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Microbiology
Table of Contents
Unit 24 Overview: Digestive System Infections
24.1 Anatomy and Normal Microbiota of the Digestive System
24.2 Microbial Diseases of the Mouth and Oral Cavity
24.3 Bacterial Infections of the Gastrointestinal Tract
24.4 Viral Infections of the Gastrointestinal Tract
24.5 Protozoan Infections of the Gastrointestinal Tract
24.6 Helminthic Infections of the Gastrointestinal Tract

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24.6 Helminthic Infections of the Gastrointestinal Tract

Citation:

Gastrointestinal helminths are parasitic worms that infect the digestive system. These sneaky invaders have complex life cycles, often starting with eggs in contaminated soil or food before developing into adult worms in our gut.

These worms can cause a range of health issues, from mild discomfort to severe complications. Diagnosis usually involves examining stool samples, while treatment typically includes anti-parasitic medications. Good hygiene and sanitation are key to preventing these pesky infections.

Helminthic Infections of the Gastrointestinal Tract

Life cycles of gastrointestinal helminths

  • Ascaris lumbricoides (roundworm)
    • Ingestion of embryonated eggs from contaminated soil or food (vegetables)
    • Larvae hatch in small intestine, migrate through bloodstream to lungs, ascend trachea, are swallowed, and mature into adult worms in small intestine
  • Trichuris trichiura (whipworm)
    • Ingestion of embryonated eggs from contaminated soil or food (unwashed fruits)
    • Eggs hatch in small intestine, larvae mature and attach to mucosa of cecum and ascending colon
  • Ancylostoma duodenale and Necator americanus (hookworms)
    • Infective larvae penetrate skin (bare feet), enter bloodstream, migrate to lungs, ascend trachea, are swallowed, and mature into adult worms in small intestine
  • Strongyloides stercoralis (threadworm)
    • Infective larvae penetrate skin or are ingested, migrate to lungs, ascend trachea, are swallowed, and mature into adult worms in small intestine
    • Autoinfection occurs when larvae penetrate intestinal mucosa or perianal skin, leading to persistent infection
  • Enterobius vermicularis (pinworm)
    • Ingestion or inhalation of eggs from contaminated surfaces (toys) or hands
    • Larvae hatch in small intestine and mature into adult worms in cecum and appendix
    • Female worms migrate to perianal region to lay eggs, causing itching and facilitating reinfection through scratching and transfer of eggs to mouth

Pathogenesis of helminthic digestive infections

  • Ascaris lumbricoides
    • Larval migration may cause pneumonitis known as Löffler's syndrome
    • Adult worms may cause intestinal obstruction, perforation, or biliary obstruction (gallbladder)
    • Light infections often asymptomatic; heavy infections may cause abdominal pain, diarrhea, and malnutrition
  • Trichuris trichiura
    • Attachment of adult worms to intestinal mucosa causes inflammation and bleeding
    • Heavy infections may lead to abdominal pain, chronic diarrhea, iron-deficiency anemia, and rectal prolapse
  • Ancylostoma duodenale and Necator americanus
    • Larval penetration of skin may cause itching and rash known as ground itch
    • Adult worms attach to intestinal mucosa and feed on blood, causing iron-deficiency anemia
    • Abdominal pain, diarrhea, and protein malnutrition may occur due to blood loss and intestinal damage
  • Strongyloides stercoralis
    • Larval migration may cause pneumonitis
    • Adult worms embed in intestinal mucosa, causing inflammation and malabsorption
    • Immunosuppressed individuals at risk for severe hyperinfection syndrome and disseminated disease affecting multiple organs
  • Enterobius vermicularis
    • Perianal itching (pruritus ani) due to egg deposition by female worms
    • Rarely, ectopic infections may cause appendicitis or genital tract inflammation (vulvovaginitis)

Diagnosis and treatment of helminth infections

  • Diagnosis
    • Stool microscopy for ova and parasites (O&P) is the primary diagnostic method
      • Multiple samples may be needed due to intermittent shedding of eggs
      • Concentration techniques (formalin-ethyl acetate) increase sensitivity of detection
    • Scotch tape test used to detect Enterobius vermicularis eggs around perianal region
    • Serologic tests available for some infections (strongyloidiasis)
    • Imaging studies (X-rays, CT scans) may reveal adult worms or complications (intestinal obstruction)
    • Eosinophilia in blood tests can indicate helminthic infection
  • Treatment
    1. Ascaris lumbricoides: Albendazole, mebendazole, or pyrantel pamoate
    2. Trichuris trichiura: Albendazole, mebendazole, or ivermectin
    3. Ancylostoma duodenale and Necator americanus: Albendazole, mebendazole, or pyrantel pamoate; iron supplementation for anemia
    4. Strongyloides stercoralis: Ivermectin or albendazole; longer courses for hyperinfection syndrome
    5. Enterobius vermicularis: Albendazole, mebendazole, or pyrantel pamoate; treat household contacts and maintain hygiene to prevent reinfection
    • These medications are examples of anthelmintic drugs used to treat helminth infections
  • Prevention strategies include improved sanitation, proper disposal of human feces, wearing shoes in areas with soil-transmitted helminths, washing hands and produce, cooking food thoroughly, and avoiding contact with contaminated water or soil

Classification and Transmission of Helminths

  • Nematodes (roundworms): cylindrical body shape, includes Ascaris, hookworms, and pinworms
  • Cestodes (tapeworms): flat, segmented body, not typically found in gastrointestinal tract infections
  • Trematodes (flukes): leaf-shaped, mainly affect liver and lungs, but some species can infect intestines
  • Transmission:
    • Fecal-oral transmission is common for many gastrointestinal helminths
    • Some helminth infections are zoonotic, transmitted between animals and humans

Key Terms to Review (83)

Albendazole: Albendazole is a broad-spectrum anthelmintic medication used to treat a variety of parasitic worm infestations. It works by inhibiting the microtubule synthesis in parasites, leading to their death.
Ancylostoma doudenale: Ancylostoma duodenale is a parasitic nematode, commonly known as the Old World hookworm, that infects the small intestine of humans. It causes significant gastrointestinal distress and anemia due to blood loss.
Ascariasis: Ascariasis is an intestinal infection caused by the parasitic roundworm Ascaris lumbricoides. It primarily affects the gastrointestinal tract and can lead to malnutrition and other complications.
Ascaris lumbricoides: Ascaris lumbricoides is a large parasitic nematode that infects the human intestine, causing ascariasis. It is one of the most common helminthic infections worldwide.
Appendix: The appendix is a small, tube-like structure attached to the cecum of the large intestine. It is considered part of the gastrointestinal tract and plays a role in gut immunity.
Cestodes: Cestodes, also known as tapeworms, are a class of parasitic flatworms that reside in the digestive tracts of vertebrates. They acquire nutrients by absorbing them directly through their skin.
Cecum: The cecum is a pouch-like structure of the large intestine situated at the junction of the small and large intestines. It plays a role in absorbing fluids and salts that remain after intestinal digestion and absorption.
Clonorchis sinensis: Clonorchis sinensis is a parasitic liver fluke that infects the bile ducts of humans and other mammals. Infection occurs through the ingestion of contaminated freshwater fish.
Colon: The colon, also known as the large intestine, is a major part of the digestive system responsible for absorbing water and electrolytes from indigestible food matter. It also houses a vast number of microorganisms that constitute the gut microbiota.
Cysticercosis: Cysticercosis is a parasitic tissue infection caused by the larval stage of the pork tapeworm, Taenia solium. It occurs when eggs are ingested and develop into cysticerci in tissues such as muscles, brain, and eyes.
Cutaneous larva migrans: Cutaneous larva migrans is a skin infection caused by hookworm larvae that penetrate the skin. It is characterized by serpiginous, erythematous tracks formed by the migrating larvae.
Cystic echinococcosis: Cystic echinococcosis is a parasitic infection caused by the larval stage of Echinococcus granulosus. It primarily affects the liver and lungs, forming cysts that can cause significant health issues.
Diphyllobothrium: Diphyllobothrium is a genus of tapeworms known to infect the gastrointestinal tract of various hosts, including humans. They are commonly acquired through the consumption of raw or undercooked fish.
Enterobiasis: Enterobiasis is a common intestinal infection caused by the pinworm Enterobius vermicularis. It primarily affects children and is highly contagious.
Fasciolopsiasis: Fasciolopsiasis is an infection caused by the giant intestinal fluke Fasciolopsis buski. It primarily affects the gastrointestinal system and is acquired through ingestion of contaminated water plants.
Fasciola: Fasciola is a genus of parasitic liver flukes, primarily affecting the liver and bile ducts of various mammals including humans. The most notable species are Fasciola hepatica and Fasciola gigantica, which cause fascioliasis.
Fascioliasis: Fascioliasis is a parasitic infection caused by liver flukes, primarily Fasciola hepatica. It affects the liver and bile ducts of humans and animals.
Fasciolopsis buski: Fasciolopsis buski is a large intestinal fluke that causes fasciolopsiasis, an infection in humans and pigs. It is primarily found in Asia and infects the gastrointestinal tract through ingestion of contaminated water plants.
Flukes: Flukes are parasitic flatworms belonging to the class Trematoda. These helminths often infect the gastrointestinal tract of their hosts, including humans.
Gallbladder: The gallbladder is a small, pear-shaped organ located under the liver that stores and concentrates bile, a digestive fluid produced by the liver. It releases bile into the small intestine to aid in the digestion of fats.
Helminth: Helminths are parasitic worms that live and feed on hosts, causing infections in various body systems. They are a significant concern in microbiology due to their impact on human health, especially within the gastrointestinal tract.
Hookworm infection: Hookworm infection is a parasitic disease caused by intestinal nematodes, primarily Ancylostoma duodenale and Necator americanus. It is acquired through contact with contaminated soil, often leading to gastrointestinal symptoms and anemia.
Hookworms: Hookworms are parasitic nematodes that infect the small intestine, causing gastrointestinal issues. They attach to the intestinal wall and feed on blood, leading to anemia and other health problems.
Hydatid disease: Hydatid disease, also known as echinococcosis, is a parasitic infection caused by the larval stage of Echinococcus tapeworms. It typically forms cysts in the liver and lungs, leading to various health complications.
Intestine: The intestine is a long, continuous tube running from the stomach to the anus, where digestion and absorption of nutrients occur. It consists of two main parts: the small intestine and the large intestine.
Ivermectin: Ivermectin is an antiparasitic drug used to treat various helminthic infections. It works by binding to glutamate-gated chloride channels in the parasite's nerve and muscle cells, causing paralysis and death of the parasite.
Intestinal flukes: Intestinal flukes are parasitic flatworms that infect the intestines of their hosts, causing helminthic infections. They are typically transmitted through the consumption of contaminated food or water.
Liver flukes: Liver flukes are parasitic flatworms that infect the liver, bile ducts, and gallbladder of various mammals, including humans. They are transmitted through the ingestion of contaminated water or food.
Mebendazole: Mebendazole is a broad-spectrum anthelmintic drug used to treat parasitic worm infections, particularly those affecting the gastrointestinal tract. It works by inhibiting the synthesis of microtubules, leading to impaired glucose uptake in helminths.
Nematodes: Nematodes are a diverse group of roundworms that can infect the gastrointestinal tract, causing various diseases. They are one of the most common helminths affecting human health.
Niclosamide: Niclosamide is an antiparasitic drug primarily used to treat tapeworm infections in the gastrointestinal tract. It works by inhibiting the parasite's ability to generate energy, leading to its death.
Opisthorchis viverrini: Opisthorchis viverrini is a parasitic liver fluke that infects the bile ducts of humans after consumption of raw or undercooked freshwater fish. It is known to cause opisthorchiasis and can lead to serious complications such as cholangiocarcinoma.
Opisthorchis felineus: Opisthorchis felineus is a parasitic flatworm, belonging to the class Trematoda, that infects the liver, gallbladder, and bile ducts of mammals including humans. It primarily causes opisthorchiasis, a significant helminthic infection in various parts of the world.
Pancreas: The pancreas is a glandular organ in the digestive system that produces enzymes and hormones, including insulin. It plays a crucial role in regulating blood sugar levels and aiding digestion.
Pharynx: The pharynx is a muscular tube that connects the nasal and oral cavities to the larynx and esophagus. It plays a role in both respiratory and digestive systems by facilitating the passage of air and food.
Pinworms: Pinworms are small, white parasitic worms that primarily infect the human gastrointestinal tract, particularly the colon and rectum. Infection occurs through the ingestion of pinworm eggs, leading to a condition known as enterobiasis.
Praziquantel: Praziquantel is an antiparasitic medication used to treat infections caused by various species of parasitic worms, specifically schistosomiasis and liver flukes. It works by causing severe spasms and paralysis of the worms' muscles, leading to their death.
Pyrantel pamoate: Pyrantel pamoate is an antihelminthic medication used to treat parasitic worm infections in the gastrointestinal tract. It works by paralyzing the worms, which are then expelled from the body through the stool.
Roundworms: Roundworms, also known as nematodes, are cylindrical helminths that infect various tissues of the host. They can cause significant gastrointestinal and systemic diseases in humans.
Scolex: The scolex is the head region of a tapeworm, equipped with suckers or hooks for attachment to the host's intestinal wall. It plays a critical role in nutrient absorption and anchoring the parasite within the gastrointestinal tract.
Small intestine: The small intestine is a long, coiled tube where most digestion and nutrient absorption occurs. It consists of three parts: the duodenum, jejunum, and ileum.
Strongyloidiasis: Strongyloidiasis is a parasitic infection caused by the nematode Strongyloides stercoralis. It primarily affects the gastrointestinal tract and can lead to severe complications, particularly in immunocompromised individuals.
Strongyloides stercoralis: Strongyloides stercoralis is a parasitic nematode causing strongyloidiasis, primarily infecting the gastrointestinal tract. It can cause both asymptomatic and severe, life-threatening infections.
Tapeworm: Tapeworms are parasitic flatworms that inhabit the digestive tract of vertebrates, including humans. They absorb nutrients through their skin and can cause serious health issues.
Taenia: Taenia is a genus of parasitic tapeworms that infect the gastrointestinal tract of humans and other animals. These helminths cause taeniasis, which can lead to various digestive and systemic symptoms.
Tapeworms: Tapeworms are parasitic flatworms that live in the intestines of their hosts, including humans. They absorb nutrients through their skin and can cause significant digestive system infections.
Taeniasis: Taeniasis is a parasitic infection caused by the ingestion of tapeworm larvae from the genus Taenia, commonly through undercooked or raw beef or pork. It primarily affects the human gastrointestinal tract and can lead to various symptoms including abdominal pain and digestive disturbances.
Thiabendazole: Thiabendazole is an anthelmintic medication used to treat a variety of worm infections in the digestive tract. It works by inhibiting the enzyme fumarate reductase in helminths, disrupting their energy production.
Trichuriasis: Trichuriasis is a parasitic infection of the large intestine caused by the whipworm Trichuris trichiura. It often results in gastrointestinal distress and can lead to more severe complications if untreated.
Trematodes: Trematodes, also known as flukes, are parasitic flatworms that infect various parts of the body including the liver, lungs, and blood vessels. They are a type of helminth with complex life cycles often involving multiple hosts.
Trichinosis: Trichinosis is a parasitic disease caused by roundworms of the Trichinella genus. It is acquired by consuming undercooked meat containing Trichinella larvae.
Triclabendazole: Triclabendazole is an antiparasitic drug primarily used to treat infections caused by liver flukes, specifically Fasciola hepatica and Fasciola gigantica. It inhibits the enzyme systems of the flukes, leading to their death.
Trichenellosis: Trichinellosis is a parasitic disease caused by roundworms of the Trichinella genus. It is typically contracted through the consumption of undercooked or raw meat from infected animals.
Whipworms: Whipworms are parasitic helminths that infect the human large intestine, causing trichuriasis. They are characterized by their whip-like shape and can lead to gastrointestinal symptoms like abdominal pain and diarrhea.
Pyrantel Pamoate: Pyrantel pamoate is an anthelmintic drug, meaning it is used to treat infections caused by parasitic worms, particularly those affecting the gastrointestinal tract. It works by disrupting the neuromuscular function of the worms, leading to their paralysis and expulsion from the host's body.
Ivermectin: Ivermectin is a broad-spectrum antiparasitic medication used to treat various parasitic infections, including those affecting the skin and eyes, as well as helminthic infections of the gastrointestinal tract. It works by disrupting the nervous system of parasites, leading to their paralysis and eventual death.
Zoonotic Infections: Zoonotic infections are diseases that can be transmitted from animals to humans. These types of infections are caused by pathogens, such as viruses, bacteria, parasites, and fungi, that are able to cross the species barrier and infect both animal and human hosts.
Small Intestine: The small intestine is a long, tubular organ that is the primary site of digestion and nutrient absorption in the human body. It is the central component of the digestive system, connecting the stomach to the large intestine.
Colon: The colon, also known as the large intestine, is the final section of the digestive tract. It plays a crucial role in the body's overall digestive and eliminative processes, serving as the site for the absorption of water and electrolytes from indigestible food matter and the elimination of waste products.
Cecum: The cecum is a pouch-like structure located at the junction of the small and large intestines, where the ileum (end of the small intestine) joins the colon (beginning of the large intestine). It serves as a reservoir for the contents of the digestive tract and is an important site for the absorption of water and the fermentation of undigested food by the resident gut microbiota.
Appendix: The appendix is a small, pouch-like structure attached to the first part of the large intestine, known as the cecum. It is part of the human digestive system and plays a role in both the anatomy and normal microbiota of the gastrointestinal tract, as well as in certain helminthic infections affecting the gastrointestinal system.
Gallbladder: The gallbladder is a small, pear-shaped organ located just beneath the liver. It serves as a storage and concentration reservoir for bile, a digestive fluid produced by the liver that aids in the breakdown and absorption of fats in the small intestine.
Fecal-Oral Transmission: Fecal-oral transmission refers to the spread of infectious agents, such as bacteria, viruses, and parasites, from the feces of an infected individual to the oral cavity of another person. This mode of transmission is a common route for the spread of gastrointestinal infections.
Enterobius vermicularis: Enterobius vermicularis, commonly known as the pinworm or threadworm, is a parasitic nematode that infects the human gastrointestinal tract. It is one of the most common helminthic infections worldwide, particularly affecting children and causing the condition known as enterobiasis or oxyuriasis.
Ancylostoma duodenale: Ancylostoma duodenale is a parasitic hookworm that infects the human gastrointestinal tract, causing a condition known as hookworm disease or ancylostomiasis. It is a significant public health concern in many parts of the world, particularly in developing countries with poor sanitation and hygiene.
Mebendazole: Mebendazole is an anthelmintic drug used to treat infections caused by various types of parasitic worms, particularly those that reside in the gastrointestinal tract. It works by interfering with the worms' ability to absorb nutrients, leading to their eventual death and expulsion from the body.
Gastrointestinal Tract: The gastrointestinal tract, also known as the digestive tract, is a complex system of organs responsible for the ingestion, digestion, absorption, and elimination of food and waste products. This tract is a crucial component in the context of helminthic infections, as many parasitic worms can reside and cause disease within its various structures.
Soil-Transmitted Helminths: Soil-transmitted helminths are a group of parasitic worms that are transmitted through contaminated soil. These worms primarily infect the gastrointestinal tract and can cause a range of health issues, including malnutrition, anemia, and impaired physical and cognitive development.
Ground Itch: Ground itch, also known as hookworm dermatitis, is a skin condition caused by the larvae of hookworm parasites burrowing into the skin. It is a common symptom associated with helminthic infections of the gastrointestinal tract, particularly those caused by the hookworm species Necator americanus and Ancylostoma duodenale.
Pruritus Ani: Pruritus ani, or itching of the anus, is a common symptom associated with various helminthic (worm) infections of the gastrointestinal tract. It is characterized by an intense, persistent, and often debilitating itch around the anus, which can significantly impact a person's quality of life.
Necator americanus: Necator americanus, also known as the hookworm, is a parasitic nematode that infects the human gastrointestinal tract, causing a condition called hookworm infection or hookworm disease. It is a significant public health concern in tropical and subtropical regions, particularly affecting populations with poor sanitation and hygiene.
Löffler's syndrome: Löffler's syndrome is a clinical condition characterized by the presence of migratory pulmonary infiltrates, peripheral blood eosinophilia, and transient pulmonary symptoms. It is often associated with helminthic infections, particularly those involving the gastrointestinal tract.
Helminthic Infections: Helminthic infections refer to parasitic infections caused by various types of worms, known as helminths, that can inhabit the gastrointestinal tract. These parasitic infections are a significant public health concern, particularly in developing countries with poor sanitation and hygiene conditions.
Trichuris trichiura: Trichuris trichiura, commonly known as the whipworm, is a parasitic nematode that infects the human gastrointestinal tract and is a significant contributor to helminthic infections, as discussed in the context of Chapter 24.6 Helminthic Infections of the Gastrointestinal Tract.
Anthelmintic Drugs: Anthelmintic drugs are a class of medications used to treat infections caused by parasitic worms, known as helminths, that reside in the gastrointestinal tract. These drugs are specifically designed to eliminate or expel these parasitic worms from the body, providing relief from the associated symptoms and preventing further complications.
Hyperinfection Syndrome: Hyperinfection syndrome is a severe and potentially life-threatening condition that can occur in individuals infected with certain types of parasitic worms, particularly Strongyloides stercoralis. It is characterized by the overwhelming multiplication and dissemination of the parasite throughout the body, leading to a systemic infection with serious complications.
Eosinophilia: Eosinophilia refers to an abnormally high number of eosinophils, a type of white blood cell, in the body. This condition is often associated with parasitic infections, particularly those involving the gastrointestinal tract.
Vulvovaginitis: Vulvovaginitis is an inflammation of the vulva and vagina, often caused by an infection or irritation. It is a common condition that can occur in women of all ages and can have various underlying causes.
Scotch Tape Test: The Scotch tape test is a simple diagnostic procedure used to detect the presence of helminth eggs or larvae in the gastrointestinal tract. It involves applying a piece of transparent adhesive tape to the perianal region and then examining the tape under a microscope for any evidence of parasitic infestations.
Cestodes: Cestodes, also known as tapeworms, are a class of parasitic flatworms that primarily infect the gastrointestinal tract of humans and other vertebrates. These parasites have a complex life cycle and can cause significant health issues in their hosts.
Albendazole: Albendazole is a broad-spectrum anthelmintic (antiparasitic) drug primarily used to treat infections caused by various types of parasitic worms, including those that can infect the skin, eyes, and gastrointestinal tract. It works by interfering with the structural integrity and function of the parasites, leading to their death and expulsion from the host's body.
Trematodes: Trematodes, also known as flukes, are a class of parasitic flatworms that infect a wide range of hosts, including humans. These worms are characterized by their flattened, leaf-like bodies and the presence of one or more suckers used for attachment and feeding.
Nematodes: Nematodes, also known as roundworms, are a diverse group of unsegmented, cylindrical worms that are found in a wide range of environments, including soil, freshwater, and as parasites in the gastrointestinal tracts of various organisms. They are an important component of the parasitic helminth infections that can affect human health.