Hymenolepis Diminuta Parasitology Quiz

Egg Morphology and Clinical Manifestations

• Egg morphology: barrel-shaped, outer and inner shell, transparent polar prominences (polar plugs)
• Clinical manifestations: headache, abdominal pain, dizziness, diarrhea, enteritis due to necrosis of intestinal epithelial cells

Hymenolepis diminuta (Rat Tapeworm)

• Hosts: rats, mice, and other rodents
• Life cycle: ingestion of intermediate host, grain weevil, containing larval stages
• Infests: dried grains, fruits, flour, and cereal
• Morphology: larger than H. nana, scolex with no hooks, eggs with no polar filaments
• Pathology: minimal and non-specific
• Treatment: Praziquantel

Taenia spp. (Tapeworms)

• Two species that infect humans: Taenia saginata and Taenia solium
• Life cycle: infective egg from human feces ingested by cow or pig, oncosphere hatches and penetrates the intestinal mucosa, localizes and encysts in muscle
• Morphology: scolex attaches to human intestine, larva: cysticercus, fluid-filled barrier with an invaginated scolex, eggs of both species are identical

Taenia saginata (Beef Tapeworm)

• MOI: ingestion of cysticercus in cow flesh
• Cysticercus: ovoidal, milky white in color, single scolex invaginated into a fluid-filled barrier
• Morphology:
  • Scolex: unarmed with 4 sucking disks
  • Gravid proglottids: 1 inch or slightly longer, uterus contains 15-20 primary branches, uterine pore located in a lateral position
  • Eggs: identical to T. solium, unsegmented region, high regenerative capacity
• Diagnosis: identify proglottids, eggs, or scolex, perianal swabs, eggs can be differentiated

Hymenolepis nana (Dwarf Tapeworm)

• Most common tapeworm infection in humans
• Definitive host: humans, rodents
• Life cycle: ingestion of embryonated eggs or insects (beetles, fleas) containing larvae, autoinfection: eggs remain in the intestine
• Diagnosis: finding eggs in feces
• Morphology:
  • Scolex: 4 sucking disks, short rostellum with hooks
  • Proglottid: broader than long, rarely seen in feces specimens
  • Body divided into two parts: anterior (long and slender) and posterior (shorter and thicker)

Hookworms (Blood-sucking Nematodes)

• Morphology: large plates in the mouth, adults with large, cylindrical, fusiform bodies, females larger than males
• Pathology: blood loss, anemia, protein loss, rectal prolapse, edematous rectal tissue, inflammation of the colon with hemorrhage

Necator americanus (Hookworm)

• Adults: small, cylindrical, fusiform, gray, females larger than males
• Copulatory bursa: catch, hold female, pair of ventral cutting plates

Ancylostoma duodenale (Hookworm)

• Slightly larger than N. americanus
• Head continuous in the same direction as body curvature
• Two pairs of curved ventral cutting teeth

Metabolism of Ascaris spp.

• Embryos: consume lipid and carbohydrate reserves during first 10 days of development, resynthesize carbohydrate from fat
• Snails: Lymnaea, aquatic plants: Nasturtium officinale (watercress), Ipomea obscura, Ipomea aquatica (kangkong)

Clonorchis sinensis (Chinese Liver Fluke)

• Bile duct and gallbladder of humans and fish-eating mammals (dogs, cats)
• Found in China, Korea, and Japan
• Egg morphology: small protuberance at the abopercular end, ovoid, yellowish to brown in color
• Mode of transmission: ingestion of metacercariae, excysts in the duodenum, attaches to mucosa of bile duct, pancreatic duct, and gallbladder through suckers and embedding in sticky mucus

Fasciola spp. (Liver Flukes)

• Liver and biliary passages of humans and herbivorous mammals (ruminants)
• Mode of transmission: ingestion of metacercariae encysted from edible aquatic plants or by drinking water with floating metacercariae
• Intermediate hosts: snails (Bulimus striatulus, Parafossarulus genera, Thiara granifera, Melanoides tuberculatus)
• Pathology: migrate by penetrating intestinal wall, peri cavity, abdominal wall, diaphragm, and lungs, immature worms settle close to the bronchi, grow, and sexually mature
• Clinical manifestations: granulomatous reaction in the lungs, development of fibrotic encapsulation, pairs of adult worms found in fibrotic capsules or cysts in lungs of infected hosts, chest pain, hemoptysis, myalgia, dyspnea, fever, fatigue