Parasites
Why is this important to us?
• Parasites in the U.S.
– Toxocariasis now a common parasitic infection among inner
city children
– Cysticercosis, caused by the tapeworm Taenia solium, is
emerging as the leading cause of epilepsy among Hispanic
populations in the US
– Toxoplasmosis is an important cause of congenital birth
defects
Why is this important to us?
“The problem is that, due to a lack of education,
most of the population doesn’t know that there’s a
parasite wriggling within them,” says Patricia
Wilkins, a scientist with the Center for Disease
Control and Prevention (CDC)
Why is this important to us?
Parasites outside the U.S.
Why is this important to us?
• http://www.youtube.com/watch?v=TuU0uEY5
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Today
• Parasite overview
– Definitions
– Life stages
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Entameoba histolytica
Giardia lamblia
Malaria
Trichomonas vaginalis
Ascaris lumbricoides
Pinworms
Naeglaria fowleri
What are parasites?
• Symbiosis: close and often long-term interaction
between two or more different biological species
• Mutualism - both individuals benefit
• Commensalism - one benefits, the other is not
significantly harmed or helped
• Parasitism - one benefits, the other is harmed
Life cycles
• Many parasites discussed today are protozoa
• Some protozoa have life stages alternating
between stages
– Trophozoites – actively feeding
– Cysts – can survive harsh conditions or long
periods without access to nutrients, water or
oxygen for extended period of time
– Encystation
– Excystation
Entameoba histolytica
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Anaerobic parasitic protozoan
Estimated to infect 50 million people worldwide
40,000 to 100,000 people worldwide die annually
90% asymptomatic
Entameoba histolytica
• Life cycle
• Fecal/oral route
• Anal/oral route
Entameoba histolytica
• histo–lytic = tissue destroying
• Ameobiasis
• Symptoms take from a few days to a few
weeks to develop and manifest themselves
– Mild diarrhea to dysentery with blood and mucus
(lining of intestine)
– About 10% of invasive cases the amoebae enter
the bloodstream
– May travel to other organs in the body (liver)
Entameoba histolytica
• Diagnosis: stool sample
• Treatment
– Metronidazole highly effective against
trophozoites
– Paramoycin for cysts in lumen
– Need both
Entameoba histolytica
• What is most important about Entameoba
histolytica?
Giardia lamblia
• Flagellated protozoan parasite
• Anaeorobes
• From the CDC:
“Giardiasis is a global disease. It infects
nearly 2% of adults and 6% to 8% of
children in developed countries
worldwide. Nearly 33% of people in
developing countries have had giardiasis.
In the United States, Giardia infection is
the most common intestinal parasitic
disease affecting humans”
Giardia lamblia
• Fecal-oral route
• Noninfective cyst
excreted from feces
of infectived
individual
• Once ingested by a
host, trophozoite
emerges to an active
state of feeding and
motility
• After feeding,
trophozoite
undergoes binary
fission
Giardia lamblia
• Giardiasis
• Colonization of gut results in inflammation
and atrophy, reducing gut’s absorptive
capability
• Diarrhea, malaise, excessive gas, epigastric
pain, bloating, nausea, diminished interest in
food
Giardia lamblia
• Accurate diagnosis requires an antigen test or, if that is
unavailable, an ova and parasite examination of stool.
• Multiple stool examinations are recommended, since
the cysts and trophozoites are not shed consistently.
• Given the difficult nature of testing to find the
infection, including many false negatives, some
patients should be treated based on symptoms.
• Treatment: Metronidazole
Giardia lamblia
• Waterborne sources
– Untreated sewage
– Cysts resistant to conventional water treatment
methods including chlorination
• Day- care centers
• Giardia is also one of the most common
parasites infecting cats, dogs and birds.
Mammalian hosts also include cattle,
beavers, deer, and sheep
Giardia lamblia
• What is most important about Giardia
lamblia?
Malaria
• Region: Most Prevalent in Tropical Regions,
but is present in the U.S.
• Caused by the plasmodium species of
protozoa
• Of the 200 plasmodium varieties, 11
effect humans.
• 4 of the plasmodium varieties induce
Malaria
• Plasmodium is carried by the Anopheles
species of mosquito.
• Over 216 million NEW infections are
estimated to occur every year
• Over 600,000 malaria related deaths occur
annually.
Malaria - Infection of the Mosquito
• Many Anopheles mosquitos in afflicted
regions are born infected.
• Can become exposed by eating the
blood of an infected organism
• Plasmodium travels through the blood
stream to the stomach
• Host Organism
• Gametes
• Travels to the salivary glands until the
mosquito’s next meal
Malaria – Infection of Humans
• Starts with the Mosquito Bite
• Enters the blood through salivary secretions
• Sporozoite phase travels to the liver
• Maturation  Merozoites
• Proliferation
• Rupture the Infected Hepatocyte,
reentering the blood stream
• Enter Erythrocytes (red blood cells)
• Feed on hemoglobin, releasing toxic
heme byproduct
• Proliferation: 48-72 hour cycles
• Rupture of the Erythrocyte
Malaria – Infection of Humans (cont.)
Malaria - Symptoms
Develop 10-28 Days After Infection
Most Common Symptoms Include
• Fever
• Chills
• Jaundice
• Enlarged Liver and Spleen
*Symptoms occur in 48-72 hour cycles. Why?
If left untreated…
• Renal, Liver, Respiratory Failure
• Liver and Spleen Rupture
• Meningitis
• Cerebritis
Malaria – Diagnosis and Treatment
Physical Exam – Enlarged Liver and Spleen
Blood Test (CBC) – Anemia
Blood Smear – Look for the parasite
Treatment: Chloroquine (antimalarial drug)
• Prevents plasmodium metabolism
• Must begin while liver is functional
• Chloroquine Resistant Strains Exist,
• Quinidine (antiarrhythmic)
• Doxycycline (antibiotic)
Prognosis: Good
Malaria – Sickle Cell Anemia
• Heterozygous-recessive trait
• Homozygous: Shortened life expectancy
• Offers the “heterozygous advantage”
• Leads to “sickling” of erythrocytes
• Due to inability to crystallize hemoglobin
• Reduces O2 Binding Capacity
• Reduces flexibility of erythrocyte
• Clotting
• Blood Vessel Occlusion
• Prevents Plasmodium from entering
and/or proliferating
• Mechanism is not certain
• Reduced O2 availability
• Prevents Plasmodium from entering
• Destroys Plasmodium membranes
Trichomonas Vaginalis
Region:
• Present Worldwide
• Most common parasitic infection in U.S.
• Estimated 3.7 million new cases annually
Species:
• Trichomonas vaginalis
• Humans are the only known vectors
• Do not have a cystic form
• Must be transmitted by direct contact
Trichomonas Vaginalis - Infection
• Generally Sexually Acquired
• Toilets
• Other Items that Contact Genitals
• “Stuck” in the trophozoite phase
• Grow flagella during development
• Proliferate via binary fission
• Inhabit genitalia
• Live in urogenital epithelium
• Feeds on:
• Bacteria  Phagocytosis
• Vaginal Secretions
Trichomonas Vaginalis – Symptoms
• Only 30% of Infected persons show any symptoms
• More common in females
• 5-28 Days
Men:
• Itching/Irritation of Penis
• Burning Sensation
• Discharge
Women:
• “Strawberry Cervix” (2%)
• Itching, Burning, Redness, Soreness of Genitals
• Discomfort during Urination
• Odorous yellow-green discharge (12%)
Trichomonas Vaginalis – Diagnosis and
Treatment
Diagnosis (12%):
• Physical Exam: Nearly Impossible
• Laboratory: Microscopic Observation of Discharge
Very Low Sensitivity
Treatment:
• Metronidazole (antibiotic)
• One large (2 gram) dose
• Passes through mucous membrane into protozoa
• Resistant Strains Exist
• Treatment is a Challenge
Prognosis:
• Most commonly cured STI
• 95%
Ascariasis
Ascariasis = Infection by parasitic nematode
Ascaris lumbricoides
Region: Present Worldwide, most common in
sub-tropical, developing nations
 Human Feces used as Fertilizer
Estimated: 1 billion infections worldwide,
4 million infected Americans
Ascariasis: “Long Intestinal Roundworm”
Cylindrical
2-6 mm in diameter,
15-35 cm (7-15 inches) long
Ascariasis - Infection
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In the soil – 18 days to become
infectious, can survive for 10 years.
Eggs pass to humans by direct
contact
Eggs travel to the small intestine,
hatch after 2 weeks.
Enter blood circulation  Lungs
Mature in Lungs for ~1 week, then
reenter the intestines.
Fully develop in the intestines,
differentiating into adult males and
females
Sexually reproduce, up to 200,000
eggs/day
2-3 Months Total
Ascariasis - Symptoms
Many People Show No Symptoms!
Lung Phase: Ascaris Pneumonitis
• Coughing
• Wheezing
• Shortness of Breath
• Cannot be diagnosed
Intestinal Phase
• Vague to Severe Abdominal Pain
• Nausea and Vomiting
• Weight loss/malnutrition
• Diarrhea and Bloody Stool
Complications
• Gall bladder obstruction  Gall stones
• Intestinal Blockage and Perforation
• Pancreatitis
Ascariasis – Diagnosis and Treatment
Diagnostic Tools
• Microscopic Study of the Stool
– 40 days
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CBC – Eosinophilia increase
– Not specific
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Abdominal CT or X-Ray
Endoscopy
Treatment Options
• Untreated Infections will often
resolve
• Two classes of medical treatment
options: Antihelminthic drugs
– Both lead to worm passage in feces
– Mebendazole (500mg): Kills worms
– Levamisole (2.5mg/kg): Paralyzes
worms
Pinworms
- Enterobius vermicularis in America
Region :
• Worldwide, most common helminth
infection in the U.S. and Western Europe.
• 11.4% (~40 million) in the U.S. are infected
• Most common in children
– 50% in England
Species:
• 1 of 3 types of parasitic pinworms, the only
one that affects humans
• Humans are the only known host
• Small (13x0.5 mm), white, and delicate
• Females have a sharp rear end
• Eggs are microscopic
Pinworms - Infection
• Eggs spread by touch
– Mouth (inhalation or
ingestion)
– Anus
• Infected persons often carry
eggs beneath fingernails
• Eggs are extremely hardy
– Can survive on inanimate
surfaces for up to 3 weeks
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Towels
Curtains
Toys
Furniture
Pinworms – Life Cycle
Takes place in a single host
• After ingestion, eggs hatch in the
duodenum
• Larvae grow and move towards colon
– Develop into adult
• Mating occurs in the cecum
– Males die after mating
• Females attach to the ascending
colon, feeding on colic contents
• Produce eggs
• Travel through large intestine
• Emerges from anus to lay eggs
– Spread by contact
– Retroinfection
Pinworms – Symptoms
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Causes enterobiasis -Often
asymptomatic
Itching in the anal region
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Especially at night
Insomnia
Anorexia
Weight Loss
Irritability
Secondary Issues:
• Vulvovaginitis
• Urinary Tract Infection
• Bacterial Infections
Pinworms – Diagnosis and Treatment
Diagnostic Tools
• “Scotch Tape Test”
• 90% Sensitivity
• Visual Observation
• Anal Swabs
Treatment
• Benzimidazole or Mebendazole
(antiparasitic)
– Target adult worms
– Prevents glycogen storage, leads to
starvation
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Hygiene!!
– Prevents reinfection
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Ivermectin for urogenital migration
– Broad Spectrum antiparasitic
Naegleria fowleri
“The brain-eating amoeba”
Region:
• Incredibly rare, but found most commonly in
the U.S
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Between 2000-2010, 32 cases
Found in warm, fresh bodies of water, soil
near such locations, and unchlorinated
swimming pools
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2 Deaths from Neti Pot Use
Species:
• Sensitive single-celled amoeba
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Thermophile
Cannot survive in salty environments
Has 3 stages to its life cycle:
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Cyst Stage: Present in unfavorable conditions,
inactive
Trophozoite: The “active” phase, it proliferates by
binary fission. They feed on bacteria.
Flagellate: Can change rapidly back and forth to
trophozoite phase, motile.
Naegleria fowleri - Infection
• The trophozoite is the
infectious form
• Gets introduced through
the nose
– Embeds in the nasal
epithelium
• Attracted to the
neurotransmitters of
Olfactory nerve
• “Eat” the olfactory nerve
and bulb, back to the
cerebrum.
• Spread to the rest of the
brain
Naegleria fowleri - Symptoms
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Causes by Primary Amoebic
Meningoencephalitis (PAM)
Symptoms take ~5 days to present, at which
time it is often too late for treatment.
– Death occurs 3-7 days after first symptoms
Symptoms: Common with other encephalitic
conditions
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Nausea
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Vomiting
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Headache
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Stiff Neck
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Delirium
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Seizures
Complications:
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Coma
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Respiratory Arrest
Naegleria fowleri – Diagnosis and
Treatment
Diagnostic Tools
• Lumbar Puncture
– Analysis of CSF
– Indicated for by Symptoms
“Treatment”
• “Heroic” dose of Amphotericin
B (systematic antifungal)
• Miltefosine and Fluconazole
– Not FDA Approved
• Testing on Phenothiazine
Antipsychotic Chlorpromazine
Prognosis: 2-3% survival rate
Questions?