoonotic transmission followed…

Rickettsial Infections

Definition Rickettsial diseases are emerging infectious diseases. Because of better diagnostic tools, increased awareness, and changes in tick exposure, new rickettsial diseases continue to be described in recent years. Three families of diseases are grouped under rickettsioses: ehrlichioses and anaplasmoses and Q fever ( Table 302-1 ). TABLE 302-1 GENETIC CLASSIFICATION OF RICKETTSIALES GENUS GROUP SPECIES SUBSPECIES Rickettsiae Rickettsia Typhus R. prowazekii R. typhi Spotted fever…

Leprosy (Hansen Disease)

Definition Leprosy (Hansen disease), which is caused by Mycobacterium leprae, is a chronic infection found worldwide but with about 75% of cases reported in India, Brazil, and Indonesia. The primary clinical manifestation is hypopigmented, hypoesthetic or anesthetic, nonpruritic skin lesions. Peripheral nerve damage, which can be a result of the immune response to the infection, leads to loss of sensation and decreased motor function. The peripheral…

The Nontuberculous Mycobacteria

Definition Nontuberculous mycobacteria generally include the growing number of mycobacteria other than Mycobacterium tuberculosis and its close relatives ( Chapter 299 ) and M. leprae ( Chapter 301 ). Other names that have been used include atypical mycobacteria , mycobacteria other than tuberculosis , and environmental mycobacteria . Over 190 species of nontuberculous mycobacteria are now known, and the number continues to grow as DNA sequencing…

Tuberculosis

Definition Tuberculosis (TB) is a granulomatous disease caused by the slow-growing, acid-fast bacillus Mycobacterium tuberculosis . Prior to the emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2; Chapter 337 ), TB was the leading infectious disease cause of death worldwide. People become infected with M. tuberculosis by inhaling infectious organisms through aerosol transmission from a person who has active TB. The Pathogen The M. tuberculosis complex…

Leptospirosis

Definition Leptospirosis is a zoonotic bacterial infection caused by pathogenic spirochetes belonging to the genus Leptospira . It has a global distribution and is most prevalent in tropical areas with poor urban infrastructure and heavy rainfall. Leptospirosis is transmitted to humans either by direct contact with infected animals or by contact with soil or water contaminated by rodent urine. The disease ranges in severity from a…

Relapsing Fever and Other Borrelia Infections

Definition Relapsing fever is a spirochetal infection with bacteria of the genus Borrelia . The two modes of transmission are epidemic louse-borne and endemic tick-borne relapsing fever. Disease is characterized by recurrent bouts of fever and spirochetemia separated by short fever-free periods. The Pathogen Members of the genus Borrelia are motile spirochetes that measure 0.5 µm in diameter and 5 to 40 µm in length. The…

Lyme Disease

Definition Lyme disease (also known as Lyme borreliosis) is a zoonotic infection that is transmitted by certain Ixodes tick species and caused by a group of related spirochetes referred to formally as Borrelia burgdorferi sensu lato, or more simply as Lyme borrelia. Lyme disease was first described in 1977 after an investigation of a cluster of cases of arthritis among children living in the area of…

Syphilis and Nonsyphilitic Treponematoses

Syphilis Definition Syphilis, which is a chronic infectious disease caused by the bacterium Treponema pallidum subspecies pallidum , is usually acquired by sexual contact with another infected individual. Syphilis is remarkable among infectious diseases for its large variety of clinical manifestations. If untreated, it progresses through primary, secondary, and tertiary stages. The early stages (i.e., primary and secondary), when lesions are present, are infectious. Spontaneous healing…

Diseases Caused by Chlamydiae

Definition Chlamydiae are obligate intracellular bacteria that cause a variety of human and animal diseases and much morbidity. Within the Chlamydia genus are now 11 validated species: C. trachomatis, C. pneumoniae, C. psittaci , C. abortus , C. avium , C. caviae , C. felis , C. gallinacea , C. muridarum , C. pecorum , and C. suis . C. trachomatis is classified into a trachoma…

Mycoplasma Infections

Mycoplasma pneumoniae Definition Mycoplasma organisms of the class Mollicutes are ubiquitous as pathogens and colonizing agents in the plant, animal, and insect kingdoms. They represent the smallest known free-living forms, but because they have fastidious growth requirements, they are difficult to culture. The presence of several species of Mycoplasma as commensals in animals and on human oral and genital mucosa frequently results in contamination of cell…

Granuloma Inguinale (Donovanosis)

Definition Granuloma inguinale, also known as donovanosis, is a chronic and progressive bacterial ulcerative disease that predominantly affects the skin and mucous membranes of the genital, inguinal, perirectal, and anal regions, often associated with sexual transmission. The Pathogen Donovanosis is caused by Klebsiella granulomatis , which is a gram-negative, facultatively aerobic coccobacillus that is intracytoplasmic, immobile, and can be encapsulated. In lesions, these microorganisms are found…

Bartonella Infections

Definition Bartonella are vector-borne bacteria responsible for a wide spectrum of human acute and chronic diseases. More than 40 different bacterial species from this genus have been isolated from animals and humans. The human infections linked to these different bacteria include cat-scratch disease, Oroya fever, verruga peruana, trench fever, endocarditis, bacillary angiomatosis, and peliosis hepatis. The Pathogen Bartonella species belong to the α-2 subgroup of Proteobacteria…

Legionella Infections

Definition Legionellosis refers to two clinical syndromes caused by Legionella bacteria: pneumonia and Pontiac fever. Legionella pneumonia (legionnaires disease) can be episodic or occur in outbreaks, and it can be acquired in the community or in health care settings. Pontiac fever is an acute, self-limited febrile illness caused by inhalation or aspiration of Legionella spp. Legionella extrapulmonary infections include meningitis, cellulitis, and skin and soft tissue…