Unit 1: Helminthic Infections

Question 1

General nematode morphology

Answer 1

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)

Question 2

Generalized life cycle of intestinal nematodes

Answer 2

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

Question 3

Causative agent of enterobiasis

Answer 3

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

Question 4

Life cycle of E. Vermicularis

Answer 4

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

Question 5

Clinical manifestations of E. vermicularis

Answer 5

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

Question 6

Dx and Tx of pinworm infection

Answer 6

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

Question 7

“Large intestinal roundworm”

Answer 7

Ascaris lumbricoides - a soil transmitted nematode

Question 8

“Whipworm”

Answer 8

Trichuris trichiura - a soil transmitted nematode

Question 9

Ascariasis

Answer 9

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

Question 10

Life cycle of ascaris lumbricoides

Answer 10

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

Question 11

Clinical manifestion of ascariasis

Answer 11

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

Question 12

Dx and Tx of Ascariasis

Answer 12

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

DOC: Mebendazole or albendazole

Question 13

What is whipworm?

Answer 13

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

Question 14

Egg capsules

Answer 14

Think Trichuris trichiura (whipworm)

Question 15

Life cycle of trichuris trichiura

Answer 15

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

Maturation occurs in the colon

Released eggs can mature in the soil

Question 16

Clinical manifestations of trichuriasis

Answer 16

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

Question 17

Dx and Tx of trichuriasis

Answer 17

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

DOC: albendazole or Mebendazole

Question 18

Tell me more about hookworms…

Answer 18

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

Question 19

Life cycle of hookworms

Answer 19

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

Question 20

Clinical characteristics of hookworm infections

Answer 20

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

Question 21

What the heck is strongyloides stercoralis?

Answer 21

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

Question 22

Life cycle of Strongyloides stercoralis

Answer 22

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

Question 23

Clinical characteristics of strongyloidiasis

Answer 23

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

Question 24

Dx and Tx of strongyloidiasis

Answer 24

Presence of larvae in stool sample or duodenal aspirate

Sputum of hyperinfected patient may also contain larvae

DOC: Thiabendazole

Question 25

Morphology of trematodes (flukes)

Answer 25

Flattened, leaflike body Presence of suckers Hermaphroditic

Question 26

Chinese liver fluke

Answer 26

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

Question 27

Life cycle of clonorchis sinensis

Answer 27

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

Question 28

Clinical characteristics of clonorchoriasis

Answer 28

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

Question 29

Tapeworms!

Answer 29

``` 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

Question 30

Taenia life cycle

Answer 30

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

Question 31

Clinical characteristics of taeniasis

Answer 31

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)

Question 32

Dx and Tx of taeniasis

Answer 32

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

Question 33

What the hell is Diphyllobothrium latum?

Answer 33

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

Question 34

Life cycle of Diphyllobothrium latum

Answer 34

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

Question 35

Clinical characteristics of diphyllobothriasis

Answer 35

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