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

“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=TuU0uEY5ft0

Why is this important to us?

Today

• Parasite overview– Definitions– Life stages

• 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• 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 - SymptomsDevelop 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 SpleenBlood Test (CBC) – AnemiaBlood 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• 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• CBC – Eosinophilia increase

– Not specific• 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• Towels• Curtains• Toys• Furniture

Pinworms – Life CycleTakes 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 • Causes enterobiasis -Often

asymptomatic • Itching in the anal region

– 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

• Hygiene!!– Prevents reinfection

• Ivermectin for urogenital migration– Broad Spectrum antiparasitic

Naegleria fowleri“The brain-eating amoeba”

Region: • Incredibly rare, but found most commonly in

the U.S– Between 2000-2010, 32 cases

• Found in warm, fresh bodies of water, soil near such locations, and unchlorinated swimming pools– 2 Deaths from Neti Pot Use

Species:• Sensitive single-celled amoeba

– Thermophile– Cannot survive in salty environments

• Has 3 stages to its life cycle:– 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• 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• Nausea• Vomiting• Headache • Stiff Neck• Delirium• Seizures

Complications:• Coma• 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?