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Microbiology > Unit 1: Helminthic Infections > Flashcards

Unit 1: Helminthic Infections Flashcards

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Biology 101 flashcards
1
Q

General nematode morphology

A

Elongated cylindrical body that tapers at either end

Covered by multi-layered cuticle - not very easily recognized by immune system

Presence of separate sexes (male spiricule)

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2
Q

Generalized life cycle of intestinal nematodes

A

Eggs shed in environment —> Larvae ingested by humans —> mature to adults in human body —> eggs shed back to environment

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3
Q

Causative agent of enterobiasis

A

Enterobius vermicularis (pinworm)

Most common helminthic disease in US (~40 mil cases)

Adults are small (8-12mm), whitish colored worms

Eggs require only a short time to become infections (autoinfections/reinfection common)

Humans are considered the only host

Children most commonly infected

Cosmopolitan in distribution but may be more common in temperate climates

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4
Q

Life cycle of E. Vermicularis

A

Eggs deposited on perianal region (self infection or person to person)

Infective eggs are ingested and larvae hatch in small intestine

Adults establish and mature in colon (~2 months)

GRAVID FEMALE (carrying eggs) migrates at night to the perianal region to deposit eggs

Deposited eggs become infectious in 4-6 hours, can survive indoors for 2-3 weeks

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5
Q

Clinical manifestations of E. vermicularis

A

Mostly asymptomatic

Most common symptom is itching in the anal region (Pruritis ani)

Heavy infections can lead to secondary bacterial infections, disturbed sleep, abdominal pain

Infections of the female genital tract have been reported

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6
Q

Dx and Tx of pinworm infection

A

Presence of eggs on perianal skin (cellophane tape method)

Considerations - can look 2-3 hours after pt goes to sleep or first thing in the morning on at least 3 consecutive days; also look under patient’s fingernails for eggs; no PCR tests, no serological tests, stool samples not helpful

Tx: Mebendazole or Albendazole
In households, all members should be treated at the same time to minimize spread
Hand washing most effective

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7
Q

“Large intestinal roundworm”

A

Ascaris lumbricoides - a soil transmitted nematode

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8
Q

“Whipworm”

A

Trichuris trichiura - a soil transmitted nematode

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9
Q

Ascariasis

A

Caused by Ascaris lumbricoides - largest intestinal nematode of humans

Adult female worm releases an average of 200,000 eggs per day

Transmitted via ingestion of contaminated soil

All ages affected, but more prevalent in children

Worldwide distribution but more prevalent in warm climates

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10
Q

Life cycle of ascaris lumbricoides

A

Infective eggs are ingested and larvae are released into the duodenum

Larvae penetrate the mucosa and travel via the bloodstream to the lungs

Larvae penetrate the alveoli and travel up the trachea to the oropharynx

Larvae are swallowed and mature in the duodenum

Adult worms produce eggs which can become infective in soil (18 days to several weeks)

Adult worms can live ~2 years

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11
Q

Clinical manifestion of ascariasis

A

Often asymptomatic

Worm burden usually determines extent of disease
• Due to blockage
• Pulmonary-Loeffler’s syndrome
• Intestinal-abdominal pains
• Complications include intestinal or duct obstruction

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12
Q

Dx and Tx of Ascariasis

A

Microscopic detection of eggs in stool sample (may be useful to concentrate sample)

DOC: Mebendazole or albendazole

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13
Q

What is whipworm?

A

Trichuris trichiura (causes trichuriasis)

Up to 800 million people infected worldwide

Small worms (40mm in length) with a whiplike morphology

Have characteristic EGG CAPSULES (pathomneumonic)

EPI:
Ingestion of contaminated soil
More prevalent in children
Worldwide distribution

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14
Q

Egg capsules

A

Think Trichuris trichiura (whipworm)

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15
Q

Life cycle of trichuris trichiura

A

Infective (embryonated) eggs are ingested and larvae are released in the duodenum

Maturation occurs in the colon

Released eggs can mature in the soil

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16
Q

Clinical manifestations of trichuriasis

A

Worm burden determines extent of disease

Light infections - asymptomatic

Heavy infections
• Frequent painful passage of stool (w associated mucus, water, blood)
• Rectal prolapse can occur
• Children may suffer growth retardation and anemia

17
Q

Dx and Tx of trichuriasis

A

Presence of eggs in stool sample (elongated capsules with bubble on either end)

DOC: albendazole or Mebendazole

18
Q

Tell me more about hookworms…

A

Necator americanus and Ancylostoma duodenale

Adult worms are small (12mm)

Worms feed on BLOOD FROM INTESTINAL MUCOSA

EPI:
• Inadequate disposal of human feces leads to presence of organism
• Eggs reach infectivity and hatch in soil
• Larvae can penetrate skin

19
Q

Life cycle of hookworms

A

Infective eggs hatch in soil

Infective stage larvae (FILARIFORM) penetrates skin and travels via the bloodstream to the lungs

Larvae penetrate the alveoli and travel up the trachea to the oropharynx

Larvae are swallowed and mature in duodenum

Adult worms produce eggs which mature and hatch in soil

20
Q

Clinical characteristics of hookworm infections

A

Extent of disease is based on worm burden and adequacy of the host’s nutrient intake

Blood-filled, pruritic lesions can occur at the site of larval penetration (“ground itch”)

Continual blood loss occurs due to feeding by adult worms (may observe anemia)

Dx: presence of eggs in stool sample

DOC: Mebendazole

21
Q

What the heck is strongyloides stercoralis?

A

Causes strongyloidiasis

Adult worms are small (2mm) - aka “threadworms”

TWO MULTIPLICATION CYCLES - in host (parasitic) or in soil (free living)

EPI:
Majority of cases in tropical/subtropical areas
Related to poor sanitation

22
Q

Life cycle of Strongyloides stercoralis

A

Infective larvae in soil can penetrate skin

Larvae travel through the bloodstream to the lungs, penetrate alveoli, and travel to the oropharynx

Larvae are swallowed and the worms mature in the mucosa of the duodenum

Following reproduction, adult female releases larvae in the feces

Free living multiplication occurs in the soil

23
Q

Clinical characteristics of strongyloidiasis

A

Related to larval migration

Intestinal Sx: diarrhea, pain, constipation, malabsorption

Autoinfection can occur, and results in a chronic infection that persists for years

Life threatening in patients with a defect in cell mediated immunity

24
Q

Dx and Tx of strongyloidiasis

A

Presence of larvae in stool sample or duodenal aspirate

Sputum of hyperinfected patient may also contain larvae

DOC: Thiabendazole

25
Q

Morphology of trematodes (flukes)

A

Flattened, leaflike body
Presence of suckers
Hermaphroditic

26
Q

Chinese liver fluke

A

Clonorchis sinensis —> clonorchoriasis

Adult worm is small (20mm)

Adults live in biliary ducts

EPI:
Common in the Far East
Transmission occurs via ingestion of larvae in raw, smoked, pickled, or salt-cured/dried fish

27
Q

Life cycle of clonorchis sinensis

A

Poorly cooked fish containing encrypted larvae (metacercariae) are eaten

Excystation occurs in the duodenum and the larvae pass directly into the bile ducts where they mature

Eggs are released and pass in the feces

Eggs are eaten by aquatic snails

Following development, larvae (cercariae) are released

Cercariae excystation under the scales or in the flesh of fish

28
Q

Clinical characteristics of clonorchoriasis

A

Most patients are asymptomatic

Chronic disease develops late, and is related to worm burden

Dx: presence of eggs in stool (geographic history helpful)

DOC: Praziquantel

29
Q

Tapeworms!

A 
Taenia solium (pork)
Taenia saginata (beef)
(Both are agents of Taeniasis)

Large worms (3-9 meters)

Posses a SCOLEX (head structure)

Eggs released in proglottids are immediately infectious

Humans are the only definitive hosts

Worldwide distribution

30
Q

Taenia life cycle

A

Infective eggs ingested by cattle (saginata) or pigs (solium) hatch in the duodenum and released larvae penetrate the wall

Cysticerci (larvae) develop in muscle of animal

Poorly cooked meat ingested by a human releases the cysticercus which develops into an adult tapeworm in the jejunum

Proglottids (segments) released in the feces contain infectious eggs

In T. solium infections, cysticercosis can develop if infective eggs are ingested by a human

31
Q

Clinical characteristics of taeniasis

A

Most patients are asymptomatic and involve only one worm

Mild GI symptoms may occur

Cysticercosis is often asymptomatic but serious secular can occur depending on infected site (blindness, seizures)

32
Q

Dx and Tx of taeniasis

A

Presence of eggs or proglottids in stool sample

Lesions demonstrated by CT scans or other methods can be presumptive for cysticercosis

Histologic demonstration is definitive

DOC: Praziquantel

33
Q

What the hell is Diphyllobothrium latum?

A

Fish tapeworm - causes diphyllobothriasis

Worm can become very long (12 meters) and contain thousands of proglottids

Eggs are released singly, not in proglottids

Eggs develop and hatch in water, and a series of host passages are required for life cycle completion

Has widespread distribution and has been reported from the Great Lakes region and Alaska

Humans and other fish eating mammals harbor the adult worms

34
Q

Life cycle of Diphyllobothrium latum

A

Infective larvae found in muscles of fish

Poorly cooked fish ingested by a human release larvae in the duodenum

Adult worm develops in the jejunum and eggs released in the feces

Eggs hatch in fresh water and the larval forms are ingested by crustaceans

Infected crustacean is ingested by a small fish

Small fish are ingested by larger fish

35
Q

Clinical characteristics of diphyllobothriasis

A

Most infections are asymptomatic

Adult worm competes with human for vitamin B12

Dx: Clinical presentation with anemia and positive histories, presence of eggs in stool, ID of adult worm

DOC: Praziquantel

Microbiology (6 decks)

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