Parasites and zoonoses

  1. Symbiosis=living together

    Mutualism/Cooperation + +
    Spite - -
    Predation + -
    Parasitism + -


  2. Types
    1. Microparasites (viruses, bacteria, fungi) or Macroparasites (platyhelminths, nemotodes, arthropods)
    2. Obligate vs. facultative
    3. Endoparasites vs. Ectoparasites


  3. Characteristics of parasites
    1. Usually smaller than host
    2. Usually physiologically dependent on host
    3. May have specificity for particular host species
    4. Usually do not kill host (but may debilitate it)
    5. May live all or part of life cycle on host, and may have complex life cycle

      1. Life cycle of deer tick (Fig. 27.14)
      2. Life cycle of tapeworm (Fig. 27.5)
      3. Life cycle of menigeal worm


  4. Zoonotic disease are those carried by nonhuman animals but transmissible to humans.

  5. Case studies

    1. Lyme disease

      1. Disease is caused by a bacterium, Borrelia burgdorferi
      2. Vector is an arachnid, the deer tick
      3. Symptoms of the disease

        1. bulls-eye rash, low grade fever, muscle aches, lethargy
        2. cardiac problems, arthritis, neurological symptoms


      4. Life cycle of deer tick and how it becomes infected

        1. Eggs (laid on ground) are not infected
        2. Eggs hatch in summer into larvae (6 legged), feed on small mammals
        3. Deer mouseis primary host and is the reservoir for the bacteria causing Lyme disease
        4. Larvae get one blood meal then drop off to metamorphose into nymphs. They are likely to become infected at the larval stage if they feed on an infected host.
        5. Nymphs (now often infected) get a blood meal. They can pass the bacterium to their host if attached to it for at least 24 hours.
        6. Nymphs drop off and metamorphose into adults. They take one more blood meal prior to laying eggs. This is usually from their primary host, the deer. Although adult ticks are often infected, they don't usually pass the disease on to humans because they are usually detected before they have been attached for 24 hrs.


      5. Incidence of Lyme disease is affected by ecological factors
        1. acorn production (food for deer mice)
        2. small mammal biodiversity


    2. Meningeal worm (a nemotode)

      1. normal host is the white tailed deer
      2. Life cycle overview
        Adults live in and around the subdural space of the cranium (covering of brain)
        when eggs are laid they travel in circulatory system to the alveoli of the lungs
        where they hatch into larvae
        From here they are coughed up into the digestive system and pass out with the feces.
        Once on the ground, they move into snails for 3-4 weeks.
        Herbivores unintentionally swallow the infected snails while they are feeding on grass.
        Once ingested, the larvae pass through the stomach wall and follow nerves toward the spinal cord.
        Here they mature and then travel up through the subdural space up to the brain.
      3. In hosts other than the deer, the worms migrate through the spinal cord itself, causing loss of coordination and eventual paralysis.
      4. Native species can be affected (moose, mule deer)
      5. Non-native species can be affected (e.g., species bred at the Conservation and Research Center)

      6. Preventive measures
        1. Keep out deer (fencing, removal, population control)
        2. Keep out snails (gravel buffers, molluscicide)
        3. Preventive treatment with dewormers (e.g., ivermectin)