Helminths I Flashcards
1
Q
Intestinal Nematodes
A
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)
2
Q
Enterobius vermicularis (pinworm)
A
- 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
3
Q
Trichuris trichiura (whipworm)
A
- 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
4
Q
Ascaris lumbricoides
A
- 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
5
Q
Hookworms (Necator americanus and Ancylostoma duodenale)
A
- 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
6
Q
Strongyloides stercoralis
A
- 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:
- 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
- Direct cycle: rhabditiform larvae pass out in feces, mature into infective larvae and penetrate the next passerby
- 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
7
Q
Strongyloides stercoralis Clinical Presentation
A
- 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.
8
Q
Tissue Nematodes
A
•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
9
Q
Toxocara canis
A
- 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
10
Q
Baylisascaris procyonis
A
- Raccoon ascarid
- 100,000 eggs per day
- Humans ingest the eggs
- Larvae migrate to the meningeseosinophilic meningitis
11
Q
Dog and Cat hookworms (Ancylostoma braziliense)
A
- 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
12
Q
Trichinella spiralis
A
- 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
13
Q
Dracunculus medinensis (guinea worm)
A
- 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
14
Q
Filariasis
A
- -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
15
Q
Wuchereria bancrofti, Brugia malayi
A
- 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
17
Q
Loa Loa
A
- 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
18
Q
Dirofilaria immitis (heart worm)
A
- 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
