Helminths I

Question 1

Intestinal Nematodes

Answer 1

All mature to adults in the human intestinal tract

• Acquired by the ingestion of eggs:

• Enterobius vermicularis (pinworm)
• Trichuris trichiura (whipworm)
• Ascaris lumbricoides (large intestinal roundworm)

•Acquired by larvae penetration through the skin:

• Necator americanus and Ancylostoma duodenale (human hookworm)
• Strongyloides stercoralis (threadworm)

Question 2

Enterobius vermicularis (pinworm)

Answer 2

• Most common helminth in the US
• Incidence 11% in US, 60% in India
• 10 mm
• Found in the “seats of the poor and the mighty”
• Anal pruritus
• Females travel down sigmoid colon and deposit eggs on perianal skin
• Diagnosis: Scotch tape test (detects eggs)
• Tx: Albendazole, mebendazole and pyrantel pamoate
• All family members need therapy
• Reinfection common. Repeat therapy several weeks later

Question 3

Trichuris trichiura (whipworm)

Answer 3

• 50 mm
• Eggs must mature in soil for ~10 days before infectious (embryonate)
• Bipolar eggs in feces (barrel-shaped)
• May be asymptomatic, or chronic diarrhea
• Heavy infestation in child may cause rectal prolapse
• Diagnosis: eggs in stool
• Treatment: Albendazole and mebendazole

Question 4

Ascaris lumbricoides

Answer 4

• Most common helminth in the world (1.2 billion cases a year)
• 30-50 cm
• 3-week incubation in the soil
• Live around 6 years
• Eggs hatch after ingestion
• Clinical presentation:
• abdominal pain
• cough, pulmonary infiltrates, eosinophilia (eosinophilic pneumonia-Löeffler’s syndrome)
• malabsorption and occasional obstruction by heavy worm loads
• may be asymptomatic
• Heat (fever and some drugs) can agitate the worms
• Diagnosis is made by identification of eggs in feces. Larvae can be occasionally seen the sputum
• Albendazole, mebendazole and pyrantel pamoate

Question 5

Hookworms (Necator americanus and Ancylostoma duodenale)

Answer 5

• Larval forms have 7-14 years of survival in soil
• Larvae enter the skin between the toes- Ground itch
• Travel to alveoli- eosinophilia and Löeffler’s syndrome
• Larvae are coughed up and swallowed
• Adult worms develop in small intestine where they attach and suck blood (iron-deficiency anemia)
• Hookworms copulate and release fertilized eggs
• Diagnosis: serial stool examinations for eggs
• Albendazole, mebendazole and pyrantel pamoate

Question 6

Strongyloides stercoralis

Answer 6

• Larval forms penetrate the skin and travel to the lung
• They are coughed up and swallowed into the small intestine and develop into adult worms
• Adult females deposit eggs in the mucosa
• The eggs are NOT passed in the stool
• Rhabditiform larvae hatch
• Life cycle:

1. Indirect cycle (free-living, sexual): rhabditiform larvae are passed in stool and develop into male and females. They mate and may propagate several generations before producing infective larvae
2. Direct cycle: rhabditiform larvae pass out in feces, mature into infective larvae and penetrate the next passerby
3. Autoinfection: rhabditiform larvae mature into infective larvae in the colon. Infective larvae penetrate the intestine directly, and go to the lungs to continue the cycle “permanent infection

Question 7

Strongyloides stercoralis Clinical Presentation

Answer 7

• Immunocompetent patients (immigrants-POW): asymptomatic- skin rash- mild abdominal pain- eosinophilia- Löeffler syndrome
• Immunocompromised patients (corticosteroids-solid organ transplantation-HTLV1):
• Strongyloides hyperinfection syndrome: the infection can be severe leading to pneumonia and sepsis (high mortality ~90%)
• The larvae can carry bacteria (enterococcus, E. coli) while penetrating the intestinal wall leading to bacteremia and bacterial meningitis
• Diagnosis: serial stool exam for rhabditiform larvae, or serology
• Ivermectin is the preferred drug of choice. Albendazole is an alternative.

Question 8

Tissue Nematodes

Answer 8

•Toxocara canis (dog ascarid)

-Visceral larva migrans

•Baylisascaris procyonis (racoon ascarid)

-Eosinophilic meningitis

•Ancylostoma braziliense (dog and cat hookworms)

-Cutaneous larva migrans

•Trichinella spiralis (pork worm)

-Trichinellosis

•Dracunculus medinensis (guinea worm)

-Guinea worm disease

•Filarial worms

-Filariasis

Question 9

Toxocara canis

Answer 9

• Dog ascarid
• Visceral larval migrans
• Infections by ingestion of eggs from dog feces
• Principally a disease of children
• Larvae hatch and penetrate the small intestine into the blood
• They are not able to penetrate out of alveolar capillaries in human and instead migrate and encyst in tissues
• Clinical features: eosinophilia, fever, hepatomegaly, retinal involvement (granulomatous endophthalmitis leading to blindness)
• Diagnosis: serology or biopsy

Question 10

Baylisascaris procyonis

Answer 10

• Raccoon ascarid
• 100,000 eggs per day
• Humans ingest the eggs
• Larvae migrate to the meningeseosinophilic meningitis

Question 11

Dog and Cat hookworms (Ancylostoma braziliense)

Answer 11

• Cutaneous larva migrans- creeping eruption
• Larvae penetrate human skin, but cannot develop further
• Larva wander causing long tortuous red tracks and die within 10 days
• People are exposed on beaches or sand boxes contaminated with dog or cat feces

Question 12

Trichinella spiralis

Answer 12

• Common in pigs, rats and bears
• Human eat larvae encysted in muscle
• Intestinal phase (2-3 weeks): Larvae are released then penetrate the intestine epithelium and become adult worms (abdominal pain, diarrhea)
• Parenteral phase: worms are expelled and deposit larvae that migrates -> lymph -> blood -> all organs (muscle pain, periorbital edema, fever, eosinophilia, splinter hemorrhage, myocarditis, CNS)
• Diagnosis: serology- muscle biopsy
• Prevention: freeze meet or cook with normal temperature

Question 13

Dracunculus medinensis (guinea worm)

Answer 13

• 1986: 3.5 million cases
• 2015: 22 cases reported
• Drinking water contaminated by copepods
• The larvae that live inside the copepods are released and penetrate the intestine -> subcutaneous tissue
• The female worm grows (>100 cm) and penetrates the skin and pokes out exposing her uterus
• Treatment: remove the worm over a stick
• Prevention: clean water

Question 14

Filariasis

Answer 14

• -Wuchereria bancrofti, Brugia malayi (lymphatic filariasis)
• -Onchocerca volvulus (river blindness)
• -Loa loa (african eye worm)
• -Dirofilaria immitis (dog heart worm)
• Spread by bites of arthropods
• Adult filariae live in lymphatic tissue and give birth to microfilariae (no eggs)
• The microfilariae circulate through blood and lymphatic system
• Microfilariae are picked up by arthropods and are transmitted to other human
• Disease is caused by allergic reaction to the worm and microfilariae
• Filarial parasites are themselves host for other dosymbioitic bacteria (Wolbachia). They can exacerbate the allergic reaction

Question 15

Wuchereria bancrofti, Brugia malayi

Answer 15

• Transmission: Mosquito bites at night
• Clinical presentation:
• Acute filariasis: fever, chills, eosinophilia, high IgE
• Can be associated with tropical pulmonary eosinophilia
• Obstructive filariasis: elephantiasis
• Asymptomatic
• Diagnosis: identification of microfilariae from blood at night, or by serology
• Treatment: Diethylcarbamazine (DEC)- may stimulate allergic response. Doxycycline may be added to kill Wolbachia and achieve full cure

Question 16

Onchocerciasis (River Blindness)

Answer 16

• Mainly in subsaharan Africa. Also exists in central and south America and middleeast
• 25 million people affected with over 1.1 million with total or partial visual impairment
• Transmitted by bite of infected Simulium black flies during the day
• Larvae (microfilariae) mature to adult worms coiled up in skin nodules
• Adult worms produce microfilariae that migrate to:
• Skin- pruritus, pigmentation, granulomas
• Eye- river blindness
• Diagnosis: identification of microfilariae in skin biopsy (skin snips)
• Treatment: Ivermectin. Doxycycline may be added to kill Wolbachia
• DEC contraindicated- Mazzotti reaction (fever, rash, hypotension) River blindness ivermectin

Question 17

Loa Loa

Answer 17

• Transmitted by Chrysops (red/deer) fly bite during the day
• Co-geographic with onchocerciasis
• Microfilariae -> adult worms that migrate to:
• Subcutaneous tissue -> Calabar swelling (angioedema response)
• Conjunctiva (eye worm)
• Diagnosis: identification of microfilaria in blood (during the day) or visualization of adult worm in the conjunctiva
• Treatment: DEC (contraindicated with high-level microfilaremia >2500 mf/mL)
• Albendazole
• Ivermectin—contraindicated

Question 18

Dirofilaria immitis (heart worm)

Answer 18

• Dog parasite
• Transmitted by mosquitos
• Clinical manifestation in dogs: heart failure (obstruction of pulmonary artery)
• Clinical manifestation in human: Nodule on chest X-ray. Usually asymptomatic