Parasites in the Liver



Parasites in the Liver


Bobbi S. Pritt, MD, MSc



9.1 INTRODUCTION

Parasites are an important cause of infections in the liver and biliary tract and are responsible for significant morbidity and mortality in many parts of the world.1,2 The spectrum of parasites includes single-celled protozoa, as well as multicellular roundworms (nematodes), tapeworms (cestodes), flukes (trematodes), and rarely, arthropods (Tables 9.1, 9.2, 9.3, 9.4, and 9.5). Several parasitic infections are classified by the World Health Organization (WHO) as neglected tropical diseases on the basis of their impact on billions of individuals living in developing countries.1 The Centers for Disease Control and Prevention (CDC) has also identified five neglected parasitic infections in the United States as priorities for public health action, of which four can involve the liver.3 This chapter will focus on the most important members of these groups that are likely to be encountered by the anatomic pathologist. It is important to note that the prevalence of these parasites varies widely with the travel history and immune status of the host. It is therefore essential to obtain a good clinical history when evaluating a specimen for parasites.


9.2 PROTOZOA


Entamoeba histolytica (amebiasis, amebic liver abscess)


Definition, etiology, and pathogenesis

The term amebiasis refers to infection with the parasitic ameba, Entamoeba histolytica. This protozoan causes primary intestinal infection and is a rare but important cause of liver disease.4,5 Transmission is through the fecal-oral route, in which individuals become infected primarily through ingestion of cysts in fecally contaminated food and water.6 It is, therefore, unsurprising that infection is most common in resource-limited settings where poor sanitary conditions exist. In developed countries, infection is usually limited to travelers and immigrants from endemic areas.4 It is estimated that 1% of the world’s population (74,000,000 individuals) is infected with E. histolytica and that there are approximately 50 million symptomatic cases and 100,000 deaths each year.7

Following ingestion of the infectious cyst form, the parasite excysts and releases a trophozoite, which colonizes the large intestine and replicates by binary fission.6US Some trophozoites eventually form


cysts, and both cysts and trophozoites are shed in the stool. If the cysts enter the environment and contaminate food or water, then the infection can be passed to other individuals. Infection can also be passed directly through oral-anal intercourse.








Table 9.1 Protozoan infections of the human liver





































Parasite (infection)

Pathology

Epidemiology


Cryptosporidium spp. (cryptosporidiosis)a

Cholangitis; intracellular parasites in bile duct ep-ithelium below the brush border; extension from intestinal disease

Worldwide, usually pro-foundly immunocompro-mised hosts


Cyclospora cayetanensis (cyclosporiasis)

Cholangitis; intracel-lular parasites in the cytoplasm of bile duct epithelial cells; extension from intestinal disease

Regions of the tropics and subtropics with poor sanitation; outbreaks in nonendemic countries due to imported produce


Cystoisospora (Isospora) belli (cyclosporiasis)

Cholangitis; intracel-lular parasites in the cytoplasm of bile duct epithelial cells; extension from intestinal disease

Regions of the tropics and subtropics with poor sanitation


Entamoeba histolyticaa,b (amebiasis)

Acute nonsuppurative hepatitis and hepatic abscess (i.e., pseudoab-scess); can involve an entire lobe. Extracellular trophozoites primarily at periphery of lesion; concurrent intestinal disease may be absent.

Regions of the tropics and subtropics with poor sanitation


Leishmania spp.a (visceral leishmaniasis, kala-azar)

Hepatomegaly (may be massive) due to parasite infiltration, fibrosis; amastigotes within Kupffer cells; Usually concurrent lymph node, spleen, and bone marrow involvement

Tropics and subtropics


Plasmodium falciparuma (malaria)

Hepatomegaly, grayblack decolorization due to hemozoin pigment in macrophages and infected erythrocytes; component of systemic disease

Tropics and subtropics


Toxoplasma gondiia (toxoplasmosis)

Hepatomegaly, hepatocellular necrosis; intracellular and extracellular tachyzoites in necrotic regions. Liver involvement is rare and a component of systemic disseminated disease.

Worldwide; usually neonates and profoundly immunocompromised hosts


a Most common parasites causing human disease.
b The term amebiasis is most commonly used to describe infection with Entamoeba histolytica but may also be used to describe infection with the free-living amebae.

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Oct 16, 2018 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Parasites in the Liver

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