Nematodes Flashcards
What is one of the clinical indicators of all nematode infections?
Eosinophilia
Is the worm burden high or low in most patients?
Usually low
What nematode lives as long as the host?
Strongyloides stercoralis
What are the tissue dwelling nematodes?
Lymphatic filariasis - Brugia malayi, Wuchereria bancrofti
Onchocerciasis - Onchocerca volvulus
Loaiasis - Loa Ioa
What are the GI nematodes?
Pinworm - Enterobius vermicularis
Hookworm - Ancylostoma duodenale or Necator americanus
Ascaris - Ascaris lumbricoides
Whipworm - Trichuris trichiura
Strongylodiasis - Strongyloides stercoralis
Trichinosis - Trichinella spiralis (pork)
Toxocariasis - Toxocara canis and T. cati (dogs and cats)
What are the drugs used to treat nematode infections?
Albendazole Mebendazole Ivermectin Piperzine Pyrantel pamoate Diethylcarbamazine
What is unique about the mechanism of action of nematode drugs?
Don’t kill the worm, just paralyzes it. Allows immune system to catch up to it and kill
What are commonalities between all nematode life cycles?
4 larval stages
Male and female adults
Either produce embryos or produce live larval forms (into the environment)
What form are nematodes transmitted as?
Embryo (mostly GI) L1 larvae (mostly filarial)
Which stage of the nematode life cycle is the infectious stage (for humans)?
L3 larval
What is the organism that causes pinworm?
Enterobius vermicularis
What is the life cycle of pinworm?
Embryos ingested
Larvae hatch in small intestine
Adults in lumen of cecum
Sticky eggs laid in perianal region by female pinworm at night
What environment are pinworm infections common?
Day care centers
Children itch and eggs stick to fingers, spread easily
What are symptoms of pinworm?
Itching around perianal area
Distrubed sleep, irritability, restlessness
Loss of appetite
How is diagnosis of pinworm made?
“scotch tape test” or “pinworm paddle” - see cluster of eggs on adhesive tape
test done at morning when there are most eggs
What are the organisms that cause hookworm?
Ancylostoma duodenale
Necator americanus
What is the life cycle of hookworm?
Eggs hatch in environment
Larvae penetrate skin (usually through bare feet)
Migrate to lungs, through respiratory tract to mouth, swallowed, goes to small intestine
Larvae develop into adults worms attached to intestinal wall
Female produces thousands of eggs a day, excreted
How do hookworms get their nutrition?
Have chitinous teeth
Allow them to disrupt capillary bed and get blood
What environment are hookworm infections common in?
Tropical and subtropical climates
Anywhere that has a freeze will kill the larvae in the environment
Can hookworm be spread person to person?
No, requires development of larvae in soil
In what population of people do you see highest parasite burden of hookworm?
Older individuals
Hookworm burden increases with age
What are the symptoms of hookworm infection?
- Itching and rash and larval penetration site
- Abdominal pain, diarrhea, weight loss, tiredness, difficulty breathing
- Anemia and protein deficiency caused by blood loss (can retard growth and mental development in children)
What is the largest nematode parasite?
Ascaris
What is the life cycle of ascaris?
Ingest eggs from environment or water
Eggs hatch in lower intestine
Larvae migrate to lungs (via liver), ascend into throat, swallowed, descend into small intestine again
Develop into adults, release eggs
In what environment are ascaris infections common?
Tropical and subtropical climate, high population density, sanitation not good
What are symptoms of ascaris?
- Intermittent abdominal pain, “flu-like” symptoms
- Coughing/wheezing as larvae migrate to lungs
- Heavy infection: vomiting, sleep disturbance, extreme abdominal pain from intestinal blockage, “ascaris pneumonia”
What organism causes whipworm?
Trichuris trichiura
What is the life cycle of whipworm?
Eggs ingested
Larvae hatch in small intestine and migrate to proximal colon
Attach to intestinal mucosa (wraps around villi) and disrupts vasculature
Produce eggs, excreted
In what environment are whipworm infections common?
Dense urban population, tropical climate, poor sanitation
What are symptoms of whipworm infection?
Light infection - flatulence, abdominal pain, diarrhea
Severe infection - bloody diarrhea, anemia, retarded growth and development, intestinal blockage, rectal prolapse
What is the life cycle of Strongyloides?
Almost same as hookworm
Walk barefoot, larvae penetrate skin
Migrate to lungs, through respiratory tract to mouth, swallowed, goes to small intestine
Larvae develop into adults worms attached to intestinal wall
Female produces thousands of eggs a day, develop into larvae, excreted
How does strongyloides differ from hookworm?
- Free-living life cycle: eggs can develop into free-living adults in the environment (if conditions are right)
- Autoinfection: instead of being excreted, larvae can penetrate gut wall and go back into blood stream, thus re-infecting
- Only have mature females in intestine
In what population does Strongyloides autoinfection present a significant problem?
Immunosuppressed individuals (HIV, cancer) Can result in huge burdens of Strongyloides
In what environment is Strongyloides common?
Tropical, subtropical climates, but now also in Appalachia and southeast
Infection associated with HIV and cancer
What are symptoms of moderate Strongyloides infection?
Recurrent rash at site of larval penetration
Coughing/wheezing - larval migration to lungs
Abdominal pain
Nausea, vomiting, diarrhea
GI bleeding
What are symptoms of severe Strongyloides infection?
Chronic colitis
Anemia due to blood loss
Chronic diarrhea
Weight loss
What are the usual hosts of Trichinella?
Rodents
But pigs and bears eat rodents, and then we get infection from eating pigs/bears
What is the life cycle of Trichinella?
Ingest encysted larva in muscle of pork/wild game
Larvae released in small intestine, mature to adults
Adults deposit larvae in mucosa
Larvae encyst INTRACELLULARLY in striated muscle cells
In what environment is Trichinella common?
Places where raw/undercooked pork (ham, sausage) is eaten
Bear hunters
What are symptoms of Trichinella infection?
Initial - nausea, diarrhea, vomiting, fever, fatigue, abdominal pain
Followed by - headaches, fevers, chills, cough, swelling aching joints/muscle pain, diarrhea
How is Trichinella diagnosed?
Muscle biopsy
How is Trichinella treated?
Albendazole treatment (prolonged)
What organisms cause toxocariasis?
Toxocara canis and Toxocara cati
What is the life cycle of toxocariasis organisms?
Adults are in intestine of dogs/cats, produce eggs that get excreted
Humans ingest, larvae don’t receive proper signals (since not in their intended host of dogs/cats) so they migrate to various organs (larval migrans)
What are the symptoms of toxocariasis?
Ocular larval migrans - larvae enter eye, can cause inflammation and scars, potential vision loss
Cutaneous (visceral) larval migrans - larvae migrate under skin, see immune response following path of parvae
What is the treatment for GI nematodes and what is the one exception?
Albendazole or mebendazole (or pyrantel pamoate)
Exception: Strongyloides treated with ivermectin
What organisms cause lymphatic filariasis?
Burgia malayi
Wuchereria bancrofti
What is the life cycle of lymphatic filariasis organisms?
Vector (mosquito) takes blood meal and introduces L3 larvae into tissue
Larvae makes way to lymphatic vessels (just afferent to major lymph node clusters)
Grow into adults
Male fertilizes female and produces eggs that hatch within female
Female releases sheathed larvae into lymph circulation
Larvae taken up by mosquito in another blood meal
Larvae mature to L3 within mosquito
What is a major presentation of filarial infection?
Lymphatic pathology - Elephantiasis due to blocked drainage of the lymphatic system
Other pathology - chyluria - when lymphatics draining GI are blocked, nutrition goes into bladder
What is the vector for lymphatic filariasis?
Mosquitoes
What is the vector for Onchocerciasis?
Black fly
What is the life cycle of Onchocerca volvulus and Loa loa?
Black fly vector introduces L3 larvae into tissue via bite wound
Larvae travel short distance and mature to adults
Connective tissue nodule forms around adults
Male fertilizes female, unsheathed larvae are produced
Larvae migrate under skin throughout body
Can migrate to eye –> river blindness
Black fly takes meal and takes up larvae
Which tissue dwelling organisms are sheathed and which are unsheathed?
Sheathed: Burgia malayi, Wuchereria bancrofti, Loa loa
Unsheathed: Onchocerca volvulus
What is the definition of sheathed v. unsheathed?
Sheathed - never actually ‘hatch’ from egg shell, egg shell turns into the sheath
Unsheathed - has egg shell that completely hatches from
What is unique about the circulation of Burgia and Wuchereria?
Appear in peripheral circulation with periodicity
Absent during day, appear at night, most abundant 12-2 am
Sequestered in vasculature of lungs, however, no manifestations in lungs
What are clinical presentations of Onchocera volvulus infection?
Dermal pathology - elephant skin (elastase disrupted), papular eruptions, sterile abscess
Ocular pathology - “River blindness” - lesions in eye, most commonly cornea
Lymphatic pathology - organism distributes randomly and can block lymphatics (though this is usually associated with lymphatic filariasis organisms)
Other pathology - high percentage suffer from depression
What is the clinical presentation of Loa loa?
Eye lesions - something moving in front of eye
Calabar swelling - parasite dies in situ and releases antigens
What is the immunological response to filariasis in infected individuals?
‘modified’ Th2 response
What is the immunological response to filariasis in putatively immune individuals?
Mixed Th1/Th17 response
What is Wolbachia?
A parasite within a parasite! An endosymbiont
Obligate intracellular Alpha-proteobacteria
What is the treatment for filarial nematodes?
Diethylcarbamazine or ivermectin
Ivermectin preffered for Onchocerca volvulus
