Nematodes of the Intestinal Tract

Apart of the Helminth GI Infection Notes

What are the nematodes of the intestinal tract that we went over?

• Enterobius

• Ascaris

• Hookworm

• Trichuris

• Strongyloides

Epidemiology of Hookworm

• aka Ancyclostoma duodenale, A. ceylanicum, and Necator americanus

• found worldwide in particularly warm, humid soil

• estimated 576-740 million individuals are infected

• human reservoir

Life Cycle of Hookworm

• hookworm larvae hatch in warm, moist soil and grow through 3 larval stages

• larva travel to high points, such as the tips of grass blades

• upon contact with human skin, filariform larvae (infective stage) penetrate the skin and travel to the blood

• from the blood, larvae travel into the lungs capillaries and into the lung

• larvae travel through the digestive tract to the small intestine; mature into adults, and feed on components of blood

• adult hookworms create eggs (diagnostic phase) which are released in feces into the environment; restarts the cycle

Infective stage and diagnostic phase of Hookworm

• infective stage - penetration from filariform larvae

• diagnostic phase - eggs

Clinical Syndrome of Hookworm

• allergic reaction and rash at entry site

• pneumonitis as migrate through lungs

• adult gives GI symptoms

• anemia (daily blood loss is estimated at 0.03 to 0.25 ml per day)

Cutaneous Larval Migrans

a zoonotic infection with hookworm species that do not use humans as a definitive host, the most common being A. braziliense and A. caninum. The normal definitive hosts for these species are dogs and cats (aka creeping eruption)

Symptoms of Hookworm Depending on Infestation

• infestations reach 25 to 100 worms: fatigue slight weight loss, and possible headaches

• infestations reach between 100-500 worms: fatigue, iron deficiency leading to anemia, loss of appetite and abdominal pains

• infestations reach over 500 worms: anemia and, depending on the diet of the person, possibly death

Diagnosis of Hookworm

stool examination reveals the characteristic non-bile stained segmented eggs

Treatment and Prevention of Hookworm

• albendazole/mebendazole with iron therapy (blood transfusion if severe anemia)

• education, improved sanitation, wear shoes in endemic areas

• vaccines are in development

Epidemiology of Ascaris lumbricoides (Roundworm)

• found in warm countries and areas of poor sanitation

• estimated 800 million infected people

  • estimated 4 million cases in the US

• most common in children 2 to 10 years old, and prevalence decreases over the age of 15 years

• human reservoir

Life Cycle of Ascaria

• infection occurs with ingestion of embryonated egg (infective stage) in feces or contaminated soil

• ingested eggs hatch, releasing small larvae that penetrate the intestinal wall

• larvae migrate to the pulmonary bed via the portal veins

• after migrating up the respiratory tract and being swallowed, they mature, copulate, and lay eggs (diagnostic stage) in the intestines

• eggs are released into the environment

Infective stage and diagnostic stage of Ascaris

eggs for both (ingestion)

Clinical Syndrome of Ascaris lumbricoides

• only a few eggs - usually asymptomatic

• pneumonitis as migrate through lungs

• migration into liver, gallbladder, and bile duct may produce severe tissue damage

• rarely fatal (8000-100000 deaths annually)

• important cause of malnutrition, particularly in children, causing protein energy loss and vitamin A and C deficiencies (cause stunting of linear growth, leading to both physical and mental deficits)

Diagnosis of Ascaris lumbricoides

• stool examination reveals characteristic knobby-coated. bile-stained fertilized or unfertilized eggs

• adult worm may pass in the stool!

Treatment and prevention of Ascaris lumbricoides

• albendazole/mebendazole

• education and improve sanitation

• eggs can persist in contaminated soil for 3 years or more

Epidemiology of Enterobius vermicularis (Pinworm)

• found worldwide (mostly temperate climates)

  • most common helminth in the US (mostly children, primary caregivers of infected children)

• Overall estimated that 200 million people are infected

  • 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, 29% in Denmark, 25% in the US

• Human reservoir

Life Cycle of Enterobius

• infection occurs via self-inoculation/ingestion of the egg or through exposure in the environment, or sexual activity (infective stage)

• larvae hatch in small intestine and adults establish in colon

• female migrates to the rear end and emerges at night, usually during the night, to deposit about 10000 to 20000 eggs in the perianal area (diagnostic stage)

Infective stage and diagnostic stage of Enterobius

• infective stage: self-inoculation/ingestion of the egg or through exposure in environment, or sexual activity

• diagnostic stage: eggs in the perianal area

Clinical Syndrome of Enterobius vermicularis

• typically, asymptomatic

• allergic reaction causes pruritus (scratching can lead to secondary bacterial infection

Diagnosis of Enterobius vermicularis

• use of anal swab with a sticky surface that picks up the eggs for microscopic examination

Treatment and prevention of Enterobius vermicularis

• pyrantel pamoate, or alternatively albendazole/mebendazole

  • to avoid reintroduction or reinfection in the family, treat entire family

• education and good hygiene

  • thoroughly clean house/wash towels and bedsheets

Epidemiology of Strongyloides stercoralis (Threadworm)

• found in warm areas, tropics, and subtropics

  • affects between 30 to 100 million persons (~100000 people in the US)

  • Hotspots are Brazil and Thailand

• Human reservoir

  • some dog and primate strains have been shown to infect humans

Life Cycle of Strongyloides

• infection occurs when filariform larvae penetrate the skin (infective stage)

• larvae migrate to the small intestines where they become adults

• females produce eggs which yield rhabditiform larvae

• rhabditiform larvae pass in the stool (diagnostic stage) or can cause auto infection

• when in the environment, rhabditiform larvae either mature into free-living adults or infective filariform larvae

Infective stage and diagnostic stage of Strongyloides

• infective stage: filariform larvae penetrate the skin

• diagnostic stage: rhabditiform larvae

Transmission of Strongyloides

larvae have been thought to locate their hosts visa urocanic acid, a histidine metabolite on the uppermost layer of skin, that is removed by sweat or the daily-skin shedding cycle

Larva currens

• cutaneous migration of Strongyloides

• a red line that appears, moves rapidly (>5 cm/day) and then quickly disappears

• pathognomonic for autoinfective larvae and can be used as a diagnostic criterion

Clinical Syndrome of Strongyloides stercoralis

• pneumonitis as migrate through lungs

• intestinal infection is usually asymptomatic; heavy load can cause inflammation and ulceration of colon, small bowl, and bile ducts

Diagnosis of Strongyloides stercoralis

examination of concentrated stool sediments reveals the larval worms (eggs are generally not seen)

Treatment and prevention of Strongloides stercoralis

• ivermectin

• education, proper santiation

• and treatment for gram-negative bacteria for immunocompromised individuals

Epidemiology for Trichuris trichuria (Whipworm)

• worldwide distribution

• more common in tropical areas and in areas of poor sanitation (nearly one quarter of the world population infection)

  • fecal pollution, dense shade near the house, and heavy rainfall, the southern Appalachian Mountains and rural Louisiana have the highest incidence rates of the US (~ 2.2 million infected)

• human reservoir

Life Cycle of Trichuris

• infection occurs when eggs are ingested (infective stage)

• eggs hatch in the small intestine, and release larvae that mature into adults

• adults establish in the colon; female shed eggs in the stool (diagnostic stage)

• eggs released into the stool develop into an infective stage adults or infective filariform larvae

Clinical Syndrome of Trichuris trichuria

• most infections are asymptomatic

• high worm burden: abdominal pain, bloody diarrhea, weakness and weight loss

• prolapse of the rectum in children

Diagnosis of Trichuris trichuria

stool examination reveals the characteristic bile-stained eggs with polar plugs

Treatment and prevention of Trichuris trichuria

• albendazole/mebendazole

• education, good personal hygiene, adequate sanitation