Biology of Parasitism CB8500

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Biology of ParasitismCB8500

• We will meet three times a week Mondays 335
  p.m., Wednesdays 9 a.m., Fridays 9 a.m.
• Two lectures (usually Mon/Fri) and one
  seminar/journal club (usually Wed)
• You find the class schedule lecture notes on
  the class web site at http//webs.cb.uga.edu/str
  iepen/biopara

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Biology of ParasitismCB8500

• Lectures will be by Boris Striepen as well as
  most of the members of UGAs Center for Tropical
  and Emerging Diseases
• This is not a survey course in Parasitology
• The class will introduce current research on
  parasites and their vectors heavily focused on
  molecular concepts of parasite cell biology,
  pathogenesis, biochemistry and immunology
• Where appropriate we will explore how these new
  concepts can be exploited towards intervention
  through drugs, vaccines and control programs
• The general goal is to give you enough background
  to be able to follow e.g. the talks at the Woods
  Hole Molecular Parasitology Meeting

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CB8500 a loafer class without exams, but

• Grading for this class is A-F
• To get credit for this class you are expected to
• Show for the lectures and seminars
• Present original research papers in the class
  seminar (one per student in the class)
• Participate in the discussions within the class
• Develop an original new research project in form
  of a (shorter version) NIH grant proposal
• Write a primary and secondary peer review of your
  fellow students research grants
• Participate in the review session at the end of
  the semester
• On the upside - this class does not have exams

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Parasitism - a way of life

• Parasite and Parasitism are terms that define a
  way of life rather than a coherent and
  evolutionary related group of organisms
• Symbiosis, Commensalism, Mutualism, Parsitism

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Parasitism - a way of life

• Parasite and Parasitism are terms that define a
  way of life rather than a coherent and
  evolutionary related group of organisms
• Symbiosis Any two organisms living in close
  association, commonly one living in or on the the
  body of the other, are symbiotic, as contrasted
  with free living. De Bary 1879
• Commensalism Sharing the table. One partner
  benefits but the other is not hurt.
• Mutualism Both partners benefit.
• Parasitism One partner (the parasit) harms or
  lives on the expense of the other (host).

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Is a lion a parasite?

• The benefit in the relationship lion and
  wildebeest seems highly skewed in favor of the
  lion

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Who is a parasite?

• Parasites are usually much smaller than their
  hosts, they also do no kill before eating.

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Is a mosquito a parasite?

• The border between parasitism and micropredation
  is blurry
• Parasites usually live in a very intimate
  relationship with their host depending on more
  than food from it
• The host is food source and more or less
  permanent habitat at the same time
• Many parasites show strict specificity for a
  single host

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Parasites are found in all groups of organisms
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Parasites a very diverse set of eukaryotic
pathogens

• Parasitology historically covers a diverse
  collection of metazoan and protozoan organisms
• Protozoa unicellular eukaryotes
• Platyhelminthes flatworms these include flukes
  and tape worms
• Nematodes elongated worms with rigid cuticula
• Arthropodes insects and ticks and mites which
  either are parasitic or transmit parasites as
  vectors
• (we only have time to discuss the most important
  groups causing human disease, there are
  additional parasites outside these groups)

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Ecto- Endoparasitism

• Ectoparasites live on, but not in their hosts
  (they can nevertheless cause severe illness). Ich
  a protozoan ectoparasite of the skin of a fish.
• Endoparasite live within the body and tissues of
  their hosts. Trypanosomes (which cause sleeping
  sickness) within the blood of an infected animal.

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Infection infestation

• Infectious diseases are caused by transmittable
  parasitic agents including bacteria, viruses,
  fungi, protozoa and a variety of metazoans
  commonly referred to as helminths or worms
• Infection usually implies replication of the
  agent resulting in a growing number of pathogens
• Infestation are characterized by a constant
  number of pathogens. Severity of disease often
  depends on infection dose.

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Obligate/facultative, and permanent/intermittent
parasites

• Most parasite are obligate parasites (exceptions
  include e.g. Naegleria)
• In some species only some life cycle stages, e.g.
  the larvae are parasitic, in others parasitic and
  free living generations can alternate depending
  on environmental conditions (Strongiloides
  stercoralis) .

Indirect
Direct
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Hosts and life cycles

• The definitive host is by definition the one in
  which the parasite reproduces sexually
• Additional hosts are then designated intermediate
  hosts
• Host which actively transmit parasites to humans
  are often called vectors
• In paratenic or transport hosts no parasite
  development occurs
• Reservoir host are alternate animal host from
  which the parasite can be transmitted to humans
  (zoonosis) or domestic animals
• Accidental host, not suitable for parasite
  development, but can cause disease

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Disease terminology

• Prepatency infected but parasite presence can
  not be detected yet
• Patency established infection, parasite stages
  can be detected (malaria parasites in blood
  smears, worm eggs in feces etc.)
• Incubation period time between infection and the
  development of symptoms
• Acute disease can lead to crisis which can
  resolve in spontaneous healing, chronic infection
  or death
• Convalescence Period after healing, absence of
  infectious agents, no symptoms, in certain case
  immunity to reinfection

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Number of people infected/affected by parasitic
diseases

• Diseases causing
• high mortality
• Malaria (400M)
• Sleeping Sickness (0.5 M)
• Chagas (18M)
• Visceral Leishmaniasis (4M)

• Diseases causing
• morbidity QL losses
• Geohelminths (2B)
• Water Foodborne Protozoans (1.5B)
• Schistosomiasis (200M)
• Lymphatic filariasis (120 M)
• Cysticercosis (?50M)
• Onchocerciasis (18M)
• Cutaneous Leishmaniasis (8M)
• Guinea worm (4M, now 60K)