Biology 625
Fall semester lecture note outline

Updated: 15 March 2005

The text below simply represents a crude lecture outline of one of the topics covered in class. It is not meant to substitute for attending lectures or ignoring the textbook. Additional material, including line drawings, kodachromes, and more extensive information on life-cycles and basic biology, will be supplied in the lectures.

Topic 19. The Rhabditid nematodes (Order Rhabditida)

  1. small worms
  2. often with 6 lips (primitive condition)
  3. usually with a conical tail
  4. most species inhabit decaying vegetation or other organic matter
  5. many are facultatively parasitic, living temporarily in wounds or passing through the gut
  6. many parthenogenic or hermaphroditic if parasitic
  7. up to two dozen different families recognized by some authors, although not all have members that are parasitic. Only a handful of families will be presented here:
    1. Angiostomatidae
      1. Angiostoma limacis in terrestrial gastropods
      2. Angiostoma plethodontis in a salamander
    2. Cephalobidae
      1. Halicephalobus gingivalis (syn. Micronema deletrix) may cause serious pathology in horses
      2. Turbatrix aceti, or vinegar eel, has been reported from the human female genito-urinary tract
    3. Cylindrocorporidae
      1. Longibucca eptesica and L. lasiura from the stomach of bats
      2. Longibucca vivipara in the intestine of the snake Pseudoboa cloelia
    4. Diplogasteridae
      1. Cephalobium microbivorum is found in the ileum of field crickets of the genus Gryllus within North America
        1. Ackert and Wadley (1921, Trans Am Microscop Soc 40: 97-115) reported a prevalence of 70% male and 91% female crickets (probably Gryllus fultoni) infected during the Fall months. Infections are sometimes heavy, and 91 nematodes were found in a single female cricket in the original study. The average infection is about two dozen worms per cricket!
        2. This rhabditid is the most commonly encountered parasitic nematode in Biology 625
    5. Rhabdiasidae
      1. Rhabdias ranae (Family: Rhabdiasidae)
        1. Tiny parasite in the lungs of frogs (R. ranae) worldwide (Western hemisphere species may be separate species)
        2. Heterogonic life-cycle (free-living generation interspersed between parasitic generations.
          1. Adult worm a protandrous hermaphrodite (functional male before a functional female)
            1. Sperm produced in early male phase (N=5 or 6)
            2. Sperm stored in seminal receptacle
            3. Gonad then produces eggs (N=6)
            4. Fertilization via stored sperm
          2. Eggs up trachea; swallowed (embryonate during transit)
          3. Hatch in gut
          4. L1 accumulate in feces, voided in feces (rhabditiform)
          5. 4 molts (free-living in environment)
          6. free-living adult males (N=5) and free-living adult females (N=6)
          7. Copulation
          8. Progeny hatch in utero; consume female from within
          9. Molt twice to L3s during consumption of female (filariform)
          10. Undergo developmental arrest
          11. Penetrate skin of anuran
          12. Lodge in various tissues
          13. All die except those that reach lungs
          14. In lungs, mature into hermaphroditic adults
      2. Other species
        1. Rhabdias bufonis in toads and frogs worldwide
        2. Rhabdias americanus in Bufo americanus
        3. Rhabdias fuscovenosa (in water snakes; most eggs yield filariform L3s that do not go on to form free-living cycle; however, a few do go on to form free-living adults. Moving towards a homogonic life-cycle)
        4. Acanthorhabdias in lungs of South American reptiles
        5. Entomelas in lungs and body of reptiles
        6. Pneumonema in lungs of Australian reptiles
    6. Rhabditidae
      1. Diploscapter coronata, a nematode normally associated with plant debris, has been reported from the human stomach when the pH is higher than normal
      2. Pelodera strongyloides (syn. Rhabditis strongyloides)
        1. adults and larvae exist at high concentrations in soil enriched with manure. Free-living normally, but occasionally invade dermis and cause mange-like dermatitis in cattle, dogs, and rarely humans.
        2. similar species with long, slender, invasive, 3rd larvae in addition to their normal larvae
          1. Rhabditis commandorica (rotting vegetation)
          2. Rhabditis punctata (freshwater soils)
          3. Rhabditis cutanea (rodent nests; 3rd stage larvae can invade conjunctival sac of rodents)
          4. Rhabditis nidicolis (rodent nests)
          5. Rhabiditis orbitalis (rodent nests; 3rd stage larvae sometimes found coiled in rodent hair follicles)
          6. Caenorhabditis and Rhabditoides are genera that can be fecal contaminants
    7. Strongyloididae
      1. Strongyloides spp. (Family: Strongyloididae)
        1. Over 40 known species
        2. Both free-living and parasitic portions of the life-cycle
          1. Free-living
            1. Adults (males and females) in environment
            2. Eggs produced; embryonate
            3. Hatch
            4. L1-L2-L3
              1. If environment unfavorable, numerous filariform L3s produced. Can only go on if suitable host found as parasites
              2. If environment stable, numerous rhabditiform L3s produced
                1. Molt to free-living L4s
                2. Molt to adult free-living males and females
          2. Parasitic phase
            1. L3s (filariform) either penetrate skin or are ingested
            2. Some species undergo lung migration, whereas other species simply find intestine
            3. If in lungs, up trachea and swallowed
            4. L4s in gut; final molt to adults
            5. All adults parthenogenic females; migrate randomly through mucosa
            6. Produce eggs which hatch during passage through gut so that L1 larvae pass out with feces
            7. L2 - L3 (either rhabditiform free-living L3, or filariform L3 that undergoes developmental arrest and capable of infecting new host)
        3. The larvae are also capable of autoinfection. If larvae have time to molt to the L3 before passed in the feces, can penetrate gut or perianal skin, undergo migration, and mature
        4. Pathology
          1. Penetration of skin can cause swelling, hemorrhage, itching
          2. During migration, damage to skin, liver, lungs, and other organs. Main problem is pulmonary eosinophilic infiltration, resulting in parasite induced asthma
          3. Adults in mucosa may cause pain, inflammation, sloughing of patches of the mucosa, ulceration, secondary bacterial infections and even septicemia.
          4. Persistent infections can cause persistent colitis
        5. Other species
          1. Strongyloides stercoralis (variety of mammals worldwide)
          2. Strongyloides fulleborni (usually non-human primates)
          3. Strongyloides papillosus (sheep, goats, cattle, zebra, camels,deer, rabbits)
          4. Strongyloides procyonis (raccoons)
          5. Strongyloides ransomi (swine)
          6. Strongyloides ratti (rodents)
          7. Strongyloides venezuelensis (old world rats)
          8. Strongyloides westeri (equids)
      2. Other genera
        1. Leipernema also has a hermaphroditic parasite stage, in edentates
        2. Parastrongyloides has a dioecious parasitic form, in insectivores and marsupials

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