This document provides an overview of medically relevant parasites presented by Dr. Karen Bennett. It discusses how parasites enter the body, replicate, and cause tissue damage. Cryptosporidium is highlighted as a parasite that causes diarrhea and is difficult to treat, especially in immunocompromised patients. It can be transmitted through contaminated water. Proper hygiene and water treatment are important for prevention. Laboratory diagnosis of parasitic diseases can be challenging but includes microscopic examination and newer techniques like PCR.

1. Medical Parasitology
Karen L. Bennett, PhD.
M609 Medical Sciences Bldg.
March 9, 2004

5. Introduction to medically relevant parasites
Parasites are eucaryotic organisms, like us, and
contain nuclei, cell organelles and, for the helminths,
tissues like our own. They are not endogenous to
humans. Therefore exposure and the means of entry
are important to the disease process.
Exposure: severity of illness often related to the
infective dose, with additional organisms acquired
over time. Parasitic infections are often chronic.
Entry: enter by ingestion or direct penetration of the
skin. Knowing the means of entry for the organisms
discussed is important for disease prevention.

6. Introduction: medically relevant parasites
Adherence: parasites adhere to specific host tissues, ie. malaria
and red blood cells or hookworms to the intestinal villi. Identifying
the methods and recognition molecules are useful subjects of
research, in order to prevent parasite adherence, but will not be
considered today.
Replication: most protozoans multiply in the host; only a few
worms do.

7. Introduction: basic clinical parasitology
Cell and tissue damage. Parasites don’t usually produce
toxins; tissue damage can be due to mechanical blockage and
inflammatory host response. Toxic products are often released
when the parasites die. The host often produces
immunopathologic responses. Parasites have developed many
elaborate means to avoid the host’s immune response.

8. Anti-parasitic agents
Why are there so few effective anti-
parasitic drugs? Only 3 new anti-malarial
drugs in past 20 years! (over 1,200 new drugs
approved by FDA in that timeframe).
Is there a problem with resistance?
Yes!
What are the current best means for
prevention? Good hygiene, simple
techniques like bed nets for mosquitoes.
How do the major anti-parasitic drugs
work? Many block critical metabolic
pathways; best are parasite specific.

10. Laboratory Diagnosis of Parasitic Diseases
Diagnosis often difficult.
Traditional methods are by microscopic exam.
Newer means, including western blots, ELISAs and PCR
are expensive.
A few, unusual, low-tech methods will be mentioned.
The medical practitioner must be aware of the possibility of
parasites.

25. Drug of choice for Trichomonas (and for Giardia, another flagellate) is Flagyl.

26. CRYPTOSPORIDIUM
TALES FROM THE “CRYPTO”

27. CASE 19
• In Milwaukee, WI water
contamination from a
sewage treatment plant
killed 100 people and
affected more than
400,000 in 1993. The
parasite that caused
the disease was
determined to be
cryptosporidium.

28. SYMPTOMS
• Immunocompetent • Immunocompromised
– Mild self-limiting – 50 or more stools per
enterocolitis (watery day
bloodless diarrhea, – Dehydration (fatigue,
abdominal pain, abdominal cramping,
nausea, vomiting, and and nausea)
fever) – Lasts months or years
– Spontaneous remission – Common in AIDS
is common (usually patients
within 10 days)

29. LAB DIAGNOSIS
• Microscopic exam
– Acid fast stain of
stool sample
– Endoscopic biopsy of
small intestine

30. Cryptosporidium oocysts with acid-fast stain

31. LAB DIAGNOSIS
• Immunodiagnosis
– Immunofluorescence
assay (IFA)
– Enzyme linked
immunoabsorbant
assay (ELISA)
• Polymerase Chain
Reaction (PCR)
– Test of choice

32. LAB DIAGNOSIS

33. LIFE CYCLE
• Cryptosporidium lives and grows in
variety of animals– geese to snakes to
cows, sheep and pigs to humans.
• Cryptosproridium completes its cycle in
a single host.
• The Species of Crypto known to infect
humans is Cryptosporidium Parvum.

34. LIFE CYCLE
• Infectious agents are the OOCYSTS
• In immunocompromised patients ID50 is about
10 to 30 oocysts
• Autoinfection takes place in 2 ways-
> Merozoites attach to nearby epithelial
cells and spread infection
> thin walled oocysts excyst and continue
to spread infection within the body

35. A scanning electron micrograph of Cryptosporidium lining the intestinal
tract. (From: Gardiner et al., 1988, An Atlas of Protozoan Parasites in
Animal Tissues, USDA Agriculture Handbook No. 651.)

36. A scanning electron micrograph of a broken meront of Cryptosporidium
showing the merozoites within. (From: Gardiner et al., 1988, An Atlas of
Protozon Parasites in Animal Tissues, USDA Agriculture Handbook No.
651.)

37. LIFE CYCLE

38. TRANSMISSION
AND
• EPIDEMIOLOGY
Person to person (fecal-
oral)
• Animal to human
• Contamination of water
supplies (result of waste
runoff)
• *WATER-BORNE
MOST COMMON*
COMMON

39. TREATMENT
• Immunocompetent • Immunocompromised
– Self-limiting – Cocktail therapy -used to treat
symptoms but NOT THE DISEASE
– Usually symptoms subside
within 10 days – Drugs include: letrazuril,
azithromycin, paramycin, and
hyperimmune bovine colostral
immunoglobulin
*The only immunity is previous exposure and
extent of this immunity is not known.*

40. PREVENTION
• Wash hands
• Wash fruits and
vegetables
• Avoid untreated water
• Treat contaminated
water
• MAINTAIN PROPER
HYGIENE!!

41. WATER PREVENTION
• Ozone
• UV light
• Inexpensive tests to
eliminate water borne
pathogens
– Resistance to
filtration
– Resistance to
chlorine
– Kills all spores after
one minute rapid
boiling
• “Chlorine not effective
against crypto!!”

42. INTERESTING FACT
• In Uganda, the human
population shares
habitat with free
ranging gorillas.
These people are
infected with animal-
adapted genotype of
Crypto spo ridium
parvum.

43. INTERESTING FACT
• There were 6
outbreaks
between 1984 and
1994 in the US.
• In MO there were
26 confirmed
cases from motel
pools in 1994.

44.
INTERESTING FACT
• Cattle alone produce
about 4.57 tons of
•
Cryptosporidium
oocysts per year in the
US
BEWARE !

45. FUN FACT
• “Crypto”-nite
– Cryptosporidium is the
main reactive agent
causing Superman
Sickness

46. Microsporidium: Encephalitozooon cuniculi

47. Microsporidia spores:
Gram positive in biopsy

48. Nature
2001
Vol
414:450

49. Nature 2001 Vol. 414:401

56. Multiple rings of P. falciparum trophozoites can be found in a single red blood cell

57. The % of red blood cells showing parasites is often low, making diagnosis difficult.
This slide shows the advanced ring stage of P. vivax

58. Seen here is a red blood cell filled with multiple schizonts ready to burst free.

59. Nature 2001 Vol. 415:670