Protozoa and Malaria Flashcards
Broad classifications of parasites
Protozoa
Helminths
Ectoparasites
Protozoa
Eukaryotic unicellular organisms that have organelles
Can be divided into amoebae, flagellates, sporozoans, coccidia, ciliates
Most important pathogens:
- entamoeba (intestinal)
- cryptosporidium (intestinal)
- plasmodium and toxoplasma (blood and tissue)
Intestinal protozoa
Entamoeba histolytica Giardia duodenalis Trichomonas vaginalis Cryptosporidium Cycloisospora, cyclospora (know these exist)
Entamoeba histolytica: source, transmission, notifiable?, clinical presentation, complications
Worldwide
Source: fresh water contaminated with human faeces
Transmission: faecal oral route
NOTIFIABLE DISEASE
Clinical presentation:
- 2-4 wks incubation
- 80-90% asymptomatic (restricted to lumen of intestine – luminal amoebiasis)
- amoebic colitis (invasive intestinal amoebiasis – AMOEBIC DYSENTERY which mimics ulcerative colitis)
- extra-intestinal manifestations e.g. amoebic liver abscess (right lobe of liver more common), pleuropulmonary/brain abscess (very rare)
Complications in severe infection:
- peritonitis, perforations, amoebic granulomas
Entamoeba histolytica: life cycle, cysts and trophozoites
Cysts and trophozoites passed in faeces –> mature cysts ingested via contamination –> excystation in small intestine –> trophozoites migrate to large intestine where it remains in colon, invades intestinal mucosa or invades blood vessels –> multiplication by binary fission
Cysts (12-15 mcm) typically found in FORMED STOOL, can survive days to wks in external environment and remain infectious
Trophozoites (15-20 mcm) typically in DIARRHOEAL STOOL and rapidly destroyed once outside the body (30 min).
- not infective as it would not survive gastric env if ingested
Entamoeba histolytica: diagnosis
Stool:
- RBC, WBC present
- active trophozoite (HOT STOOL i.e. immediate sample)
- direct wet mount (INGESTION OF RBC BY TROPHOZOITES IS DIAGNOSTIC)
- special stains e.g. PARA stain or trichrome
Liver abscess aspirate
- low yield
- PCR, Ag detection
- microscopy and culture to exclude bacterial
Serology test
- Ab detection for invasive amoebiasis/ extra-intestinal cases
Tissue biopsy
Entamoeba histolytica: treatment
Systemic treatment followed by luminal agent for cases of diarrhoea/dystentery and extra-intestinal infection
METRONIDAZOLE PO or Tinidazole
+
PARONOMYCIN (to prevent relapse)
Giardia duodenalis - source, transmission, clinical presentation, diagnosis, treatment
Source: soil, food, contaminated water with infected faeces
Transmission: faecal-oral route, mainly water-borne infection
Infection duodenum, ileum –> WATERY DIARRHOEA
Diagnosis:
- Stool direct microscopy using simple counterstain –> visualise cysts and trophozoites; “falling leaf” movement in wet mount, characteristic “face”
- Immunoassay, PCR
- Duodenal aspirate direct microscopy for trophozoites
Treatment:
- Tinidazole PO single dose
(alternatives: metronidazole)
Cryptosporidium - source, clinical presentations, diagnosis, treatment
Worldwide
Many species: C. hominis, C. parvum
Outer shell very tolerant to chlorine disinfection
One of the commonest and serious cause of WATERBORNE DIARRHOEA
Clinical presentations:
- immunocompetent: 7-10 days incubation, acute watery diarrhoea, self-limiting (1-2 wks)
- AIDS: transient infection (1 month), chronic diarrhoea lasting for >2 months (60%) or fulminant infection for >2L watery diarrhoea/day (10%)
Diagnosis:
- Stool for MODIFIED ACID-FAST STAIN –> oocytes 4-6 mcm (difficult to see on wet mount)
- Ag detection, PCR
Treatment: Nitazoxanide
Microsporidia - clinical presentations, diagnosis
Not commonly diagnosed due to low suspicion
- obligate eukaryotic intracellular parasites closely related to fungi
- production of RESISTANT SPORES
Clinical presentation:
- gastroenteritis (MC)
- CNS encephalitis
- OCULAR INFECTIONS (punctate KERATOPATHY and conjunctivitis)
Diagnosis:
- special stain: CHROMOTROPE 2R –> stain spore and spore wall bright pinkish red
- transmission electron microscopy as gold standard which is necessary for diagnosis
Trichomonas vaginalis - source, transmission, clinical presentation, diagnosis, treatment
Pear-shaped trophozoite Jerking or twitching movement Source: humans (infect humans only) Transmission: direct contact (STD) No cyst stage
Clinical presentation
- 30% symptomatic
- female: vaginitis - copious foamy discharge, purulent, malodorous
- male: commonly asymptomatic, urethritis
- increases risk of STDs
Complications:
- pregnancy: increase risk of preterm delivery, prematurity and low birth weight
Diagnosis:
- vaginal/urethra/prostatic secretions –> direct microscopy (wet mount), PCR
Treatment:
- Tinidazole PO
- Metronidazole PO
- treat all sexual partners
Blood and tissue protozoa
**Plasmodium Babesia Trypanosomiasis **Toxoplasma Leischmaniasis
Malaria - importance of clinical suspicion
Late recognition in a febrile patient can lead to mortality - MUST ALWAYS ASK TRAVEL HISTORY AND CONSIDER IF RETURNING FROM ENDEMIC REGION e.g. subsaharan africa, india
Malaria: life cycle
Transmission by female Anopheles mosquitoes
- Liver stage
Mosquito bite –> inject SPOROZOITES –> infect liver cell –> form SCHIZONT in hepatocytes (i.e. cell full of mature merozoites) –> ruptured schizont kills host cells and releases MEROZOITES - Blood stage (symptomatic)
Merozoites infect RBC –> morph into immature TROPHOZOITES (ring form) –> multiply in RBC to become mature (compact)
==> either form schizont - rupture - haemolysis
or
==> if body condition not favourable for parasite to survive, sexual reproduction –> GAMETOCYTES which are infective to mosquitoes
Plasmodium Falciparum - resistance to drugs, incubation period, clinical manifestations
Most severe form
Chloroquine resistant cases are widespread, mefloquine resistance also found in some areas of SE Asia and Africa
Incubation period: 12-14 days
- longer in semi-immune individuals or those with ineffective malaria prophylaxis
Tertian/Quartan fever if not treated promptly
Clinical manifestations
- UNCOMPLICATED malaria (tolerate oral medication, no sx of severe malaria)
- -> non-specific flu like illness, palpable spleen, mild jaundice
- SEVERE malaria (if untreated mild form)
- -> RBC adhering to small blood vessels to cause small infarcts, leakage and organ dysfunction
- -> cerebral (fits, coma), metabolic acidosis, anaemia (haemolysis), coagulopathy, shock, hypoglycaemia, AKI, liver failure, pulmonary oedema, ARDS
