Microbiology: Helminths

Question 1

What are characteristics of trematodes (flukes)?

Answer 1

• Flat, fleshy, leaf-shaped worms
• Usually have two muscular suckers
• Usually hermaphroditic
• Require intermediate hosts (usually snails or clams)

Question 2

How are Fasciolopsis buski acquired, diagnosed, and treated?

Answer 2

Acquired: Eating encysted larval stage on aquatic vegetation (i.e. water chestnuts)

Develop in small intestine over 3 months

Symptoms: Usually asymptomatic
Can Cause:
Diarrhea
fever
Abdominal pains
ulceration
hemorrhage

Dx: Eggs in stool

Rx: Praziquantel

Question 3

What are general characteristics of tapeworms (cestodes)?

Answer 3

• All (except D. latum) have suckers with hooklets on head
• Flat, ribbon-like bodies with proglottid segments that contain reproductive organs –> egg making machines
• No digestive system, food absorbed through body wall
• In order to infect a human, larval form must be ingested

Question 4

What are characteristics, Dx, and Rx of Taenia saginatum?

Answer 4

• A tapeworm acquired by eating larvae in undercooked beef
• Few symptoms, can grow up to 10m

Dx: proglottids and eggs in stool

Rx: praziquantel or albendazole

Question 5

What are characteristics, Dx, and Rx of Taenia solium?

Answer 5

• a tapeworm acquired by eating pork with larvae

Eggs lead to neurocysticercosis by traveling to the brain

Adult tapeworm causes few symptoms

Dx: proglottids and eggs in stool

Rx: praziquantel or albendazole

Question 6

What are characteristics and symptoms of Diphyllobothrium latum?

Answer 6

• A tapeworm acquired by eating fish with larvae

B12 deficiency can be found in 40% of patients

Question 7

What is neurocysticercosis?

Answer 7

Caused by ingestion of Taenia solium eggs

–> oncosphere penetrates intestinal wall, circulates in tissue, and often develops cysts in brain

• “swiss cheese” brain MRI
• No physical loss of brain cells (unless inflammation develops)

–> no loss of cells means neurological exam is often normal, but can cause:
seizures
hydrocephalus
headaches
focal neurologic deficits

Question 8

How is neurocysticercosis diagnosed and treated?

Answer 8

Definitive Dx = tissue biopsy

Presumptive = imaging

Cysticercosis serology can be supportive

Treatment:
Albendazole or praziquantel
+/- corticosteroids (for inflammation)

Question 9

What are anatomical characteristics of nematodes (roundworms)?

Answer 9

• Nonsegmented round worms
• Flexible outer coating (cuticle)
• Muscular layer under the cuticle
• Nervous, digestive, renal, and reproductive organs

Question 10

What are the most common intestinal nematodes?

Answer 10

Ascaris

Trichuris

Hookworm

Strongyloides

Pinworm

Question 11

What are severe long-term morbidities of intestinal nematodes?

Answer 11

Stunted growth

Reduced physical activity

Decreased cognitive performance

Reduced school attendance

Possible factors: iron deficiency, anemia, decreased appetite, malabsorption, hypoalbuminemia, decreased vit. A and zinc

Question 12

How do people get infected with intestinal helminths?

Answer 12

1. Eating eggs in fecally contaminated food or soil
   (ascaris, trichuris)
2. Direct penetration through skin
   (hookwormss, strongyloides)
3. Eating infected food
   (Trichinella, anisakis)

Question 13

What is the life cycle of strongyloides and hookworm?

Answer 13

Skin –> lungs –> gut

Strongyloides has the ability to reproduce inside humans

Question 14

What is the life cycle of ascaris?

Answer 14

Gut –> liver –> lungs –> gut