MICROPARA - NEMATODES

• Nematos


  Means a thread
• One of the most abundant types of worms in the world
• 12,000 species named, estimated 500,000 species worldwide yet to be discovered
• Live in a wide variety of habitats: ocean, freshwater lakes and streams, soil, from the poles to the equator
• Filariform larvae

  The 3rd or infective stage; Long, thread-like; Designed for penetration

  
• Rhabditiform larvae

  Characterized by the presence of a muscular esophagus and bulbular pharynx. The worms leaving the egg are termed "rhabditiform" larvae

  
• Pseudocoelum


  Fluid-filled body cavity lying inside the external body wall of the nematode
• Egg


  Characteristic of the genus. Size & shape are relatively consistent
• Larvae


  Undergo several molts (third stage usually the infective stage)
• Adult


  Varies in size from genus to genus; Range from less than 1 mm to over one meter
• Good topsoil may contain billions of nematodes/acre
• Parasitize almost every type of plant and animal
• Most average about 5 cm (2 inches) in length
• However, they range in size from being microscopic to some almost 1 meter in length
• Nematodes


  • Move by using fluid pressure generated in their pseudocoelom
  • This fluid-filled chamber that provides structure and locomotion is called a hydrostatic skeleton
  • Hydrostatic skeletons work by transferring the force of muscular contractions to a non-compressible fluid (hydraulic fluid pressure)
  • The pressure is confined by a thick, elastic cuticle made of collagen
• Nematode locomotion


  • Circular muscles are absent
  • Longitudinal muscles work antagonistically against the outer cuticle like a spring
  • When the longitudinal muscles contract, the cuticle on the opposite side is stretched
  • When the longitudinal muscles relax, the cuticle relaxes and the body cavity returns to its original shape
  • This causes nematodes to move erratically
• Nematode digestive system


  Complete but simple, consisting of a mouth, pharynx, intestine, rectum and anus

  
• Nematode nervous system


  Consists of a ring-shaped ganglia at the anterior end of the body that connects to two nerve cords that run the length of the body
• General nematode life cycle

  1. Humans ingest infective eggs

  2. Larvae hatch in intestine

  3. Male and female adults develop in the intestine

  4. With Ascaris lumbricoides, hookworms, and Strongyloides larvae penetrate the intestinal mucosa and initiate a heart - lung cycle enroute to the intestinal tract to mature to adults
• General nematode diagnosis


  1. Fertilized eggs are produced

  2. Diagnostic stages, eggs or larvae, exit the host in its feces

  3. Larvae develop within the egg in warm, moist soil (except for Strongyloides stercoralis, whose eggs hatch in the intestine, with larvae passing in the feces)
• Types of nematodes


  • Plant Parasitic Nematodes (Ectoparasitic, Endoparasitic)
  • Human Parasitic Nematodes (Bio-source nematodes: Filaria, Trichinella spiralis; Soil-transmitted Nematodes: Ascaris, Pinworm, Whipworm, Hookworm)

  
• Human parasitic nematodes


  • Intestinal Nematodes: Threadworm/Pinworm, Whipworm, Roundworm, Hookworm, Strongyloides
  • Tissue Nematodes: Filarial Worms, Trichinella or Trichina worms

  
• Pinworm, Threadworm, Seatworm


  Enterobius vermicularis - the pinworm
• Enterobius vermicularis life cycle

  1. Eggs are ingested, hatch in intestine, larvae mature to adults

  2. Gravid females migrate to the perianal area at night to lay eggs

  3. Eggs develop to infective stage within 4-6 hours. Eggs can survive for extended periods in cool, moist environment
• Enterobius vermicularis adults


  Female: creamy white, ~ 8-13 mm long, with sharply pointed tails; Wing-like flaps (cervical alae) at head end; Male: small (2-5 mm) with strongly curved posterior

  
• Enterobius vermicularis eggs

  50 to 60 x 20 to 32 microns, broadly oval, and flattened on one side. Compressed laterally; Normally are embryonated (contain a larva)

  
• Enterobius vermicularis diagnosis


  1. Recovery and identification of eggs or adults from the perianal region utilizing the cellophane tape preparation

  2. Specimens must be collected the first thing in the morning upon waking, especially before bathing or bowel movements

  3. Eggs are rarely found in fecal samples because release is usually external to the intestines
• Enterobius vermicularis pathology and symptoms


  • One third of all cases are asymptomatic
  • Infections rarely cause serious lesions
  • Symptoms associated with the migration of the female out of the anus to lay her eggs include: perianal itching, nausea or vomiting, loss of sleep, irritability, irritation of the intestinal mucosa, vulval irritation in females due to migrating worms entering the vagina instead of the re-entering anus
• Enterobius vermicularis is the most prevalent nematode in the United States. Humans are the only known host, and perhaps 10% of the U.S. population may harbor pinworms, especially children

  
• Enterobius vermicularis treatment


  Mebendazole (children), Albendazole (adult)
• Trichuris trichiura


  The whipworm

  
• Trichuris trichiura life cycle


  1. Infective, fully embryonated eggs are ingested, larvae hatch in small intestine, penetrate and develop in the intestinal villi, return to lumen and migrate to the area of the cecum

  2. Larvae mature and live in the colon. Worms embed their anterior portion (as much as two-thirds of the worm) into the mucosa

  3. Barrel-shaped eggs are released into the stool

  4. Eggs must undergo development in the soil for approximately 10 days to 3 weeks before they become infective

  5. The worm's life span is estimated to be 4 - 8 years

  
• Trichuris trichiura adults


  Females: 35 to 50 mm long, anterior two-thirds is long and threadlike, expanding into a broader posterior; Males: 30 to 45 mm long, similar to female but exhibiting a strong curvature of tail
• Trichuris trichiura eggs


  50 to 55 x 22 to 25 microns, barrel-shaped, with clear polar plug at each end
• Trichuris trichiura diagnosis


  Recovery and identification of eggs in the feces
• Trichuris trichiura pathology and symptoms

  • Slight infections - usually asymptomatic
  • Heavy infections - surface of colon is matted with worms which causes bloody or mucous diarrhea, weight loss and weakness - infections with 200 or more worms in children may cause a chronic dysentery, profound anemia and growth retardation
  • Abdominal pain and tenderness, increased peristalsis and rectal prolapse, especially in children

  
• Trichuris trichiura is commonly found in refugees from tropical areas. It is the third most common intestinal helminth infection. Higher prevalence in warm countries and areas of poor sanitation, especially in countries which utilize "night soil" for fertilizer. Common among children and in the institutionalized mentally retarded. Commonly seen along with Ascaris lumbricoides because of the similar mode of infection
• Trichuriasis treatment


  Anti-helminthic medications, such as Albendazole
• Ascaris lumbricoides


  Large Intestinal Roundworm
• Life cycle


  1. Humans ingest embryonated eggs containing infective larvae

  2. Larvae hatch from the eggs in the small intestine, penetrate the intestine wall, enter the bloodstream, migrate to the liver, travel to the lung via the blood stream

  3. Larvae break out of lung capillaries into alveoli, travel to the bronchioles, and are coughed up to the pharynx. They are swallowed and return to the intestine. Two molts to 4th stage larvae take place in alveoli

  4. Larvae mature to adults in the small intestine

  5. Worms do not attach to the intestinal wall, but maintain their position by constant movement. Worms have a life span of approximately 1 year

  6. Undeveloped eggs are passed in the feces. These eggs develop in soil and are infective after two weeks to one month. The egg shell is very thick and resistant to environmental changes

  7. Eggs can remain infective for up to 5 years if protected from direct sunlight and desiccation