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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