Parasitology Flashcards
Tx for Strongyloides
Ivermectin
Tx for parasitic worms (except Strongyloides)
Albendazole
Dx of chronic Strongyloides (asymptomatic)
Serology
What are the main components of the Th2 immune profile?
IL-4, IL-5, Eosinophils, IgE
Which virus is associated with hyperinfection (reactivation) of latent Strongyloides?
HTLV-1
What is the organism commonly known as Pinworm ?
Enterobius vermicularis
What is the life cycle of Enterobius vermicularis ?
Ingest eggs. Eggs hatch in proximal duodenum. Larvae migrate to ileum to become adults and copulate. Gravid (pregnant) females migrate to the rectum. At night, females exit through the anus and induce pruritus (itching). Host’s nails tear the female apart, liberating eggs which are ingested and the cycle repeats.
What is the classic diagnosis of Enterobius vermicularis?
Scotch tape test (scotch tape on the anus in the morning or at night to reveal adult female worms).
Tx for Enterobius vermicularis (pinworm)?
Albendazole
What is the nematode commonly known as whipworm?
Trichuris trichuria
What is the life cycle of Trichuris trichuria (whipworm)?
Eggs are ingested from contaminated soil. Eggs hatch, larvae mature in GI tract. Anterior portion of nematode embeds itself in an epithelial syncytium and releases eggs into the lumen. Eggs are shed in the feces to incubate in soil for 2 weeks. Adult worms may persist in intestines for years.
Symptoms of Trichuris whipworm ?
GI mucosal inflammation (local eosinophilia). Mucosal bleeding. Heavy infection can cause prolapse, at which point worms can be visible.
Heavy infection is associated with dysentery and low iron anemia. Also clubbing of fingers.
Trichuris trichuria (whipworm) diagnosis ?
Stoof for ova and parasites
What is the largest intestinal nematode ?
Ascaris lumbricoides. Females up to 40 cm long.
What causes asthma-like symptoms in Ascaris infection?
Larvae migrating through the lungs cause eosinophilic inflammation and hypersecretion of mucous. Infiltrates on CXR.
What is the most serious complication of Ascaris infection?
Bowel obstruction from a bolus of adult worms. Children are especially at risk. Other obstructions are possible (e.g. bile duct, pancreatic duct, appendicitis, bile duct perforation with peritonitis).
Diagnosis for Ascaris lumbricoides?
Stool for ova and parasites reveals characteristic ova.
Tx for Ascaris lumbricoides?
Albendazole
What are the two species known as Hookworm?
Necator americanus and Ancylostoma
duodenale.
What is the lifecycle of Hookworms?
Eggs are passed in feces into soil.
They hatch to liberate larvae which infect host through skin of barefeet.
Migration from skin to bloodstream to lungs (perforate alveoli) through respiratory tract up trachea, down esophagus into GI tract where they attach to mucosa, suck blood, and mature to adults and lay eggs.
Clinical manifestation of Hookworm infection?
Local dermatitis (under feet). Asthma like symptoms when larvae pass through lungs. Peptid-ulcer like symptoms when larvae attach to GI mucosa. Hallmark of chronic hookworm infection is iron deficiency anemia, which results in chronic fatigue, lassitude, apathy. Cardiac symptoms (palpitations, sinus tachycardia) are common.
Diagnosis and treatment for Hookworm?
Stool for ova and parasites reveals characteristic ova.
Tx is albendazole (how to treat pregnant women?)
What is the life cycle of Ascaris lumbricoides?
Eggs are ingested and hatch in the Jejunum. Larvae pierce through the intestinal wall, and migrate via the hepatic venules to the right side of the heart where they enter pulmonary circulation. They perforate the alveoli and climb up the respiratory tract to be swallowed down into the esophagus and into the intestine where they become adults. From ingested eggs to egg producing adults takes 10-12 weeks.
What is the life cycle of Strongyloides stercoralis?
Filariform (infectious) larvae from contaminated soil pierce host skin and enter the bloodstream until they reach the lungs which they perforate. They ascend the respiratory tract, are swallowed and descend into the GI tract. In the intestines, they mature to adults which produce rhabditiform (non-infectious) larvae which are excreted in the feces. The transition from rhabditiform to filariform (non-infectious to infectious) larvae usually occurs in the soil but auto-infection in humans can occur when rhabditiform larvae manage to transform rapidly into filariform larvae. The process repeats ad nauseam and the infection lasts the lifetime of the host.
Clinical manifestation of acute strongyloides infection?
1) Dermatitis at site of skin perforation and initial migration (larva currens)
2) Epigastric abdominal pain / diarrhea when adults perforate the intestine.
3) Respiratory symptoms when larvae pierce through alveoli.
Describe chronic persistent Strongyloidiasis in immunocompetent individuals?
Chronic persistent strongyloidiasis is generally asymptomatic. Patients have high peripheral eosinophilia (> 250 IU/ml).
Who is at risk for Strongyloides hyperinfection syndrome?
HTLV-1 infected patients (#1), immunocompromised patients, patients using steroids. Generally, inactivation of the Th2 immune profile results in hyperinfection.
What is the pathophysiology of Strongyloides hyperinfection syndrome?
Loss of immune function leads to uncontrolled conversion of Rhabditiform larvae to Filariform (infectious) larvae which disseminate widely to any organ. Penetration of large numbers of larvae through the intestinal wall may result in bacterial sepsis.
Extensive lung damage is also common (bronchospasm, cavitation, alveolar hemorrhage).
Is strongyloides hyperinfection syndrome dangerous?
86% mortality rate.
Diagnosis of Strongyloidiasis ?
Acute:
Stool for ova and parasites. Or serology.
Chronic persistent:
Serology (due to low egg count).
Hyperinfection:
Stool or sputum show large numbers of ova and parasites.
Who should be screened for asymptomatic chronic strongyloides?
Patients at-risk (geographically) for Strongyloides infection who are:
1) newly diagnosed with HTLV-1
2) about to begin steroids
3) transplant candidates
Tx for strongyloides?
Ivermectin
What is cutaneous larva migrans?
Cutaneous larva migrans is the dermatitis caused by the migration of nematode larvae.
Which nematode species accounts for the majority of cutaneous larva migrans cases?
Anyclostoma braziliense and caninum (hookworms) account for most cases of larva migrans.
What is the life cycle of Ancylostoma braziliense and caninum (cutaneous larva migrans hookworms)?
The life cycle plays out in the dog or cat. Eggs are released in the feces which hatch into rhabditiform larvae and can become filariform (infective) larvae which penetrate the human epidermis but don’t move to deeper tissues. Humans are an aberrant host.
What is a definitive host?
A definitive host is a host in which the parasite matures and reproduces.
Clinical manifestation of Cutaneous Larva Migrans?
Inflammation and pruritus. Tracks of larva migrans are visible as encrusted and scarred tissue.
Diagnosis of larva migrans caused by cat/dog hookworm?
Clinical presentation and history.
Tx of larva migrans?
Albendazole (or ivermectin).
What nematode species cause Visceral Larva Migrans (VLM) and Ocular Larva Migrans (OLM)?
Toxocara caniis (toxocariasis) and Toxocara cati.
How is Toxocara transmitted from cats and dogs to humans?
Toxocara eggs are shed in the feces and ingested by humans. The eggs hatch in the host intestine and migrate to the liver. They can travel to numerous organs, including the lung.
What disease manifestation is most common in young children with Toxocariasis?
Hepatitis as larvae migrate through liver, with hepatomegaly.
Pneumonitis as larvae migrate through lungs, with pulmonary infiltrates.
Lymphadenopathy, fever, and eosinophilia are present.
Diagnosis of Toxocariasis?
Serology (ELISA)
Treatment of Toxocariasis?
Most commonly Albendazole.
What is the primary target organ of Baylisascaris procyonis (Baylisascariasis)?
Baylisascaris primarily targets the CNS and eye.
What animal sheds Baylisascaris in its feces?
The raccoon.
What is the serious complication associated with Baylisascariasis?
Eosinophili Meningoencephalitis (>50% of cases).
Diagnosis of Baylisascariasis?
Serology performed by CDC, and detection of typical larvae in tissues.
What is the treatment for Baylisascariasis?
There is no current treatment.
What region is Loa loa endemic to?
West and Central African rainforests.
In what tissues does Loa loa migrate?
In subcutaenous tissues and across the eye (eye worm).
At what time are microfilaria larvae found in the peripheral blood?
At noon.
How is Loa loa transmitted?
The Chrysops fly picks up the larvae from human peripheral blood (fly feeds at noon). The larvae become infective in the fly and are transmitted to a new host to become adults.
What is the most serious complication of Loiasis?
High numbers of microfilaria in peripheral blood may lead to eosinophilic meningoencelephalitis, especially following treatment with DEC (Diethylcarbamazine).
Treatment of Loa loa?
DEC (Diethylcarbamazine). Be careful not to cause meningoencephalitis.
Diagnosis of Loaisis?
Microscopic examination revealing microfilaria, or identification of the adult worm removed from subcutaneous tissue / eye.
What nematode causes “river blindness”?
The nematode Onchocerca volvulus causes onchocerciasis or river blindness.
How is Onchocerca transmitted?
By the bite of a black fly (Simulium).
Where is Onchocerciasis found?
Worldwide distribution including Central
Africa, the northern part of South America, and the Arabian Peninsula.
What is the life cycle of Onchocerca volvulus?
Black fly bite transmits larvae to host skin. Larvae mature to adults inside of subcutaneous nodules. Gravid females produce thousands of tissue-invading microfilariae daily which invade skin, eyes and subcutaneous tissues.