Helminthology Quiz on Nematodes and Treatment

Helminths

• Helminths are parasitic worms
• Lecture time for intestine nematodes (STH) is 50 minutes
• Lecture time for intestine nematodes (non STH) is 50 minutes

Classification of Helminths

• Helminths are divided into nematodes and platyhelminths
• Nematodes/Aschelminths include roundworms
• Platyhelminths include cestodes (tapeworms) and trematodes (flukes)

Nematodes

• Nematodes are cylindrical in shape
• They are covered by a cuticle
• They have a complete digestive system
• They have separate sexes
• Their life cycle includes ova, larval and adult stages
• They are classified into intestinal and blood/tissue nematodes

Intestinal Nematodes

• Soil-transmitted helminths include Ascaris lumbricoides, Trichuris trichiura, hookworms (Ancylostoma duodenale and Necator americanus), and Strongyloides stercoralis
• Non-soil transmitted helminths include Enterobius vermicularis and Trichinella spiralis

Nematodes in Animals

• Cutaneous larva migrans include Ancylostoma braziliense and Ancylostoma caninum
• Visceral larva migrans include Toxocara cati and Toxocara canis

Ascaris lumbricoides

• It is a soil-transmitted helminth
• The distribution is cosmopolitan, tropical, and subtropical areas
• The infection is caused by poor sanitation practices
• The infection is called Ascariasis

Ascaris lumbricoides Morphology

• Adult worms, females are 20-35 cm long, and males are less than 30 cm long
• The shape is similar to a pencil
• They have a creamy white or pinkish color
• The cuticle has fine circular striations
• The mouth has three oval lips

Ascaris lumbricoides Eggs

• Fertile eggs are 50-70 × 40-50 μm, and subspherical or round, yellowish-brown to dark brown
• The outer coating is thick with a mammilated protein coat
• Fertile decorticated eggs are thin-shelled, without protein coat
• Infertile eggs are 60-90 × 40-60 μm, elongated ellipsoidal, and have a more irregular outer appearance
• They are brown to dark brown, with a large number of granules inside

Ascaris lumbricoides Life Cycle

• The life cycle has 9 developmental stages
• The diagnostic stage of the egg is the 1-9 stages

Ascaris lumbricoides Pathology and Symptoms

• Larval infection may result in pneumonitis with eosinophilia (Loeffler syndrome)
• Adult worms may cause abdominal distention, diarrhea, vomiting, malnutrition, and symptoms like appendicitis or pancreatitis, and bowel obstruction

Ascaris lumbricoides Diagnosis

• Feces examination for eggs using direct smear, Lugol's solution, eosin, Kato-Katz technique or centrifugation

Ascaris lumbricoides Treatment

• Treatment includes Albendazole and Mebendazole

Trichuris trichiura

• It is a whipworm
• The adult worm is thread-like at the anterior end and bigger at the posterior
• Males are smaller than females and have a coiled tail
• Habitat : Cecum
• Adult worm invades intestinal mucosa

Trichuris trichiura Eggs

• The eggs are 50-54 × 22-23 μm, barrel-shaped, and brown to dark brown
• They have polar plugs at either end
• The shell has two layers
• Feces contain unsegmented stages of eggs

Trichuris trichiura Life Cycle

• Embryonated eggs are ingested, larvae hatch in the small intestine and migrate to the cecum
• The adult worm lives in the cecum

Trichuris trichiura Pathogenesis and Symptoms

• Mild infections may be asymptomatic
• Heavy infections may cause abdominal pain, distention, bloody or mucoid diarrhea
• Symptoms may be similar to appendicitis or prolapse recti

Trichuris trichiura Diagnosis

• Feces examination for eggs, same as ascariosis

Trichuris trichiura Treatment

• Treatment includes Mebendazole and Albendazole

Hookworm

• Includes Ancylostoma duodenale and Necator americanus
• Distribution: Tropical and subtropical areas
• Infections: Ancylostomiasis and Necatoriasis
• Morphology: Adult worms are "C" shaped for Ancylostoma duodenale and "S" shaped for Necator americanus; Females are about 1cm, Males are about 0.8 cm
• Mouth: Ancylostoma duodenale have teeth, Necator americanus have cutting plates
• Habitat: Small intestine; attach to mucosa, suck blood and mucosal substances, anti-coagulating secretion facilitates blood sucking

Hookworm Eggs

• Eggs are 55-75 μm × 35-40 μm, oval, thin-shelled, transparent
• They contain blastomeres (4-8 cells)

Hookworm Larvae

• Rhabditiform larvae (RL)
• Filariform larvae (FL) infective form
• N.a infective form = cutaneous

Hookworm Life Cycle

• Larvae penetrate skin (cutaneous)
• Develop to adult worms in small intestine
• Eggs passed in feces

Hookworm Pathology and Symptoms

• Larval: skin (ground itch), mild pulmonary symptoms
• Adult: Anemia (iron deficiency), gastrointestinal symptoms

Hookworm Diagnosis

• Eggs in stool
• Harada-Mori technique to differentiate species (FL)

Hookworm Treatment

• Albendazole, Mebendazole, Pirantel pamoate

Prevention

• Prevention of transmission to follow life cycle