Foodborne Zoonoses — MCQs

10 questions

What is the most common mode of transmission of Brucella?

Prion disease is caused by

A cook prepares sandwiches for 10 people going for a picnic. Eight out of them develop severe gastroenteritis within 4-6 hours of consuming the sandwiches. It is likely that on investigation, the cook is found to be the carrier of -

What is the most common route of transmission for Toxoplasma gondii in adults?

All of the following diseases may be acquired by ingestion except -

Kallu, a 22 year old male had an outing with his friends and developed fever of 38.50C, diarrhoea, and vomiting following eating chicken salad, 24 hours back. Two of his friends developed the same symptoms. The diagnosis is -

Which of the following statements regarding prion diseases is NOT true?

Consumption of uncooked pork is likely to cause which of the following helminthic disease -

Poliomyelitis is diagnosed by:

Q10

A patient was admitted with bloody diarrhea after consumption of oysters. The organism exhibits the Kanagawa phenomenon. What is the correct organism?

Foodborne Zoonoses Indian Medical PG Practice Questions and MCQs

Question 1: What is the most common mode of transmission of Brucella?

A. Water
B. Air
C. Aerosol
D. Milk (Correct Answer)

Explanation: ***Milk*** - **Brucellosis** is primarily a **zoonotic disease** that can be transmitted to humans through the consumption of **unpasteurized milk** and dairy products from infected animals. - The bacteria *Brucella* can survive in milk and infect individuals once ingested. *Water* - While *Brucella* can potentially contaminate water, it is not considered the primary or most common mode of transmission for brucellosis in humans. - **Ingestion of contaminated water** is a less frequent route compared to exposure through dairy products or animal contact. *Air* - **Airborne transmission** is not a typical mode for *Brucella*; the bacteria are not commonly spread through respiratory droplets in the general population. - Though *Brucella* can be aerosolized in specific laboratory or occupational settings (e.g., slaughterhouses), this is not a common community transmission route. *Aerosol* - As mentioned, **aerosol transmission** of *Brucella* mainly occurs in specific high-risk environments, such as laboratories working with concentrated cultures or close contact with infected animal tissues during veterinary procedures. - It is not a significant mode of transmission for the vast majority of human brucellosis cases.

Question 2: Prion disease is caused by

A. Denaturation of protein
B. Reduced formation of proteins
C. Misfolding of proteins (Correct Answer)
D. Excess formation of proteins

Explanation: ***Misfolding of proteins*** - Prion diseases are caused by the accumulation of abnormally **misfolded prion proteins (PrPSc)**, which convert normal cellular prion proteins (PrPC) into the harmful form. - This **conformational change** leads to the aggregation of these misfolded proteins, forming amyloid plaques that result in neurodegeneration. *Denaturation of protein* - **Denaturation** refers to the loss of a protein's tertiary and secondary structure, often caused by external stressors like heat or pH changes, but it doesn't describe the specific, self-propagating misfolding seen in prion diseases. - While misfolding involves a change in protein structure, denaturation itself is a broader term and doesn't fully capture the infectious nature of prions. *Reduced formation of proteins* - Prion diseases are generally not characterized by a **reduction in protein synthesis**; instead, they involve an alteration in the existing protein structure and its subsequent accumulation. - A decrease in protein formation would lead to different pathological outcomes, such as deficiencies or loss of function, rather than neurodegenerative plaques. *Excess formation of proteins* - Although there is an accumulation of misfolded prion proteins, the disease is not primarily caused by the **overproduction of normal prion protein (PrPC)**. - The critical event is the **conversion** of correctly folded PrPC into the misfolded PrPSc, not merely an increased quantity of the native form.

Question 3: A cook prepares sandwiches for 10 people going for a picnic. Eight out of them develop severe gastroenteritis within 4-6 hours of consuming the sandwiches. It is likely that on investigation, the cook is found to be the carrier of -

A. Salmonella typhi
B. Vibrio cholerae
C. Entamoeba histolytica
D. Staphylococcus aureus (Correct Answer)

Explanation: ***Staphylococcus aureus*** - The rapid onset of symptoms (4-6 hours) and the development of severe gastroenteritis in multiple individuals after consuming common food items (sandwiches) strongly suggest a **preformed toxin ingestion**. - **_Staphylococcus aureus_** is a common cause of food poisoning due to its ability to produce enterotoxins that are heat-stable and cause rapid onset of nausea, vomiting, and diarrhea. *Salmonella typhi* - **_Salmonella typhi_** causes typhoid fever, which typically has an incubation period of **1-3 weeks**, much longer than the 4-6 hours seen in this case. - The symptoms of typhoid fever are also more systemic, including high fever, headache, and abdominal pain, rather than acute gastroenteritis with rapid onset. *Vibrio cholerae* - **_Vibrio cholerae_** causes cholera, characterized by **profuse watery diarrhea** with a typical incubation period of **1-5 days**. - The rapid onset of symptoms in this scenario (4-6 hours) does not align with the incubation period of cholera. *Entamoeba histolytica* - **_Entamoeba histolytica_** causes amoebiasis, which has an incubation period ranging from **several days to weeks or even months**. - It typically presents with **bloody diarrhea** and abdominal pain, and its slow onset is inconsistent with the acute event described.

Question 4: What is the most common route of transmission for Toxoplasma gondii in adults?

A. Transmission through blood transfusion
B. Ingestion of undercooked meat containing tissue cysts (Correct Answer)
C. Congenital transmission from mother to fetus
D. Fecal-oral transmission via contaminated cat feces

Explanation: ***Ingestion of undercooked meat containing tissue cysts*** - Consuming **undercooked or raw meat** (especially pork and lamb) containing **tissue cysts (bradyzoites)** is the **most common route** of *Toxoplasma gondii* transmission in adults in most countries - These cysts are highly resistant and survive digestion, releasing bradyzoites that cause systemic infection - This accounts for **30-63%** of infections in various populations *Fecal-oral transmission via contaminated cat feces* - Contact with **oocysts** from cat feces (in litter boxes, contaminated soil/water) is an important route - However, it's less common than meat consumption in most developed countries - Oocysts require 1-5 days to sporulate and become infective *Transmission through blood transfusion* - **Rare route** - tachyzoites have short survival in stored blood - Modern screening practices have made this extremely uncommon - Not a significant transmission route in general populations *Congenital transmission from mother to fetus* - Occurs when **primary maternal infection** happens during pregnancy - Important clinically but represents a small proportion of total infections - Does not apply to adult acquisition of infection

Question 5: All of the following diseases may be acquired by ingestion except -

A. Leishmaniasis (Correct Answer)
B. Taeniasis
C. Guinea worm
D. Toxoplasmosis

Explanation: ***Leishmaniasis*** - Leishmaniasis is typically acquired through the bite of an infected **sandfly vector**, not by ingestion. - The parasite lives and multiplies in the sandfly's midgut and is transmitted to humans during a blood meal. *Taeniasis* - **Taeniasis** is acquired by ingesting undercooked meat containing **Taenia larvae** (cysticerci). - Humans can get infected by eating raw or undercooked beef (for *Taenia saginata*) or pork (for *Taenia solium*). *Guinea worm* - **Guinea worm disease** (*Dracunculus medinensis*) is acquired by ingesting water contaminated with water fleas (copepods) that harbor the infective larvae. - The larvae mature in the human host after ingestion of the infected water. *Toxoplasmosis* - **Toxoplasmosis** can be acquired by ingesting undercooked meat containing **Toxoplasma cysts** or by consuming food/water contaminated with cat feces (containing oocysts). - It can also be transmitted congenitally from mother to fetus.

Question 6: Kallu, a 22 year old male had an outing with his friends and developed fever of 38.50C, diarrhoea, and vomiting following eating chicken salad, 24 hours back. Two of his friends developed the same symptoms. The diagnosis is -

A. Vibrio cholerae
B. Salmonella enteritis (Correct Answer)
C. Bacillus cereus
D. S. aureus

Explanation: ***Salmonella enteritis*** - The onset of **fever**, **diarrhea**, and **vomiting** 24 hours after eating potentially contaminated chicken salad, affecting multiple individuals, is highly characteristic of **Salmonella food poisoning** [2], [4]. - **Salmonella enteritidis** is a common cause of foodborne illness associated with poultry and eggs, and causes an **invasive infection** leading to systemic symptoms like fever [2]. *Vibrio cholerae* - **Vibrio cholerae** typically causes profuse, watery diarrhea ("rice-water stools") with severe dehydration, a much shorter incubation period (hours), and less pronounced fever, if any [3]. - It is usually associated with contaminated water sources in endemic areas and not typically isolated cases from common food items like chicken salad. *Bacillus cereus* - **Bacillus cereus** can cause two types of food poisoning: diarrheal (onset 6-15 hours) and emetic (onset 1-6 hours), usually associated with **reheated rice** [1]. - While it causes vomiting and diarrhea, the 24-hour incubation period for the symptoms described makes it less likely, and fever is less prominent than with Salmonella [1], [4]. *S. aureus* - **Staphylococcus aureus** food poisoning typically has a very rapid onset (1-6 hours) after consuming food contaminated with preformed toxins [2], [4]. - Symptoms are predominantly **nausea**, **vomiting**, and abdominal cramps, with diarrhea sometimes present, but fever is uncommon or mild due to the toxin-mediated nature rather than an invasive infection [2].

Question 7: Which of the following statements regarding prion diseases is NOT true?

A. Myoclonus found only in 10% cases (Correct Answer)
B. They are caused by infectious proteins
C. Brain biopsy is diagnostic
D. Neurodegenerative disease

Explanation: ***Myoclonus found only in 10% cases*** - This statement is incorrect because **myoclonus (sudden, involuntary muscle jerks)** is a very common and prominent feature of **Creutzfeldt-Jakob disease (CJD)** and other prion diseases, occurring in more than 90% of cases as the disease progresses. - The prevalence of myoclonus is significantly higher than 10%, making this an inaccurate representation of the clinical presentation. *They are caused by infectious proteins* - This statement is true; prion diseases are unique neurodegenerative disorders caused by the misfolding and aggregation of a host-encoded protein called the **prion protein (PrP)**. - These rogue proteins, known as **prions (PrPSc)**, can induce normal PrP molecules to misfold, leading to a chain reaction of protein aggregation and neuronal damage [1]. *Brain biopsy is diagnostic* - This statement is true; **brain biopsy** and post-mortem examination are considered definitive diagnostic methods for prion diseases like CJD. - These procedures allow for the detection of **spongiform changes**, **neuronal loss**, and the presence of **PrPSc aggregates** in brain tissue [1]. *Neurodegenerative disease* - This statement is true; prion diseases are characterized by progressive **neurodegeneration**, meaning they cause irreversible damage and loss of neurons in the brain. - This leads to a decline in cognitive function, motor control, and ultimately, death.

Question 8: Consumption of uncooked pork is likely to cause which of the following helminthic disease -

A. Taenia saginata
B. Taenia solium (Correct Answer)
C. Trichuris trichiura
D. None of the options

Explanation: ***Taenia solium*** - Infection with **_Taenia solium_** (pork tapeworm) occurs by consuming raw or undercooked **pork** containing **cysticerci** (larval cysts). - This can lead to **taeniasis** (intestinal tapeworm infection) and, if humans ingest the eggs, **cysticercosis**, a more severe disease involving larval cysts in tissues like the brain. *Taenia saginata* - **_Taenia saginata_** (beef tapeworm) is acquired by eating raw or undercooked **beef** containing larval cysts, not pork. - While it causes gastrointestinal symptoms, it does not typically lead to systemic cysticercosis in humans. *Trichuris trichiura* - **_Trichuris trichiura_** (whipworm) infection is caused by ingesting **embryonated eggs** from contaminated soil, typically associated with poor sanitation. - It is not transmitted through the consumption of undercooked meat. *None of the options* - This option is incorrect because **_Taenia solium_** is definitively associated with the consumption of uncooked pork.

Question 9: Poliomyelitis is diagnosed by:

A. Clinical presentation
B. Antibody titer measurement in blood
C. Isolation of virus from blood
D. Isolation of virus from stool (Correct Answer)

Explanation: ***Isolation of virus from stool*** - Viral culture from **stool samples** is the most reliable method for diagnosing poliomyelitis, as the **poliovirus** is shed in feces for several weeks after infection. - This method confirms the presence of the live virus, which is crucial for distinguishing between active infection and prior exposure or vaccination. *Clinical presentation* - The clinical presentation of poliomyelitis, such as **flaccid paralysis**, can be similar to other neurological conditions, making it non-specific for definitive diagnosis. - A definitive diagnosis requires laboratory confirmation to differentiate it from other causes of **acute flaccid paralysis**, such as **Guillain-Barré syndrome**. *Antibody titer measurement in blood* - While antibody titers can indicate **exposure to poliovirus**, they do not differentiate between recent infection, past infection, or vaccination. - A significant rise in **antibody titers** between acute and convalescent phase samples might suggest recent infection, but it's not practical for rapid diagnosis. *Isolation of virus from blood* - **Poliovirus** is rarely isolated from the blood, as **viremia** is typically transient and occurs early in the infection before the onset of overt symptoms. - Detection of the virus in blood indicates an early stage of systemic spread but is less likely to be positive once neurological symptoms manifest.

Question 10: A patient was admitted with bloody diarrhea after consumption of oysters. The organism exhibits the Kanagawa phenomenon. What is the correct organism?

A. Staphylococcus aureus
B. Vibrio parahaemolyticus (Correct Answer)
C. Campylobacter jejuni
D. Salmonella typhi

Explanation: ***Vibrio parahaemolyticus*** - This organism is a common cause of **gastroenteritis** linked to consumption of **raw or undercooked seafood**, especially oysters, and is known for causing **bloody diarrhea**. - The **Kanagawa phenomenon** refers to the production of **thermostable direct hemolysin (TDH)** by *V. parahaemolyticus*, which is a key virulence factor causing hemolysis and is detectable by a specific agar assay. *Staphylococcus aureus* - While *S. aureus* can cause **food poisoning** through its toxins, it typically presents with **nausea, vomiting**, and **abdominal cramps**, not bloody diarrhea. - Food poisoning from *S. aureus* is usually rapid-onset (within hours) and is associated with **improperly handled foods**, particularly those requiring no cooking after preparation (e.g., salads, custards). *Campylobacter jejuni* - This bacterium is a common cause of **bacterial gastroenteritis** and can lead to **bloody diarrhea**, but it's typically acquired from **poultry** or contaminated water, not specifically oysters. - **Guillain-Barré syndrome** is a serious complication that can follow *C. jejuni* infection, which is not characteristic of *Vibrio* infections. *Salmonella typhi* - *Salmonella typhi* causes **typhoid fever**, a systemic illness characterized by **sustained fever, headache, malaise**, and can lead to a "rose spot" rash. - While it can cause gastrointestinal symptoms, **bloody diarrhea is not the predominant symptom**, and raw oyster consumption is not its typical mode of transmission; it's usually spread through contaminated food or water by asymptomatic carriers.

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