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Herpes Simplex Virus

The 2 closely related herpes simplex viruses (HSVs), HSV type 1 (HSV-1) and HSV type 2 (HSV-2), cause a variety of illnesses, depending on the anatomic site where the infection is initiated, the immune state of the host, and whether the symptoms reflect primary or recurrent infection. Common infections involve the skin, eye, oral cavity, and genital tract. Infections tend to be mild and self-limiting, except…

Parvoviruses

The parvoviruses are small, single-stranded DNA viruses. They are common infectious agents of a variety of animal species, including mammals, birds, and insects. Parvoviruses as a group include a number of important animal pathogens. There are 5 different types of parvoviruses known to infect humans: the dependoviruses, also called adeno-associated viruses (AAV), parvovirus B19 (B19V), human bocaviruses (HBoV), parvovirus 4 (PARV4), and human bufavirus (HBuV). B19V…

Nonpolio Enteroviruses

The genus Enterovirus contains a large number of viruses spread via the gastrointestinal and respiratory routes that produce a broad range of illnesses in patients of all ages. Many of the manifestations predominantly affect infants and young children. Etiology Enteroviruses are nonenveloped, single-stranded, positive-sense viruses in the Picornaviridae (“small RNA virus”) family, which also includes the rhinoviruses, hepatitis A virus, and parechoviruses. The original human enterovirus…

Polioviruses

Etiology The polioviruses are nonenveloped, positive-stranded RNA viruses belonging to the Picornaviridae family, in the genus Enterovirus, species Enterovirus C and consist of 3 antigenically distinct serotypes (types 1, 2, and 3). Polioviruses spread from the intestinal tract to the central nervous system (CNS), where they cause aseptic meningitis and poliomyelitis, or polio. The polioviruses are extremely hardy and can retain infectivity for several days at…

Mumps

Mumps is an acute self-limited infection that was once commonplace but is now uncommon in developed countries because of widespread use of vaccination. It is characterized by fever, bilateral or unilateral parotid swelling and tenderness, and the frequent occurrence of meningoencephalitis and orchitis. Although infrequent in countries with extensive vaccination programs, mumps remains endemic in the rest of the world, warranting continued vaccine protection. Nonetheless, outbreaks…

Rubella

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

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…

Principles of Antiviral Therapy

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

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…

Mucormycosis

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…

Sporotrichosis (Sporothrix schenckii)

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,…

Paracoccidioides brasiliensis

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…

Coccidioidomycosis ( Coccidioides Species)

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…

Blastomycosis ( Blastomyces dermatitidis and Blastomyces gilchristii )

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…

Histoplasmosis (Histoplasma capsulatum)

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…

Aspergillus

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…

Cryptococcus neoformans and Cryptococcus gattii

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…

Candida

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…

Principles of Antifungal Therapy

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…