Rubella ( German measles or 3-day measles ) is a mild, often exanthematous disease of infants and children that is typically more severe and associated with more complications in adults. Its major clinical significance is transplacental infection and fetal damage as part of the congenital rubella syndrome (CRS). Etiology Rubella virus is a member of the family Togaviridae and is the only species of the genus…
Measles is highly contagious, but endemic transmission has been interrupted in the United States as a result of widespread vaccination; indigenous or imported cases have occasionally resulted in epidemics in the United States in unimmunized or partially immunized American or foreign-born children (adopted children, refugees, returning tourists). In some areas of the world, measles remains a serious threat to children ( Fig. 273.1 ). Open full…
Antiviral chemotherapy typically requires a delicate balance between targeting critical steps in viral replication without interfering with host cellular function. Because viruses require cellular functions to complete replication, many antiviral agents exert significant host cellular toxicity, a limitation that has hindered antiviral drug development. In spite of this limitation, a number of agents are licensed for use against viruses, particularly herpesviruses, respiratory viruses, and hepatitis viruses…
Pneumocystis jirovecii pneumonia (interstitial plasma cell pneumonitis) in an immunocompromised person is a life-threatening infection. Primary infection in the immunocompetent person is usually subclinical and goes unrecognized. The disease most likely results from new or repeat acquisition of the organism rather than reactivation of latent organisms. Even in the most severe cases, with rare exceptions, the organisms remain localized to the lungs. Etiology P. jirovecii is…
Etiology Mucormycosis refers to a group of opportunistic fungal infections caused by fungi of the order Mucorales, which are primitive, fast-growing fungi that are largely saprophytic and ubiquitous. These organisms are found commonly in soil, in decaying plant and animal matter, and on moldy cheese, fruit, and bread. Mucormycosis was previously called zygomycosis, and the causative organisms were referred to as Zygomycetes, but this terminology has…
Etiology Sporotrichosis is a rare fungal infection that occurs worldwide both sporadically and in outbreaks. The etiologic agent, Sporothrix schenckii, exhibits temperature dimorphism, existing as a mold at environmental temperatures (25-30°C [77-86°F]) and as a yeast in vivo (37°C [98.6°F]). Epidemiology S. schenckii is found throughout the world, but most cases of sporotrichosis are reported from North America, South America, and Japan. In the United States,…
Etiology Paracoccidioidomycosis (South American or Brazilian blastomycosis, Lutz-Splendore-Almeida disease) is the most common systemic mycosis in Latin America. It is a fungal infection that is endemic in South America, with cases reported in Central America and Mexico. Brazil accounts for more than 80% of all reported cases. The etiologic agent, Paracoccidioides brasiliensis, is a thermally dimorphic fungus found in the environment in the mycelial (mold) form…
Etiology Coccidioidomycosis (valley fever, San Joaquin fever, desert rheumatism, coccidioidal granuloma) is caused by Coccidioides spp., a soil-dwelling dimorphic fungus. Coccidioides spp. grow in the environment as spore-bearing (arthroconidia-bearing) mycelial forms. In their parasitic form, they appear as unique, endosporulating spherules in infected tissue. The 2 recognized species, C. immitis and C. posadasii, cause similar illnesses. Epidemiology Coccidioides spp. inhabit soil in arid regions. C. immitis…
Etiology Blastomyces dermatitidis and Blastomyces gilchristii belong to a group of fungi that exhibit thermal dimorphism. In the soil (22-25°C [71.6-77°F]), these fungi grow as mold and produce spores, which are the infectious particles. Following soil disruption, aerosolized mycelial fragments and spores inhaled into the lungs (37°C [98.6°F]) convert into pathogenic yeast and cause infection. In addition to B. dermatitidis and B. gilchristii, 4 additional species…
Etiology Histoplasmosis is caused by Histoplasma capsulatum, a dimorphic fungus found in the environment as a saprobe in the mycelial (mold) form and in tissues in the parasitic form as yeast. Epidemiology Two varieties of Histoplasma cause human histoplasmosis. The most common variety, H. capsulatum var. capsulatum , is found in soil as the saprotrophic form throughout the midwestern United States, primarily along the Ohio and…
The aspergilli are ubiquitous fungi whose normal ecological niche is that of a soil saprophyte that recycles carbon and nitrogen. The genus Aspergillus contains approximately 250 species, but most human disease is caused by Aspergillus fumigatus , A. flavus , A. niger , A. terreus, and A. nidulans . Invasive disease is most commonly caused by A. fumigatus . Aspergillus reproduces asexually via production of spores…
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Etiology While more than 30 cryptococcal species have been described, 2 species ( Cryptococcus neoformans and C. gattii ) are responsible for the vast majority of disease. These species can be further classified by serologic and molecular typing techniques. Both C. neoformans and C. gattii are encapsulated, facultative intracellular pathogens. There is significant overlap in the disease caused by these pathogens; however, important differences in epidemiology…
Candidiasis encompasses many clinical syndromes that may be caused by several species of Candida . Invasive candidiasis ( Candida infections of the blood and other sterile body fluids) is a leading cause of infection-related mortality in hospitalized immunocompromised patients . Candida exists in 3 morphologic forms: oval to round blastospores or yeast cells (3-6 mm in diameter); double-walled chlamydospores (7-17 mm in diameter), which are usually at the…
Invasive fungal infections are a major cause of morbidity and mortality in the growing number of immunocompromised children. Fortunately, the therapeutic armamentarium for invasive fungal infections has markedly increased since the turn of the century ( Tables 260.1 and 260.2 ). Table 260.1 Suggested Dosing of Antifungal Agents in Children and Neonates DRUG FORMULATIONS SUGGESTED PEDIATRIC DOSAGE COMMENTS Amphotericin B deoxycholate IV 1 mg/kg/day Generally less toxicity…
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,…
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…
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 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…
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…