Parasites and zoonoses
- Symbiosis=living together
|Spite ||- -
|Predation ||+ -
|Parasitism ||+ -
- Types - parasites can be classified along a variety of dimensions
- Microparasites (viruses,
or Macroparasites (platyhelminths, nemotodes, arthropods)
- Obligate vs. facultative
- Endoparasites vs. Ectoparasites
- Characteristics of parasites
- Usually smaller than host
- Usually physiologically dependent on host
- May have specificity for particular host species
- Usually do not kill host (but may debilitate it)
- May live all or part of life cycle on host, and may have complex life cycle
- Life cycle of deer tick
- Life cycle of tapeworm
- Life cycle of menigeal worm
- Zoonotic disease are those carried by nonhuman animals but transmissible to humans.
- Case studies
- Lyme disease
- Disease is caused by a bacterium, Borrelia burgdorferi
- Vector is an arachnid, the deer tick
- Symptoms of the disease
- bulls-eye rash, low grade fever, muscle aches, lethargy
- cardiac problems, arthritis, neurological symptoms
- Life cycle of deer tick and how it becomes infected
- Eggs (laid on ground) are not infected
- Eggs hatch in summer into larvae (6 legged), feed on small mammals
- White-footed mouse is primary host and is the reservoir for the bacteria causing Lyme disease
- 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.
- 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.
- 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.
- Humans are most likely to get the disease from nymphs
- Seasonal activity of the nymphs coincides most closely with when humans are likely to be in tick infested areas (summer)
- 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.
- Incidence of Lyme disease is affected by ecological factors
- + = positive influence
- - = negative influence
- green star = ticks can get infected with Borrelia
- red stars = ticks cannot get infected with Borrelia
- T= environmental temperature
- RH= relative humidity
- acorn production (food for deer mice)
- small mammal biodiversity (relative density of reservoir hosts vs dilution hosts, presence of predators)
Watch this interview with primatologist Robert Sapolsky on toxoplasmosis (watch up to about 20:00).
Or this one
Here is an additional popular science article that gives some background on the links between toxoplasmosis and human behavioral disorders.