Tortora chapter 12

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Tortora chapter 12

• Eukaryotes Fungi, Algae, Protozoa, and Helminths

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Fungi

• Fungi can be beneficial or harmful
• They are especially harmful to people who are
  compromised or are in the hospital for other
  infections (nosocomial)
• Fungi are important in the food chain because
  they decompose dead plant matter and recycle
  nutrients
• The study of fungi is called mycology

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Medically important Phyla

• Zygomycota-conjugation fungi
• An example is the common black bread mold
• Ascomycota-sac fungi
• Have asexual spores that are conidia produced in
  long chains from conidiophore -conidia freely
  circulate in dust
• An ascospore results from the fusion of the
  nuclei from 2 cells and are produced in a sac
  like structure called an ascus

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Phyla continued

• Basidiomycota-club fungi
• includes mushrooms
• base pedestal is called a basidium
• basidiospores are produced externally on this
  pedestal

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Fungal diseases

• Any fungal infection is a mycosis
• These are long lasting and hard to treat
• Classify these into 5 groups according to degree
  of tissue involvement and mode of entry into
  host
• 1. systemic
• 2. cutaneous
• 3. superficial
• 4. subcutaneous
• 5. opportunistic
• http//www.doctorfungus.org/imageban/index.htm

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Systemic

• Infections deep in the body
• Can affect a number of tissues and/or organs
• Usually caused by inhalation of spores from fungi
  that live in the soil
• Include histoplasmosis and coccidioidomycosis

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subcutaneous

• Infections beneath the skin
• Caused by saprophytic fungi that live in soil or
  on vegetation
• Often enter through puncture wound
• Example is sporotrichosis

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Cutaneous

• Fungi that infect only hair, epidermis, and nails
  are dermatophytes or cutaneous mycoses
• These produce an enzyme that degrades keratin
  (keratinase)
• Can spread by contact (human/human, animal/human)

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Superficial

• Localized along hair shafts and in superficial
  (surface) epidermal cells
• Prevalent in tropics (hot and wet areas)

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Opportunistic

• Harmless in normal habitat but can become
  pathogenic if given the opportunity
• Pneumocystis is commonly found in AIDS patients
• Recently reclassified from a protozoan to a
  fungus after RNA studies
• Stachybotrys grows on cellulose in dead plants
  AND on water damaged walls in homes
• This one has TOXIC spores that can cause fatal
  pulmonary hemorrhage in infants. BAD NEWS.

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Aspergillosis

• Aspergillus causes aspergillosis
• http//www.doctorfungus.org/mycoses/images/gram_co
  rnea_a_flavus.jpg
• http//www.doctorfungus.org/mycoses/human/aspergil
  lus/aspergillosis.htm

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Candida albicans

• Candidiasis or yeast infection
• Can be thrush (oral) or vulvovaginal candidiasis
• Found in newborns, AIDS patients, and in people
  who have just completed antibiotic
• Is also one cause of diaper rash!

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Protozoa

• Unicellular
• Eukaryotic
• Chemoheterotrophic
• Feeding stage is called trophozoite and usually
  eat bacteria or small particulate nutrients
• Few cause problems for humans

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Characteristics

• Life cycle
• Produce asexually by fission, budding, or
  schizogeny
• Schizogeny is multiple fission, the nucleus
  undergoes many divisions before the cell divides
• Some may reproduce sexually by conjugation
• In conjugation, two cells fuse and a haploid
  nucleus from each migrates to the other and fuses
• When the parent cells separate, each is fertilized

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Encystment

• Some may form a protective capsule called a cyst
  that helps the organism survive hard times
• Helps parasitic forms survive outside the host
  when they are excreted in feces

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Medically important phyla

• Archaezoa-lack mitochondria, but have an
  organelle called a mitosome
• Live in host as a parasite
• 1. Example of human parasite is Trichomonas
  vaginalis
• Transmitted by sexual contact (no cyst stage)
• http//www.cdc.gov/ncidod/dpd/parasites/trichomona
  s/factsht_trichomonas.htmwhat
• 2. Giardia lamblia -parasite found in small
  intestine of humans and other mammals
• Ingest in contaminated water and get major
  diarrhea
• http//www.cdc.gov/ncidod/dpd/parasites/giardiasis
  /factsht_giardia.htmwhat

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More phyla

• Amoebozoa-amoebas have pseudopods to help them
  move
• Example is Entamoeba histolytica
• Causes amoebic dysentery
• Uses proteins called lectins to attach to
  galactose of cell membrane and causes lysis
• Transmitted by ingestion of cysts from feces

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Even more phyla

• Apicomplexa-obligate intracellular parasites and
  arent motile as adults
• Complex life cycle that involves several hosts
• Plasmodium causes malaria which affects 10 of
  the worlds population!
• Grows by sexual reproduction in the Anopheles
  mosquito (yep, they are in Arkansas)

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Life cycle of Plasmodium

• Anopheles mosquito bites and transmits the
  sporozoite into the blood stream
• This quickly travels to liver and undergoes
  schizogony and asexually produces merozoites
  (daughter cells)
• Merozoites go back into blood stream and infect
  red blood cells
• Young trophozoites (ring stage) inside blood cell
  are the actively feeding stage
• Repeatedly reproduce and eventually ruptures RBC,
  releasing merozoites
• Some develop into sexual forms (gametocytes)
  which are picked up by a mosquito and the sexual
  cycle begins which eventually forms more
  sporozoites

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continued

• http//www.cdfound.to.it/HTML/pla1.htmpf4
• Mosquito is definitive host because it harbors
  the sexually reproducing stage
• The human is the intermediate host
• Tell which type of malaria a person has by the
  interludes between fever caused by release of
  merozoites

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Helminths

• Spend all or part of their lives in humans
• 2 phyla (Nematoda and Platyhelminthes)
• These are multicellular eukaryotic organisms
• Have advanced systems like circulatory,
  digestive, and reproductive
• Very specialized to live inside host

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Life cycle

• Complex
• May have larval stages that involve a series of
  intermediate hosts
• Adults are dioecious (2 separate sexes) or may
  have both sexes in one individual (monoecious or
  hermaphroditic)

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Platyhelminthes

• Flatworms include trematodes and cestodes
• Trematodes-also called flukes are flat bodied
  with a ventral sucker and an oral sucker which
  just hold the worm in place
• Absorb food through cuticle (outer covering of
  body)

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Life cycle of lung fluke

• Lung fluke (Paragonimus westermani) lives in
  bronchioles of lungs
• Hermaphrodite releases eggs which may be coughed
  out or swallowed then released by feces
• If feces enters water, the eggs hatch and become
  a miracidium which enters a snail
• Inside snail it develops into a redia which
  reproduces asexually to produce rediae
• Several cercariae develop in each redia
• These leave snail and enter crayfish, which is
  eaten raw or undercooked by a human!

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Schistosoma

• This is a blood fluke!
• The cercariae burrow through skin of host and
  enter circulatory system!
• http//siera104.com/bio/flatworms.html
• A common cutaneous result is swimmers itch

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Cestodes-tapeworms

• Intestinal parasites
• Look like a segmented ribbon
• Head is scolex and has suckers for attaching to
  intestines
• Body contains proglottids which have both male
  and female parts and eventually contain eggs
• These are released when mature and exit via the
  feces

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Taenia saginata

• Beef tape worm
• Humans are definitive hosts
• Worms can grow up to 6 meters
• Eggs are ingested by grazing animal (cow) and
  hatch into larvae and bore through intestinal
  wall
• Larva migrate to muscle and encyst (measly beef)
• If meat is ingested by humans (undercooked) the
  scolex anchors in small intestine and produces
  proglottids

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Echincoccus granulosus

• Human is intermediate host
• Dogs and coyotes are definitive host
• Eggs excreted with feces are ingested by humans
  (or other animals)
• Hatch in intestine and larva migrate to lungs or
  liver
• Larva develop into hydatid cyst which contains
  brood capsules for hundreds of scoleces
• Humans are dead end for this parasite (nothing
  eats humans normally)
• If deer is host, it is eaten by wolf, then wolf
  becomes the host
• http//www.stanford.edu/class/humbio103/ParaSites2
  006/Echinococcus/main.html

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Nematodes

• Round worms have a complete digestive system with
  a mouth, intestine, and anus
• Most are dioecious
• Males are usually smaller and have spicules on
  posterior end to guide sperm to females genital
  pore

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Pinworms

• Enterobius vermicularis spends its entire life in
  the host (dont get them from animals)
• Adults are in the large intestine
• Female migrates to anus and deposits eggs on
  perianal skin (this itches)
• Eggs may be ingested again by same host or be
  spread on clothes or bedding
• Use sticky tape method to spot eggs!

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Hookworms

• Necator americanus -live in small intestine and
  eggs are excreted in feces
• Larva hatch in soil and eat bacteria
• Larva bore thorough hosts skin (never walk in
  yard barefooted if you own a dog!)
• Enter blood stream, migrate to lungs, coughed up
  and swallowed, then ends up in small intestine

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Vectors

• Creatures than carry diseases
• Arthropods are a type of vector
• These include mechanical vectors that just carry
  the organism on a body part
• OR biological vectors are used by the organism to
  reproduce
• Vectors include mites, ticks, lice, fleas, true
  flies (mosquito, tsetse fly), and true bugs