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Coccidioides immitis and Coccidioides posadasii (Coccidioidomycosis)

Coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii . These fungi are endemic to the southwestern US, Mexico, Guatemala, and sporadic regions within Central and South America. Infection is caused by inhalation of highly infectious and environmentally resistant spores following soil disruption and aerosolization. Primary infection is often manifest as an acute respiratory illness although the spectrum of disease ranges…

Blastomyces Species (Blastomycosis)

Blastomyces , the etiologic agent of blastomycosis, can infect both people with healthy immune systems and those with impaired immune defenses. The Blastomyces genus consists of 7 different species, of which B. dermatitidis and B. gilchristii cause the majority of infections in North America. Most blastomycosis infections are sporadic; however, at least 13 outbreaks have involved pediatric patients. An estimated 2%–13% cases of blastomycosis occur in…

Pneumocystis jirovecii

Description of Pathogen Pneumocystis jirovecii (formerly called P. carinii ) is an opportunistic human respiratory pathogen. Although Pneumocystis organisms share some of the common features of protozoa, molecular genetic comparisons have definitively placed Pneumocystis among the ascomycetous fungi. , Pneumocystis organisms display strict host-species specificity, and the name P. jirovecii designates a genetically and phenotypically distinct form capable of infecting humans but not other mammals. In…

Histoplasma capsulatum (Histoplasmosis)

Histoplasmosis is the most common primary systemic mycosis in the Americas, affecting hundreds of thousands of people living in urban and rural areas of the Ohio and Mississippi river valleys, some mideastern states, and parts of Central and South America. , The fungus is also endemic in other continents such as Australia, Africa, and Asia. The Pathogen Histoplasmosis is caused by the dimorphic fungus Histoplasma capsulatum…

Cryptococcus Species

The majority of human cryptococcal infections are caused by one of two species: Cryptococcus neoformans and Cryptococcus gattii. These species were previously separated into 3 varieties: C. neoformans var. neoformans, C. neoformans var. grubii, and C. neoformans var. gattii, which were classified into 8 molecular genotypes and 5 serotypes based on capsular polysaccharide antigens. Serotypes A and D and the hybrid diploid AD strains belong to…

Sporothrix schenckii Complex (Sporotrichosis)

Sporotrichosis is a chronic subcutaneous fungal infection caused by thermally dimorphic fungal species in the Sporothrix schenckii complex . This species complex is found worldwide in soil, on decomposing vegetation, and on plant material, such as sphagnum moss, hay bales, rosebushes, and wood. In nature, S. schenckii grows as a filamentous mold, but in tissue it forms small budding yeast cells. Sporotrichosis has a worldwide distribution…

Malassezia Species

Microbiology Malassezia (formerly called Pityrosporum ) is a genus of lipophilic, basidiomycetous yeasts lacking ballistospores and classified in the order Malasseziales . Its phylogenetic placement within the Ustilaginomycotina (Basidiomycota) is highly supported. Malassezia increasingly is recognized as an opportunist affecting both humans and animals. , Newer identification methods have made the characterization of several new species possible and also have enhanced our understanding of the ecology…

Agents of Mucormycosis

Mucormycosis (formerly zygomycosis) is an uncommon but emerging infection that occurs in immunocompromised patients, including children and neonates. Previously, the term zygomycosis was used to refer to syndromes of mucormycosis and entomophthoromycosis, but updates in taxonomy determined that the phylum name Zygomycota is invalid. Because the phylum Zygomycota no longer exists, the term zygomycosis has become obsolete. , Molds causing these infections are now in the…

Agents of Hyalohyphomycosis and Phaeohyphomycosis

Agents of hyalohyphomycosis and phaeohyphomycosis are ubiquitous filamentous molds. (Moulds is the preferred spelling by many mycologists.) These molds are soil saprobes and plant pathogens that have gained notoriety as emerging pathogens in immunocompromised hosts, including children. The pathogenesis of infections with these organisms is not clearly established because many of these organisms are minimally pathogenic in humans. However, fungal conidia can cause infection in severely…

Aspergillus Species

Although yeasts such as Candida species are the most common causes of invasive fungal infections in children, Aspergillus infections are increasing and have a dismal mortality rate. Invasive aspergillosis is a prominent infection because of more intensive chemotherapies for certain malignant diseases, immunosuppressive therapies for graft-versus-host disease (GvHD), increased use of mismatched or unrelated donor transplantations, newer preparative regimens to avoid graft rejection or disease relapse,…

Candida Species

Candida infections occur frequently in neonates, infants, and children, ranging from superficial skin infections to invasive disease. The number of children at risk for invasive candidiasis (IC) continues to increase due to new cancer therapies, increasing numbers of immunosuppressed solid organ and bone marrow transplant recipients, immune modulating agents for a wide range of autoimmune and autoinflammatory diseases, and utilization of novel medical devices. Epidemiology The…

Classification of Fungi

Fungal disease contributes significantly to patients’ morbidity and mortality in certain clinical settings. Extensive medical interventions, immunosuppression, and a heightened awareness of fungal disease, particularly opportunistic mycoses in the setting of immune compromise, have all necessitated an increased understanding of fungal etiologic agents and their classification, identification, and clinical manifestations. The Agents Definition Fungi are heterotrophic (using organic compounds as a primary source of energy and…

Hepatitis E Virus

Hepatitis E virus (HEV) is the major etiologic agent of enterically transmitted non-A viral hepatitis worldwide. It is a spherical, nonenveloped, single-stranded, positive-sense RNA virus that is approximately 32–34 nm in diameter. HEV is the sole member of the family Hepeviridae , genus Orthohepevirus . The HEV genome is approximately 7.2 kilobases and consists of 3 open reading frames (ORF 1, ORF 2, and ORF 3).…

Astroviruses

Astroviruses were first described in 1975 when they were detected by electron microscopy on stool specimens of infants with gastroenteritis. , Since 1990, with development of sensitive and specific diagnostic methods, including enzyme immunoassays (EIAs) and reverse transcriptase polymerase chain reaction (RT-PCR), astroviruses have been identified as relatively common causes of community-acquired and hospital-acquired gastroenteritis. Astroviruses are among the most common viral causes of gastroenteritis among…

Caliciviruses

Pathogens and Pathogenesis The first calicivirus was discovered in 1972 by electron microscopic examination of stool samples from children affected by an outbreak of gastroenteritis in a school in Norwalk, Ohio, several years previously. This discovery of the subsequently named Norwalk virus marked the first identification of a virus as a cause of gastroenteritis. Norwalk virus and other viruses with similar morphologic features are now classified…

Rhinoviruses

Acknowledgment Dr. Pappas retains the coauthorship of the late Dr. J. Owen Hendley as a tribute to his substantial contribution to our knowledge of respiratory viruses and to this chapter. Rhinoviruses ( rhino meaning “nose”) are the most common causes of the common cold, and they account for at least 50% of upper respiratory tract infections in children and adults. Rhinoviruses are difficult to detect, but…

Hepatitis A Virus

The Pathogen Hepatitis A virus (HAV) is a positive-sense RNA virus and a member of the Picornaviridae family. The single-stranded RNA genome is approximately 7500 nucleotides long and contains a single open reading frame. The encoded polyprotein includes structural proteins for the 27–28 nm diameter capsid, nonstructural proteins with protease or polymerase activities, and other proteins with functions that have not been fully determined. , Although…

Enteroviruses and Parechoviruses

The human enteroviruses and parechoviruses are members of the Picornaviridae family that are commonly transmitted by enteric and respiratory routes. They cause a wide spectrum of illnesses in people of all ages. The enteroviruses are divided among 4 species within the genus Enterovirus (i.e., human enterovirus A , B , C , and D ) based on RNA sequence relatedness. Enterovirus species C polioviruses and 3…

Polioviruses

Pathogen and Pathophysiology Polioviruses are positive-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They have a naked protein capsid consisting of 4 structural proteins, VP1 to VP4. The RNA-dependent RNA polymerase encoded for genome replication lacks a proofreading mechanism. Consequently, poliovirus can mutate rapidly with replication. The 3 serotypes of poliovirus are antigenically distinct, but all 3 have 70% nucleotide identity. Polioviruses…