Parasitology Practice Questions

Q: Which among the following parasites directly invade the skin?

Schistosoma mansoni. ***Schistosoma mansoni***- The infectious stage, the **cercariae**, actively penetrate the intact skin of the human host when swimming or wading in contaminated water. - This stage bypasses the need for an insect vector and directly initiates infection, often causing **'swimmer's itch'** at the site of entry.*Dracunculus medinensis*- This infection is acquired by the oral route through ingestion of **copepods** (water fleas) containing the larval stage in drinking water.- While the mature female worm creates a painful **blister** to exit the skin, it does not invade the skin to initiate the infection.*Wuchereria bancrofti*- This parasite is transmitted by the bite of an **infected mosquito** (e.g., *Culex*), which deposits infective larvae near the bite site.- The larvae enter the host through the **puncture wound** created by the mosquito bite, not by actively penetrating intact dermal layers.*Onchocerca volvulus*- The transmission involves the bite of an infected **blackfly** (*Simulium* species), which transmits the infective larvae (microfilariae) into the host.- The larvae enter through the **wound site** created by the fly bite and subsequent manipulation of the wound by the vector (not direct skin invasion).

Q: Choose the organisms that have two morphological forms: 1. Acanthamoeba 2. Naegleria 3. Giardia 4. Trichomonas

1, 3 are correct. ***1, 3 are correct*** - **Acanthamoeba** has exactly **two morphological forms**: the **trophozoite** (active, feeding form) and the **cyst** (dormant, resistant form). The cyst form allows survival in adverse environmental conditions. - **Giardia lamblia** also has exactly **two forms**: the **trophozoite** (flagellated, binucleate form that colonizes the small intestine) and the **cyst** (quadrinucleate, infectious form passed in feces). - Both organisms strictly exhibit a **two-stage life cycle** with trophozoite and cyst stages only. *Incorrect: 1, 2 are correct* - While **Acanthamoeba** does have two forms, **Naegleria fowleri** has **THREE morphological forms**: amoeboid trophozoite, temporary flagellate form, and cyst. - The flagellate form of Naegleria is a distinctive third morphological stage that appears under certain environmental conditions (e.g., distilled water). - Therefore, Naegleria does **not** meet the criteria of having exactly two forms. *Incorrect: 1, 2, 3, 4 are correct* - **Trichomonas vaginalis** exists **only as a trophozoite** and has **no cyst stage**, making it a single-form organism. - The absence of a cyst form in Trichomonas explains why it requires direct transmission (sexual contact) and cannot survive long outside the host. - This option incorrectly includes both Naegleria (three forms) and Trichomonas (one form). *Incorrect: 1, 4 are correct* - **Trichomonas vaginalis** lacks a cyst stage entirely, existing only as a motile trophozoite with four anterior flagella and an undulating membrane. - This makes Trichomonas unsuitable for the answer as it does not have two morphological forms.

Q: A child presents with anal pruritus. Microscopy of the stool sample reveals a plano-convex egg. Identify the pathogen.

Enterobius. ***Enterobius*** - **_Enterobius vermicularis_** (pinworm) is the classic cause of **perianal pruritus** (anal itching), especially at night, which is a hallmark symptom in children. - The eggs are characteristically **plano-convex** (flattened on one side) or D-shaped, matching the description in the question. Diagnosis is typically confirmed with the **Graham sticky tape test**. ***Trichuris*** - The eggs of **_Trichuris trichiura_** (whipworm) are **barrel-shaped** with prominent **polar plugs** at each end, which does not match the description. - Heavy infections can lead to **rectal prolapse**, abdominal pain, and dysentery, but not typically isolated anal pruritus. ***Ascaris*** - **_Ascaris lumbricoides_** eggs are either corticated (with a bumpy, mamillated outer layer) or decorticated (smooth), but they are round-to-oval, not plano-convex. - Clinical features include **pneumonitis** during larval migration (**Loeffler's syndrome**) and potential **intestinal or biliary obstruction** in heavy infections. ***Ancylostoma*** - The eggs of **_Ancylostoma duodenale_** (hookworm) are oval with a thin, smooth shell, containing a developing embryo (blastomeres), which is morphologically distinct. - Hookworm infection is a major cause of **iron deficiency anemia** due to chronic blood loss from the intestine.

Q: Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - This parasite is unique among helminths for its ability to cause **autoinfection with hyperinfection syndrome**, a potentially life-threatening condition. - The **rhabditiform larvae** can accelerate development directly into invasive **filariform larvae** within the host's large intestine. - This transformation allows the infectious filariform larvae to penetrate the intestinal mucosa or perianal skin, leading to persistent infection and potentially fatal **hyperinfection syndrome** in immunocompromised hosts. - This makes *S. stercoralis* the most clinically significant parasite causing autoinfection. *Incorrect: Ancylostoma duodenale* - This hookworm does not cause autoinfection, as its eggs must exit the host and mature in the soil to form infectious **filariform larvae**. - Infection occurs through **percutaneous penetration** (skin penetration) by larvae from the external environment. *Incorrect: Ascaris lumbricoides* - This large roundworm requires an environmental phase where unembryonated eggs mature in the soil before becoming infectious upon ingestion (**fecal-oral route**). - Its life cycle involves migration through the lungs (pulmonary phase), but it lacks the mechanism for internal autoinfection. *Incorrect: Hymenolepis nana* - *H. nana* (dwarf tapeworm) is capable of internal autoinfection where eggs hatch within the intestinal lumen and **oncospheres** invade the villi directly. - However, it does **not** cause hyperinfection syndrome like *S. stercoralis*, making it clinically less significant in this context. - The question specifically asks about autoinfection leading to hyperinfection syndrome, which is unique to *Strongyloides stercoralis*.

Q: A middle-aged man from an endemic region presents with progressive swelling of the lower limb. A peripheral blood smear shows the following structure. What is the most likely cause of his limb swelling?

Lymphatic obstruction. ***Lymphatic obstruction*** - The image displays **microfilariae** (suggesting **Lymphatic Filariasis**), where the adult worms settle in the lymphatics, physically blocking flow. - This obstruction results in chronic, progressive edema (known as **lymphedema** or **elephantiasis**) due to the failure of lymphatic drainage in the affected limb. *Hypoalbuminemia* - Edema from **hypoalbuminemia** is due to low plasma oncotic pressure and typically results in generalized, pitting edema, which is not characteristic of chronic, localized filarial swelling. - While malnutrition might co-exist, the core pathology shown by the presence of **microfilariae** points specifically to mechanical lymphatic blockage. *Hypoproteinemia* - **Hypoproteinemia** is a general cause of edema via reduced **oncotic pressure**, leading to fluid shift into the interstitial spaces, usually causing generalized rather than localized swelling. - This systemic cause does not account for the specific parasitic damage to the lymphatics demonstrated by the presence of the **filarial worms**. *increased hydrostatic pressure* - Increased hydrostatic pressure (e.g., in conditions like DVT or CHF) leads to fluid leakage from capillaries, causing pitting edema. - The root cause here is the parasitic **destruction and obstruction of lymph nodes and channels**, which specifically impairs lymph return, not capillary hydrostatic pressure regulation.

Q: A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Enterobius vermicularis. ***Enterobius vermicularis*** - The clinical presentation of **nocturnal perianal itching** (pruritus ani) in a child is highly characteristic of **pinworm infection** (enterobiasis). - The image shows a classic **D-shaped** or planoconvex egg, frequently found on the **adhesive tape test**, which are key identifiers for *Enterobius vermicularis*. *Ancylostoma duodenale* - This parasite causes **hookworm disease**, typically manifesting as **iron-deficiency anemia** and rarely perianal itching. - *Ancylostoma* eggs are oval, thin-shelled, and typically found in the **stool**, not via a tape test. *Hymenolepis nana* - This is the **dwarf tapeworm**, which usually causes mild or asymptomatic infection, though heavy infections can cause abdominal discomfort. - The eggs are small, oval, and possess **polar filaments** between the shell and the oncosphere, which are absent in the image. *Trichuris trichiura* - This parasite, the **whipworm**, causes trichuriasis, which presents with bloody diarrhea and occasionally **rectal prolapse** in heavy infections. - *Trichuris* eggs are distinctively **barrel-shaped** with two prominent bipolar mucoid plugs at each end.

Q: The given image shows:

Spaghetti plot. ***Spaghetti plot*** - A **spaghetti plot** displays multiple overlapping individual trajectory lines, with each line representing one subject's data over time or across conditions, creating a visual that resembles **strands of spaghetti**. - It is commonly used in **longitudinal studies** to show individual patient responses or changes, allowing visualization of both individual patterns and overall trends. *Kaplan Meier plot* - A Kaplan-Meier plot is a **survival curve** that shows the probability of survival over time with characteristic **step-wise decreases** at each event occurrence. - It is specifically used for **time-to-event analysis** and does not show multiple individual trajectory lines like a spaghetti plot. *Funnel plot* - A funnel plot is used in **meta-analyses** to assess **publication bias** by plotting study effect sizes against their precision (standard error). - It creates a **symmetrical funnel shape** when no bias is present and does not show individual subject trajectories over time. *Forest plot* - A forest plot is used in **meta-analyses** to display individual study results and **pooled effect estimates** with confidence intervals. - It features **squares or diamonds** representing effect sizes with **horizontal lines** for confidence intervals, not overlapping trajectory lines.

Q: The larva shown belongs to which mosquito?

Anopheles. ***Anopheles*** - The larva is characterized by its **orientation parallel to the water surface**, due to the absence of a long breathing siphon. - Presence of **palmate hairs** on the thorax and abdomen helps in flotation at the water surface. *Culex* - The larva of *Culex* mosquitoes typically has a **long, slender breathing siphon** and hangs downwards from the water surface at an angle. - It does not possess the prominent palmate hairs seen in *Anopheles* for surface flotation. *Mansonia* - *Mansonia* larvae are unique because they have a **modified siphon adapted for piercing aquatic plant stems** to obtain oxygen, rather than breathing directly from the surface. - Consequently, they are typically found attached to submerged vegetation and do not float at the water surface. *Aedes* - Similar to *Culex*, *Aedes* larvae possess a **siphon for breathing**, causing them to hang downward from the water surface. - However, the siphon of *Aedes* is generally **shorter and stouter** than that of *Culex*, and they also lack palmate hairs for surface flotation.

Q: The following diagram depicts blood smear of which species?

Plasmodium falciparum. ***Plasmodium falciparum*** - The image displays characteristic **crescent-shaped or banana-shaped gametocytes** (stages 16-20), which are **pathognomonic for *Plasmodium falciparum*** - The earlier stages (1-5) represent ring forms (multiple rings per RBC, delicate ring forms) - Subsequent stages (6-15) show maturation culminating in the distinct **crescentic gametocytes** - This morphology is the **key distinguishing feature** of P. falciparum *Plasmodium vivax* - Produces **oval-shaped gametocytes**, not crescent-shaped - Characterized by enlarged RBCs with **Schüffner's dots** - Shows amoeboid trophozoites, not seen in this smear *Plasmodium malariae* - Produces **oval to round gametocytes** - Characteristic **band forms** and **rosette-shaped schizonts** (8-12 merozoites) - Not crescent-shaped as shown in the image *Plasmodium ovale* - Produces **oval gametocytes** similar to P. vivax - RBCs show **fimbriated edges** and Schüffner's dots - Does not produce crescent-shaped gametocytes

Q: A 20-year-old lady presents with high grade fever and incoherent talking for 1 day. The following peripheral smear shows presence of:

Gametocyte. ***Gametocyte*** - The image clearly shows a **crescent-shaped** parasite within a red blood cell, which is characteristic of the **gametocytes of *Plasmodium falciparum***. - The patient's symptoms of **high-grade fever** and **non-coherent talking** (suggesting cerebral malaria) are consistent with severe *P. falciparum* infection, where gametocytes are often seen on peripheral smears. *Sporozoite* - Sporozoites are the **infectious forms of malaria parasites** transmitted from the mosquito to humans; they are typically found in the **salivary glands of mosquitoes** and briefly in human blood before infecting liver cells. - They are generally **not observed in peripheral blood smears** during the symptomatic phase of malaria. *Merozoite* - Merozoites are the forms that emerge from **infected liver cells** and then subsequently from **infected red blood cells** to invade new red blood cells, thus perpetuating the asexual cycle. - They are very **short-lived extracellularly** and are rarely seen in peripheral blood smears; instead, **ring forms, trophozoites, and schizonts** (representing asexual stages) are typically observed inside red blood cells. *Schistocyte* - Schistocytes are **fragmented red blood cells** that result from **mechanical damage** to red blood cells, often seen in conditions like microangiopathic hemolytic anemia or disseminated intravascular coagulation. - They are not a life stage of the malaria parasite; their presence would indicate a co-existing or secondary hematological issue, not a parasitic form.

Question 1

Which among the following parasites directly invade the skin?

Accepted Answer

Schistosoma mansoni

Answer

Wuchereria bancrofti

Answer

Onchocerca volvulus

Answer

Dracunculus medinensis

Question 2

Choose the organisms that have two morphological forms: 1. Acanthamoeba 2. Naegleria 3. Giardia 4. Trichomonas

Accepted Answer

1, 3 are correct

Answer

1, 2, 3, 4 are correct

Answer

1, 4 are correct

Answer

1, 2 are correct

Question 3

A child presents with anal pruritus. Microscopy of the stool sample reveals a plano-convex egg. Identify the pathogen.

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichuris

Answer

Ancylostoma

Question 4

Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Ancylostoma duodenale

Answer

Hymenolepis nana

Question 5

A middle-aged man from an endemic region presents with progressive swelling of the lower limb. A peripheral blood smear shows the following structure. What is the most likely cause of his limb swelling?

Accepted Answer

Lymphatic obstruction

Answer

Hypoalbuminemia

Answer

Hypoproteinemia

Answer

Increased hydrostatic pressure

Question 6

A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Accepted Answer

Enterobius vermicularis

Answer

Hymenolepis nana

Answer

Trichuris trichiura

Answer

Ancylostoma duodenale

Question 7

The given image shows:

Accepted Answer

Spaghetti plot

Answer

Kaplan Meier plot

Answer

Funnel plot

Answer

Forest plot

Question 8

The larva shown belongs to which mosquito?

Accepted Answer

Anopheles

Answer

Culex

Answer

Mansonia

Answer

Aedes

Question 9

The following diagram depicts blood smear of which species?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Answer

Plasmodium vivax

Question 10

A 20-year-old lady presents with high grade fever and incoherent talking for 1 day. The following peripheral smear shows presence of:

Accepted Answer

Gametocyte

Answer

Sporozoite

Answer

Merozoite

Answer

Schistocyte

Parasitology — MCQs

Parasitology — MCQs

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