Parasites 1 Flashcards
Giardiasis Life Cycle and Transmission
Giardia lamblia
• Cysts spread by the fecal-oral route 
– Food or water supplies
– person-to-person
– Animal reservoirs ‘Beaverfever’
• Common in campers, groups of children, travelers returning from abroad
• Prevalence in the developing world may be as high as 10%.
• Cysts
– survive more than 2 months in cold water
– resistant to chlorine
Giardiasis Diagnosis
• O&P;microscopy 
– Cysts: 11-14 μm, oval, 4
nuclei
– Trophs: 12-15 μm, pear-shaped, 2 nuclei
• Antigen detection
- florescent stain
• Trophozoites may be obtained using the Enterotest kit or by duodenal aspiration, and detected in wet mounts
Giardia lamblia
Cyst: 4 nuclei; oval, 11- 14 x 7-10 um, prominent longitudinal fibers
Trophozoite: 2 nuclei;leaf-shaped longitudinal fibers
Things that look like Giardia lamblia but not pathogenic
Chilomastix mesnili
-Cyst: 7-9 x 4-6 um
-Trophozoite: Lemon-shaped with anterior hyaline knob and distinct cytosine near nucleus
Dientamoeba fragilis
Cyst: No cyst form
Trophozoite: 7-12 um; Usually binucleated; no peripheral chromatin; Vacuolated cytoplasm with debris, bacteria. nuclei can look like “die”
Endolimax nana
Cyst: 6-8 um ; 1-4 nuclei
Trophozoite: 7-12 um; One nucleus; No peripheral chromatin;Large karyosome
B. hominis
Cyst: 6-40 uM;Multiple, peripheral nuclei, large central body (similar to a large vacuole)
Trophozoite: Rarely present
May not be a pathogen
Cryptosporidium and Cyclospora

Coccidian Parasites
Same group as Plasmodium, Babesia, Toxoplasma

– Obligate intracellular pathogens; invade host cells with specialized organelles in the apical complex


Cryptosporidium
Life Cycle & Transmission
•ID = ~130 oocysts
• Person to person,animal to person, waterborne
• Day-care,nosocomial, other institutional
• Direct transmission– no intermediate hosts
• Worldwide distribution
- cysts immediately infective
Cryptosporidium
Diagnosis & therapy
• Directvmicroscopy
– Modified acid-fast (not standard stain)
– 4-6 um diameter
• Antigen detection–EIA/IFA
• PCR (investigational)
• Nitazoxanide used to treat, as well as anti-diarrheal agents
Cyclospora
Life cycle and transmission
• Oocysts shed in stool – sporulate externally 8-11 days before infective – resistant to formalin or chlorination • Transmission by food or water, probably not person to person • Seasonal, spring-summer • Worldwide distribution  
Cyclospora - Diagnosis and therapy
• Microscopy
– acid-fast staining • 7.5-10 um diameter
– autoflourescence
– safranin
- looks very much like crytospordium but twice the size
• Therapy
– responds to trimethoprim/sulfa
– long-term suppression for compromised hosts
Amebiasis - Life Cycle & Transmission
• Entamoeba histolytica
– Motile trophozoite reproduces and causes disease
– Entamoeba dispar is non-pathogenic but morphologically indistinguishable
- ingested red cells == histolytica
– Report as E. histolytica/dispar unless antigen or other testing done to distinguish
• Cysts spread by the fecal-oral route
– Food or water supplies
– person-to-person
• Cysts can survive for days or weeks, resistant to:
– drying
– gastric acidity
– chlorine
• 10% of the world population is colonized or infected
Amebiasis Diagnosis
•O&P; microscopy • Serodiagnosis - single nucleus, central karysome - cysts 4 nuclei – valuable in extraintestinal amebiasis, being positive in >90% of cases.
Microsporidia
•Protozoa (OOPS! Now they’re fungi!) belonging to order Microsporida, phylum Microspora
– >1000 species, 11 described in humans; newly described – many unknowns
• Obligate intracellular pathogens
Microsporidia Epidemiology
– Species involved in human disease
• Encephalitozoon, Enterocytozoon in GI disease
• Encephalitozoon, Nosema, Vittaforma, others, in ocular disease
– Immunosuppressed patients
• chronic diarrheal syndromes, esp. in HIV+ but also in other forms of immunosuppression
• disseminated disease with Encephalitozoon species
– Immunocompetent patients
• Diarrhea in travelers and others
Microsporidia Diagnosis – Stool Microscopy
• GI Infection – Stool exam • Weber’s trichrome & other stains • E. bineusi: 1.5x.9 um • E. intestinalis: 2.5-3.0 um • Size, shape similar to many bacteria
Microsporidia Diagnosis – Cytology
• Ocular, urinary/renal, biliary, pulmonary infections
– Require special stains
• H&E/Pap insensitive
• Chromotrope or Gram-based stains
Microsporidia Diagnosis – Histology
- Can visualize intracellular spores with appropriate stains
- May be present in small numbers – serial sections may be required
- EM provides species diagnosis
Microsporidia Diagnosis – The Future
• Antibody-based methods
– Available for Encephalitozoon species only
• Nucleic acid-based methods
Malaria Life Cycle & Transmission
• Four species of Plasmodium
– P. falciparum
– P. vivax
– P. malariae
– P. ovale
• Primarily insectborne; Anopheles mosquitoes
• Malaria is also transmitted by blood transfusion, needle sharing, and congenitally
Malaria Epidemiology
- Worldwide prevalence of >100 million cases
- kills over 1 million people per year, mostly children, in Africa alone.
- Half of all human deaths since the Stone Age have been due to malaria
Malaria - P. falciparum
Worldwide in the tropics & subtropics • The deadliest form • A medical emergency – very high parasitemias – parasitized cells stick to the capillary endothelium, causing renal, pulmonary, and cerebral complications – resistance to chloroquine
Malaria - P. vivax
• Widely prevalent in tropics, subtropics, & temperate regions
– Not found in West Africa
• Less severe than P. falciparum
• Requires treatment of latent form in liver
Malaria - P. malariae
- Widely prevalent in tropics, subtropics, & temperate regions – Not as common as vivax and falciparum
- No latent form in liver
Malaria - P. ovale
- Most common in tropical Africa, but also found rarely in Asia and South America
- Requires treatment of latent form in liver
Malaria - P. ovale
- Most common in tropical Africa, but also found rarely in Asia and South America
- Requires treatment of latent form in liver
P. knowlesi
- Primarily a rhesus monkey pathogen; emerging in humans in southern Asia.
- Resembles P. malariae morphologically; more severe clinically.
- Overall importance still being assessed.
How To Remember Which Is
Where
• Two types of malaria that don’t recur from the liver:
– P. falciparum – high incidence and severity
– P. malariae – lower incidence and severity
– Both worldwide in the tropics
• Two types of malaria that do recur from the liver divide the world between them:
– P. vivax – high incidence, most of the world except Western Africa
– P. ovale – lower incidence, occupies the niche in Western Africa
