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Ectoparasites

Some arthropods are of medical importance predominantly because of the direct effect of infestation and these are considered in this chapter. Arthropods that cause illness through envenomation (mainly arachnids) are discussed in the following chapter along with other noxious exposures (bites, stings, venoms, toxins). Others, considered elsewhere ( Chapter 1 ), are responsible for disease primarily because they are vectors of viral, bacterial or parasitic pathogens.…

Infections Acquired by Airborne Transmission

Pneumonia continues to exert a terrible toll on health, especially in childhood, where it is the leading infectious cause of death in under-fives. Airborne infections, whether viral, bacterial or fungal, are principally acquired by inhalation of pathogenic organisms, either directly from the environment as spores or attached to dust particles, or within aerosolized droplets and droplet nuclei generated by the respiratory tract mucosa. Some respiratory tract…

Infections Acquired Through the Gastrointestinal Tract

Many of the important pathogens that gain entry through the gastrointestinal tract are cosmopolitan in their distribution. They include viruses, bacteria, protozoa, helminths and endoparasitic arthropods. The first three of these can be directly infectious for humans when they are passed in the faeces but, in the case of helminths, the eggs may become infectious only after maturation in the soil (e.g. Ascaris lumbricoides ) or…

Infections Acquired Percutaneously

Soil There are estimated to be billions of microorganisms in a handful of soil, so it might be considered surprising that it does not serve as a source for more pathogens. Indeed, given that soil cannot be decontaminated globally, and thus soil-acquired infections like tetanus can never be eradicated, this is fortunate. ‘Soil-transmitted helminths’ (STHs) is the collective term (interchangeable with ‘geohelminths’) applied principally to three…

Arthropod-Borne Diseases

Arthropods can transmit viruses, bacteria and parasites. To date, there is no known arthropod-borne fungal infection. Mosquitoes transmit more disease, and a greater variety of disease, than any other arthropod. However, other biting flies, fleas, ticks, lice and mites are also responsible for transmission of some infections. Most of these infections are zoonotic; animal and human hosts may exhibit disparate behaviour and inhabit differing environments, thus…

Clostridioides difficile infection

Clostridioides difficile , formerly knowns as Clostridium difficile, is a Gram-positive, anaerobic bacillus, with a spore phase that prolongs survival in the environment. Ingestion of spores that are resistant to gastric acid results in maturation into the bacillus stage. C. difficile replicates disproportionally to other colonic flora when the balance is affected by another pathogen, absence of enteral feeds, exposure to antimicrobials, or chemotherapeutics. C. difficile…

Gastrointestinal viruses

Diarrheal disease is the second most common cause of death in children younger than 5 years worldwide, according to the World Health Organization (WHO). In the United States, viruses are the major cause of acute gastroenteritis in children; norovirus, rotavirus, adenovirus, astrovirus, and sapovirus are the most commonly detected. Viral gastroenteritis also affects immunocompromised children, in whom it causes more morbidity and mortality, including longer duration…

Strongyloides, cryptosporidium , and other parasitic infections

Parasitic infections are an uncommon but potentially important cause of morbidity and mortality in children undergoing solid organ transplantation (SOT). Although few data have been published relating to parasitic infections in children undergoing hematopoietic stem cell transplantation (HSCT) or being treated for cancer, the high degree of immunodeficiency relating to treatment with chemotherapy and ablation therapy early after HSCT transplant, as well as the potential presence…

Pneumocystis pneumonia

Epidemiology and risk factors Pneumocystis jirovecii (formerly Pneumocystis carinii ) is an infrequent though potentially deadly cause of fungal pneumonia ( P. jirovecii pneumonia [PJP]) in immunocompromised patients. P. jirovecii is a ubiquitous unicellular organism found around the world with an affinity for the respiratory tract. Most individuals are exposed in childhood and many are colonized, but disease occurs almost exclusively in immunocompromised hosts. Individuals with…

Nocardia and actinomyces

Nocardia Epidemiology and risk factors Nocardia species are a heterogeneous group of ubiquitous aerobic, gram-positive filamentous organisms that reside in soil and decaying organic matter and are associated with an array of infections in both immunocompetent and immunocompromised hosts. First described by Edmond Nocard in 1888, Nocardia infections are associated with a range of illnesses, from localized suppurative skin lesions and chronic mycetomas, to invasive pulmonary…

Toxoplasma gondii

Epidemiology and risk factors Toxoplasma gondii is a protozoan parasite in the phylum Apicomplexa. It infects humans and almost all warm-blooded animals, including mammals and birds. Transmission of T. gondii is linked to its biological life cycle and occurs most frequently with the ingestion of oocysts in soil and water or with the ingestion of tissue cysts from infected animals and, less frequently, with transplacental dissemination…

Histoplasmosis, blastomycosis, and coccidioidomycosis

Histoplasmosis, blastomycosis, and coccidioidomycosis are the most common endemic mycoses in North America. Their geographic distribution encompasses close to two-thirds of the United States and parts of Canada, Mexico, Central and South America, and Africa. Histoplasma capsulatum , Blastomyces dermatitidis , Coccidioides immitis , and C. posadasii are dimorphic fungi that grow as yeast in the human body and as a mycelial form in the environment.…

Cryptococcosis and other rare invasive yeasts infections

The vast majority of invasive yeast infections in organ transplant recipients and patients with malignancy are caused by Candida species. However, a variety of other yeasts are important opportunistic pathogens for these patients and are reviewed in this chapter. This includes the Cryptococcus neoformans–Cryptococcus gattii complex, which is the second most common cause of invasive yeast infections in this cohort and an important cause of fungal…

Candidiasis

The Candida genus represents a group of more than 200 species present in both human flora and the environment. Of these, approximately 20 have been implicated in human disease. Typically, the pathogens from this genus are divided into C. albicans and non- albicans Candida species. The epidemiologic distribution of Candida spp. in children differs somewhat from that of adults. C. albicans is the most common species,…

Mucormycosis, fusariosis, scedosporiasis, and other invasive mold diseases

Although invasive aspergillosis is the most common invasive mold disease (IMD), mucormycosis and other non- Aspergillus opportunistic mold infections are increasingly associated with significant morbidity and mortality among highly immunocompromised patients. Early clinical suspicion is critically important to accurately distinguish, diagnose, and appropriately treat these life-threatening infections. Their relative rarity compared with other infections in these patient populations makes diagnosis and treatment challenging because of the…

Aspergillosis

Aspergillus is a ubiquitous organism with an ecological niche in the soil. Most disease is primarily caused by A. fumigatus , A. flavus , A. niger , A. terreus , and A. nidulans, and classification of the genus has been revised multiple times to incorporate newer molecular definitions. A. fumigatus causes approximately 70% to 80% of cases of invasive aspergillosis (IA), but it is difficult to…

BK and other polyomavirus associated diseases in children

Polyomavirus (PyV) infections were first described in mice in 1952 as a cause of tumors in newborn animals. Since then, PyVs have been found in virtually all vertebrates, including primates, monkeys, cows, rabbits, birds, and fish. BK polyomavirus (BKPyV) was isolated in 1971 from a kidney transplant patient shedding decoy cells in the urine. The isolation of JC polyomavirus (JCPyV) was also reported in 1971 from…

Adenoviruses

Adenoviruses In the past few decades, significant progress has been made in understanding the epidemiology of adenovirus infections and developing preventative and therapeutic strategies. However, adenovirus infections remain a clinical and diagnostic challenge. Isolation of adenovirus does not necessarily correlate with invasive disease because the virus may persist asymptomatically in lymphocytes. Adenoviruses are classified within seven species (A through G) based on guanine and cytosine content…

Respiratory viruses

Epidemiology and risk factors The seasonality of respiratory virus infections among immunocompromised children is similar to that in the community ( Fig. 21.1 ). Respiratory syncytial virus (RSV) typically circulates in the community from November through March, with peak detection in January. Human metapneumovirus follows a similar pattern although often somewhat later. Influenza epidemiology can vary somewhat from year to year, with typical seasons lasting from…