Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Trichuriasis (Trichuris trichiura)

Etiology Trichuriasis is caused by the whipworm , Trichuris trichiura, a nematode, or roundworm, that inhabits the cecum and ascending colon. The principal hosts of T. trichiura are humans, who acquire infection by ingesting embryonated, barrel-shaped eggs ( Fig. 319.1 ). The larvae escape from the shell in the upper small intestine and penetrate the intestinal villi. The worms slowly move toward the cecum, where the…

Hookworms ( Necator americanus and Ancylostoma spp.)

Etiology Two major genera of hookworms, which are nematodes, or roundworms, infect humans. Necator americanus, the only representative of its genus, is a major anthropophilic hookworm and is the most common cause of human hookworm infection. Hookworms of the genus Ancylostoma include the anthropophilic hookworm Ancylostoma duodenale, which also causes classic hookworm infection, and the less common zoonotic species Ancylostoma ceylanicum (restricted mostly to Southeast Asia).…

Ascariasis (Ascaris lumbricoides)

Etiology Ascariasis is caused by the nematode, or roundworm , Ascaris lumbricoides. Adult worms of A. lumbricoides inhabit the lumen of the small intestine. The reproductive potential of Ascaris is prodigious; a gravid female worm produces 200,000 eggs per day. The fertile ova are oval in shape with a thick, mammillated covering measuring 45-70 µm in length and 35-50 µm in breadth ( Fig. 317.1 ). After passage…

Toxoplasmosis (Toxoplasma gondii)

Toxoplasma gondii, an obligate, intracellular, apicomplexan protozoan, is acquired perorally, transplacentally, or rarely parenterally in laboratory accidents, transfusions, or from a transplanted organ. In immunologically normal children, acute acquired infection most often is asymptomatic or unrecognized, but may cause lymphadenopathy or affect almost any organ. Once acquired, latent encysted organisms persist in the host throughout life. In immunocompromised persons, initial acquisition or recrudescence of latent organisms…

Babesiosis (Babesia)

Babesiosis is a malaria-like disease caused by intraerythrocytic protozoa that are transmitted by hard body ( ixodid ) ticks. The clinical manifestations of babesiosis range from subclinical illness to fulminant disease resulting in death. Etiology More than 100 species of Babesia infect a wide variety of wild and domestic animals throughout the world. Only a few of these species have been reported to infect humans, including…

Malaria (Plasmodium)

Malaria is an acute illness characterized by paroxysms of fever, chills, sweats, fatigue, anemia, and splenomegaly. It has played a major role in human history, causing harm to more people than perhaps any other infectious disease. Although substantial progress has been made in combating malaria in endemic areas, with a 37% reduction in malaria incidence and 60% reduction in malaria mortality, malaria remains one of the…

American Trypanosomiasis (Chagas Disease; Trypanosoma cruzi )

American trypanosomiasis or Chagas disease is caused by the protozoan Trypanosoma cruzi . Its natural vectors are the reduviid insects, specifically triatomines , variably known as wild bedbugs, assassin bugs, or kissing bugs. It can also be transmitted orally from contaminated food, vertically from mother to child, and through blood transfusion or organ transplantation. Signs and symptoms of acute Chagas disease are usually nonspecific, whereas chronic…

African Trypanosomiasis (Sleeping Sickness; Trypanosoma brucei Complex)

Sixty million people in 36 countries are at risk for infection with Trypanosoma brucei complex, the causative agent of sleeping sickness. Also known as human African trypanosomiasis (HAT) , this disease is restricted to sub-Saharan Africa, the range of the tsetse fly vector. It is a disease of extreme poverty, with the highest disease burden observed in remote rural areas. HAT comes in 2 geographically and…

Leishmaniasis (Leishmania)

The leishmaniases are a diverse group of diseases caused by intracellular protozoan parasites of the genus Leishmania, which are transmitted by phlebotomine sandflies. Multiple species of Leishmania are known to cause human disease involving the skin and mucosal surfaces and the visceral reticuloendothelial organs ( Table 311.1 ). Cutaneous disease is usually localized and mild but may cause cosmetic disfigurement. Rarely, cutaneous infection can disseminate or…

Trichomoniasis (Trichomonas vaginalis)

Trichomoniasis is caused by the protozoan Trichomonas vaginalis. It is the second most common sexually transmitted infection worldwide. Vulvovaginitis is the symptomatic disease form, but T. vaginalis has been implicated in pelvic inflammatory disease, pregnancy loss, chronic prostatitis, and an increased risk of HIV transmission. Epidemiology Over 276 million new cases of trichomoniasis occur annually, making it the most common nonviral sexually transmitted infection globally. Most…

Cryptosporidium, Cystoisospora, Cyclospora, and Microsporidia

The spore-forming intestinal protozoa Cryptosporidium, Cystoisospora (formerly Isospora ), and Cyclospora are important intestinal pathogens in both immunocompetent and immunocompromised hosts. Cryptosporidium, Cystoisospora, and Cyclospora are coccidian parasites that predominantly infect the epithelial cells lining the digestive tract. Microsporidia were formerly considered spore-forming protozoa but have been reclassified as fungi. Microsporidia are ubiquitous, obligate intracellular parasites that infect many other organ systems in addition to the…

Giardiasis and Balantidiasis

Giardia duodenalis Chandy C. John Giardia duodenalis is a flagellated protozoan that infects the duodenum and jejunum. Infection results in clinical manifestations that range from asymptomatic colonization to acute or chronic diarrhea and malabsorption. Infection is more prevalent in children than in adults. Giardia is endemic in areas of the world with poor levels of sanitation. It is also an important cause of morbidity in developed countries,…

Amebiasis

Entamoeba species infect or colonize up to 10% of the world's population, particularly in resource-limited settings. In most infected individuals, Entamoeba histolytica or a related species parasitizes the lumen of the gastrointestinal tract and causes few symptoms or sequelae. Although E. histolytica is the only invasive species, other Entamoeba species have been implicated in human disease, and molecular epidemiology is helping to detail the role that…

Primary Amebic Meningoencephalitis

Naegleria, Acanthamoeba, Balamuthia, and Sappinia are small, free-living amebae that cause human amebic meningoencephalitis, which has two distinct clinical presentations. The more common is an acute, fulminant, and usually fatal primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri that occurs in previously healthy children and young adults. Granulomatous amebic meningoencephalitis, which is caused by Acanthamoeba, Balamuthia, and Sappinia, is a more indolent infection that typically occurs…

Principles of Antiparasitic Therapy

Parasites are divided into three main groups taxonomically: protozoans, which are unicellular, and helminths and ectoparasites, which are multicellular. Chemotherapeutic agents appropriate for one group may not be appropriate for the others, and not all drugs are readily available ( Table 305.1 ). Some drugs are not available in the United States, and some are available only from the manufacturer, specialized compounding pharmacies, or the Centers…

Transmissible Spongiform Encephalopathies

The transmissible spongiform encephalopathies (TSEs, prion diseases) are slow infections of the human nervous system, consisting of at least four diseases of humans ( Table 304.1 ): kuru; Creutzfeldt-Jakob disease (CJD) with its variants—sporadic CJD (sCJD), familial CJD (fCJD), iatrogenic CJD (iCJD), and new-variant or variant CJD (vCJD); Gerstmann-Sträussler-Scheinker syndrome (GSS); and fatal familial insomnia (FFI), or the even more rare sporadic fatal insomnia syndrome. TSEs…

Human T-Lymphotropic Viruses (1 and 2)

Etiology Human T-lymphotropic viruses 1 (HTLV-1) and 2 (HTLV-2) are members of the Deltaretrovirus genus of the Retroviridae family and are single-stranded RNA viruses that encode reverse transcriptase, an RNA-dependent DNA polymerase that transcribes the single-stranded viral RNA into a double-stranded DNA copy. HTLV-1 was the first human retrovirus discovered, isolated in 1979 by the Gallo laboratory from a cutaneous T-cell lymphoma. The closely related virus…

Human Immunodeficiency Virus and Acquired Immunodeficiency Syndrome

Advances in research and major improvements in the treatment and management of HIV infection have brought about a substantial decrease in the incidence of new HIV infections and AIDS in children. Globally, from 2000 to 2015, there has been an estimated 70% decline in new infections in children aged 0-14 yr, largely the result of antiretroviral treatment (ART) of HIV-infected pregnant women for the prevention of mother-to-child…

Rabies

Rabies virus is a bullet-shaped, negative-sense, single-stranded, enveloped RNA virus from the family Rhabdoviridae, genus Lyssavirus. There currently are 14 species of Lyssavirus. The classic rabies virus (genotype 1) is distributed worldwide and naturally infects a large variety of animals. The other genotypes are more geographically confined, with none found in the Americas. Seven Lyssavirus genotypes are associated with rabies in humans, although genotype 1 accounts…