Global health impact of parasitic infections US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Global health impact of parasitic infections. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Global health impact of parasitic infections US Medical PG Question 1: A 4-year-old girl presents with recurrent abdominal pain and a low-grade fever for the past 2 months. The patient’s mother says that she has lost her appetite which has caused some recent weight loss. She adds that the patient frequently plays outdoors with their pet dog. The patient is afebrile and vital signs are within normal limits. On physical examination, conjunctival pallor is present. Abdominal examination reveals a diffusely tender abdomen and significant hepatomegaly. There is also a solid mass palpable in the right upper quadrant measuring about 3 x 4 cm. Laboratory findings are significant for the following:
Hemoglobin (Hb%) 9.9 g/dL
Total count (WBC) 26,300/µL
Differential count
Neutrophils 36%
Lymphocytes 16%
Eosinophils 46%
Platelets 200,000/mm3
Erythrocyte sedimentation rate 56 mm/h
C-reactive protein 2 mg/L
Serum globulins 5 g/dL
Laparoscopic resection of the mass is performed, and a tissue sample is sent for histopathology. Which of the following is the organism most likely responsible for this patient’s condition?
- A. Ancylostoma braziliense
- B. Ascaris lumbricoides
- C. Toxocara canis (Correct Answer)
- D. Trichuris trichiura
- E. Toxocara cati
Global health impact of parasitic infections Explanation: ***Toxocara canis***
- The child's history of playing outdoors with a pet dog, **eosinophilia**, **hepatomegaly**, abdominal mass, and **elevated globulins** are highly suggestive of **visceral larva migrans (VLM)**, most commonly caused by *Toxocara canis*.
- *Toxocara canis* larvae migrate through human tissues, particularly the liver, causing granuloma formation that can present as palpable masses and systemic symptoms.
*Ancylostoma braziliense*
- This hookworm primarily causes **cutaneous larva migrans**, presenting as an intensely pruritic, serpiginous rash.
- It does not typically cause systemic symptoms like hepatomegaly, abdominal masses, or significant eosinophilia in the way described.
*Ascaris lumbricoides*
- *Ascaris lumbricoides* causes **ascariasis**, primarily manifesting as intestinal symptoms, malnutrition, or pulmonary symptoms during larval migration (Löffler syndrome)
- While it can cause eosinophilia, it rarely presents with solid hepatic masses or the specific constellation of symptoms seen here.
*Trichuris trichiura*
- *Trichuris trichiura* causes **trichuriasis** (whipworm infection), primarily leading to **gastrointestinal symptoms** such as abdominal pain, diarrhea, and rectal prolapse in heavy infections.
- It is not associated with migratory visceral larvae, hepatomegaly, or palpable liver masses.
*Toxocara cati*
- While *Toxocara cati* also causes visceral larva migrans, it is associated with **cats** rather than dogs. The patient's history specifically mentions a pet dog.
- The clinical presentation with hepatomegaly, abdominal mass, and eosinophilia would otherwise be consistent with *Toxocara* infection.
Global health impact of parasitic infections US Medical PG Question 2: An 11-year-old African American boy is brought to your office by his parents with a 1-day history of severe left hip pain. It is too painful for him to walk without support. He took ibuprofen, which brought no relief. He has had no chills or sweats. Similar painful episodes in the past required multiple hospitalizations. He returned from a trip to Kenya with his family 2 months ago. His vaccinations are up-to-date. His temperature is 38°C (100.4° F), pulse is 100/min, blood pressure is 120/80 mm Hg. Physical examination shows pale conjunctivae. The abdomen is soft with no organomegaly. Passive movement of the hip causes severe pain. There is tenderness on palpation, but no swelling, warmth, or erythema of the hip. His laboratory studies show a hematocrit of 25% and leukocyte count of 14 000/mm3. A peripheral blood smear would most likely show which of the following?
- A. Howell-Jolly bodies (Correct Answer)
- B. Decreased number of reticulocytes
- C. Trophozoites
- D. Decreased number of thrombocytes
- E. Gram-negative bacilli
Global health impact of parasitic infections Explanation: ***Howell-Jolly bodies***
- The patient's history of recurrent pain, African American ethnicity, and profound anemia (hematocrit 25%) are highly suggestive of **sickle cell disease**.
- Howell-Jolly bodies are **nuclear remnants** in red blood cells, typically removed by the spleen. Their presence indicates **functional asplenia**, which is common in sickle cell disease due to splenic auto-infarction.
*Decreased number of reticulocytes*
- This patient is experiencing a **painful vaso-occlusive crisis** and significant anemia, which usually stimulates increased erythropoiesis.
- A decreased reticulocyte count would suggest **aplastic crisis** (e.g., due to parvovirus B19), which is a possible complication but less likely the primary finding in an active crisis with marked anemia.
*Trophozoites*
- Trophozoites on a peripheral blood smear are characteristic of **malaria**, which is a consideration given his recent travel to Kenya.
- However, the history of **recurrent painful episodes** since childhood points more strongly to an underlying chronic condition like sickle cell disease, and malaria would typically present with cyclic fevers, chills, and sweats, which are absent here.
*Decreased number of thrombocytes*
- A decreased number of thrombocytes (thrombocytopenia) is not a typical finding in an uncomplicated sickle cell crisis.
- While possible in severe illness or specific complications, the presenting symptoms do not specifically point to a primary platelet disorder.
*Gram-negative bacilli*
- The presence of Gram-negative bacilli on a peripheral blood smear would indicate **bacteremia** or **sepsis**.
- While patients with sickle cell disease are at increased risk of infection, especially encapsulated bacteria due to functional asplenia, the primary diagnostic finding in the context of recurrent pain and anemia would be related to the underlying sickle cell pathology rather than an immediate infectious agent in this scenario.
Global health impact of parasitic infections US Medical PG Question 3: Three days after starting a new drug for malaria prophylaxis, a 19-year-old college student comes to the physician because of dark-colored urine and fatigue. He has not had any fever, dysuria, or abdominal pain. He has no history of serious illness. Physical examination shows scleral icterus. Laboratory studies show a hemoglobin of 9.7 g/dL and serum lactate dehydrogenase of 234 U/L. Peripheral blood smear shows poikilocytes with bite-shaped irregularities. Which of the following drugs has the patient most likely been taking?
- A. Dapsone
- B. Doxycycline
- C. Primaquine (Correct Answer)
- D. Ivermectin
- E. Pyrimethamine
Global health impact of parasitic infections Explanation: ***Primaquine***
- The patient's symptoms, including **dark urine**, **fatigue**, **scleral icterus**, **anemia** (hemoglobin 9.7 g/dL), elevated **LDH**, and **bite cells** on peripheral smear, are classic signs of **acute hemolytic anemia**.
- **Primaquine** is an antimalarial drug known to cause oxidative stress, leading to hemolysis in individuals with **glucose-6-phosphate dehydrogenase (G6PD) deficiency**. The "bite cells" are a hallmark of G6PD deficiency, as they result from the spleen removing Heinz bodies (oxidized hemoglobin).
*Dapsone*
- While **dapsone** can also cause **hemolytic anemia** in G6PD-deficient patients due to its oxidative properties, it is **not used for malaria prophylaxis**.
- Dapsone is primarily used for conditions like leprosy, dermatitis herpetiformis, and Pneumocystis pneumonia prophylaxis, making it an unlikely choice in this clinical scenario.
*Doxycycline*
- **Doxycycline** is a tetracycline antibiotic commonly used for malaria prophylaxis.
- Its common side effects include **photosensitivity**, **gastrointestinal upset**, and **esophageal irritation**, but it does not typically cause hemolytic anemia or bite cells.
*Ivermectin*
- **Ivermectin** is an antiparasitic drug used for conditions like onchocerciasis, strongyloidiasis, and scabies, but **not for malaria prophylaxis**.
- Side effects usually involve **neurological symptoms**, **skin reactions**, and **gastrointestinal disturbances**, but not hemolytic anemia.
*Pyrimethamine*
- **Pyrimethamine** is an antifolate drug used in combination with other drugs for malaria treatment and prophylaxis.
- Its primary adverse effects relate to **bone marrow suppression** (e.g., megaloblastic anemia, leukopenia), not hemolytic anemia or bite cells.
Global health impact of parasitic infections US Medical PG Question 4: 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
Global health impact of parasitic infections 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.
Global health impact of parasitic infections US Medical PG Question 5: A 31-year-old male traveler in Thailand experiences fever, headache, and excessive sweating every 48 hours. Peripheral blood smear shows trophozoites and schizonts indicative of Plasmodia infection. The patient is given chloroquine and primaquine. Primaquine targets which of the following Plasmodia forms:
- A. Schizont
- B. Hypnozoite (Correct Answer)
- C. Trophozoite
- D. Merozoite
- E. Sporozoite
Global health impact of parasitic infections Explanation: ***Hypnozoite***
- **Primaquine** is a **radical cure** for malaria caused by *Plasmodium vivax* and *Plasmodium ovale* because it targets the dormant **hypnozoite** forms in the liver.
- The presence of **hypnozoites** leads to relapses, as they can reactivate and re-initiate the erythrocytic cycle.
*Schizont*
- **Schizonts** are merozoite-producing forms in red blood cells (**erythrocytic schizonts**) or liver cells (**hepatic schizonts**).
- While chloroquine targets **erythrocytic schizonts**, primaquine's primary unique action is against the dormant liver stages.
*Trophozoite*
- **Trophozoites** are the feeding and growing stages of the parasite within red blood cells, which mature into schizonts.
- **Chloroquine** is highly effective against **erythrocytic trophozoites** and schizonts, resolving acute malarial symptoms.
*Merozoite*
- **Merozoites** are released from ruptured schizonts and infect new red blood cells during the erythrocytic cycle.
- No specific antimalarial drug solely targets **merozoites** as a primary form; they are an infective stage for red blood cells.
*Sporozoite*
- **Sporozoites** are the forms injected by infected mosquitoes, which then travel to the liver and infect hepatocytes.
- While some drugs like atovaquone have activity against sporozoites, primaquine is specifically indicated for destroying the **hypnozoite** stage, preventing relapses.
Global health impact of parasitic infections US Medical PG Question 6: A 31-year-old woman presents to your office with one week of recurrent fevers. The highest temperature she recorded was 101°F (38.3°C). She recently returned from a trip to Nigeria to visit family and recalls a painful bite on her right forearm at that time. Her medical history is significant for two malarial infections as a child. She is not taking any medications. On physical examination, her temperature is 102.2°F (39°C), blood pressure is 122/80 mmHg, pulse is 80/min, respirations are 18/min, and pulse oximetry is 99% on room air. She has bilateral cervical lymphadenopathy and a visible, enlarged, mobile posterior cervical node. Cardiopulmonary and abdominal examinations are unremarkable. She has an erythematous induration on her right forearm. The most likely cause of this patient's symptoms can be treated with which of the following medications?
- A. Sulfadiazine and pyrimethamine
- B. Atovaquone and azithromycin
- C. Primaquine
- D. Chloroquine
- E. Fexinidazole (Correct Answer)
Global health impact of parasitic infections Explanation: ***Fexinidazole***
- This patient's symptoms (recurrent fevers, cervical lymphadenopathy, erythematous induration after a trip to Nigeria with a painful bite) are highly suggestive of **African trypanosomiasis (sleeping sickness)**.
- **Fexinidazole** is an oral nitroimidazole derivative approved for treating both first and second-stage human African trypanosomiasis (HAT) caused by *Trypanosoma brucei gambiense*.
*Sulfadiazine and pyrimethamine*
- This combination is primarily used to treat **toxoplasmosis**, an infection caused by the parasite *Toxoplasma gondii*.
- While it can cause fever and lymphadenopathy, the travel history to Nigeria and a "painful bite" are not typical for toxoplasmosis transmission.
*Atovaquone and azithromycin*
- This combination is utilized for treating **Babesiosis**, a tick-borne parasitic infection.
- While Babesiosis can cause fever and fatigue, the characteristic erythematous induration and prominent lymphadenopathy point away from this diagnosis.
*Primaquine*
- **Primaquine** is an antimalarial drug specifically used for the **radical cure of *Plasmodium vivax*** and ***Plasmodium ovale*** malaria, targeting the hypnozoite liver stages.
- Although the patient has a history of malaria and a travel history to an endemic area, the current presentation with distinct lymphadenopathy and skin lesion points away from a straightforward malarial relapse or new infection primarily requiring primaquine as the sole treatment.
*Chloroquine*
- **Chloroquine** is an antimalarial drug, but its use is limited primarily to areas where **chloroquine-sensitive *Plasmodium falciparum*** strains are prevalent.
- While the patient traveled to Nigeria, a region where malaria is endemic, the specific constellation of symptoms, including the bite and lymphadenopathy, is less characteristic of typical malaria than of trypanosomiasis.
Global health impact of parasitic infections US Medical PG Question 7: 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
Global health impact of parasitic infections 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.
Global health impact of parasitic infections US Medical PG Question 8: 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
Global health impact of parasitic infections 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.
Global health impact of parasitic infections US Medical PG Question 9: 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
Global health impact of parasitic infections 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.
Global health impact of parasitic infections US Medical PG Question 10: A 31-year-old man comes to the physician because of severe muscle pain and fever for 4 days. He likes to go hunting and consumed bear meat 1 month ago. Examination shows periorbital edema and generalized muscle tenderness. His leukocyte count is 12,000/mm3 with 19% eosinophils. The release of major basic protein in response to this patient’s infection is most likely a result of which of the following?
- A. Increased expression of MHC class II molecules
- B. Interaction between Th1 cells and macrophages
- C. Antibody-dependent cell-mediated cytotoxicity (Correct Answer)
- D. Increased expression of MHC class I molecules
- E. Immune complex-dependent complement activation
Global health impact of parasitic infections Explanation: ***Antibody-dependent cell-mediated cytotoxicity***
- The patient's symptoms (fever, muscle pain, periorbital edema, eosinophilia) after consuming undercooked bear meat are highly suggestive of **trichinellosis**, a parasitic infection.
- **Eosinophils** are crucial in the immune response against parasites. They release cytotoxic substances like **major basic protein** through antibody-dependent cell-mediated cytotoxicity (ADCC), where antibodies (IgE or IgG) bind to the parasite, and eosinophils then bind to the Fc region of these antibodies to mediate parasite killing.
*Increased expression of MHC class II molecules*
- **MHC class II molecules** are primarily expressed on antigen-presenting cells (APCs) and are involved in presenting extracellular antigens to **CD4+ T cells**, initiating a helper T cell response.
- While important for activating the immune system, increased MHC class II expression doesn't directly explain the release of major basic protein by eosinophils in response to parasitic infection.
*Interaction between Th1 cells and macrophages*
- **Th1 cells** primarily activate **macrophages** to kill intracellular pathogens and are involved in cell-mediated immunity.
- This pathway is less prominent in directly killing large extracellular parasites like *Trichinella*, where eosinophil-mediated ADCC is key.
*Increased expression of MHC class I molecules*
- **MHC class I molecules** are expressed on almost all nucleated cells and present endogenous antigens to **CD8+ cytotoxic T cells**, primarily targeting intracellular viral infections and tumor cells.
- This mechanism is not directly involved in the eosinophil effector function against extracellular parasitic infections.
*Immune complex-dependent complement activation*
- **Immune complexes** (antigen-antibody complexes) can activate the complement system, leading to immune complex-mediated tissue damage or pathogen clearance.
- While complement can be involved in parasitic infections, it does not directly lead to the release of **major basic protein** by eosinophils, which is a specific cytotoxic mechanism.
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