Welcome to Parasitology

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Welcome to Parasitology
Ugra S. Singh, Ph.D. Pathology, Immunology, and
Virology USC School of Medicine Columbia, SC
29209
Contact information- Tel. [phone] Email
Ussingh_at_gw.med.sc.edu Office Buildg, 1. B-30
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Some definitions
Parasite An organism that obtains food and
shelter from another organism and derives all the
benefits from this association Obligate When
the parasite can live only in host Facultative
When the parasite can live in the host as well as
in free form Endoparasites When the parasite
lives inside the body Ectoparasites When the
parasite survives on the body surface
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Some definitions
Continued..
Pathogenic When the parasite causes harm to the
host Commensals Those parasites which benefit
from the host without causing harm Host The
organism that harbors the parasite and suffers a
loss caused by the parasite Primary host or
definitive host In which the parasite reaches
its maturity or if applicable reproduces
sexually Secondary host or intermediate host
Where the parasite lives its asexual stage for a
short period
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Some definitions
Continued..
Dead-end host is an intermediate host that does
not allow the transmission to the definite host,
thereby preventing the parasite from completing
its development Reservoir Hosts other than
humans that harbor the parasite, ensure the
continuity of the life cycle, and act as
additional sources of infection Vector An
organism (usually an insect) that is responsible
for transmitting the parasite infection
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PREVALENCE OF PARASITIC DISEASES I
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PREVALENCE OF PARASITIC DISEASES II
Continued--
Estimates of the prevalence of parasitic diseases
are at best extremely rough, as morbidity
reporting is nonexistent or very inaccurate in
many of the areas in which these diseases occur.
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Some characteristics of parasitic diseases

• Prevalence in underdeveloped countries specially
  in the lower income group of population
• Low mortality and morbidity
• Limited drug development
• No vaccines

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Number of specimen positive for parasites in
South Carolina
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Intestinal and uro-genital protozoa of man
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Intestinal and uro-genital protozoa of man
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What you need to know?

• Morphology
• Geographic distribution
• Life cycle
• Symptoms
• Pathogenesis and immunity
• Diagnosis
• Treatment and prevention

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Amebiasis

• Etiologic agent
• Entamoeba histolytica
• Disease
• Amoebic dysentery
• Liver, lung, brain and other
  abscesses

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Amebiasis
Although anyone can have this disease, it is most
common in the people who live in developing
countries that have poor sanitation
conditions. In parts of Africa, Latin America,
India and South East Asia amebiasis is
endemic. In US upto 4 population probably
carries the parasite, mostly found in immigrants
from developing countries.
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Amebiasis
A 37 years old businessman complains of central
abdominal pain, diarrhea and flatulence of
10-days duration which started 2 days after
returning from a trip to Central-South America.
His wife and children who did not travel with him
have no GI complaints. He has no fever and the
physical examination is otherwise normal. The
stool contains mucus and blood (leucocytes and
monocytes).
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E. histolytica morphology
10-15 mm
The active trophozoite stage exists only in the
host and in the fresh loose stool.
Cysts often found in the stool survive outside of
the host, in water, soil and on foods.
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Fecal-oral life cycle
Excystation
Trophozoite
Cyst
Encystment

• Passed in feces
• Non motile
• Resistant to hostile environment
• Does not multiply

• Metabolically active
• Motile
• Multiplies by replication

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E. histolytica life cycle
Ingestion of cyst in the contaminated water and
food
Excystation occurs in the small intestine. Eight
trophozoits produced from one cyst. Trophozoits
migrate to large intestine where they multiply or
may encyst for excretion
Cysts exit hosts in the stool
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Symptoms of acute amebiasis
Abdominal pain frequent bloody dysentery with
necrotic mucosa
Small and large intestine
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Symptoms of chronic amebiasis
Recurrent bloody and mucoid dysentery with
intervening constipation appendicitis
pseudopolyps perforation

• Small and large intestine

Abscess hepatitis

• Liver

Abscess pneumonia

• Lung

Abscess encephalitis

• Brain

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Chronic amebiasismucosal erosion and crater
formation
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Chronic amebiasisdrainage of a liver abscess
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Chronic amebiasis drainage of a lung abscess
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Chronic amebiasis brain abscess
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E. Histolytica pathology and Immunology

• Immunology
• Antibodies are detectable in chronic infections
  but they are of questionable protective value

• Pathology
• Invasiveness and abscess formation are due to
  amoebic proteolytic enzymes

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Amebiasis Differential diagnosis
Amebiasis is different from giardiasis and
bacterial dysentery

• Mucus and blood in stool
• No granulocytosis
• No high fever

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E. Histolyticathe diagnostic features
When amebic dysentery is suspected, a fresh fecal
sample or a swab should be examined under
microscope. If examined quickly the colorless
motile trophozoite can be seen. The motile
trophozoite has one nucleus
H/E stained
Staining-
Lugol staining --- General morphology Iodine
staining --- Glycogen Iron/Haematoxylin staining
Chromatoidal bodies
Fresh sample
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E. Histolytica prevention and treatment

• Prevention
• Better hygiene
• Efficient sewage treatment and disposal
• Treatment
• Iodoquinol for acute amebiasis
• Metronidazole for chronic amebiasis

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Giardiasis

• Etiologic agent Giardia lamblia
• Disease Giardia affects humans, but is also one
  of the most common parasites infecting cats, dogs
  and birds.
• Diarrhea, lipid and vitamin B12 and other
  nutrient mal-absorption

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Giardiasis
A 37 year old businessman complains of central
abdominal pain, diarrhea and flatulence of
10-days duration which started the day after
returning from a trip to Leningrad. His wife and
children who did not travel with him have no GI
complaints. He has no fever and the physical
examination is otherwise normal. Milk
consumption makes the symptoms worse. The stool
is bulky, foul smelling and floats on the water
surface. It contains no mucus or blood.
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Giardiasis
HIV positive cases mostly affected 2.5 million
cases each year in US
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Giardia lambliamorphology
The active trophozoite attaches to the lining of
small intestine with a sucker responsible for
causing the signs and symptoms of
giardiasis. Giardia do not have mitochondria
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Giardia lamblialife cycle
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Giardiasis
symptoms
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Giardiasis pathology and Immunology

• Immunology
• Some protective role for IgA and IgM
• Increased incidence in immunodeficiency

• Pathology
• Covering of the epithelium by trophozoites and
  flattening of the mucosal surface (no
  invasiveness)

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Giardiasis
Differential diagnosis
Giardiasis is different from amebiasis and
bacterial dysentery

• No mucus, blood
• No granulocytosis and no fever

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Giardiasis
diagnosis
The mainstay of diagnosis of Giardia is stool
microscopy, this can be for distinctive oval
cyst and motile trophozoite
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Giardiasis prevention and treatment

• Prevention
• Better hygiene
• Efficient sewage treatment and disposal

• Treatment
• Iodoquinol
• Metronidazole

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