Parasitology Practice Questions

Q: Which of the following is NOT an intermediate host for Toxoplasma gondii?

Cat. ***Correct: Cat*** - Cats are the **definitive hosts** for *Toxoplasma gondii*, not intermediate hosts - The parasite completes its **sexual life cycle** in cat intestines and produces oocysts - Oocysts are shed in cat feces and contaminate the environment - Definitive host = where sexual reproduction occurs *Incorrect: Human* - Humans are **intermediate hosts** for *Toxoplasma gondii* - Infection occurs by ingesting oocysts (from cat feces, contaminated soil/food) or tissue cysts (from undercooked meat) - The parasite forms **tissue cysts** in muscle and brain but does NOT undergo sexual reproduction *Incorrect: Sheep* - Sheep are common **intermediate hosts** for *Toxoplasma gondii* - They become infected by ingesting oocysts from contaminated environment - The parasite forms **tissue cysts** in their meat, which can transmit infection to humans or cats if consumed *Incorrect: Pig* - Pigs are **intermediate hosts** for *Toxoplasma gondii* - Infection acquired by ingesting oocysts from the environment - Parasite forms **tissue cysts** in muscle tissue, making undercooked pork a source of human infection

Q: Which among the following statements about congenital toxoplasmosis is false?

IgG is diagnostic. ***IgG is diagnostic*** - **IgG antibodies** against *Toxoplasma gondii* cross the placenta from mother to fetus, so their presence in a neonate merely reflects maternal immunity rather than confirming congenital infection. - Therefore, the presence of IgG alone in a neonate is **NOT diagnostic** of congenital toxoplasmosis; specific tests like **IgG avidity testing** or demonstrating rising IgG titers over months are needed. - **This statement is FALSE.** *IgA is better than IgM for detection in neonates* - This statement is **TRUE** because **IgA antibodies** have superior sensitivity and specificity compared to IgM for diagnosing congenital toxoplasmosis. - IgA testing has fewer false positives and better diagnostic accuracy in neonates. - Both IgA and IgM can be used, but IgA is generally more reliable. *Congenital toxoplasmosis is diagnosed using serological tests* - This statement is **TRUE** as **serological testing** (IgM, IgA, IgG avidity) forms the cornerstone of diagnosis. - Combined with **PCR testing** of amniotic fluid or other specimens and clinical/radiological findings, serology provides crucial diagnostic information. *IgM detection in cord blood is not diagnostic* - This statement is **TRUE** because while **IgM antibodies** don't cross the placenta (making their presence suggestive of infection), they have significant limitations. - IgM can give **false positives** (rheumatoid factor, maternal blood contamination) and **false negatives** (up to 25% of infected infants may be IgM-negative at birth). - Therefore, IgM alone cannot be relied upon as a standalone diagnostic marker.

Q: Which organism is responsible for causing malignant hydatid cysts?

E. multilocularis. ***E. multilocularis*** - This species causes **alveolar echinococcosis**, characterized by the formation of **multiloculated, infiltrative cysts** that behave like a malignant tumor. - The parasitic lesions have a highly invasive nature, often spreading to adjacent tissues and forming **metastatic foci**, primarily in the liver. *Echinococcus granulosus* - This species is responsible for **cystic echinococcosis**, which typically presents as **unilocular, slow-growing cysts**. - While cysts can be large and cause significant morbidity, they are generally **well-encapsulated** and do not exhibit the same infiltrative, malignant-like growth pattern as *E. multilocularis*. *E. vogeli* - This species causes **polycystic echinococcosis**, which involves the formation of multiple, interconnected cysts, primarily in the liver, but it lacks the infiltrative and metastatic potential seen with *E. multilocularis*. - Infections are rare and typically found in Central and South America. *E. oligarthus* - This species causes **polycystic echinococcosis** similar to *E. vogeli*, but it is even rarer and primarily affects wild felids as definitive hosts. - Human infections are extremely uncommon and do not typically present with malignant-like cystic growth.

Q: Which of the following parasites passes through three hosts?

Clonorchis sinensis. ***Clonorchis sinensis*** - *Clonorchis sinensis* (the Chinese liver fluke) requires **three hosts** to complete its life cycle: a **snail** (first intermediate host), a **freshwater fish** (second intermediate host), and a **mammalian definitive host** (e.g., humans). - Humans acquire the infection by consuming undercooked infected fish, where the **metacercariae** excyst in the duodenum and migrate to the biliary ducts. *Fasciola hepatica* - *Fasciola hepatica* (the common liver fluke) is a **two-host parasite**, requiring a **snail** as the intermediate host and a **mammalian herbivore** (or human) as the definitive host. - Humans are infected by ingesting **metacercariae** on contaminated aquatic vegetation. *Fasciolopsis buski* - *Fasciolopsis buski* (the giant intestinal fluke) is a **two-host parasite**, with freshwater **snails** acting as the intermediate host and **pigs and humans** as definitive hosts. - Infection occurs when humans consume raw or undercooked aquatic plants contaminated with **metacercariae**. *Schistosoma haematobium* - *Schistosoma haematobium* (the urinary blood fluke) is a **two-host parasite**, requiring an aquatic **snail** as the intermediate host and **humans** as the definitive host. - Infection is acquired through contact with fresh water containing **cercariae**, which penetrate the skin.

Q: Which of the following organisms produces acid-fast oocysts that exhibit autofluorescence under UV light?

Cyclospora. ***Cyclospora*** - **Cyclospora cayetanensis** oocysts are **acid-fast** and exhibit characteristic **blue autofluorescence under UV light (365 nm)**, which is a distinctive diagnostic feature. - They are spherical, 8-10 µm in diameter, and contain two sporocysts (visible after sporulation). - The autofluorescence property is unique to Cyclospora and helps differentiate it from other acid-fast coccidian parasites. *Cryptosporidium* - **Cryptosporidium parvum** produces **acid-fast oocysts** (4-6 µm), but they **do not exhibit autofluorescence**. - These smaller oocysts stain uniformly with modified acid-fast stain (pink-red) but lack the UV fluorescence characteristic of Cyclospora. *Isospora* - **Isospora (Cystoisospora) belli** produces large, ellipsoidal **acid-fast oocysts** (20-30 µm), but they **do not show autofluorescence**. - Their characteristic elongated shape and larger size help differentiate them, but UV fluorescence is absent. *Giardia* - **Giardia lamblia** produces cysts that are **not acid-fast** and do not exhibit autofluorescence. - Giardia cysts are identified using iodine staining, showing their characteristic oval shape with internal nuclei and median bodies.

Q: Which of the following is the most characteristic diagnostic feature of the trophozoites of Entamoeba histolytica?

Shows erythrophagocytosis. ***Shows erythrophagocytosis*** - The presence of **engulfed red blood cells** within the cytoplasm (**erythrophagocytosis**) is the **pathognomonic and most diagnostic feature** of **Entamoeba histolytica** trophozoites. - This indicates the amoeba's invasive nature and its ability to damage host tissues, leading to symptoms like **dysentery**. - This feature distinguishes it from non-pathogenic amoebae like *E. dispar* and *E. coli*. *Has a central karyosome* - **Entamoeba histolytica** does have a **small, dot-like, centrally located karyosome** within its nucleus. - However, this feature alone is **not diagnostic** as it is shared with *E. dispar*, which is morphologically identical but non-pathogenic. - Differentiation requires molecular methods or identification of erythrophagocytosis. *Nuclear membrane with chromatin* - **Entamoeba histolytica** trophozoites do have **fine, uniform peripheral chromatin** along the nuclear membrane. - While this is a correct morphological feature, it is **not pathognomonic** and is also present in *E. dispar*. - This helps differentiate from *E. coli* (which has coarse, clumped chromatin) but not from other *Entamoeba* species. *Presence of bacteria outside the cell* - The presence of bacteria outside the cell is an **environmental factor**, not a morphological feature of the trophozoite. - **Entamoeba histolytica** rarely ingests bacteria, preferring red blood cells and host tissue. - In contrast, non-pathogenic *E. coli* commonly ingests bacteria, which can be a distinguishing feature.

Q: A 30-year-old patient presented with features of acute meningoencephalitis in the casualty. His CSF on wet mount microscopy revealed motile unicellular microorganisms. The most likely organism is:

Naegleria fowleri. ***Naegleria fowleri*** - This organism causes **primary amoebic meningoencephalitis (PAM)**, which is an acute, fulminant infection primarily in healthy individuals exposed to contaminated fresh water. - Its presence in **CSF wet mount microscopy** as **motile unicellular microorganisms** is a classic diagnostic feature. *Acanthamoeba* - This amoeba typically causes **granulomatous amoebic encephalitis (GAE)**, which is a subacute to chronic infection, often in immunocompromised individuals. - While it can be found in CSF, its presentation is less acute, and it's more commonly associated with **keratitis** in contact lens wearers. *Trypanosoma cruzi* - This protozoan causes **Chagas disease**, which can involve the central nervous system, particularly in the chronic phase. - However, it is typically diagnosed by identifying **trypomastigotes in blood smears** or tissue biopsies, not as motile unicellular organisms in CSF wet mount in acute meningoencephalitis. *Entamoeba histolytica* - This parasite causes **amoebic dysentery** and **liver abscesses**. - Central nervous system involvement is rare and usually occurs as part of disseminated disease, and the organism is typically identified via serology, stool examination, or aspiration of abscesses, not as motile forms in CSF in acute meningoencephalitis.

Q: Romana's sign is seen in infection due to:

Trypanosoma cruzi. ***Trypanosoma cruzi*** - **Romana's sign** is characteristic of the **acute phase** of **Chagas disease**, caused by *Trypanosoma cruzi*. - It presents as **unilateral periorbital edema** and swelling, indicating the site of parasite entry, often from the bite of a **reduviid bug** near the eye or by rubbing the parasite-laden feces into the eye. *Trypanosoma brucei* - This parasite causes **African trypanosomiasis** (sleeping sickness), which presents with distinct symptoms like **fever**, **headache**, **lymphadenopathy** (winterbottom's sign), and later neurological involvement [2]. - Ocular signs are not typically a primary or diagnostic feature in the way Romana's sign is for Chagas disease. *Leishmania donovani* - *Leishmania donovani* is the causative agent of **visceral leishmaniasis** (**kala-azar**), characterized by **fever**, **splenomegaly**, **hepatomegaly**, and **pancytopenia** [1]. - It does not cause Romana's sign; ocular involvement, if present, is usually different and not a hallmark diagnostic feature. *Onchocerca volvulus* - This filarial nematode causes **onchocerciasis** (river blindness), primarily associated with **subcutaneous nodules**, **dermatitis**, and **ocular lesions** leading to blindness. - While it causes eye pathology, it does not involve the specific periorbital edema known as Romana's sign.

Q: Filariasis is caused due to lymphatic obstruction by which of the following?

V. bancrofti. ***V. bancrofti*** - **Wuchereria bancrofti** is a parasitic nematode that causes **lymphatic filariasis**, leading to lymphatic obstruction. - The adult worms reside in the lymphatic vessels and disrupt normal lymphatic drainage, resulting in chronic **lymphedema** and **elephantiasis**. *P. vivax* - **Plasmodium vivax** is a species of parasite that causes **malaria**, a disease characterized by fever, chills, and anemia. - It primarily infects **red blood cells** and liver cells, and does not cause lymphatic obstruction. *C. sinensis* - **Clonorchis sinensis** is a **liver fluke** that causes **clonorchiasis**, an infection of the biliary ducts. - It leads to inflammation and fibrosis of the bile ducts and is not associated with lymphatic obstruction. *S. haematobium* - **Schistosoma haematobium** is a **blood fluke** that causes **urinary schistosomiasis**. - It infects the **bladder** and urinary tract, leading to hematuria and fibrosis, but does not cause lymphatic obstruction.

Question 1

Which of the following is NOT an intermediate host for Toxoplasma gondii?

Accepted Answer

Cat

Answer

Sheep

Answer

Human

Answer

Pig

Question 2

Which among the following statements about congenital toxoplasmosis is false?

Accepted Answer

IgG is diagnostic

Answer

Congenital toxoplasmosis is diagnosed using serological tests.

Answer

IgM detection in cord blood is not diagnostic

Answer

IgA is better than IgM for detection in neonates

Question 3

Which organism is responsible for causing malignant hydatid cysts?

Accepted Answer

E. multilocularis

Answer

Echinococcus granulosus

Answer

E. vogeli

Answer

E. oligarthus

Question 4

Diagnosis of falciparum malaria is typically made by which of the following methods?

Accepted Answer

Microscopy (blood smear examination)

Answer

pLDH (Plasmodium Lactate Dehydrogenase)

Answer

HRP II antigen detection

Answer

PCR (Polymerase Chain Reaction)

Question 5

Which of the following parasites passes through three hosts?

Accepted Answer

Clonorchis sinensis

Answer

Fasciola hepatica

Answer

Schistosoma haematobium

Answer

Fasciolopsis buski

Question 6

Which of the following organisms produces acid-fast oocysts that exhibit autofluorescence under UV light?

Accepted Answer

Cyclospora

Answer

Cryptosporidium

Answer

Isospora

Answer

Giardia

Question 7

Which of the following is the most characteristic diagnostic feature of the trophozoites of Entamoeba histolytica?

Accepted Answer

Shows erythrophagocytosis

Answer

Has a central karyosome

Answer

Nuclear membrane with chromatin

Answer

Presence of bacteria outside the cell

Question 8

A 30-year-old patient presented with features of acute meningoencephalitis in the casualty. His CSF on wet mount microscopy revealed motile unicellular microorganisms. The most likely organism is:

Accepted Answer

Naegleria fowleri

Answer

Acanthamoeba

Answer

Trypanosoma cruzi

Answer

Entamoeba histolytica

Question 9

Romana's sign is seen in infection due to:

Accepted Answer

Trypanosoma cruzi

Answer

Trypanosoma brucei

Answer

Leishmania donovani

Answer

Onchocerca volvulus

Question 10

Filariasis is caused due to lymphatic obstruction by which of the following?

Accepted Answer

V. bancrofti

Answer

C. sinensis

Answer

S. haematobium

Answer

P. vivax

Parasitology — MCQs

Parasitology — MCQs

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