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StrongyloidiasisErwin Beya
Introduction
❖ Strongyloidiasis is a parasitic disease caused by roundworms in the genus Strongyloides.
❖ Over 40 species within the genus can infect reptiles, birds, amphibian, livestock, and mammals.
❖ Strongyloides stercoralis is the primary species responsible for human disease.
Strongyloides stercoralis❖ Kingdom: Animalia
❖ Phylum: Nematoda
❖ Class: Secernentea
❖ Order: Rhabditida
❖ Family: Strongyloididae
❖ Genus: Strongyloides
❖ Species: S. stercoralis
Strongyloides stercoralis❖ Common name: Threadworm.
❖ S. stercoralis is both dioecious and parthenogenetic➢ Parthenogenesis: a form of asexual reproduction in which growth and
development of embryos occur without fertilization.
❖ Threadworms are both free-living and parasitic.➢ Only females act as parasites.
❖ Strongyloides are known to exist on all continents except for Antarctica.
❖ most common in the tropics, subtropics, and in warm temperate regions.
❖ Estimated 30–100 million infected persons worldwide.
Prevalence
Larval developmentL1 (Rhabditiform Larvae)
L2
Infective L3 (Filariform larvae)
Parasitic Adult Female
Free-Living L3
Free-Living Adult Male & Female
Larvae❖ Eggs hatch large intestines or in soil❖ Rhabditiform Larvae (L1).
➢ Non-parasitic.➢ Feed on organic debris in soil.➢ 220 x 15 µm
❖ Final larval stage is the Filariform larvae (L3).➢ Infectious through skin contact.➢ Non-feeding➢ 600 X 20 µm
Adult Anatomy
Life Cycle❖ Two life cycles
➢ Parasitic cycle■ Soil-borne transmissions
● Direct transmission● Indirect transmission
■ Autoinfection➢ Free-Living Cycle
Adult female Worms lay eggs on the intestinal wall.The Eggs migrate to the large intestinal lumen, hatch
Rabditiform Larvae in soil
Rabditiform larvae molt twice and become filariform larvae
Excretion in stool
Filariform larvae penetrate the skin
Enter the venous bloodstream Reach the right side of heart
Reach the lungs & enter the Alveolar space
Travel up the trachea, past the epiglottis
Larvae are swallowed & reach the small intestine.Molt into adult females.
Parthenogenetic replication
Direct Transmission
Adult female Worms lay eggs on the intestinal wall.The Eggs migrate to the large intestinal lumen and hatch
Rabditiform Larvae in soil
Development of free-living adult males and females (4 molts)
Excretion in stool
Females lay eggsRabditiform larvae hatch from eggs
Enter the venous bloodstream
Reach the right side of heart
Reach the lungs & enter the Alveolar space
Travel up the trachea, past the epiglottis
Larvae are swallowed & reach the small intestine.Molt into adult females.
Parthenogenetic replication
Larvae penetrate the skin
Rabditiform larvae molt twice & and become filariform larvae
Indirect & Free-Living Cycle
Adult female Worms lay eggs on the intestinal wall.The Eggs migrate to the large intestinal lumen, hatch
Enter the venous bloodstream
Reach the right side of heart
Reach the lungs & enter the Alveolar space
Travel up the trachea, past the epiglottis
Larvae are swallowed & reach the small intestine.Molt into adult females.
Parthenogenetic replication
Rabditiform larvae molt twice & become filariform larvae
Larvae burrow through the intestinal wall or penetrate the skin
Autoinfection
Symptoms & Pathology❖ Acute Infection
➢ Often show no symptoms.➢ Lower extremity itching.
■ maculopapular rash at the site of infection.
➢ Cough, wheezing, difficulty breathing.■ Pulmonary Migration
➢ Fever and Fatigue.■ Eosinophilia
➢ Epigastric pain and discomfort, nausea, vomiting and diarrhea.■ Larvae become female adults and colonize the large intestines
Symptoms & Pathology❖ Chronic infection
➢ Can be asymptomatic➢ Abdominal pain, Nausea, vomiting, diarrhea & constipation➢ Weight loss
■ Heavy infections
➢ Larva Currens■ Ranges from lower extremities to waist area
➢ Chronic Urticaria■ Immune response
➢ Eosinophilia
Larva Currens
Severe complications❖ Hyperinfection syndrome and disseminated strongyloidiasis occurs
when patients with chronic infection become immunosuppressed. (80-90% mortality)
❖ Both lead to accelerated autoinfection and an overwhelming number of migrating larvae.➢ Larvae mostly remain in the GI tracts and lungs➢ Larvae spread to other organs and translocate intestinal
■ CNS is most common (Meningitis)
➢ Translocation of intestinal bacteria to other organs■ Leads to sepsis
Severe symptoms❖ Severe infection
➢ Severe abdominal pain, distention➢ Pulmonary symptoms
■ Hemoptysis: Coughing up blood
➢ Stiff neck and Headaches■ If the worm spreads to the CNS
➢ Fever/Chills➢ Hematemesis
■ Vomiting blood
➢ Hematochezia■ Blood in stool
➢ Larva Currens
Diagnosis❖ Testing for larvae in the stool❖ ELISA
➢ Elevated IgG during acute and chronic phase❖ Eosinophil count
➢ Eosinophilia during acute & chronic phase, absent in severe infections
❖ Larvae in Sputum❖ Endoscopic duodenal biopsy and aspirate
Prevention❖ Good sanitation❖ Proper waste disposal❖ Wearing closed toe shoes❖ Clothes and sheets should be washed with enzyme washing powder
and dried on high heat.❖ Education
Treatment❖ Ivermectin.
➢ Binds neurons and muscles and causes paralysis of worm➢ Does not prevent reinfection
❖ Albendazole➢ Inhibits glucose uptake➢ Does not prevent reinfection
❖ Both only kill adults➢ Repeat dosing is necessary➢ Follow up test (2 weeks after initial treatment)
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