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74 Cards in this Set

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NEMATODES
NEMATODES
What is another name for nematodes?
Roundworms
Describe the general body plan of nematodes:
Nematodes have complete digestive tracks with a mouth and anus, and separate sexes.
Name the nematodes that infect the intestinal tract and the disease they cause:
ENTEROBIUS causes pinworm infection; ASCARIS causes ascariasis; TRICHURIS causes whip worm infection; NECATOR and ANCYLOSTOMA cause hookworm infection; STRONGYLOIDES causes strongyloidiasis; and TRICHINELLA causes trichinosis.
Name the nematodes that infect blood and tissue and the disease they cause:
WUCHERERIA causes filariasis (elephantiasis); ONCHOCERCA causes onchocerciasis (river blindness);LOA LOA causes loiasis; and DRACUNCULUS causes guinea worm infection.
Which nematodes are transmitted by ingestion of eggs?
ENTEROBIUS, ASCARIS, or TRICHURIS
Mnemonic: EAT eggs.
What is the most frequent helminth parasite in the United States?
ENTEROBIUS VERMICULARIS
How do E. VERMICULARIS infections usually present?
Intense perianal pruritus in children
What area of the gastrointestinal (GI) tract does E. VERMICULARIS infect? How do you diagnose pinworm?
Large intestine. Diagnosis with the scotch-tape test
How do you treat pinworm?
Mebendazole, albendazole, or pyrantel pamoate
Who should be treated if a child has an infection caused by E. VERMICULARIS?
The patient (child) and all family members (close household contacts)
What is the most common helminth worldwide?
ASCARIS LUMBRICOIDES, the largest round worm, infects up to 25% of the world’s population.
How do A. LUMBRICOIDES infections usually present?
Early infection presents with fever, cough, and wheezing as the larvae are migrating through the tissue. Late infection presents with obstructive GI symptoms such as cramping, small bowel obstruction, pancreatitis, and cholecystitis.
Which nematodes have a lung infiltrating phase followed by coughing and subsequent swallowing of larvae?
ASCARIS LUMBRICOIDES, NECATOR AMERICANUS, ANCYLOSTOMA, and STRONGYLOIDES STERCORALIS
What two nematodes will not present with an elevated eosinophil count because they do not invade tissue?
1. TRICHURIS TRICHIURA
2. ENTEROBIUS VERMICULARIS
How do T. TRICHIURA infections usually present?
Most cases of whipworm infection are asymptomatic and there is no pulmonary migration phase. Physical complaints may include abdominal tenderness, anemia, and rectal prolapse.
Which nematodes are transmitted by direct invasion of skin by larval forms?
NECATOR, ANCYLOSTOMA, or STRONGYLOIDES
The filariform larva of this helminth penetrates intact skin of bare feet. It can also cause a microcytic anemia and its eggs are shed in stool. Identify the helminth:
NECATOR AMERICANUS (hookworm)
The filariform larva of this helminth penetrates intact skin but cannot mature in humans. This infection presents with intense skin itching. What is the most likely nematode?
ANCYLOSTOMA (cutaneous larva migrans)
The filariform larva of this helminth penetrates intact skin with larvae, but not eggs, being shed in the stool. Patients may present with pneumonitis, abdominal pain, diarrhea, malabsorption, ulcers, and bloody stools; and immunocompromised patients may present with invasive disseminated infection that often coexists with gram-negative sepsis. Identify the helminth:
STRONGYLOIDES STERCORALIS (threadworm)
With what nematode infection will you not find eggs in stool samples?
STRONGYLOIDES STERCORALIS. This is the only nematode capable of replicating in the host.
What nematode is transmitted by ingestion of inadequately cooked meat containing larvae?
TRICHINELLA
How do TRICHINELLA infections usually present?
Patients present with fever, severe muscle pain, splinter hemorrhages, and periorbital swelling. Peripheral blood smear shows eosinophilia, and x-ray shows fine alcifications in the muscle. Serum creatine phosphokinase may also be elevated.
Which nematodes are transmitted by larvae-contaminated insect bites?
WUCHERERIA, L. LOA, ONCHOCERCA, and BRUGIA MALAYI
Which filarial worms can cause elephantiasis? How are they transmitted?
WUCHERERIA BANCROFTI and BRUGIA. The nematodes block lymphatic drainage. Transmitted via mosquitoes
Diagnosis of elephantiasis is made by the identification of microfilariae in blood drawn at what time during a 24-hour period? What is the treatment for elephantiasis?
Nighttime (nocturnal periodicity). Diethylcarbamazine
What eye worm is transmitted by biting flies?
LOA LOA
What roundworm is responsible for causing river blindness and is trasmitted by the bite of an infected blackfly?
ONCHOCERCA VOLVULUS
How do you treat O. VOLVULUS?
IVERMECTIN
Name the tissue-invasive nematode that is transmitted by drinking water contaminated with larvae-infected microscopic copepods:
DRACUNCULUS MEDINESIS
How do D. MEDINENSIS infections usually present?
Painful skin blister/ulcer in the extremity with a visible worm inside
How is dracunculiasis treated?
Medically with niridazole. However, treatment since ancient times involves wrapping the exposed worm around a stick and slowly twisting the stick to extract the worm. This nearly eradicated disease may be the inspiration for the universal symbol of medicine, the staff of Asklepios.
TREMATODES
TREMATODES
What is another name for platyhelminthes and name the two groups:
Flatworms

1. Trematodes
2. Cestodes
Describe the general body plan of flatworms:
No digestive tract. Most reproduce sexually as hermaphrodites. Blind gut (has mouth, but no anus)
What is another name for trematodes?
Flukes
Name the medically important trematodes and the diseases they cause:
SCHISTOSOMA (blood fluke) causes schistosomiasis, CLONORCHIS (liver fluke) causes clonorchiasis, and PARAGONIMUS (lung fluke) causes paragonimiasis.
The first intermediate host regarding trematode infections:
Snails
Which trematode is not hermaphroditic?
SCHISTOSOMA
How common are SCHISTOSOMA infections?
Quite common, estimated more than 200 million people are infected worldwide.
How does schistosomiasis usually present?
Acute schistosomiasis (Katayama fever) presents with fever, headache, malaise, and cough. Chronic cases present with hepatosplenomegaly, eosinophilia, bloody diarrhea, and granulomas/fibrosis in the liver.
What are the most common SCHISTOSOMA that cause human infection?
SCHISTOSOMA JAPONICUM, SCHISTOSOMA MANSONI, and SCHISTOSOMA HAEMATOBIUM
What is unique about S. HAEMATOBIUM?
SCHISTOSOMA JAPONICUM and S. MANSONI migrate to the mesenteric venules, but S. HAEMATOBIUMmigrates to the bladder veins. It is associated with an increased incidence of squamous cell carcinoma of the bladder and is endemic in Egypt.
What is swimmer’s itch?
An intense pruritus caused by a variety of SCHISTOSOMA endemic to freshwater snails, typically after a swim in the Great Lakes. The itching is caused by the host inflammatory response to the dead parasites. Humans are aberrant hosts in swimmer’s itch.
How does SCHISTOSOMA evade host defenses?
They incorporate host antigen, including major histocompatibility complexes (MHCs) and blood group antigens into their surface. They also produce factors which prevent the migration of resident skin antigen presenting cells (APCs) (Langerhan cells) from migrating to the draining lymph nodes, thus preventing the activation of the immune response.
How is schistosomiasis diagnosed?
Infection with S. HAEMATOBIUM is diagnosed by urinalysis (hematuria and/or presence of eggs in the urine). SCHISTOSOMA JAPONICUM and S. MANSONI are diagnosed by stool specimens.
What is the drug of choice for schistosomiasis?
Praziquantel
Pharmacology Correlate: What is the mechanism of action for praziquantel?
Praziquantel causes paralysis and spasm by causing a rapid influx of Ca2+ inside the SCHISTOSOMA.
Immediately following the administration of praziquantel for schistosomiasis, why is there an exacerbation of symptoms?
Death of the SCHISTOSOMA induces a vigorous immune response.
What is unique about CLONORCHIS sinensis?
CLONORCHIS SINENSIS infections can cause choledocholithiasis (common bile duct obstruction) and cholangiocarcinoma.
What is unique about PARAGONIMUS WESTERMANI?
PARAGONIMUS WESTERMANI infection is caused by ingesting undercooked crabs or crayfish and can mimic pulmonary tuberculosis. It causes recurrent bacterial pneumonia, and presents with fever, hemoptysis, and dyspnea.
CESTODES
CESTODES
What is another name for cestodes?
Tapeworms
Name the medically important cestodes and the disease they cause:
TAENIA SOLIUM (pork tapeworm) causes taeniasis and cysticercosis; TAENIA SAGINATA (beef tapeworm) causes taeniasis; DIPHYLLBOTHRIUM LATUM (fish tapeworm) causes diphyllobothriasis; andECHINOCOC-CUS GRANULOSUS (dog tapeworm) causes unilocular hydatid cyst disease
Describe the morphology of cestodes:
Cestodes consist of a head (scolex), a neck, which produces the proglottids, and the segments or proglottids. As proglottids mature they move further away from the scolex
Do cestodes have GI tracts?
No, they absorb nutrients from the host’s GI tract. The only helminths with GI tracts are nematodes
How are tapeworms transmitted?
Ingestion of cysts in the flesh of the intermediate host
What are the symptoms of tapeworm infection?
Patients may complain of vague abdominal pain, nausea, weight loss, anorexia, or increased appetite
Tapeworm infections are more serious when humans are what type of host?
Intermediate hosts because of cysticerci (occurs when humans ingest the eggs)
What are cysticerci? Name a few manifestations of cysticercosis:
Encysted larvae found in intermediate hosts. May manifest as blindness, seizures, focal neurologic deficits, and hydrocephalus
What is unique about D. LATUM?
Fish tapeworm can cause vitamin B12 deficiency and megaloblastic anemia. They average 10 meters in length
Pathology correlate: How is megaloblastic anemia diagnosed?
Increased mean corpuscular volume and hypersegmented neutrophils
Why are ECHINOCOCCUS infections particularly dangerous?
Echinococcus cause hydatid cyst disease, which may remain as an asymptomatic cyst until it causes amass effect on an organ. Surgical excision of these cysts is also particularly challenging because cyst rupture may be associated with local spread of infection or with anaphylactic reaction to echinococcal antigens
CLINICAL VIGNETTES
CLINICAL VIGNETTES
A 65-year-old Egyptian ex-professional swimmer presents with hematuria, dysuria, and increased urinary frequency. After a thorough workup and biopsy, squamous cell carcinoma of the bladder is diagnosed. What is the most likely infectious cause of this cancer?
SCHISTOSOMA HAEMATOBIUM can cause a chronic infection that has a strong association with bladder carcinoma in Egypt and Africa. The parasite penetrates the skin and matures in bladder veins.
A 5-year-old boy has multiple night awakenings accompanied by intense perianal itching. The family physician instructs the mother to dab the perianal area with a STICKY SWAB and bring it into the office for analysis. The physician finds ova with a flattened side and filled with larvae. What is the most likely helminth involved?
ENTEROBIUS VERMICULARIS (pinworm)
A 12-year-old girl, newly emigrated from Southeast Asia, presents with abdominal cramping. She is febrile, has a dry cough, pulmonary infiltrate on chest x-ray, and a high eosinophil count in the blood and sputum. Diagnosis is made by identification of eggs in feces, and a sputum examination reveals larvae. Peripheral blood smear also shows an increased number of eosinophils. What nematode is first on your differential diagnosis?
ASCARIS LUMBRICOIDES
A 37-year-old woman presents with rectal prolapse. The physician has found barrel-shaped eggs with bipolar plugs in the patient’s stool. Which nematode is the most likely culprit in this case?
TRICHURIS TRICHIURA (whipworm)
A 12-year-old boy from West Africa presents with an itchy LEOPARD rash and worms in the eyes. What is the most likely nematode involved and what is its vector?
ONCHOCERCA VOLVULUS (river blindness). Vector is blackfly.
Mnemonic: river blindness from the blackfly, treat with ivermectin (vision is BLACK when BLINDED).
A 35-year-old tourist to South America acquires a helminth infection and subsequently develops portal hypertension. What is the most likely helminth involved? Infection with which helminth can lead to pulmonary hypertension?
SCHISTOSOMA JAPONICUM. S. MANSONI can cause pulmonary hypertension. Results from fibrosis of the portal venous system and pulmonary arterioles respectively secondary to an immune reaction against the eggs of the helminth.
A 34-year-old woman who enjoys eating raw freshwater fish presents with nonspecific abdominal symptoms. Peripheral blood smear is significant for an increased mean corpuscular volume (MCV), and hypersegmented neutrophils. What is the most likely diagnosis?
DIPHYLLOBOTHRIUM LATUM (fish tapeworm) with vitamin B12 deficiency
A 56-year-old man goes in for surgical removal of a pulmonary cyst. During the procedure, the surgeon accidentally nicks the cyst, which results in leakage of cystic fluid. Immediately after the fluid leakage, the patient goes into anaphylaxis. Which helminthic infection is responsible for these series of events?
ECHINOCOCCUS (hydatid cyst disease)
A 25-year-old man presents with vague abdominal pains. The patient reveals that he eats rare pork quite often (which is inadvisable). Proglottids and eggs were found in his stool. What is the diagnosis?
TAENIA SOLIUM (pork tapeworms)
A 16-year-old girl presents with nausea and vomiting. She directs your attention to a painful skin blister, and upon further examination you observe a visible worm within the ulcer. She also tells you that she has been drinking out of a local pond that may be contaminated with tiny crustaceans. What parasite is most likely responsible for her illness and how do you treat her?
DRACUNCULUS MEDINENSIS. Treat with niridazole or manually remove worm by wrapping the exposed part around a small stick and gently twist to extract.