Parasites/Fungi

Parasites/Fungi US Medical PG Question 1: A 22-year-old man presents with abdominal cramps and diarrhea over the last few weeks. He notes that several of his bowel movements have a small amount of blood. Past medical history is significant for an intermittent cough that has been persistent since returning from Mexico last month. The patient takes no current medications. On physical examination, there is diffuse tenderness to palpation. Which of the following medications is indicated for this patient’s condition?

• A. Pyrantel
• B. Praziquantel
• C. Albendazole
• D. Mebendazole
• E. Ivermectin (Correct Answer)

Parasites/Fungi Explanation: ***Ivermectin*** - This patient's symptoms (abdominal cramps, bloody diarrhea, persistent cough, recent travel to Mexico) are highly suggestive of **Strongyloidiasis**. **Ivermectin** is the drug of choice for this parasitic infection. - Strongyloidiasis larvae can cause a **transient cough** as they migrate through the lungs, and adult worms in the intestines lead to gastrointestinal symptoms like **diarrhea** and abdominal pain. *Pyrantel* - **Pyrantel** is primarily effective against **pinworms**, **roundworms**, and **hookworms**, but not Strongyloides. - It works by neuromuscular blockade, causing paralysis and expulsion of the worms. *Praziquantel* - **Praziquantel** is the drug of choice for treating **tapeworm** infections (e.g., Taenia species) and **schistosomiasis**. - It acts by increasing the permeability of the worm's cells to calcium, leading to paralysis and death. *Albendazole* - **Albendazole** is a broad-spectrum anthelmintic effective against many intestinal nematodes, including **hookworm**, **roundworm**, and **whipworm**, and some tissue nematodes. - While it has some activity against Strongyloides, **Ivermectin is generally preferred** due to higher efficacy and fewer side effects in many cases of strongyloidiasis. *Mebendazole* - **Mebendazole** is effective against various intestinal worms such as **pinworms**, **roundworms**, and **hookworms**. - Its mechanism of action involves inhibiting microtubule synthesis, thereby impairing glucose uptake by the worms.

Parasites/Fungi US Medical PG Question 2: A scientist in Boston is studying a new blood test to detect Ab to the parainfluenza virus with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity even greater than what she had originally hoped for. She travels to South America to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with the parainfluenza virus. The scientist tests these 1,200 patients’ blood and finds that only 120 of them tested negative with her new test. Of the following options, which describes the sensitivity of the test?

• A. 82%
• B. 86%
• C. 98%
• D. 90% (Correct Answer)
• E. 84%

Parasites/Fungi Explanation: ***90%*** - **Sensitivity** is calculated as the number of **true positives** divided by the total number of individuals with the disease (true positives + false negatives). - In this scenario, there were 1200 infected patients (total diseased), and 120 of them tested negative (false negatives). Therefore, 1200 - 120 = 1080 patients tested positive (true positives). The sensitivity is 1080 / 1200 = 0.90, or **90%**. *82%* - This value was the **original sensitivity** of the test before the scientist improved it. - The question states that the scientist believes she has achieved a sensitivity "even greater than what she had originally hoped for." *86%* - This value is not directly derivable from the given data for the new test's sensitivity. - It might represent an intermediate calculation or an incorrect interpretation of the provided numbers. *98%* - This would imply only 24 false negatives out of 1200 true disease cases, which is not the case (120 false negatives). - A sensitivity of 98% would be significantly higher than the calculated 90% and the initial stated values. *84%* - This value is not derived from the presented data regarding the new test's performance. - It could be mistaken for an attempt to add 2% to the original 82% sensitivity, but the actual data from the new test should be used.

Parasites/Fungi US Medical PG Question 3: A family doctor in a rural area is treating a patient for dyspepsia. The patient had chronic heartburn and abdominal pain for the last 2 months and peptic ulcer disease due to a suspected H. pylori infection. For reasons relating to affordability and accessibility, the doctor decides to perform a diagnostic test in the office that is less invasive and more convenient. Which of the following is the most likely test used?

• A. Steiner's stain
• B. Culture of organisms from gastric specimen
• C. Stool antigen test (Correct Answer)
• D. Detection of the breakdown products of urea in biopsy
• E. Serology (ELISA testing)

Parasites/Fungi Explanation: ***Stool antigen test*** - This **non-invasive** and **cost-effective** test detects *H. pylori* antigens in stool, making it suitable for a rural setting with limited resources. - It is highly sensitive and specific, useful for both initial diagnosis and confirming eradication after treatment. *Steiner's stain* - **Steiner's stain** (Steiner silver stain) is primarily used for histological visualization of *Legionella* species, and **not for** *H. pylori* detection in routine clinical practice. - It requires an **endoscopic biopsy**, making it more invasive and costly than the stool antigen test. *Culture of organisms from gastric specimen* - This method requires an **endoscopic biopsy** and specialized culture facilities, which may not be available in a rural doctor's office. - It is more expensive and time-consuming, and primarily used when **antibiotic resistance** is suspected. *Detection of the breakdown products of urea in biopsy* - This refers to the **rapid urease test** (e.g., CLOtest), which is performed on a **gastric biopsy** obtained during endoscopy. - While quick, it is an **invasive procedure** requiring endoscopy, which contradicts the patient's and doctor's preferences for a less invasive test. *Serology (ELISA testing)* - **Serology** detects antibodies to *H. pylori* but cannot differentiate between **active infection** and **past exposure**. - Its utility in monitoring eradication is limited, and it's generally not recommended as the primary diagnostic test due to its inability to confirm active infection.

Parasites/Fungi US Medical PG Question 4: A 45-year-old woman comes to the physician because of a 5-kg (11-lb) weight loss and difficulty swallowing. She is able to swallow liquids without difficulty but feels like solid foods get stuck in her throat. Physical examination shows taut skin and limited range of motion of the fingers. There are telangiectasias over the cheeks. An esophageal motility study shows absence of peristalsis in the lower two-thirds of the esophagus and decreased lower esophageal sphincter pressure. Further evaluation of this patient is most likely to show which of the following?

• A. Microcytic, pale red blood cells
• B. Budding yeasts on the oral mucosa
• C. Arteriolar wall thickening in the kidney (Correct Answer)
• D. Amyloid deposits in the liver
• E. Parasite nests in the myocardium

Parasites/Fungi Explanation: **Arteriolar wall thickening in the kidney** * The patient's presentation is classic for **Systemic Sclerosis (Scleroderma)**: progressive dysphagia for solids, **taut skin** (cutaneous sclerosis), sclerodactyly (limited finger motion), **telangiectasias**, and esophageal dysmotility with absent peristalsis and decreased LES pressure. * **Renal involvement** is a major systemic complication of scleroderma. **Scleroderma renal crisis** occurs in 10-15% of patients and involves proliferative vasculopathy with **arteriolar wall thickening** (particularly affecting afferent renal arterioles), leading to acute kidney injury and malignant hypertension. * This histologic finding of **arterial intimal proliferation and medial thickening** is the hallmark of scleroderma renal crisis and would be seen on kidney biopsy. *Microcytic, pale red blood cells* * This finding suggests **iron deficiency anemia** from chronic GI bleeding or malabsorption. * While patients with scleroderma can develop **esophageal dysmotility** leading to reflux and Barrett's esophagus, and intestinal involvement causing malabsorption, iron deficiency anemia is not the most direct or specific systemic complication expected with this presentation. *Budding yeasts on the oral mucosa* * This indicates **oral candidiasis (thrush)**, seen in immunosuppressed patients or those with esophageal dysmotility. * While scleroderma patients with severe esophageal dysmotility can develop candida esophagitis, oral candidiasis is not a primary systemic manifestation of the disease itself and would be secondary to esophageal stasis. *Amyloid deposits in the liver* * **Amyloidosis** involves extracellular deposition of insoluble fibrillar proteins in various organs. * The clinical presentation here (taut skin, telangiectasias, specific esophageal findings with decreased LES pressure) is characteristic of scleroderma, not amyloidosis. Amyloidosis typically presents with nephrotic syndrome, hepatomegaly, macroglossia, and cardiac involvement—different from this patient's features. *Parasite nests in the myocardium* * This describes **Chagas disease** (caused by *Trypanosoma cruzi*), which causes **megaesophagus** and cardiomyopathy. * While Chagas can cause esophageal dysmotility, it presents with **dilated esophagus** (megaesophagus) rather than the scleroderma pattern, and lacks the characteristic **skin changes** (taut skin, telangiectasias) and **decreased LES pressure** seen in this patient.

Parasites/Fungi US Medical PG Question 5: A 32-year-old man is brought to the emergency department with fever, dyspnea, and impaired consciousness. His wife reports that he has also had an episode of dark urine today. Two weeks ago, he returned from a trip to the Republic of Congo. His temperature is 39.4°C (103°F), pulse is 114/min, and blood pressure is 82/51 mm Hg. Physical examination shows scleral icterus. Decreased breath sounds and expiratory crackles are heard on auscultation of the lungs bilaterally. His hemoglobin concentration is 6.3 g/dL. A blood smear shows red blood cells with normal morphology and ring-shaped inclusions. Further laboratory testing shows normal rates of NADPH production. Which of the following is the most appropriate pharmacotherapy for this patient?

• A. Proguanil
• B. Dapsone
• C. Chloroquine
• D. Artesunate (Correct Answer)
• E. Atovaquone

Parasites/Fungi Explanation: ***Artesunate*** - This patient presents with **severe malaria**, indicated by fever, impaired consciousness, hypotension, dyspnea, dark urine (hemoglobinuria), scleral icterus (hemolysis), and anemia, following travel to an endemic area (Republic of Congo). The blood smear finding of **ring-shaped inclusions** with normal red cell morphology is characteristic of **Plasmodium falciparum** infection. - **Artesunate** is the drug of choice for **severe malaria** due to its rapid parasitic clearance and superior efficacy compared to other antimalarials, especially in regions with high chloroquine resistance, as is typical in the Republic of Congo for *P. falciparum*. *Proguanil* - Proguanil is primarily used in **malaria prophylaxis** or in combination with other drugs (e.g., atovaquone-proguanil) for uncomplicated malaria. - It is not indicated as monotherapy for **severe *P. falciparum* malaria**, nor is it suitable for emergency treatment of life-threatening infections. *Dapsone* - Dapsone is an **antibiotic** primarily used in the treatment of **leprosy** and prevention of *Pneumocystis jirovecii* pneumonia or toxoplasmosis in immunocompromised patients. - It has **no significant role** in the treatment of malaria, especially severe *P. falciparum* infection. *Chloroquine* - Chloroquine was historically a first-line treatment for malaria but is largely ineffective against **chloroquine-resistant *P. falciparum***, which is widely prevalent in the Republic of Congo and contributes to severe disease. - Administering chloroquine in this context would likely lead to **treatment failure** and worsening of the patient's severe condition. *Atovaquone* - Atovaquone, usually combined with proguanil (Malarone), is effective for **uncomplicated malaria** and prophylaxis. - However, it is **not the preferred agent for severe malaria** due to slower action and lack of intravenous formulation for initial critical management.

Parasites/Fungi US Medical PG Question 6: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

• A. "Does the diarrhea typically precede the constipation, or vice-versa?"
• B. "Is the diarrhea foul-smelling?"
• C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
• D. "Are the symptoms worse in the morning or at night?"
• E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)

Parasites/Fungi Explanation: ***Can you tell me more about the symptoms you have been experiencing?*** - This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis. - In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions. *Does the diarrhea typically precede the constipation, or vice-versa?* - While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience. - It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture. *Is the diarrhea foul-smelling?* - Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions. - However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed. *Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life* - Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time. - However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially. *Are the symptoms worse in the morning or at night?* - Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related. - This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.

Parasites/Fungi US Medical PG Question 7: A 16-year-old female presents to her pediatrician complaining of 2 weeks of fever and 1 week of swollen lumps in her left armpit. Upon examination of the left upper extremity, her physician notes the presence of a single papule which the patient claimed appeared one week ago. The patient started her first job at a pet store 2.5 weeks ago. Which of the following is the vector of transmission of the causative agent?

• A. Cats (Correct Answer)
• B. Rabbits
• C. Animal urine
• D. Parrots
• E. Armadillos

Parasites/Fungi Explanation: ***Cats*** - The combination of **fever**, **swollen lymph nodes** (lumps in the armpit), a **single papule**, and a recent history of working at a **pet store** strongly suggests **cat scratch disease**. - **Cat scratch disease** is caused by *Bartonella henselae*, which is primarily transmitted to humans through the **scratch or bite of a cat**, especially kittens. *Rabbits* - Rabbits are known vectors for diseases like **tularemia**, which can cause fever and swollen lymph nodes. - However, the typical presentation of tularemia often includes a more prominent **ulcerative lesion** at the site of inoculation, and the papule described is less characteristic. *Animal urine* - While animal urine can transmit diseases like **leptospirosis**, which can cause fever and various systemic symptoms, it typically does not present with a localized papule followed by regional lymphadenopathy in this manner. - Exposure to animal urine usually occurs through contact with contaminated water or soil, and the pet store context points more towards direct animal contact. *Parrots* - Parrots are associated with **psittacosis** (parrot fever), caused by *Chlamydia psittaci*. - Psittacosis primarily manifests as a **respiratory illness** (pneumonia) and does not typically present with a localized papule and regional lymphadenopathy. *Armadillos* - Armadillos are significant reservoirs for **Mycobacterium leprae**, the causative agent of **leprosy**. - Leprosy has a very long incubation period and presents with skin lesions, nerve damage, and sometimes lymphadenopathy, but a 2-week onset and the described acute symptoms are inconsistent with leprosy.

Parasites/Fungi US Medical PG Question 8: A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?

• A. Noninfectious inflammation of the bladder
• B. Ascending bacteria from the endocervix
• C. Decreased renal calcium reabsorption
• D. Decreased urinary pH
• E. Ascending bacteria from the bladder (Correct Answer)

Parasites/Fungi Explanation: ***Ascending bacteria from the bladder*** - The patient presents with **fever**, **nausea**, **weakness**, and **right costovertebral angle (CVA) tenderness**, which are classic symptoms of **acute pyelonephritis**. - **Pyelonephritis** most commonly results from an **ascending urinary tract infection**, where bacteria (typically *E. coli*) from the bladder travel up the ureters to infect the kidneys. - This accounts for approximately **95% of pyelonephritis cases** in young women. *Noninfectious inflammation of the bladder* - **Noninfectious cystitis** (interstitial cystitis) would not typically present with systemic symptoms like **fever** and **nausea**, or with **CVA tenderness**, which indicates kidney involvement. - Bladder inflammation typically causes dysuria and frequency without systemic signs of infection. *Ascending bacteria from the endocervix* - **Ascending bacteria from the endocervix** can cause **pelvic inflammatory disease (PID)**, which presents with lower abdominal pain, cervical motion tenderness, and vaginal discharge. - While PID can cause fever, the **normal pelvic examination** in this patient rules out this diagnosis, and PID **does not typically cause CVA tenderness**. *Decreased renal calcium reabsorption* - **Decreased renal calcium reabsorption** is associated with **hypercalciuria** and **nephrolithiasis** (kidney stones), which can present with acute flank pain if obstruction occurs. - However, this condition does not explain the **fever** and systemic symptoms characteristic of an acute infectious process. *Decreased urinary pH* - **Decreased urinary pH** (acidic urine) can predispose to certain types of kidney stone formation but is not a direct cause of **pyelonephritis**. - It does not explain the presence of **fever**, **CVA tenderness**, and systemic symptoms indicative of a bacterial kidney infection.

Parasites/Fungi US Medical PG Question 9: A 32-year-old woman comes to the emergency department with a 2-day history of abdominal pain and diarrhea. She has had about 8 voluminous stools per day, some of which were bloody. She visited an international food festival three days ago. She takes no medications. Her temperature is 39.5°C (103.1°F), pulse is 90/min, and blood pressure is 110/65 mm Hg. Examination shows a tender abdomen, increased bowel sounds, and dry mucous membranes. Microscopic examination of the stool shows polymorphonuclear leukocytes. Stool culture results are pending. Which of the following most likely caused the patient's symptoms?

• A. Home-canned vegetables
• B. Yogurt dip
• C. Reheated rice
• D. Toxic mushrooms
• E. Omelette (Correct Answer)

Parasites/Fungi Explanation: **Omelette** - The symptoms, including **bloody diarrhea**, fever, and exposure to an international food festival suggest a **bacterial infection**, likely from contaminated eggs (e.g., **Salmonella**). - The presence of **polymorphonuclear leukocytes** in the stool indicates an **invasive bacterial infection**, consistent with salmonellosis. *Home-canned vegetables* - Poorly preserved home-canned vegetables are a classic cause of **botulism**, which presents with **neurological symptoms** (e.g., flaccid paralysis) and is not characterized by bloody diarrhea or fever. - While it can cause gastrointestinal upset, bloody stools are not typical, and the primary concern is neurotoxicity due to **Clostridium botulinum toxin**. *Yogurt dip* - Yogurt is a dairy product, and contamination typically leads to **non-bloody diarrhea** and vomiting, often caused by bacteria like *Staphylococcus aureus* or *Bacillus cereus* producing enterotoxins. - The symptoms would likely be less severe and lack the invasive features (bloody stools, fever, PMNs) seen in this patient. *Reheated rice* - Reheated rice is commonly associated with **Bacillus cereus** food poisoning, which typically causes either an emetic (vomiting) or diarrheal syndrome. - The diarrhea caused by *Bacillus cereus* is usually **watery and non-bloody**, and it rarely presents with significant fever or invasive features like polymorphonuclear leukocytes in stool. *Toxic mushrooms* - Mushroom poisoning can present with a wide range of symptoms, including gastrointestinal distress (vomiting, diarrhea), but the presentation varies greatly depending on the mushroom species. - **Bloody diarrhea** with fever and polymorphonuclear leukocytes in stool is not a typical hallmark of common toxic mushroom ingestions, which often involve hepatotoxicity or neurotoxicity.

Parasites/Fungi US Medical PG Question 10: 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

Parasites/Fungi 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.

Parasites/Fungi Flashcard 1 of 10

Question: The gametocytes of Plasmodium malariae are _____ (shape)

Answer: round

Parasites/Fungi Flashcard 2 of 10

Question: _____ include Protozoa and Fungi

Answer: Eukaryotes (Prokaryotes or Eukaryotes)

Parasites/Fungi Flashcard 3 of 10

Question: Antibiotics kill vaginal microflora, allowing microbes such as _____ to flourish

Answer: Candida albicans (which fungus)

Parasites/Fungi Flashcard 4 of 10

Question: The repeating polysaccharide capsular antigens of the Cryptococci capsule are the main virulence factor of the fungus, making it _____

Answer: anti-phagocytic

Parasites/Fungi Flashcard 5 of 10

Question: Ancylostoma duodenale/Necator americanus (hookworm)

Answer:

Extra Information: intestinal infection with anemiabendazoles or pyrantel pamoatelarvae penetrate skin

Parasites/Fungi Flashcard 6 of 10

Question: Dracunulus medinensis

Answer:

Extra Information: skin inflammation and ulcerationphysical extraction of wormcontaminated water

Parasites/Fungi Flashcard 7 of 10

Question: Onchocerca volvulus

Answer:

Extra Information: river blindnessivermectinfemale blackfly bite

Parasites/Fungi Flashcard 8 of 10

Question: Loa loa

Answer:

Extra Information: worm in conjunctivadiethylcarbamazinedeer fly, horse fly, mango fly

Parasites/Fungi Flashcard 9 of 10

Question: Wuchereria bancrofti

Answer:

Extra Information: elephantiasisdiethylcarbamazinemosquito

Parasites/Fungi Flashcard 10 of 10

Question: Toxocara canis

Answer:

Extra Information: visceral larva migransalbendaole or mebendazoledogs (humans incidental host)contaminated food