Microbiology-Tissue Invasive Nematodes Flashcards
What are filariae?
Tissue-invasive, threadlike, round worms that are transmitted by insect vectors
Life cycle of filariae
Microphilaria picked up by insect -> Molt twice and become infectious -> Migrate from mosquito midgut to muscle and hang out where the mosquito bites -> Gets into animal host -> Molts twice -> Becomes an adult -> Mates and releases microphilaria in animal host and can be picked up by insect again
Most common causes of filarial infections of humans? Where are the adults found and where are the microfilariae found in each species?
1) Wuchereria bancrofti (tropics worldwide, adults = lymphatics, microfilariae = blood at night) 2) Onchocerca volvulus (Africa and Americas, adults = subQ nodules, microfilariae = skin) 3) Loa loa (Africa, adults = move in subQ, microfilariae = blood in day)
Treatment of filariasis
DEC and ivermectin. Note that treatment with these in someone with large amounts of microfilaria in their blood can cause encephalopathy and death.
A patient presents with descending linear red markings on the inner aspect of his thigh. He has painful fever and swollen testicles. What tissue invasive nematode could be causing his condition?
Lymphatic filariasis is one of the only pathogens that causes descending lymphangitis. Clogging of lymph vessels can cause hydrocele, filarial fever and lymphedema.
Why do people get elephantiasis?
Obstruction of the lymph vessels causes swelling. Swelling results in microtears and recurrent infection that leads to recurrent soft tissue destruction and remodeling. It is more difficult to clear local infections because adaptive immune cells can’t make it to the lymph nodes.
A patient from the tropics immigrated to the US. 20 years later he goes back to visit his home and develops severe paroxysmal nocturnal asthma after 2 months. Labs show marked elevation of serum IgE. What is likely causing his condition?
Tropical pulmonary eosinophilia occurs due to excessive immune response to reinfection by microfilariae in lung vasculature.
A patient presents with descending linear red markings on the inner aspect of his thigh. He has painful fever and swollen testicles. How do you diagnose tis condition? How do you treat?
Diagnose lymphatic filariasis with ultrasound of lymph nodes, look in blood at nighttime or an antigen test. Treat with DEC. Once you get rid of the worm, then you can treat for superimposed bacterial and fungal infections.
Location of onchocerciasis?
West Africa and South America
Tissues affected by onchocerciasis
Eye (punctate keratitis)), skin (nodules, really bad itching, hypopigmentation) and lymphatics (elephantiasis)
Why is onchocerciasis called river blindness?
It is transmitted by black flies that only hang out near rivers.
Diagnosing and treating onchocerciasis?
Serology (anti-filarial) and skin snips. Treat with ivermectin (works by inhibiting glutamate-gate Cl channels that paralyzes the worms) which only kills the microfilaria that cause river blindness. The patient will need to take this for a long time until the adult worms die off. You can add doxycycline because the Wolbachia need the bacteria to survive.
Presentations of loiasis
Hives and itching. Worm crawling across front of eye. Calabar swelling.
Diagnosing and treating loiasis
Diagnose: adult worm in sub conjunctiva, microfilaria in blood during daytime, antifilarial antibodies. Treat: DEC or albendazole.
25 year old returns from Thailand with terrible headache, photophobia, neck stiffness, paresthesias and peripheral eosinophilia. What is your diagnosis? How is it transmitted? How do you treat it?
Angiostrongylus cantonensis (rat lungworm). Most common cause of eosinophilic meningitis worldwide. People typically get if from eating, prawns, crabs and snails.
A group of hunters go out and shoot a wild pig. It is not cooked well but they eat it anyway. A couple weeks later they develop abdominal pains, diarrhea and a few weeks later they develop muscle pain and periorbital edema. Muscle biopsy is shown below. Labs show eosinophilia. What is causing their illness?
Trichinellosis. Eating infected meat causes larva to develop into an adult in the GI tract. Adults release larvae that migrate to striated muscle and cause muscle pain.
A 6 year old boy has a pet dog, likes to play and eat in a sandbox. He presents with fever, hepatosplenomegaly, wheezing, increased liver enzymes and eosinophilia. Fundoscopic exam is shown below. What is causing his condition?
Toxocariasis. Dog or cats releas toxocara eggs in its feces. People swallow the eggs and they hatch in the GI tract. They migrate through the lungs and return back to the GI tract. In children the worms migrate everywhere and cause visceral larva migrans. In older kids the worms migrate behind the retina and cause ocular larva migrans.
People in South Korea catch a fish out of the ocean and make fresh sushi. A patient comes to see you complaining of mild urticaria, itching in the back of the throat and anaphylaxis. What is causing his condition?
Anisakis comes from raw fish. When you eat it, it hatches and burrows into the gastric mucosa. This person is not allergic to fish, he is reacting to anisakis.
