Parasites 2 Flashcards
Nematodes
General Aspects
• Roundworms – Enormously prevalent and successful phylum, exceeded only by arthropods in diversity – 138 species infect humans – True gut cavity, cuticle • Enormously prevalent diseases – billions and billions served… – high morbidity, modest mortality – associated with and contribute to poverty, malnutrition, underdevelopment
Nematodes
The Major GI Nematodes – Enterobious vermicularis (pinworm) – Tricuris triciuria (whipworm) – Ascaris lumbricoides – Hookworms – Strongyloides stercoralis
Enterobius vermicularis (pinworm) Epidemiology
Enormously widespread. – 200 million infections worldwide – Temperate parts of the world • Primarily a parasite of young children – Adults in households with infected kids
Enterobius vermicularis (pinworm) Life Cycle & Transmission
• Ova laid on the perianal skin by females • Become infective in 4-6h • May remain infective in cool, moist conditions for up to a week • Infective by ingestion or inhalation
Enterobius vermicularis (pinworm) Diagnosis and Therapy
• A cellophane tape prep of the perianal skin may be used to
detect the eggs or adults
• The eggs are elongate and
flattened on one side, 50-60 um long by 20-40 um wide.
• Adult females are 8-13 mm long and may be detected visually,
particularly during the night and early morning
• Treated with mebendazole,
albendazole, or pyrantal pamoate
Trichuris trichiura (whipworm) Epidemiology
• Distribution is cosmopolitan in
warm, moist regions.
• The world prevalence is thought to be 350 million or more. In
parts of the SE US 20-25% of children may be infected.
Tricuris trichiura (whipworm) Life Cycle and Transmission
• Eggs produced at a rate of 1,000 to 7,000 per female per day • Infective after about 21d in soil • Infection is via swallowing infective eggs • Following infection there is an ~3 month prepatent period
Trichuris trichiura (whipworm) Clinical Presentation
• Adults are 30-50 mm in length and can live for up to 10 years • Symptoms depend on the worm load – Many infections asymptomatic – Diarrhea with dysentery, cramping, dehydration, weight loss, or anemia can occur in heavy infections.
Trichuris trichiura (whipworm) Diagnosis and Therapy
• The eggs are barrelshaped and brown, with thick shells, and measure 50-55 um long by 22-24 um wide. At each end of the egg is a lucent mucoid plug • Treated with mebendazole, albendazole, or pyrantal pamoate
Ascaris lumbricoides
Epidemiology
• The largest and most prevalent of the intestinal nematodes
– Over 1 billion infected worldwide
– 20-60% of children infected in parts of SE US
– 90% in parts of Indonesia
Ascaris lumbricoides
Life Cycle & Transmission
• Eggs produced at a rate of upto 200,000 per female per day – Develop in soil for ~3 weeks before becoming infective – Exceptionally resistant forms, can embryonate successfully in 2% formalin or 50% nitric acid • Can infect a host after 10 years of storage. • Have been found in windblown dust and on circulating banknotes. • Prepatent period is about 2 months.
Ascaris lumbricoides
Clinical Presentation – Larvae
• Pathology caused both by
larvae and adult worms.
• Migrating larvae can cause
granulomatous pneumonitis
Ascaris lumbricoides Clinical Presentation – Adult Worms
• adult females are 20-35 cm long; males from 15-30 • adults live 12-20 months – in large numbers can cause bowel obstruction – malnutrition and decreased growth • individuals can migrate – especially during febrile illnesses, anesthesia, or trauma – biliary obstruction or cholangitis – intestinal perforation/peritonitis – out nose or mouth
Ascaris lumbricoides
Diagnosis & Therapy
• Detection of ova in stool – fertile eggs are 55-75 um long by 35-50 um wide, with a thick transparent shell and a ruffled outer layer. Unfertilized eggs are elongated and lack the thick shell of the fertilized egg. • Treated with mebendazole, albendazole, or pyrantal pamoate
The Hookworms - Epidemiology
• Two major species – Necator americanus worldwide, – Ancylostoma duodenale Africa, China, Japan, India • Nearly 1 billion infected worldwide • Most pathology produced in children
Hookworms
Life Cycle & Transmission
• Eggs produced at a rate of about 9,000 eggs/female/day (Necator) or 25-30,000/day (Ancylostoma)
– hatch in the soil, infective larvae
develop in about a week
• Larvae
– penetrate the skin, migrate to the lungs, and are swallowed
– mature within the intestine, attached to the mucosa
• The prepatent period is ~5 weeks
Hookworms
Clinical Presentation
• The adults have teeth or cutting plates anteriorly to anchor themselves to the mucosa – Necator adults are 7-11 mm long, while Ancylostoma are 8-13 mm long – Live for 1-2 years, but occasionally as long as 10. • Pathogenesis related to worm burden – a major cause of iron-deficiency anemia worldwide – liver function abnormalities; hypoproteinemia, hepatosplenomegaly – developmental delay and malnutrition
Hookworms
Dignosis and Therapy
• Detection of ova in stool
– eggs of species are indistinguishable
– range from 55-75 um long by 36-40 um wide
– Lucent shell with early embryo inside
– Usually in the 4-16-cell stage when shed
• Treated with mebendazole,
albendazole, or pyrantal pamoate
Strongyloides stercoralis
Epidemiology
• Widely distributed in the tropics and subtropics, as well as into moist temperate regions
• Maintenance in an area requires
continuously moist soil
• 10-20% prevalence in areas of Africa, S. America, and Asia, but usually <1%
Strongyloides stercoralis
Life Cycle & Transmission
• Several dozen eggs produced per female per day.
– Hatch, first larval stage passed in the feces
• Larvae in the soil
– become mature infectious larvae…
– …or undergo sexual differentiation and mate
• may also mature and become
infectious within the gut and
autoinfect
• Penetrate skin, migrate to the lungs, up the trachea, and are swallowed to mature in the small intestine.
Strongyloides stercoralis
Clinical Presentation 1 – Normal Host
• The adults are 2-2.5 mm long and live within the intestinal
mucosa. Because of autoinfection, infections can last for decades
• Initial infection can cause ground itch & pneumonitis
• Chronic eosinophilia
Strongyloides stercoralis
Clinical Presentation 2 –
Immunocompromised
• Autoinfection with progressive
increase in worm burden
– presents as pneumonia or as
massive diarrhea.
– invade any organ of the body, and dispose to gramnegative
sepsis, meningitis, and other infections.
Strongyloides stercoralis
Diagnosis
• The first-stage larvae (in
the stool) are .18 to .38 mm long
• In latent infections few larvae may be present and multiple specimens required
• Serology is helpful in O&P negative cases, but does not reflect disease activity.
• Treat with thiabendazole,
ivermectin or albendazole
Strongyloides vs. Hookworm
Larvae
• Hookworm
– Long buccal canal
– No genital primordium
• Strongyloides
– Short buccal canal
– Prominent genital primordium
Trematodes and Cestodes
• Trematodes – General aspects – Schistosomes – Other flukes • Cestodes – Taenia infections – Diphyllobothrium latum – Other tapeworms • 173 species isolated from humans
Trematodes – General
• Flatworms without a true gut
• All have a snail in the life cycle
somewhere
• “Some molluscs (not many) can have children merely by sitting around and thinking about it…
others are like us, dioecious, possessed of only one sexual nature but thankful for small favors.”
-James Thurber, Is Sex Necessary?
The Schistosomes
Epidemiology – S. mansoni
• Schistosoma mansoni – Africa, the Middle East, South America, and the Caribbean – Roughly 83 million cases – Some animal reservoirs
