Parasitology: Worms Part 2 Summary

Trichuriasis (Trichuris trichiura)

• Eggs become infective in 15-30 days (geohelminth)
• Transmission: Soil-contaminated hands or food
• Adult worm (~4 cm) in cecum/colon ascendens
• Produces 3000-20000 eggs/day
• Third most common roundworm (800 million infected)
• Common in tropical regions with poor sanitation
• Mostly asymptomatic; heavy infections can cause abdominal pain, diarrhea; rarely rectal prolapse

Trichinellosis (Trichinella, e.g., T. spiralis)

• Transmission: Ingestion of undercooked meat with encysted larvae
• Worms are small (1-3 mm)
• Worm releases larvae (doesn't produce eggs)
• Larvae migrate to striated muscle and encyst
• Humans are both definitive and intermediate hosts
• Light infections may be asymptomatic
• Symptoms: Gastrointestinal issues, larval migration symptoms (facial edema, conjunctivitis, fever, myalgias, splinter hemorrhages, rashes, eosinophilia)
• Severe manifestations: Myocarditis, CNS involvement, pneumonitis
• Larval encystment causes myalgia and weakness
• Diagnosis: Patient history, symptoms, eosinophilia, antibody detection, muscle biopsy

Ascariasis

• Adult worms live in the small intestine; female produces up to 200,000 eggs/day
• Egg maturation in soil (geohelminth) takes 2-3 weeks
• Larva hatches, migrates, is coughed up, and swallowed, developing into an adult in the small intestine (worms live 1-2 years)
• Approximately 1 billion infected worldwide
• Symptoms: Usually asymptomatic; heavy infections in children: stunted growth; high worm burden: abdominal pain, intestinal obstruction, perforation; migrating worms can cause biliary tract occlusion, appendicitis, or nasopharyngeal expulsion
• Diagnosis: Detection of eggs in stool, eosinophilia, serology

Toxocariasis (Toxocara canis, Toxocara cati)

• Humans are accidental intermediate hosts
• Larvae released in the intestine, migrate to organs, and are arrested
• Most infections are asymptomatic
• Visceral larva migrans (VLM): affects small children; symptoms include fever, myalgia, cough, eosinophilia
• Ocular larva migrans (OLM): affects older children/young adults; causes unilateral visual impairment (uveitis, retinitis, endophthalmitis), and can lead to permanent visual damage/blindness
• Prevention: Regular pet deworming

Dracunculiasis (Dracunculus medinensis)

• Transmission: Drinking unfiltered water containing copepods with L3 larvae
• Larvae mature and reproduce in subcutaneous tissues
• Female worm emerges from skin one year post-infection and releases larvae

Antiparasitic Treatment

• Avermectin - Ivermectin: Novel therapy against infections caused by roundworm parasites.

Lymphatic Filariasis (Elephantiasis)

• Caused by Wuchereria bancrofti, Brugia malayi, Brugia timori

Microfilariae (Lymphatic Filariasis)

• Diagnostic: Microfilariae from blood (collected at night due to nocturnal periodicity)
• Distinguishing features: size, head space, nuclei in the tail

Onchocerciasis (River Blindness)

• Caused by Onchocerca volvulus
• Transmitted by blackflies (genus Simulium)

Loiasis

• Caused by Loa loa
• Transmitted by flies (genus Chrysops)

Dirofilariasis

• Caused by Dirofilaria repens, Dirofilaria immitis, Dirofilaria tenuis