Chapter 21: Protozoa

1
Chapter 21 Protozoa

• Autonomous unicellular eukaryotic organisms,
  which are often motile possess various degrees
  of specialization
• Many w/ organelles (evolved) that mimic organs of
  multicellular organisms
• Reproduction mitotic binary fission - asexual
  some species via sexual (meiotic) reproduction
• Giemsas Stain laboratory staining procedure
  for parasitic microorganism identification

2
Protozoa

• General characteristics
• Kingdom Protista (Subkingdom Protozoa)
• Parasitic Protozoa are mostly Facultative
  Anaerobes (live grow w/ or w/o O2)
• Mostly Heterotrophic, Chemo-organotrophs
• Heterotroph an organism requiring complex
  organic food in order to grow develop
• Chemo-organotroph use organic compounds for E
• 2 Life Stages
• Trophozoite active metabolizing pathologic stage
  or active vegetative stage
• Actively motile, feeding stage growing form
• Cyst latent survival form dormant,
  environmentally resistant
• Immotile, quiescent, resistive, INFECTIVE stage

3
Protozoa

• General Characteristics contd.
• Cyst stage permits survival when
  environmental conditions are hostile
• General Sites of Infection
• Intestines
• Urogenital Tract
• Blood Tissues
• -Protozoan infections common in developing,
  tropical subtropical regions w/ poor sanitary
  conditions control of transmission vectors

4
Clinically Important Protozoa Classification

• Amebas (sarcodina)
• Move by extending psuedopodia (cytoplasmic
  profections or false feet) outward from the
  main cell body gt Ameboid action
• Feed by engulfing food particles w/ pseudopodia
• Flagellates (mastigophora)
• Move via 2 or more whip-like projections
  (flagella) that rotate propel the cells thru
  liquid environment
• Ingest food thru oral groove cytostome
• Ciliates (ciliophora)
• Move via many hair-like projections (cilia) arrd
  in rows cover entire cells beat in synchrony
• Most w/ cysostomes that pass food thru
  cytopharynx ? vacuoles (food digestion site)
• Sporozoa (apicomplexa)
• Obligate, intracellular parasites generally have
  non-motile adult forms
• Complex life cycles w/ gt1 host
• DEFINITIVE HOST harbors sexually reproducing
  stage
• INTERMEDIATE HOST provides environment in which
  asexual reproduction occurs

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Intestinal Protozoal Infections

• Amebic Dysentery Amebiasis
• Etiological agent Entamoeba histolytica
• Trophozoite sarcodine protozoa slowly moves
  among crypts of LI are are shed into feces
• Cyst latent survival (infective) stage
  significant in transmission spherical w/ 4
  nuclei
• Colitis w/ diarrhea (sometimes bloody), w/
  abdominal pain cramping
• Extraintestinal amebiasis a complication of
  intestinal amebiasis in which the trophozoites
  enter the blood are carried to other organs,
  most often the LIVER, causing abcesses (4-5 of
  cases) abscesses can also form in brain, lungs
  or heart.
• DEATH may result from disseminated disease

6
Intestinal Protozoal Infections

• Amebic Dysentery Amebiasis
• Pathogenesis
• Ingest cysts (w/ 4 nuclei) from contaminated
  food/water ? pass thru stomach, where exposure to
  gastric acid stimulates release of pathogenic
  trophozoite in Duodenum of SI ? formation of
  trophozoites in the SI encystment (cyst ?s
  into 4 small trophozoite forms) ? trophozoites
  carried to LI, where they continue to grow
  divide by binary fission and feed on intestinal
  bacteria amebas invade/penetrate into intestinal
  mucosa (epithelium) d/t release of enzyme that
  lyses tissues ? subsurface lesions develop, which
  may coalesce into extensive ulcerations, leading
  to severe dysentery w/ stools containing bloody
  mucus.
• Disseminated amebiasis small - amebas
  penetrate mesenteric venules lymphatics
  spread to internal organs abscesses usually
  develop in LIVER (4-5 of cases), but also in
  brain, lungs, heart.
• DEATH can result from disseminated disease

7
Intestinal Protozoal Infections

• Amebic Dysentery Amebiasis
• Diagnosis
• Microscopic observation of trphozoite or cyst
  stage of ameba in feces (pt. stool sample)
• Serological tests helpful in Dx of disseminated
  disease
• New test available designed to detect fecal Ag
  trophozoite DNA
• Liver abscesses should be biopsied from abscess
  edge, where active amebas accumulate
• Treatment - available
• Epidemiology
• Reservoir infected humans ONLY, both
  asymptomatic symptomatic
• 10-50 of world is infected worldwide
  distribution
• Prevalence in U.S. 1-2
• Asymptomatic individuals chronic carriers
  pass cysts
• MAIN SOURCE OF FOOD WATER CONTAMINATION
• Transmission Person-to-person, indirect,
  fecal-oral
• food, water, fomites
• Fecal contamination of fresh vegetables, water
• Flies cockroaches also transmit cysts to food
  fomites

8
Intestinal Protozoal Infections

• Giardiasis
• Etiological agent Giardia lamblia
• Flagellate protozoan
• m/c protozoan affecting human intestinal tract
• Trophozoite stage flagellate protozoan
  (teardrop-shaped cell) w/ 2 large nuclei, large
  sucking disc and 4 flagella face-like
  appearance
• Cyst stage slightly smaller than trophozoite w/
  4 nuclei and parabasal body
• Mostly affects SI
• Mild diarrhea to severe malabsorption syndrome
• Sudden onset of watery diarrhea, often fowl
  smelling, w/ abdominal cramps, flatulence
  STEATORRHEA (fatty stools fat in stools)

9
Intestinal Protozoal Infections

• Giardiasis
• Pathogenesis
• Ingestion of cysts (10-25 min. infective dose)
• Gastric acid stimulates encystment and releases
  trophozoite into Duodenum Jejunum of SI, where
  it attached via sucking disc to intestinal villi
• Alteration of villi inflammation of mucus
  membrane ? malabsorbtion NO obvious tissue
  necrosis
• Spontaneous recovery w/in 10-14 days
• Chronic infection problem in pts w/ IgA
  deficiency diverticula (diverticulosis)

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Intestinal Protozoal Infections

• Giardiasis
• Diagnosis
• Cysts trophozoites observable in feces w/ onset
  of sxs
• In absence of observable cyst test now available
  for detection of fecal Ag (Ag of cyst in stool)
• Treatment - available
• Epidemiology
• Sylvatic (natural) Reservoir occurs naturally
  in nature, esp. around lakes streams
• Domestic Reservoir humans animals
• Mode of Transmission m/c fecal-oral via
  contaminated water
• In U.S. domestic setting fecal-oral fomites
  transmission is very common in day-care settings
• Also under-cooked contaminated veggies fruits
  can be source of cysts
• Today Giardia lamblia is 3rd m/c organism that
  causes dysentery in day-care settings
• Cyst stage is RESISTANT to traditional
  chlorination methods

11
FYI

• m/c organisms causing DYSENTERY in day-care
  settings
• Shigella sonnei
• Enteropathogenic E. coli
• Giardia lamblia

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Intestinal Protozoal Infections

• Cryptosporidiosis
• Etiological agent Cryptosporidium parvum
• Intracellular parasite inhabiting epithelial
  cells of brush-border (villi) of lower SI
• Is a spore-former
• No motility
• Major non-viral cause of cause of gastroenteritis
• Enterocolitis is characterized by watery diarrhea
  w/out blood
• Associated diarrhea self-limiting (only lasts
  1 day) in immunocompetent individuals d/t
  cell-mediated (T-cell) response in
  immunocompromised individuals (i.e., AIDS pts)
  infection may be sever unpredictable

13
Intestinal Protozoal Infections

• Cryptosporidiosis
• Pathogenesis
• Cryptospordia found w/in brush border of
  intestinal epithelium ONLY
• destroy brush border loss of brush-border
  enzymes ? malabsorption fluid loss d/t resultant
  watery diarrhea
• Attach to surface of the intestinal cells
  replicate by process that involves both
  SCHIZOGONY GAMETOGONY
• Schizogony asexual reproductive cycle
• Gametogony sexual reproductive cycle
• Oocysts get released from cells transmitted
• Infective stage transmitted by fecal-oral route
• Oocysts are infectious when passed resistant to
  disinfectants numerous reservoir hosts

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Intestinal Protozoal Infections

• Cryptosporidiosis
• Diagonosis
• Oocysts in the feces acid-fast stain of stool
  sample
• Assay for fecal Ag
• Epidemiology
• Reservoir variety of mammals, fish and reptiles
• Host will seed the environment (i.e., water) w/
  oocysts
• Mode of Transmission
• Person-to-person, indirect, fecal-oral
  contaminated water/fecal droplets
• Person-to-person, indirect fecal-oral/oral-anal
  fomite/direct contact
• High risk groups
• Homosexuals
• Day-care children/adults
• Animal handlers, esp. Veterinarians and personnel
  
• Immunoscompromised pts unremitting
  enterocolitis up to 50 watery stools/day is
  possible d/t intracellular multiplication of the
  parasite

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Urogenital Tract Infections

• Trichomoniasis
• Etiological agent Trichomonas vaginalis
• ONLY SEXUALLY-TRANSMITTED PARASITE
• Globular-shaped cell 15 µm in length
• Pear-shaped flagellates w/ undulating membranes
• 4 anterior flagella w/ short undulating membrane
  (external membrane capable of wave-like movement)
• Exists ONLY in trophozoite stage no cyst stage
• Responsible for m/c form of human trichomoniasis
  (STD)
• ? causes inflammation of mucosal tissue of
  vagina, vulva and cervix accompanied by copious,
  yellowish, malodorous discharge
• ? less common infects urethra, prostate and
  seminal vesicles, producing white discharge

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Urogenital Tract Infections

• Trichomoniasis
• Pathogenesis
• Extensive inflammation erosion of vaginal or
  urethral epithelium causing itching, burning and
  painful urination
• Clinically vaginitis urethritis
• Vaginitis is sometimes accompanied by scant
  watery discharge
• Diagnosis
• Microscopic examination of vaginal or urethral
  discharge for characteristic trophozoites
• Treatment - available
• Epidemiology
• Human reservoir w/ many asymptomatic carriers,
  esp. males females can be asymptomatic
• Common STD estd. 5-7 million cases occur
  annually in U.S.
• Worldwide distribution
• 1 Mode of Transmission sexual intercourse

17
Blood Tissue Protozoal Infections

• Malaria
• Plasmodium species
• Toxoplasmosis
• Toxoplasma species
• Trypanosomiasis
• Trypanosoma species
• Leishmaniasis
• Leishmania species

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Malaria

• Sporozoa includes 4 species of genus Plasmodium,
  which cause most infections in humans Plasmodium
  vivax (80), Plasmodium malariae, Plasmodium
  falciparum (15) and Plasmodium ovale
• Plasmdodial parasite is transmitted to humans
  thru bite of ? Anopheles mosquito or by an
  injected, blood-contaminated, needle
• Sporozoans reproduce asexually in human cells
  (schizogony) gt multiple nuclear divisions ?
  envelopment of the nuclei by cell walls,
  producing Merozoites ?? Trophozoites
• Merozoite asexually reproducing form of the
  malarial parasite is infective for human RBCs
• Sexual reproduction occurs in the mosquito

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Malaria

• Transmission Epidemiology
• 1 host for plasmodia ? Anopheles mosquito
  humans are intermediate hosts
• Major Mode of Transmission bite of the
  Anopheles mosquito
• Other modes of transmission include chronically
  infected ? may congenitally transmit malaria to
  offspring blood transfusions or unsterilized
  paraphernalia used in injection of illicit
  narcotics
• Not a disease commonly transmitted in U.S.
• But, in 2002, 2 cases reported in N. Carolina
  that had their respective origins traced to this
  country (1st time in 75 years)

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Malaria

• Life cycle of Plasmodia
• Mosquito becomes infected by taking blood meal
  from infected person
• w/in mosquito plasmodial gametocytes go thru
  sexual reproduction cycle
• Result accumulation of large s of infectious
  sporozoites in salivary glands
• Mosquito then feeds, transferring sporozoites
  into susceptible host
• Sporozoites are rapidly filtered from blood
  specifically infect LIVER cells (hepatocytes)
• Parasite maturation in heptocytes after 7-10
  days merozoites released into the blood
• Merozoites infect RBCs, using Hb as nutrition,
  and develop further eventually ending w/ RBC
  lysis/rupture w/ subsequent release of large s
  of new merozoites gametocytes.
• These merozoites infect more RBCs and the cycle
  repeats
• Lysis of RBCs basis of clinical sxs

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Malaria

• Clinical symptoms
• Result of lysis of large s of RBCs massive
  release of toxic substances
• When enough RBCs burst release cellular
  debris, parasites and by-products, the onset of
  Malaria paroxysm (sudden onset) is triggered
• Chills for 15-60 min, w/ either HA or vomiting or
  nausea
• Chilling sensation abates, but high FEVER
  develops, lasting several hours
• Maybe accompanied by severe HA, increased nausea
  and vomiting, profuse sweating, and often mild
  delirium
• Paroxysm lasts for 8-12 hours terminates as
  exhausted pt. goes to sleep
• Upon awakening, pt feels pretty well
• Growth of parasite w/in RBCs occurs _at_ fixed
  intervals this factor determines frequency of
  paroxysms
• 48 hours P. vivax and P. ovale
• 32-48 hours P. falciparum - MOST SEVERE
• Every 72 hours P. malariae

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Malaria

• Laboratory Diagnosis
• Microscopic observation of malarial parasites in
  stained slides of blood
• Thick blood smears stained w/ Giemsa stain most
  sensitive visual test
• Treatment
• All clinical cases of malaria are txed w/
  Chloroquine, except those caused by
  Chlorquine-resistant strains of P. falciparum
  (txed instead by various combination drugs)

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Toxoplasmosis

• Coccidian protozoan of world wide distribution
  that infects a wide range of animals, birds, but
  does not appear to cause disease in them.
• Definitive host various felines (cats), w/ the
  domestic cat being chief transmitters to humans
• Cats become infected by eating mice, birds, raw
  meat and infected feces of other cats
• Humans become infected by accidental ingestion of
  oocysts present in cat feces, by eating raw or
  undercooked meat, congenitally from an infected
  mother, or from blood transfusion

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Toxoplasmosis

• Etiological agent Toxoplasma gondii
• Intracellular sporozoan parasite
• Grows intracellularly w/in many tissues is
  confined to intestines in cats/felines
• Goes thru sexual phase of reproduction in
  intestinal tract of cats
• Oocytes are shed in feces in 3-4 days gt 8
  infectious sporozoites develop w/in each oocyst
• Mature oocyst can remain viable up to 1 year
  infect humans animals when ingested
• Infected tissues release psuedocysts containing
  bradyzoites
• Feline (cat) intestines release oocysts
  containing tachyzoites

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Toxoplasmosis

• Pathogenesis Clinical Significance
• Normal hosts cats/felines only hosts in which
  oocyst can develop during the sexual stage
• Protozoan invades cats SI ??sexual fusion of
  gametes oocyst forms
• If oocyst is ingested by birds and mammals (incl.
  humans) infection established in which asexual
  reproduction of oocyst occurs

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Toxoplasmosis

• Pathogenesis Clinical Significance
• 2 kinds of Toxoplasmosis trophozoites found in
  human infections
• Rapidly-growing tachyzoites seen in body fluids
  in early, acute infections
• Directly destroy cells
• Slowly-growing bradyzoites contained in cysts
  in muscles brain tissue and in eye (quiescent
  cysts chronic dis)
• If released from ruptured tissue cysts get
  local inflammation w/ blockage of blood vessels
  necrosis
• Tissue cysts are infective when ingested by cats
• Once ingested, oocyte releases infectious
  sporozoites
• No sexual reproduction of parasite in humans or
  non-feline animals
• Sporozoites do proliferate by binary fission and
  circulate thru-out the body
• Parasite penetrates cells continues to
  proliferate until the cell bursts
• Cellular death d/t intracellular multiplication
  of trophozoites esp. severe in fetal cerebral
  tissue

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Toxoplasmosis

• Pathogenesis Clinical Significance
• Clinical Disease sxs
• Fever
• Weakness
• Respiratory illness
• Mycorditis
• Infectious Mononucleosis-like illness w/ swollen
  lymph nodes
• Fever, chills, HA, myalgia. lymphadenitis,
  fatigue
• Most cases gt mild self-limiting
• Maybe severe in AIDS pts, immunosuppressed
  individuals developing fetuses
• Major concern Congenital Toxoplasmosis

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Toxoplasmosis

• Congenital Toxoplasmosis
• Occurs when pregnant ? develops 1 case of
  toxoplasmosis by being in contact w/ cat (feces
  in litter box) of by eating raw or rare meat
• T. gondii is able to pass placental barrier
  infect developing fetus
• Tissues of brain eye affected
• Some infants die in utero others born w/ serious
  CNS defects die shortly after birth
• Rate 1 out of every 1000 children born in U.S.

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Toxoplasmosis

• Diagnosis
• Initial detection of parasites in tissue
  specimens can be inconclusive
• Serological detection of Ab against parasite Ag
  ELISA test for IgG IgM Abs most reliable
• Epidemiology
• Reservoir variety of mammals bird humans
  included
• Route of Transmission Fecal-oral transmission of
  oocytes form cats
• m/frequent contact w/ pseudocysts imported,
  poorly cooked meat
• Risk groups pregnant ?s and immunocompromised

30
Toxoplasmosis

• Epidemiological Clinical Examples
• Oocysts in urine feces of cat that eats raw
  meat/contaminated soil ? into litter box ?
  pregnant ? in contact w/ cat litter ? to fetus ?
  congenital defects ( brain damage, blindness,
  mental retardation)
• Immunocompromised pts, AIDS pts, transplant
  recipients or cancer pts gt in contact w/ cat
  urine, feces raw/rare meat or contaminated soil ?
  may develop severe CNS damage or seizures or may
  die

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Toxoplasmosis

• Prevention
• If pregnant ? acquired toxoplasmosis w/ resulting
  Ab immunity BEFORE becoming pregnant gt
  developing fetus is PROTECTED
• 30 of ?s of child-bearing age in U.S. have the
  Abs
• If ? w/ NO Abs gt AVOID contact w/ cats of their
  feces, and AVOID raw/rare meat
• Treatment
• combination drugs

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Trypanosomiasis

• 2 chronic, eventually fatal, diseases
• African Sleeping Sickness
• CNS infection progressing to lethargy, tremors,
  meningoencephalitis, convulsions, coma and death
• American Trypanosomiasis Chagas Disease (in S.
  America)
• Systemic infection beginning w/ fever, chills,
  malaise, myalgia, fatigue and chagoma
  (erythematous indurated area _at_ site of bug
  bite) progresses to involve heart brain

33
Trypanosomiasis

• Etiological agents
• African Sleeping Sickness
• Trypanosoma brucei gambiense West/Central
  Africa
• Trpanosoma brucei rhodesience East Africa
• American Trypanosomiasis/Chagas Disease
• Trypanosoma cruzi S. America

34
African Sleeping Sickness

• Found only in geographical areas where tsetse
  (glossina) fly lives
• Tsetse fly is necessary link in life cycle of T.
  gambiense T. rhodesiense functions as vector
  fro transmission to humans animals
• Major hosts and Reservoirs cattle, swine,
  various wild animals

35
African Sleeping Sickness

• Pathogenesis
• Human is bitten by an infected tsetse fly result
  local lesion or chancre _at_ site of bite d/t
  trpanosomes
• Protozoa then spread become lodged in local
  lymph nodes and reproduces extracellularly in
  blood, producing chronic infection
• Trypanosomes can spread to CNS inflammation of
  brain spinal cord (mediated by release of
  toxins), producing characteristic sxs
• Pt. becomes SOMNOLENT (drowsy or sleepy)
  eventually goes into coma and dies
• Trypanosomes deprive the brain of Amino Acids
• CNS infection slow, progressive pathology 1-3
  years to death

36
American Trypanosomiasis

• T. cruzi found in Central S. America
  transmission is Arthropod-borne by cone-nosed
  Reduviid (tritomine) bugs small biting bugs
  that live in cracks of domestic dweelings
• Reservoir Domestic animals (dogs, cats)
  various wild animals
• Transmission Reduviid bugs bite humans _at_ night
  and defecate when they feed
• T. cruzi are in feces, which contaminate bite
  wound or other skin abrasions or are carried by
  fingers to mucosa of mouth or nose or to
  conjunctiva of eyes to cause infection

37
American Trypanosomiasis

• Epidemiology
• Persons living in huts w/ dirt floors or walls
  m/likely to become infected, esp. if sleeping on
  floor/ground
• Pathogenesis Clinical Significance
• Lesions produced _at_ site of bite by parasite
• Protozoa then spread thru body, multiply in cells
  and cause cell death
• Acute diseases in children, involving heart
  (cardiomyopathy) and CNS 10 death rate

38
Trypanosomiasis

• Diagnosis of Trypanosomal Diseases
• Demonstration of presence of motile protozoa in
  blood, lymph node aspirates, CSF
• Giemsa-stained smears of body fluids
• Confirmation by highly-specific serological tests
• Treatment
• Effective treatments available for both African
  Sleeping Sickness American Trypanosomiasis

39
Leishmaniasis

• Group of infections caused by flagellate protozoa
  of genus Leishmania
• Etiological agents
• Leishmania donovani MOST SEVERE w/ HIGH
  MORTALITY
• Leishmania tropica
• Leishmania braziliensis
• Epidemiology
• Tropical subtropical regions around the world
• Reservoir wide variety of mammals, incl. humans,
  wild rodents dogs
• Transmission arthropod-borne via bite of
  sandflies ( vectors) of genus Phlebotomus or
  Lutzomyia

40
Leishmaniasis

• Clinical Significance
• Visceral Leishmaniasis (kala-azar) caused by L.
  donovani
• India, East Africa and China
• Parasite initially infects macrophages, which
  then migrate to spleen, liver BM parasite
  rapidly multiplies
• Gradual onset of fever, chills, sweating,
  diarrhea and anemia, which progresses to
  enlargement of liver spleen jaundice may
  develop most cases resolve spontaneously
• complications of 2 infections emaciation
  result in death

41
Leishmaniasis

• Clinical Significance
• Cutaneous Leishmaniasis (oriental sore) caused
  by L. tropica
• North West Africa, Iran Iraq
• Characterized by ulcerating single or multiple
  skin sores
• Most cases spontaneously heal, but ulcers leave
  unsightly scars

42
Leishmaniasis

• Clinical Significance
• Mucocutaneous Leishmaniasis caused by L.
  braziliensis
• Central South America, esp. Amazon regions
• Parasites attacks tissue _at_ mucosal-dermal
  junctions of nose mouth, producing multiple
  lesions
• Extensive spreading into mucosal tissue can
  obliterate nasal septum buccal cavity
• Death from 2 infection

43
Leishmaniasis

• Diagnosis
• Examination of Giemsa-stained tissue fluid
  samples for non-flagellated from (amastigote),
  which is only from of organism that occurs in
  humans
• Cutaneous mucocutaneous can be diagnosed from
  tissue samples taken from edges of lesions or
  lymph node aspirates
• Visceral disease liver, spleen or BM biopsy
• Various Serologic tests used by CDC
• Treatment
• Can be difficult d/t considerable drug toxicity,
  high failure rates

44
Helminths

• Metazoa Parasites True Multicellular Organisms
• Classification Kingdom Anamalia (Animal Kingdom)
• Subkingdom Metazoa
• Phylum Nematoda Nematodes Roundworms
• Phylum Platyhelminths Trematodes
  Flatworms/Flukes
• 
  Cestodes Tapeworms

45
Chapter 22 Helminths

• Helminths are parasitic worms
• 3 groups
• Cestodes (tapeworms)
• Trematodes (flukes)
• Nematodes (roundworms)
• Intestines common site for worm infestation
  little damage
• Dissemination is possible to vital organs, such
  as brain, lungs or liver gt severe damage
• 70 of worlds population is infected w/ a
  parasitic worm
• Variable mode of transmission
• Includes ingestion of larva in raw or undercooked
  pork, beef or fish and eggs in feces, by insect
  bites, or by direct skin contact

46
Cestodes

• Tapeworms Long, flat, ribbon-like intestinal
  worms consisting of many segments
• Segments Proglottids
• Lack a digestive system do not ingest
  particulate matter
• Absorb soluble nutrients directly thru
  surrounding cuticle
• Some species grow up to length as long as 15
  meters w/in SI
• Ex. Diphyllobothrium latum
• Cause clinical injury by
• Sequestering hosts nutrients
• Excreting toxic waste
• Causing mechanical blockage of intestine (massive
  infestations)

47
Cestodes

• Scolex anterior end of the worm head
• Bulbous structure w/ hooks _at_ suckers
• Specialized for attachment to brush border
  intestinal epithelium
• Usually has 4 muscular, cup-shaped suckers
  crown of hooklets (little hooks)
• Sucking disc is found on scolex hooklets off of
  sucking disc further attachment mechanism
• Stroblia body of worm consists of proglottids
  (segments), which form behind scolex
• Chain of Proglottids Stroblia or Body

48
Cestodes

• Proglottid
• Basic functional unit of the worm individual,
  separate functional unit for reproduction
• Each w/ complete set of sex organs, both ? and ?
  thus, cestodes are monoecious (hermaphroditic)
  each mature proglottid contains ovaries testes
• Generate fertilized eggs via self-fertilization
  reproduction occurs in w/in single worm!
• Mature, egg-filled proglottids are located _at_
  posterior end can break off chain pass out of
  stool
• Ova product of fertilization is survival form
  of cestode, which is transmitted form one host to
  another via passage out thru intestines.

49
Trematodes

• AKA Flukes
• Small (1 cm), flat, leaf-shaped, fleshy
  (soft-bodied) worms w/ many different shapes
• Named w/ regard to the area of body of the tissue
  where the organism is found
• Attachment to tissue via specialized sucker
• Has a Definitive Host humans!
• Has pair of suckers bipartite gut that ends
  blindly w/ no anus
• Blind alimentary canal small gallot takes
  nutrients in no anus
• Has surrounding cuticle keeps fluke from
  breaking down

50
Trematodes

• Are monoecious contains both ovaries testes
  in same worm (self-fertilization), but
  x-fertilization can occur
• X-fertiliaztion distinguishes Trematodes from
  cestodes
• Must have 2 flukes coming together to reproduce
  move sperm form one ? other
• Ova product of x-fertilization is stage that
  is transmitted is survival stage outside the
  host

51
Trematodes

• Standard Life Cycle of Hermaphroditic flukes in
  Definitive Host (Humans)
• Egg production in humans ? exit GIT via excretion
  via feces ? H2O environment ? 1st larval stage
  (miracidium) develops in eggs ? larvae infect
  Snails (Intermediate Host) ? asexual reproduction
  occurs w/in the snail ? release cercaria
  (intermediate developmental forms) ? into H2O ?
  2nd Intermediate Host (a fish or crustacean) ?
  formation of cysts ( metacercaria remain
  viable indefinitely) ? back to humans when
  infected raw or undercooked fish or crustacean is
  eaten metacaria excysts fluke invades tissues
  such as lung or liver, begins producing eggs ?
  life cycle completed and can repeat

52
Trematodes

• Standard Life Cycle of Sexual Flukes
  (Schistosomes)
• Similar to that of hermaphroditic flukes
• 2 differences as compared to hermaphroditic
  flukes
• Shistosomes only have 1 intermediate host snail
• Schistosomiasis is NOT acquired by injestion of
  contaminated food, but rather from schistosome
  cercaria DIRECTLY penetrating skin of waders
  swimmers in contaminated rivers lakes

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Trematodes

• After dissemination development in human host,
  adult schistosomes take up residence in abdominal
  veins, hence term Blood Flukes
• Schistosomes have separate distinct sexes
• Long groove or schist on ventral surface of large
  male allows for smaller female to reside
  continuously mate w/ male
• Occurs in human liver
• Fertilized eggs then pass into intestines or
  bladder thru vascular walls, finally exiting body
  in feces or urine
• In fresh H2O organisms infect snails ?
  multiplication ? cercaria production ? release
  into fresh H2O ? cycle completion

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Nematodes

• Roundworms elongated, cylindrical,
  non-segmental worms, ranging in size from few
  millimeters to several centimeters
• Are parasites b/c they derive ALL life needs from
  the host absorb all of its nutrients from human
  host
• Are tapered _at_ both ends w/ complete digestive
  system (mouth, intestine spanning most of body
  length anus)
• Have thick, tough protective Cuticle thru which
  pre-digested nutrients are absorbed protection
  from being digested by gastric juices when
  residing in human intestines

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Nematodes

• Have separate, anatomically distinctive sexes
• All Nematodes are Diecious BOTH ? ? worms
• Fertile ova produced by ? worm following mating
• Mode of transmission varies, depending on species
• Direct skin penetration by infectious larvae
• Ingestion of contaminated soil
• Eating undercooked pork
• Insect bites

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Nematodes

• Can infect almost any part of body
• Liver, kidneys, intestines, subcutaneous tissues,
  eys
• Categorized by whether they infect intestine of
  other tissues
• m/c nematode infection in U.S. Enterobiasis
  (pinworm disease) causes anal itching
• m/serious disease w/ worldwide distribution
  Ascariasis, caused by Ascaris lumbricoides
• m/c roundworm in the WORLD

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Commonly Encountered Cestode Infections

• Echinicoccosis
• Causative agent Echinicoccus granulosis (dog
  tapeworm)
• Ingestion of eggs in dog feces Sheep
  Intermediate Host
• Infection produces large hydatid cysts in liver,
  lung and brain
• If cyst ruptures gt anaphylactic reaction to worm
  Ags
• DX CT scan or biopsy of infected tiss
• Taeniasis
• Causative agent adult Taenia solium (pork
  tapeworm)
• Named on basis of Intermediate Host Swine
• Disease is transmitted by larvae in undercooked
  pork or by ingesting tapeworm eggs
• 1 site of infection intestines diarrhea
  possible
• Most infections asymptomatic

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Commonly Encountered Cestode Infections

• Cysticercosis
• Causative agent Taenia solium larvae
• Disease follows ingestion or eggs from human
  feces
• Infection produces cysticerci in brain, causing
  seizures, HA, vomitting and in eyes
• Cysticerci sexually immature stage of T.
  solium normally infects pigs
• DX CT scan or biopsy
• Taeniasis
• Causative agent larval form of Taenia saginata
  (beef tapeworm)
• Transmission larvae in undercooked or raw beef
• Site of infection primarily intestines NO
  cysticerci
• DX detection of proglottids in stool

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Commonly Encountered Cestode Infections

• Diphyllobothriasis
• Causative agent Diphylllobothrium latum (fish
  tapeworm)
• Adult worm found in host intestines up to 15
  meters in length
• Transmission by larvae in raw or undercooked
  fish
• DX by detection of eggs in stool

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Commonly Encountered Trematode Infections

• Paragonimiasis
• Causative agent Paragonimus westermani (lung
  fluke)
• Transmission eating raw crab meat
• Organisms move from GIT ? lung, which is 1 site
  of damage
• 2 bacterial infections can result in cough,
  producing bloody sputum
• DX ID of eggs in sputum feces
• Clonorchiasis
• Causative agent Clonorchis sinensis (Oriental
  liver fluke)
• Transmission via eating raw freshwater fish
• Site of infection pirmarily biliary tract,
  where resulting inflammatory response can cause
  firbrosis hyperplasia
• DX ID of eggs in stool

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Commonly Encountered Trematode Infections

• New World Shistosomiasis
• Causative agent Schistosoma mansoni
  Schistosoma japonicum
• Transmission direct skin penetration
• Site of infection GIT damage to intestinal
  epithelium is d/t hosts inflammatory response to
  eggs deposited eggs secrete proteolytic enzymes
  that further damage tiss
• Clinical Presentation GI bleeding, diarrhea,
  liver damage
• DX ID of eggs in stool
• Old World Schistosomiasis
• Causative agent Schistosoma haematobium
• Transmission direct skin penetration
• Site of infection veins of urinary bladder
  eggs can induce fibrosis, granulomas hematuria
• DX ID eggs in urine or bladder

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Commonly Encountered Nematode Infections

• Enterobiasis (Pinworm Disease)
• Causative agent Enterobius vermicularis
• M/C helminthic infection in U.S.
• Transmission ingesting organisms eggs humans
  only host
• Clinical pruritus ani w/ white worms visible in
  stools or perianal region
• DX ID eggs present around perianal region
  Scotch Tape Test (Early Bird gets the Worm)
• Ascariasis (Roundworm Disease)
• Causative agent Acaris lumbricoides one of the
  largest nematodes (8-12)
• M/C helminthic infection in the world
• 1/3 worlds population infected
• 2nd m/c helminthic infection in U.S.
• Transmission ingestion of soil containing
  organisms eggs ? Humans only host ? larva grow
  in SMALL INTESTINE
• Clinical abdominal sxs, including abdominal
  obstruction
• Roundworms may pass to blood ? circulates to
  heart ? pumped into pulmonary circulation ?
  lungs, where larvae rupture alveoli ? larvae
  burrow out of lungs coughed up swallowed ?
  back to GIT ? SI ? cycle cont.
• DX ID eggs in stool

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Commonly Encountered Nematode Infections

• Hookworm Disease
• Causative agent Ancylostoma duodenale (Old World
  Hookworm) Necator americanus (New World
  Hookworm)
• Transmission direct skin penetration by larvae
  in soil
• Site of infection worm attachment to intestinal
  mucosa
• Clinical anorexia, ulcer-like sxs and chronic
  intestinal blood loss ??? anemia
• DX ID of eggs in feces
• Elephantiasis (Filariasis)
• Causative agents Wuchereria bancrofti Brugia
  malayi
• Transmission bite of infected ? Anopheles
  Culex mosquito
• Clinical worms block the flow of lymph, causing
  edematous arms, legs and scrotum gt lower extr.
  disproportionately large
• DX detection of microfilariae in blood

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Commonly Encountered Nematode Infections

• Dracunculiasis
• Causative agent Dracunculus medinensis fiery
  serpent
• Transmission in contact w/ or drinking H2O
  containing Intermediate Host copepods (water
  fleas) in which larvae live
• Clinical skin inflammation ulceration
• DX finding of head of worm in skin lesion or
  larvae released from a lesion following contact
  w/ water
• TX surgically removing subcutaneous worms or
  winding the worms on a thin stick
• Trichinosis
• Causative agent Trichinella spiralis
• Transmission eating undercooked pork
• Clinical larvae burrow into blood from GIT and
  then burrow into striated muscles where they
  encyst encysts in muscle tissue of humans
• DX locating coiled encysted larvae in muscle
  biopsy