Focus on pathogens: Babesia microti

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Focus on pathogens Babesia microti

• Facts / life-cycle B. microti, which causes
  babesiosis, is the only member of the genus that
  infects man. This organism is similar to the
  bacterium causing Lyme disease in that both are
  endemic to the NE US (especially CN), both use
  the white footed mouse as resevoir (IH) and both
  are transmitted by deer tick bite (40 of which
  are coinfected). However, B. microti is much
  more likely to be sub-clinical.
• cont ?

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Facts / life-cycle continued

• Although the life-cycle is complex, that
  involving human pathology is not. Trophs
  (comparable to malarial sporozoites) are
  introduced via tick bite, migrate to RBCs,
  develop to the ring form, and divide asexually to
  form merozoites which can follow an
  auto-infective cycle parasitizing additionaly
  RBCs. Either form may also be introduced via
  blood transfusion. The sexual cycle can only
  occur in the tick which makes him the DH (like
  Plasmodium). The cycle in the white footed mouse
  is identical to that of humans with the added
  twist that merozoites can divide by meiosis to
  form gametes in the mouse, but zygote formation
  and maturation must occur in the tick. So, we
  may think of the mouse as the primary IH, and
  humans as accidental IH.

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Focus on pathogens Babesia microti

• Epidemiology
• found exclusively in areas endemic to the Ixodes
  deer tick
• causes 200-500 cases annually in the US
  concentrated around CN, Nantucket Island and
  other coastal NE locals.
• mortality runs 6.5, basically all of which are
  immune suppressed individuals.

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Focus on pathogens Babesia microti

• Pathology / clinical symptoms
• symptoms are not distinctive, therefore history
  of endemic area and knowledge of possible tick
  bite are helpful
• flu-like or mono-like symptoms discomfort,
  fatigue, fever, hepatic dysfunction, decrease RBC
  count via hemolysis

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Focus on pathogens Babesia microti

• Laboratory diagnosis
• 1-3uM trophs in RBCs resembling early ring forms
  of Plasmodium falciparum
• mature trophs characteristically appear as
  doublets like rabbit ears or tetrads ie.
  maltese cross formation

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Focus on pathogens Babesia microti
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Focus on pathogens Pneumocystis carinii

• Facts / life-cycle P. carinii is often how
  referred to as P. pneumonia or PCP. As much as
  any recognized human pathogen, this is an
  organism of uncertain affiliation. It has
  morphological, biochemical and nucleic acid
  homological characteristics that conflict to
  resemble both a protozoan and a fungus. We will
  call it both or neither.
• Transmission is person to person via cough
  droplets.

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Focus on pathogens Pneumocystis carinii

• Epidemiology PCP is an infection of
  immunosuppressed individuals, particularly AIDS
  patients. Mortality is high due to severely
  compromised state of most patients.

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Focus on pathogens pathology / clinical symptoms

• Causes pneumocystosis, among the more common
  causes of non-bacterial pneumonia is
  immunocompromised (IC) patients in the US, and is
  a leading cause of death of AIDS patients.
• Common symptoms include fever, non-productive
  cough and hepatosplenomegaly. Histologically, a
  characteristic alveolar exudate with a foamy or
  honeycomb matrix property due to the presence of
  cysts is recoverable. PCP can be rapidly fatal
  among IC patients, but is treatable in the case
  of relatively healthy patients.

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Focus on pathogens Pneumocystis carinii

• Laboratory diagnosis medical history, x-ray,
  examination of respiratory fluid or biopsy from
  lungs of affected individuals stained with
  Gomori methanomine silver stain or rapid
  toluidine blue stain.
• Trophs small, pleomorphic to roughly circular
  with dark central nucleus (may be hard to see).
  Trophs sometimes 1-2 microns (sporozoites?), and
  others 4-5 micron (merozoites?).
• Cysts 6-8 microns, may contain some number of
  visible trophs intermally. GMS stain stain cyst
  walls black.

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Trophs toluidine blue (top) Cysts Ag stain
Giemsa (below