Somatic Nematodes

• Somatic Nematodes


  Found in extraintestinal sites
• Types of Somatic Nematodes


  • Filarials
  • Non-filarials
• Filarials


  • Reside in subcutaneous tissues, lymphatic tissues, or serous cavities of humans
• Non-filarial Somatic Nematodes


  • Trichinella spiralis
  • Dracunculus medinensis
  • Parastrongylus cantonensis
  • Anisakis
  • Dirofilaria immitis
• Trichinella spiralis


  Also known as muscle worm/trichina worm, smallest nematode, largest intracellular parasite
• Other Trichinella species


  • Trichinella britovi
  • Trichinella nativa
  • T. murelli, T. nelsoni, T. papuae, and T.pseudospiralis
• Hosts for Trichinella spiralis


  • Humans
  • Rats
  • Dogs
  • Cats
• Adult Male Trichinella spiralis


  • Measures 0.62 to 1.58 mm by 0.025 to 0.033 mm, dies soon after fertilizing the female
• Adult Female Trichinella spiralis


  • Measures about 1.26 to 3.35 mm by 0.029 to 0.038 mm, are viviparous, dies after discharging the larvae
• Infective Larva Trichinella spiralis


  • Encysted in striated muscle fibers, cysts develop in muscles of diaphragm, biceps, masseter, extraocular, lie longitudinally along the muscle fibers
• Life Cycle of Trichinella spiralis


  1. Ingestion of raw of insufficiently cooked meat

  2. Infective encysted larvae enter the host

  3. Maturation occurs in the intestine

  4. Larvae enter the circulation and migrate to striated muscles

  5. Encystation occurs in the muscles
• Optimum host for Trichinella spiralis


  Pig, man is accidental and dead-end host
• Trichinosis, Trichiniasis, Trichinellosis


  Self-limiting disease, referred to as the Great Imitator, depends on the stage of the parasite
• Stages of Trichinosis


  • Enteric phase
  • Invasion phase
  • Convalescent phase
• Enteric phase of Trichinosis


  • May resemble acute food poisoning, includes diarrhea or constipation, vomiting, abdominal cramps, malaise, nausea
• Invasion phase of Trichinosis


  • Migrating larvae trigger immunological, pathological, and metabolic reactions, includes severe myalgia, periorbital edema, eosinophilia, high remittent fever and chills, headache, dyspnea, dysphagia, difficulty in chewing, occasional paralysis of the extremities, splenomegaly
• Larval Migration in Trichinosis


  • Larvae can migrate to cardiac muscles and brain, encapsulation lasts 1 to 8 months after infection
• Diagnostic methods for Trichinosis


  • Muscle biopsy
  • Non-specific lab tests (eosinophilia, muscle enzymes, total IgE serum)
  • Serology (ELISA, Western blot, Latex agglutination)
  • Bachman Intradermal Test
  • Bentonite flocculation test
  • Animal inoculation (Beck's Test)
• Treatment for Trichinosis


  • Bed rest, antipyretics, and analgesics for mild infection, Mebendazole and Albendazole for active stages, Glucocorticoids for severe infections
• Dracunculus medinensis


  Also known as guinea worm, dragon worm, fiery serpents the Israelites, longest tissue nematode (1 meter)
• Adult Female Dracunculus medinensis


  • Measures 60–120 cm in length and 1–2 mm in thickness, usually found in the subcutaneous tissue, is viviparous
• Adult Male Dracunculus medinensis


  • Measure 10–40 mm long and 0.4 mm thick, rarely seen
• Larva Dracunculus medinensis


  • Measures 500–750 μm in length and 15–25 μm in breadth, cuticle shows prominent striations, swims about with a coiling and uncoiling motion
• Life Cycle of Dracunculus medinensis (in Man)


  1. Ingestion of water containing infected cyclops

  2. Larvae penetrate wall of duodenum and migrate to subcutaneous tissues

  3. Maturation of larvae to adults, mating, and migration of fertilized female to site of contact with water

  4. Blister formation and release of larvae
• Life Cycle of Dracunculus medinensis (in Cyclops)


  Larvae penetrate the gut wall of the cyclops and enter its body cavity, larvae develop to L3
• Hosts and Transmission of Dracunculus medinensis


  • Intermediate host: freshwater cyclops
  • Definitive host: man
  • Infective stage (to intermediate host): L1 larvae
  • Infective stage (to definitive host): L3 larvae
  • Mode of transmission: ingestion of water
• Filarial Nematodes


  Slender thread-like worms, transmitted by the bite of blood-sucking insects, reside in subcutaneous tissues, lymphatic system, body cavities
• Filarial Nematodes


  • Females are ovoviviparous, release larvae called microfilariae that can be detected in the peripheral blood or cutaneous tissues, microfilariae can exhibit nocturnal periodicity, diurnal periodicity, or no periodicity, microfilariae do not multiply or undergo any further development in the human body
• General Life Cycle of Filarial Nematodes


  1. Requires an intermediate host (blood-sucking arthropods)

  2. Microfilariae development and production of infective larval stages in the intermediate host

  3. Definitive host: man
• Male Filarial Nematodes


  • Tail has perianal papillae, unequal spicules but no caudal bursa
• Female Filarial Nematodes


  • Are viviparous, give birth to microfilariae (peripheral blood and cutaneous tissues), microfilariae can be sheathed (retained egg membranes) or unsheathed (ruptured egg membranes), adults generally measure 80–100 mm in length and 0.25–0.30 mm in breadth
• Filarial Nematodes by Location


  • Subcutaneous Tissues: Loa loa, Onchocerca volvulus, Mansonella streptocerca
  • Serous Tissues: Mansonella perstans, Mansonella ozzardi
  • Lymphatics: Wuchereria bancrofti, Brugia malayi, Brugia timori
• Lymphatic Filariasis


  One of the most debilitating diseases plaguing many tropical countries, second leading cause of permanent and long term disability, can cause physical and psychological effects, most common mosquito-borne causative agents are Wuchereria bancrofti and Brugia malayi
• Wuchereria bancrofti


  • Adult worms reside in the lymphatic system, microfilariae are found in blood
• Adult Wuchereria bancrofti


  • Creamy white, long, and filiform in shape, males measure 20 to 40 mm, females measure 80 to 100 mm, have smooth cuticle and tapering ends
• Microfilariae of Wuchereria bancrofti


  • Appear as minute snake-like organisms, measure 270 to 290 μm, body nuclei are visible, sheath does not take up the stain, cephalic end has a space, show several curvatures, show nocturnal periodicity in peripheral circulation
• Brugia malayi


  • Adult worms reside in the lymphatic system, microfilariae are found in blood
• Wuchereria bancrofti


  Adult worms reside in the lymphatic system, microfilariae are found in blood
• Brugia malayi


  Adult worms reside in the lymphatic system, microfilariae are found in blood
• Periodicity


  Refers to the time when most of the microfilariae are found in the peripheral blood