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Q Fever (Coxiella burnetii)

Q fever (for query fever, the name given following an outbreak of febrile illness in an abattoir in Queensland, Australia) is rarely reported in children but is probably underdiagnosed. Symptomatic patients can have acute or chronic disease. Etiology Although previously classified within the order Rickettsiales, Coxiella burnetii (the causative agent of Q fever) is genetically distinct from the genera Rickettsia, Orientia , Ehrlichia, and Anaplasma. Hence,…

Ehrlichiosis and Anaplasmosis

Etiology Ehrlichiosis in humans was 1st described in 1987, when clusters of bacteria confined within cytoplasmic vacuoles of circulating leukocytes (morulae), particularly mononuclear leukocytes, were detected in the peripheral blood of a patient with suspected Rocky Mountain spotted fever (RMSF). The etiologic agent, Ehrlichia chaffeensis, was cultivated from blood of an infected patient in 1990 and identified as the predominant cause of human ehrlichiosis. Investigations showed…

Typhus Group Rickettsioses

Members of the typhus group of rickettsiae (see Table 255.1 in Chapter 255 ) include Rickettsia typhi, the cause of murine typhus, and Rickettsia prowazekii, the cause of louse-borne or epidemic typhus. R. typhi is transmitted to humans by fleas, and R. prowazekii is transmitted in the feces of body lice. Louse-borne or epidemic typhus is widely considered to be the most virulent of the rickettsial…

Scrub Typhus (Orientia tsutsugamushi)

Scrub typhus is an important cause of acute febrile illness in South and East Asia and the Pacific and could be emerging in the Middle East and South America. The causative agent is distinct from, but related to, Rickettsia species. The infection is transmitted via chigger (larval mite) bites and involves many antigenically diverse strains of Orientia tsutsugamushi , hampering vaccine development. Etiology The causative agent…

Spotted Fever Group Rickettsioses

Rickettsia species were classically divided into spotted fever and typhus groups based on serologic reactions and the presence or absence of the outer membrane protein A (ompA) gene. Sequencing of at least 45 complete genomes has refined distinctions. However, there is controversy regarding phylogeny, and some data suggest that diversity and pathogenicity are the result of gene loss and lateral gene transfer from other prokaryotes or…

Psittacosis (Chlamydia psittaci)

Chlamydia psittaci, the agent of psittacosis (also known as parrot fever and ornithosis ), is primarily an animal pathogen and rarely causes human disease. In birds, C. psittaci infection is known as avian chlamydiosis . Etiology C. psittaci affects both psittacine birds (e.g., parrots, parakeets, macaws) and nonpsittacine birds (ducks, turkeys); the known host range includes 130 avian species. The life cycle of C. psittaci is…

Chlamydia trachomatis

Chlamydia trachomatis is subdivided into 2 biovars: lymphogranuloma venereum (LGV) and trachoma, which is the agent of human oculogenital diseases other than LGV. Although the strains of both biovars have almost complete DNA homology, they differ in growth characteristics and virulence in tissue culture and animals. In developed countries, C. trachomatis is the most prevalent sexually transmitted disease, causing urethritis in men, cervicitis and salpingitis in…

Chlamydia pneumoniae

Chlamydia pneumoniae is a common cause of lower respiratory tract diseases, including pneumonia in children and bronchitis and pneumonia in adults. Etiology Chlamydiae are obligate intracellular pathogens that have established a unique niche in host cells. Chlamydiae cause a variety of diseases in animal species at virtually all phylogenic levels. The most significant human pathogens are C. pneumoniae and Chlamydia trachomatis (see Chapter 253 ). Chlamydia…

Genital Mycoplasmas ( Mycoplasma hominis, Mycoplasma genitalium , and Ureaplasma urealyticum )

Etiology Mycoplasma species are small pleomorphic bacteria that typically lack a cell wall and are bound by a cell membrane. Many of the biologic properties of mycoplasmas are in fact due to the absence of a rigid cell wall, including resistance to β-lactam antibiotics. These ubiquitous organisms are difficult to cultivate and belong to the family Mycoplasmataceae in the class Mollicutes and represent the smallest self-replicating…

Mycoplasma pneumoniae

Among the 7 Mycoplasma species isolated from the human respiratory tract, Mycoplasma pneumoniae remains the most common species causing respiratory infections in school-age children and young adults. The Organism Mycoplasmas are the smallest self-replicating prokaryotes known to cause disease in humans. Their size of 150-250 nm is more on the order of viruses than bacteria. Mycoplasma pneumoniae is a fastidious double-stranded DNA bacterium that is distinguished by…

Lyme Disease (Borrelia burgdorferi)

Lyme disease is the most common vector-borne disease in the United States and is an important public health problem. Etiology Lyme disease is caused by the spirochete Borrelia burgdorferi sensu lato (broad sense). In North America, B. burgdorferi sensu stricto (strict sense) causes almost all cases; a recently discovered species in the upper Midwestern United States, Borrelia mayonii (belonging to the group B. burgdorferi sensu lato),…

Relapsing Fever (Borrelia)

Relapsing fever is characterized by recurring fevers and flu-like symptoms such as headaches, myalgia, arthralgia, and rigors. Etiology Relapsing fever is an arthropod (lice or ticks)-transmitted infection caused by spirochetes of the genus Borrelia . Louse-borne (epidemic) relapsing fever is caused by Borrelia recurrentis and is transmitted from person to person by Pediculus humanus, the human body louse. Human infection occurs as a result of crushing…

Leptospira

Leptospirosis is a common and widespread zoonosis caused by aerobic, motile spirochetes of the genus Leptospira. Etiology Leptospira spp. are thin, helix-shaped members of the phylum Spirochaetes. There are 22 species identified within the genus Leptospira , and these are further divided into over 300 serovars. There are at least 10 pathogenic Leptospira species, with serovars demonstrating preferential host specificity. Epidemiology Leptospirosis has a worldwide distribution,…

Nonvenereal Treponemal Infections

Nonvenereal treponemal infections—yaws, bejel (endemic syphilis), and pinta—are caused by different subspecies of Treponema pallidum and occur in tropical and subtropical areas. The causative agents of nonvenereal treponematoses— T. pallidum pertenue, T. pallidum subspecies endemicum, and Treponema carateum —cannot be distinguished from T. pallidum subspecies pallidum by morphologic or serologic tests. In general, nonvenereal treponematoses have prominent cutaneous manifestations and relapsing courses, as in venereal syphilis,…

Syphilis (Treponema pallidum)

Syphilis is a chronic systemic sexually or vertically (mother to child) transmitted infection that can be easily treated if detected early but manifests with protean clinical symptoms and significant morbidity if left unchecked. Etiology Syphilis is caused by Treponema pallidum, a delicate, tightly spiraled, motile spirochete with finely tapered ends belonging to the family Spirochaetaceae. The pathogenic members of this genus include T. pallidum subspecies pallidum…

Nontuberculous Mycobacteria

Nontuberculous mycobacteria ( NTM ), also referred to as atypical mycobacteria and mycobacteria other than tuberculosis (MOTT), are all members of the genus Mycobacterium and include species other than Mycobacterium tuberculosis complex and Mycobacterium leprae . The NTM constitute a highly diverse group of bacteria that differ from M. tuberculosis complex bacteria in their pathogenicity, interhuman transmissibility, nutritional requirements, ability to produce pigments, enzymatic activity, and…

Hansen Disease (Mycobacterium leprae)

Leprosy (Hansen disease) is a heterogeneous, curable infection caused by Mycobacterium leprae that primarily affects the upper airway, skin, and peripheral nerves. Disease manifestations are mainly determined by the host's immunologic response to infection, resulting in a wide clinical spectrum. The majority of exposed individuals never develop clinical disease. Hansen disease ( HD ) is currently the accepted designation of leprosy, and contrary to popular folklore,…

Tuberculosis (Mycobacterium tuberculosis)

Tuberculosis has caused human disease for more than 4,000 yr and is one of the most important infectious diseases worldwide. Etiology There are 5 closely related mycobacteria in the Mycobacterium tuberculosis complex: M. tuberculosis, M. bovis, M. africanum, M. microti, and M. canetti. M. tuberculosis is the most important cause of tuberculosis (TB) disease in humans. The tubercle bacilli are non–spore-forming, nonmotile, pleomorphic, weakly gram-positive curved rods…

Principles of Antimycobacterial Therapy

The treatment of mycobacterial infection and disease can be challenging. Patients require therapy with multiple agents, the offending pathogens commonly exhibit complex drug resistance patterns, and patients often have underlying conditions that affect drug choice and monitoring. Several of the drugs have not been well studied in children, and current recommendations are extrapolated from the experience in adults. Single-drug therapy of Mycobacterium tuberculosis and nontuberculous mycobacteria…

Other Anaerobic Infections

Anaerobic bacteria are among the most numerous organisms colonizing humans. Anaerobes are present in soil and are normal inhabitants of all living animals, but infections caused by anaerobes are relatively uncommon. Obligate anaerobes are markedly or entirely intolerant of exposure to oxygen. Facultative anaerobes can survive in the presence of environmental oxygen but grow better in settings of reduced oxygen tension. This chapter concentrates on conditions…