Nematodes (roundworms) US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Nematodes (roundworms). These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Nematodes (roundworms) US Medical PG Question 1: A 34-year-old man comes to the physician because of progressive swelling of the left lower leg for 4 months. One year ago, he had an episode of intermittent fever and tender lymphadenopathy that occurred shortly after he returned from a trip to India and resolved spontaneously. Physical examination shows 4+ nonpitting edema of the left lower leg. His leukocyte count is 8,000/mm3 with 25% eosinophils. A blood smear obtained at night confirms the diagnosis. Treatment with diethylcarbamazine is initiated. Which of the following is the most likely route of transmission of the causal pathogen?
- A. Penetration of the skin by hookworms in feces
- B. Penetration of the skin by cercariae from contaminated fresh water
- C. Deposition of larvae into the skin by a female black fly
- D. Ingestion of encysted larvae in undercooked pork
- E. Deposition of thread-like larvae into the skin by a female mosquito (Correct Answer)
Nematodes (roundworms) Explanation: ***Deposition of thread-like larvae into the skin by a female mosquito***
- The symptoms described, including progressive **nonpitting edema** (lymphedema), a history of **fever** and **lymphadenopathy** after travel to an endemic area (India), and significant **eosinophilia**, are classic for **lymphatic filariasis**.
- Lymphatic filariasis, caused by filarial worms like *Wuchereria bancrofti* or *Brugia malayi*, is transmitted by **mosquitoes** that deposit infectious larvae onto the skin during a blood meal.
*Penetration of the skin by hookworms in feces*
- This describes the transmission of **hookworm infection**, which causes **iron deficiency anemia** and gastrointestinal symptoms, not lymphedema or high eosinophilia with nocturnal microfilaremia.
- While hookworms can cause eosinophilia, the clinical presentation of chronic lymphedema and the need for a nocturnal blood smear point away from hookworm infection.
*Penetration of the skin by cercariae from contaminated fresh water*
- This is the transmission method for **schistosomiasis**, which can cause symptoms depending on the species and affected organs, such as **urinary tract disease**, **hepatic fibrosis**, or **intestinal inflammation**.
- Schistosomiasis does not typically present with the progressive lymphedema and episodic lymphadenitis characteristic of filariasis.
*Deposition of larvae into the skin by a female black fly*
- This describes the transmission of **onchocerciasis** (river blindness), caused by *Onchocerca volvulus*.
- Onchocerciasis primarily causes skin disease (intense **pruritus**, dermatitis) and **ocular lesions** leading to blindness, not extensive lymphedema of the limbs.
*Ingestion of encysted larvae in undercooked pork*
- This is the route of transmission for **trichinellosis**, caused by *Trichinella spiralis*.
- Trichinellosis involves **muscle pain**, fever, and periorbital edema, but not chronic lymphedema of the extremities or the specific nocturnal periodicity for diagnosis.
Nematodes (roundworms) US Medical PG Question 2: A 19-year-old woman presents to the emergency department with chronic diarrhea, fatigue, and weakness. She also had mild lower extremity edema. On examination, she was noted to be pale. Blood testing revealed peripheral eosinophilia (60%) and a Hb concentration of 8 g/dL. The stool examination revealed Fasciolopsis buski eggs. Which of the following drugs would most likely be effective?
- A. Albendazole
- B. Oxamniquine
- C. Niclosamide
- D. Praziquantel (Correct Answer)
- E. Bithionol
Nematodes (roundworms) Explanation: ***Praziquantel***
- **Praziquantel** is the **drug of choice** for treating trematode infections, including those caused by **Fasciolopsis buski**.
- Its mechanism of action involves increasing the permeability of the parasite's cell membrane to calcium, leading to paralysis and death of the fluke.
- It is highly effective, well-tolerated, and the standard first-line treatment.
*Albendazole*
- **Albendazole** is primarily used for various **nematode (roundworm)** infections, such as ascariasis, hookworm, and trichuriasis.
- While it has some activity against certain cestodes, it is not the first-line treatment for **Fasciolopsis buski**, a **trematode (fluke)**.
*Oxamniquine*
- **Oxamniquine** is an anthelmintic specifically used for the treatment of **schistosomiasis**, particularly against *Schistosoma mansoni*.
- It works by damaging the adult worms' teguments, but it is not effective against **Fasciolopsis buski**.
*Niclosamide*
- **Niclosamide** is an effective treatment for **cestode (tapeworm)** infections, such as *Taenia saginata* and *Hymenolepis nana*.
- Its mechanism involves inhibiting parasitic mitochondrial oxidative phosphorylation, but it is not active against **fluke** infections like **Fasciolopsis buski**.
*Bithionol*
- **Bithionol** is used primarily for treating **Fasciola hepatica** (the common liver fluke) and **Paragonimus westermani** (lung fluke) infections.
- While it has trematocidal activity, it is **not the drug of choice** for **Fasciolopsis buski**—**praziquantel** is preferred due to its superior efficacy, broader spectrum against intestinal flukes, better safety profile, and widespread availability.
Nematodes (roundworms) US Medical PG Question 3: A 30-year-old man presents to the physician after he discovered a raised, red, string-shaped lesion beneath the skin on his right foot. The lesion seems to move from one location to another over the dorsum of his foot from day to day. He says that the lesion is extremely itchy and has not responded to over the counter topical treatment. He and his wife recently returned from a honeymoon in southern Thailand, where they frequented the tropical beaches. The physician diagnoses him with a parasitic infection and prescribes albendazole for the patient. With which of the following organisms is the patient most likely infected?
- A. Ancylostoma braziliense (Correct Answer)
- B. Dracunculus medinensis
- C. Necator americanus
- D. Strongyloides stercoralis
- E. Wuchereria bancrofti
Nematodes (roundworms) Explanation: ***Ancylostoma braziliense***
- This clinical presentation of a **pruritic, migratory, serpiginous rash** on the foot after exposure to contaminated sand (tropical beach in Thailand) is classic for **cutaneous larva migrans**, caused by hookworm larvae, predominantly *Ancylostoma braziliense*.
- The larvae penetrate the skin but cannot complete their life cycle in humans, instead migrating subcutaneously, causing the characteristic **"creeping eruption"**.
*Dracunculus medinensis*
- This parasite causes **dracunculiasis**, where the adult female worm migrates to the skin, creating a painful blister, often on the lower limbs, from which it emerges.
- It is acquired by ingesting **copepods** (water fleas) containing larvae, not by direct contact with contaminated sand, and the lesion typically ulcerates rather than migrating repeatedly.
*Necator americanus*
- This is a human hookworm that causes **iron deficiency anemia** and can lead to **cutaneous larva currens** from larval penetration, which is a rapidly advancing linear lesion, but it typically progresses to systemic infection where the worms reside in the small intestine.
- While it can cause an itchy rash at the site of penetration (ground itch), it does not cause the **chronic, migratory, serpiginous eruption** characteristic of cutaneous larva migrans.
*Strongyloides stercoralis*
- This parasite can cause **larva currens** (a rapidly moving linear skin eruption) and systemic complications, particularly in immunocompromised individuals.
- While it can cause skin lesions, the typical description is of a much faster-moving lesion that usually spreads from the anus and is less serpiginous and persistent in one area compared to the classic presentation of cutaneous larva migrans.
*Wuchereria bancrofti*
- This nematode causes **lymphatic filariasis** (elephantiasis), characterized by lymphedema, hydrocele, and chyluria, and is transmitted by **mosquito bites**.
- It does not cause cutaneous migratory lesions on the foot; its pathology relates to chronic lymphatic obstruction by adult worms.
Nematodes (roundworms) US Medical PG Question 4: A 16-year-old boy is brought to the physician by his host parents for evaluation of a progressively pruritic rash over his shoulders and buttocks for the past 6 months. He recently came to the United States from Nigeria to attend a year of high school. He reports that it has been increasingly difficult for him to read the whiteboard during classes. Physical examination shows symmetrically distributed papules 4–8 mm in diameter, excoriation marks, and patchy hyperpigmentation over his shoulders, waist, and buttocks. There is nontender inguinal lymphadenopathy and several firm, nontender subcutaneous nodules along the right iliac crest. Six skin snip biopsies are taken from the pelvic girdle, buttocks, and thigh, and are then incubated in saline. After 24 hours, microscopic examination shows motile microfilariae. Which of the following is the most likely diagnosis?
- A. Cysticercosis
- B. Onchocerciasis (Correct Answer)
- C. Lymphatic filariasis
- D. Cutaneous larva migrans
- E. Trichuriasis
Nematodes (roundworms) Explanation: ***Onchocerciasis***
- The presentation of **pruritic rash with papules**, **subcutaneous nodules** (onchocercomas), and **visual difficulties** (river blindness) in an individual from an endemic area (Nigeria) is classic for **onchocerciasis**.
- The presence of **motile microfilariae in skin snips** after saline incubation is a diagnostic hallmark of this condition, caused by *Onchocerca volvulus*.
*Cysticercosis*
- This condition is caused by the larval stage of *Taenia solium* and typically presents with **calcified lesions** in the muscle and brain (neurocysticercosis), which can lead to seizures.
- It does not typically cause the generalized pruritic rash, subcutaneous nodules, or ocular symptoms described, nor would **motile microfilariae** be found in skin snips.
*Lymphatic filariasis*
- Caused by *Wuchereria bancrofti* or *Brugia malayi*, this disease is characterized by **lymphedema** and **hydrocele**, eventually leading to **elephantiasis**.
- While it involves filarial worms and can cause lymphadenopathy, it does not typically manifest with the described rash, vision problems, or **subcutaneous nodules** (onchocercomas).
*Cutaneous larva migrans*
- This condition, caused by hookworm larvae (e.g., *Ancylostoma braziliense*), presents as a **serpiginous, intensely pruritic eruption** where the larvae migrate under the skin.
- It does not cause subcutaneous nodules, generalized papular rash, or ocular involvement, and skin snips would not show **microfilariae**.
*Trichuriasis*
- Caused by the **whipworm** (*Trichuris trichiura*), this is an intestinal nematode infection that can lead to **abdominal pain**, **diarrhea**, **rectal prolapse**, and **anemia**.
- It does not present with skin lesions, subcutaneous nodules, or visual impairment, and diagnosis is typically made by finding **ova in stool samples**, not microfilariae in skin snips.
Nematodes (roundworms) US Medical PG Question 5: A 32-year-old woman presents to your office with abdominal pain and bloating over the last month. She also complains of intermittent, copious, non-bloody diarrhea over the same time. Last month, she had a cough that has since improved but has not completely resolved. She has no sick contacts and has not left the country recently. She denies any myalgias, itching, or rashes. Physical and laboratory evaluations are unremarkable. Examination of her stool reveals the causative organism. This organism is most likely transmitted to the human host through which of the following routes?
- A. Insect bite
- B. Penetration of skin (Correct Answer)
- C. Sexual contact
- D. Inhalation
- E. Animal bite
Nematodes (roundworms) Explanation: ***Penetration of skin***
- The symptoms of **abdominal pain**, **bloating**, **intermittent copious non-bloody diarrhea**, and a recent **cough** are highly suggestive of a **hookworm infection**.
- Hookworm larvae (filariform larvae) primarily penetrate the skin, usually through bare feet, as their mode of entry into the human host.
*Insect bite*
- Although some parasitic infections are transmitted by insect bites (e.g., malaria, Chagas disease), hookworms are not transmitted this way.
- **Insect-borne diseases** typically present with different clinical manifestations or geographical associations.
*Sexual contact*
- **Sexually transmitted infections** involve direct contact of mucous membranes or body fluids during sexual activity.
- Hookworm infection transmission through sexual contact is not a recognized route.
*Inhalation*
- **Inhalation** is a route of transmission for respiratory pathogens (e.g., influenza, tuberculosis) or certain fungal infections, but not for hookworms.
- While hookworm larvae migrate through the lungs, the initial infection pathway is not via inhalation.
*Animal bite*
- **Animal bites** transmit diseases like rabies or certain bacterial infections, but not parasitic hookworms.
- Hookworm infection does not result from direct contact with an animal's saliva or puncture wound.
Nematodes (roundworms) US Medical PG Question 6: A 37-year-old man makes an appointment with his primary care physician because he has been feeling tired and is no longer able to play on a recreational soccer team. He also says his coworkers have commented that he appears pale though he has not noticed any changes himself. He says that he has been generally healthy and that the only notable event that happened in the last year is that he went backpacking all over the world. Based on clinical suspicion, a series of blood tests are performed with partial results presented below:
Hemoglobin: 9.8 g/dL
Platelet count: 174,000/mm^3
Mean corpuscular volume: 72 µm^3 (normal: 80-100 µm^3)
Iron: 22 µg/dL (normal: 50-170 µg/dL)
Ferritin: 8 ng/mL (normal: 15-200 ng/mL)
Lactate dehydrogenase: 57 U/L (normal: 45-90 U/L)
Urine hemoglobin: absent
Infection with which of the following types of organisms could lead to this pattern of findings?
- A. Nematode (Correct Answer)
- B. Mosquito-borne protozoa
- C. Double-stranded virus
- D. Single-stranded virus
- E. Tick-borne protozoa
Nematodes (roundworms) Explanation: ***Nematode***
- The patient's symptoms (fatigue, pallor) and lab results (**microcytic anemia** with **low hemoglobin**, **low MCV**, **low iron**, and **low ferritin**) are highly suggestive of **iron deficiency anemia**. The history of backpacking worldwide increases the suspicion of **hookworm infection**, which is a nematode that causes chronic gastrointestinal blood loss leading to iron deficiency.
- **Hookworms** (e.g., *Ancylostoma duodenale*, *Necator americanus*) attach to the intestinal wall, causing persistent blood loss as they feed, which depletes iron stores over time.
*Mosquito-borne protozoa*
- **Mosquito-borne protozoa** primarily refers to *Plasmodium* species which cause malaria. While malaria can cause anemia, it typically presents with **hemolytic anemia** (elevated LDH, jaundice), intermittent fevers, and splenomegaly, not the profound iron deficiency seen here.
- The anemia in malaria is usually **normocytic or macrocytic** due to increased erythropoiesis, and profound iron deficiency is not the primary mechanism.
*Double-stranded virus*
- **Double-stranded viruses** (e.g., adenoviruses, herpesviruses, some papillomaviruses) typically cause acute infections, and while some can lead to anemia through bone marrow suppression or chronic inflammation, they do not directly cause **iron deficiency anemia** with this specific lab profile.
- The clinical picture of chronic fatigue and iron depletion after travel is not characteristic of common viral infections caused by double-stranded viruses.
*Single-stranded virus*
- **Single-stranded viruses** (e.g., influenza, measles, HIV, dengue, enteroviruses) cause a wide range of illnesses. While some can lead to anemia, often through **bone marrow suppression** or chronic inflammation, they are not typically associated with the profound **iron deficiency** and microcytic anemia seen in this patient.
- Travel history can be relevant for some single-stranded viral infections (e.g., HIV, dengue), but the specific laboratory findings point away from a primary viral etiology for the anemia.
*Tick-borne protozoa*
- **Tick-borne protozoa** most commonly refers to *Babesia* species, which cause babesiosis. This disease primarily leads to **hemolytic anemia** (intravascular hemolysis, elevated LDH), fever, chills, and fatigue, which is distinct from the **iron deficiency anemia** presented in the case.
- **Babesiosis** would typically present with signs of hemolysis, such as elevated LDH and sometimes hemoglobinuria, which are absent in this patient.
Nematodes (roundworms) US Medical PG Question 7: A 27-year-old male who works on an organic farm is diagnosed with infection by N. americanus, a helminthic parasite. Eosinophils require which antibody isotype to destroy these parasites via antibody-dependent cellular cytotoxicity?
- A. IgE (Correct Answer)
- B. IgA
- C. IgG
- D. IgM
- E. IgD
Nematodes (roundworms) Explanation: ***IgE***
- **IgE** antibodies are crucial in the immune response against helminthic parasites, including *N. americanus*, by sensitizing **mast cells** and **eosinophils**.
- When **IgE** binds to the surface of parasites, the **Fc receptor** on eosinophils recognizes the Fc portion of IgE, leading to the release of cytotoxic granules that destroy the parasite (antibody-dependent cellular cytotoxicity).
*IgA*
- **IgA** is primarily found in **mucosal secretions** and plays a role in defending against pathogens at mucosal surfaces, but it is not the primary isotype involved in eosinophil-mediated **ADCC** against helminths.
- While IgA can bind to some immune cells, its main function is to **neutralize toxins** and prevent microbial adhesion at mucosal sites.
*IgG*
- **IgG** is the most abundant antibody in serum and is involved in various immune functions, including **opsonization**, **neutralization**, and **complement activation**.
- Although IgG can mediate ADCC by **NK cells** and **macrophages**, it is not the primary isotype for eosinophil-mediated killing of helminths, which is dominated by IgE.
*IgM*
- **IgM** is typically the first antibody produced during a primary immune response and is very effective at **activating the complement system**.
- Its large pentameric structure also limits its diffusion into tissues, and it does not play a direct role in eosinophil-mediated ADCC against helminthic parasites.
*IgD*
- **IgD** primarily functions as a **B cell receptor** on naive B lymphocytes, signaling for their activation and differentiation.
- It is present in very low concentrations in serum and its role in host defense against parasites or in ADCC is negligible.
Nematodes (roundworms) US Medical PG Question 8: A 2-year-old girl who emigrated from Pakistan 2 weeks ago is brought to the emergency department because of lower limb weakness for one-day. One week ago, she had a 3-day episode of flu-like symptoms that resolved without treatment. She has not yet received any routine childhood vaccinations. Deep tendon reflexes are 1+ in the right lower extremity and absent in the left lower extremity. Analysis of cerebrospinal fluid shows a leukocyte count of 38 cells/mm3 (68% lymphocytes), a protein concentration of 49 mg/dL, and a glucose concentration of 60 mg/dL. Which of the following is the most likely diagnosis in this patient?
- A. Poliomyelitis (Correct Answer)
- B. Tetanus
- C. Guillain-Barre syndrome
- D. Botulism
- E. HSV encephalitis
Nematodes (roundworms) Explanation: ***Poliomyelitis***
- The patient's presentation with **acute flaccid paralysis** (lower limb weakness with absent reflexes), recent emigration from a region with potential **endemic polio** (Pakistan), and **lack of vaccination** are highly suggestive of poliomyelitis.
- The **CSF findings** (mild pleocytosis with lymphocytic predominance and normal glucose) are consistent with a viral infection of the central nervous system, which is characteristic of polio.
*Tetanus*
- Tetanus typically presents with **spastic paralysis**, muscle rigidity, and **lockjaw**, not flaccid paralysis.
- The onset of symptoms is also usually preceded by a wound contamination, which is not mentioned in this case.
*Guillain-Barre syndrome*
- While GBS can cause **flaccid paralysis** and is often preceded by a viral illness, it typically presents with **ascending paralysis** and the CSF classically shows **albumino-cytological dissociation** (high protein with normal or low cell count), which is not fully consistent with the CSF findings here.
- The rapid onset of significant asymmetry in reflexes is also less typical for GBS.
*Botulism*
- Botulism causes **descending flaccid paralysis**, often starting with cranial nerve palsies (e.g., ptosis, diplopia), and is typically associated with ingestion of contaminated food or honey in infants.
- The patient's symptoms are more focused on lower limb weakness without initial cranial nerve involvement, and the CSF findings are usually normal in botulism.
*HSV encephalitis*
- HSV encephalitis typically presents with **fever, seizures, altered mental status, and focal neurological deficits**, not primarily acute flaccid paralysis.
- While it is a viral encephalitis, the predominant symptom pattern and the specific lower limb weakness are not characteristic of HSV encephalitis.
Nematodes (roundworms) US Medical PG Question 9: A 22-year-old man comes to the physician because of abdominal pain, diarrhea, and weight loss that started after a recent backpacking trip in Southeast Asia. He does not smoke or drink alcohol. His leukocyte count is 7,500/mm3 (61% segmented neutrophils, 13% eosinophils, and 26% lymphocytes). Stool microscopy shows rhabditiform larvae. This patient is most likely to develop which of the following?
- A. Perianal serpiginous rash (Correct Answer)
- B. Hematuria
- C. Rectal prolapse
- D. Peripheral lymphedema
- E. Muscle tenderness
Nematodes (roundworms) Explanation: ***Perianal serpiginous rash***
- The patient's symptoms (abdominal pain, diarrhea, weight loss, recent travel to Southeast Asia, eosinophilia, and rhabditiform larvae in stool) are highly suggestive of **Strongyloidiasis**.
- The **rhabditiform larvae** of **Strongyloides stercoralis** can autoinfect the host, migrating through the skin from the perianal area, causing a characteristic **larva currens** or **perianal serpiginous rash**.
*Hematuria*
- **Hematuria** is typically associated with **Schistosomiasis** (especially *Schistosoma haematobium*), which involves the genitourinary tract.
- While schistosomiasis is prevalent in some parts of Southeast Asia, the patient's presentation with **rhabditiform larvae** and **eosinophilia** points away from it.
*Rectal prolapse*
- **Rectal prolapse** can occur with chronic straining due to severe diarrhea or constipation, or in conditions like **Trichuriasis (whipworm infection)**.
- While diarrhea is present, the specific finding of **rhabditiform larvae** and the high eosinophil count are not characteristic of conditions directly leading to rectal prolapse.
*Peripheral lymphedema*
- **Peripheral lymphedema** is a hallmark symptom of **Filariasis**, caused by parasitic worms like *Wuchereria bancrofti* or *Brugia malayi*, transmitted by mosquitoes.
- The patient's presentation, particularly the **rhabditiform larvae in stool**, does not support a diagnosis of filariasis.
*Muscle tenderness*
- **Muscle tenderness** and myalgia can be associated with several parasitic infections, most notably **Trichinellosis**, caused by *Trichinella spiralis*.
- However, the finding of **rhabditiform larvae in stool** and the absence of specific symptoms like periorbital edema or splinter hemorrhages make trichinellosis less likely than strongyloidiasis.
Nematodes (roundworms) US Medical PG Question 10: A 38-year-old man comes to the physician because of a 2-week history of abdominal pain and an itchy rash on his buttocks. He also has fever, nausea, and diarrhea with mucoid stools. One week ago, the patient returned from Indonesia, where he went for vacation. Physical examination shows erythematous, serpiginous lesions located in the perianal region and the posterior thighs. His leukocyte count is 9,000/mm3 with 25% eosinophils. Further evaluation is most likely to show which of the following findings?
- A. Rhabditiform larvae on stool microscopy (Correct Answer)
- B. Entamoeba histolytica antibodies on stool immunoassay
- C. Branching septate hyphae on KOH preparation
- D. Oocysts on acid-fast stool stain
- E. Giardia lamblia antibodies on stool immunoassay
Nematodes (roundworms) Explanation: ***Rhabditiform larvae on stool microscopy***
- The patient's symptoms, including **abdominal pain**, **diarrhea with mucoid stools**, **itchy rash (larva currens)**, and **eosinophilia** after traveling to Indonesia, are highly suggestive of **Strongyloidiasis**.
- **Rhabditiform larvae** are typically found in stool samples during the diagnostic phase of strongyloidiasis, as adult worms live in the small intestine and release these larvae.
*Entamoeba histolytica antibodies on stool immunoassay*
- While *Entamoeba histolytica* can cause **dysentery**, **abdominal pain**, and fever, it does not cause an **itchy migratory rash** or significant **eosinophilia**.
- Diagnosis typically involves detecting **trophozoites or cysts** in stool or specific **antigen detection**, not usually antibodies in stool.
*Branching septate hyphae on KOH preparation*
- **Branching, septate hyphae** are characteristic of **fungal infections**, such as dermatophytosis, which primarily affect the skin.
- This finding would not explain the systemic symptoms like **abdominal pain**, **diarrhea**, **fever**, and eosinophilia described in the patient.
*Oocysts on acid-fast stool stain*
- **Oocysts detected by acid-fast stain** are indicative of parasitic infections like **Cryptosporidiosis** or **Cyclosporiasis**, which cause **watery diarrhea** and abdominal cramps.
- These infections do not typically present with the **pruritic serpiginous rash** (larva currens) or the high level of **eosinophilia** seen in this patient.
*Giardia lamblia antibodies on stool immunoassay*
- *Giardia lamblia* causes **giardiasis**, characterized by **diarrhea**, **abdominal cramps**, **bloating**, and **malabsorption**.
- However, giardiasis typically does not cause **eosinophilia** or an **itchy migratory rash**, which are key features in this case.
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