Focus on pathogens: Acanthamoeba

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Focus on pathogens Acanthamoeba

• Trophs size 15-45 µm
• Irregular shape due to presence of pseuodopods
  (lobopodia) for motility but also slender,
  pointed acanthopodia which are extension of
  axial filaments in the cell core
• in trichrome stain the cytoplasm of trophozoites
  appears greenish pink, the central located
  kariosome pink or red.
• Cysts size 15-20uM
• Spherical having a thick double wall. The outer
  wall may be spherical or wrinkled, the inner wall
  appear stellate or polyhedral. Unlike N.
  fowleri, cysts are commonly found in clinical
  specimens.
• Both forms have a single nucleus with a large
  centrally located karyosome. With trichrome
  stain, the cysts stain red.

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Trophs trichrome cysts in
hematoxylin
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Focus on pathogens Trypanosomes

• Facts / life-cycle Trypanosomes are
  hemoflagellates they require hematin obtained
  from blood. Their life-cycle includes an insect
  intermediate host which serves as the vector and
  a vertebrate definitive host which includes
  humans and other animals (see next page). The
  life-cycle is complex including up to 8 stages,
  many occuring in the GI tract of the IH.
• All trypanosomes possess a unique organelle
  called a kinetoplast, which is (or is associated
  with) a large mitochondrion linked to movement of
  an undulating dorsal membrane which terminates as
  a single free flagellum. Book says posterior
  kinetoplast.?

Cont. ?
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T. brucei facts / life-cycle continued

• T. brucei is transmitted directly via the bite of
  the tse-tse fly. In one case, it appears that
  transmission is primarily from human-fly-human,
  where in the other it seems more to be
  human-fly-animal-fly-human. The disease causing
  troph stage is called a tryp(an)omastigote, which
  implies that the troph has the characteristic
  Trypanosome morphology. These trophs invade the
  circulatory system making their way to lymph
  nodes ultimately the CNS. Due to the antigenic
  variability of T. brucei cell surface
  glycoproteins, host humoral immunity can NOT
  prevent multiplication in host blood stream.
  Therefore, these guys do not have to divide
  intracellularly as does T. cruzi.

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• T. brucei sub-species gambiense (slow
  developing)
• sub-species rhodensiense (rapidly
  developing)
• disease African trypanosomiasis, sleeping
  sickness
• intermediate host tse-tse fly
• definitive host humans
• cattle, swine, wild animals
  (antelope)

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T. brucei life-cycle
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Focus on pathogens Trypanosomes

• T. brucei Epidemiology
• Limited to the continent of Africa where the
  tse-tse fly resides, mainly Sudan, Zaire, Angola
  surrounding countries.
• 60 million Africans at risk with perhaps 3-4
  million currently infected, 20,000 new cases
  annually. Numbers?
• Treatment is more available as time passes, but
  historically the condition has a high mortality
  rate. Numbers?
• Recurrent epidemics are due (in theory) to
  ecological disturbances in the environment
  forcing encounters between an infected fly and a
  human.
• Situation compounded by antigenic variability.
  Sub-species gambiense (Gambia) is endemic to the
  tropical forest areas of NW-central Africa.
  Sub-species rhodensiense (Rhodesia, now Zimbabwe)
  is endemic to south-central Africa.
• Caucasians (especially non-natives) are more
  susceptible than native black Africans.

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Focus on pathogens Trypanosomes

• T. brucei pathology / clinical symptoms
• progression
• non-pustular, painful itchy chancre at site of
  entry no scar
• recurring fever
• lymphodenopathy, esp. posterior cervical neck
  nodes
• organism invades CNS sleeping sickness stage
• behavioral changes due to progressive
  meningoencephalitis apathy, fatigue, confusion,
  drowsiness
• eventual loss of consciousness
• coma ? death
• without treatment it is universally fatal
  within 2 years

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Focus on pathogens Trypanosomes

• T. brucei Laboratory diagnosis of trophs
• sample blood, lymph biopsy, CSF
• size 15-30uM long 1.5-3.5uM wide
• elongated body with a finely pointed end and
  more rounded end
• dorsally located undulating membrane that
  originates at the kinetoplast on the rounded end
  and runs the length of the troph to a single
  whip-like flagellum on the pointed end
• nucleus located in the center of the troph