Infectious Diseases Practice Questions

Q: The infectivity of a convalescent case of cholera lasts for

7-14 days. ***7-14 days*** - The infectivity of a convalescent case of **cholera** typically lasts for **7 to 14 days** after the onset of symptoms, during which time the individual continues to shed *Vibrio cholerae* in their feces. - This is the **most common duration** of bacterial shedding in convalescent cholera patients, as documented in standard epidemiological references including Park's Textbook of Preventive and Social Medicine. - This period is critical for public health measures, as convalescent carriers can still transmit the disease, especially in areas with poor sanitation. - After appropriate antibiotic treatment, the duration may be shortened to **3-5 days**. *14-21 days* - While some individuals may continue to shed *Vibrio cholerae* for **14-21 days**, this represents an **extended or atypical duration** rather than the typical convalescent period. - This longer shedding period may occur in patients with delayed treatment or incomplete antibiotic therapy, but is not the standard expected duration. - The typical duration of infectivity is shorter, usually resolving within **2 weeks**. *Less than 7 days* - While antibiotic treatment (especially with doxycycline or azithromycin) can significantly shorten the duration of bacterial shedding to **3-5 days**, most untreated or partially treated convalescent cases continue to shed for at least a week. - This duration is **too short** to represent the typical convalescent carrier period without aggressive antimicrobial therapy. *21-28 days* - Shedding beyond **21 days** is uncommon and represents **chronic carrier status**, which is rare with cholera (unlike typhoid fever where chronic carriers are more common). - Prolonged shedding for 3-4 weeks may occur in immunocompromised individuals or those with underlying gallbladder disease, but this is not the typical pattern for convalescent cholera cases. - The vast majority of patients clear the organism within **2 weeks** of symptom onset.

Q: In Guinea worm prophylaxis, all are true, except -

Mass treatment with anti-helminthic drugs. ***Mass treatment with anti-helminthic drugs*** - Guinea worm disease (Dracunculiasis) is caused by the parasite *Dracunculus medinensis*, which is transmitted through contaminated drinking water containing **copepods (water fleas)** harboring larvae. - Unlike many other helminthic infections, Guinea worm disease **does not respond to anti-helminthic drugs** for treatment or prevention, making mass treatment ineffective. *Identification of carriers* - Identifying and containing individuals who are actively expelling worms is crucial to prevent further contamination of water sources. - This strategy focuses on interrupting the parasite's life cycle by preventing infected individuals from entering communal water bodies. *Acute search of new cases* - Active surveillance and rapid detection of new cases enable prompt intervention, such as safe containment of the emerging worm and prevention of water source contamination. - This helps in monitoring incidence and targeting interventions effectively to achieve eradication. *Health education to people to use a sieve for straining drinking water* - This is a cornerstone of Guinea worm prophylaxis, as it directly addresses the mode of transmission by filtering out the **copepods** from drinking water. - Providing **cloth filters** or using fine-mesh sieves is a simple and effective way to ensure safe drinking water and interrupt the life cycle.

Q: Which of the following is a mosquito-borne infection?

Japanese encephalitis. ***Japanese encephalitis*** * **Japanese encephalitis** is a viral disease primarily transmitted to humans through the bite of infected mosquitos, particularly those belonging to the **Culex species**. * The virus is maintained in a cycle involving mosquitos, pigs, and wading birds, with humans being **incidental hosts**. *HIV* * **HIV (Human Immunodeficiency Virus)** is primarily transmitted through direct contact with infected bodily fluids, such as during **sexual intercourse**, sharing of **contaminated needles**, and from **mother to child** during pregnancy, childbirth, or breastfeeding. * There is **no evidence** that HIV is transmitted by mosquitos or other insects, as the virus cannot replicate within the mosquito. *Plague* * **Plague** is a bacterial infection caused by *Yersinia pestis*, primarily transmitted to humans through the bite of **infected fleas** that have fed on infected rodents. * It is **not transmitted by mosquitos**; the primary vector is the flea, particularly the oriental rat flea (*Xenopsylla cheopis*). *Leprosy* * **Leprosy** is a chronic infectious disease caused by *Mycobacterium leprae*, primarily affecting the skin, peripheral nerves, upper respiratory tract, eyes, and testes. * It is believed to be transmitted via **droplets from the nose and mouth** during close and frequent contact with an untreated infected person, and **not through mosquito bites**.

Q: Urban malaria is spread by

Anopheles stephensi. ***Anopheles stephensi*** - This mosquito species is a predominant vector for **urban malaria**, particularly in India and the Middle East, due to its ability to breed in artificial containers and urban water sources. - Its presence in urban environments facilitates the transmission of malaria in densely populated areas. *Culex fatigans* - This species is better known as **Culex quinquefasciatus** and is a primary vector for **filariasis** (elephantiasis), not malaria. - It also transmits **West Nile virus** and **Japanese encephalitis**, but is not a significant vector for human malaria. *Anopheles gambiae* - This is the primary vector for malaria in **sub-Saharan Africa** due to its highly efficient transmission and opportunistic breeding habits. - While it causes significant malaria burden globally, its distribution is largely rural and sub-Saharan, not typically urban malaria in the context of the Indian subcontinent. *Anopheles culicifacies* - This species is a major vector for **rural malaria in India**, thriving in agricultural areas and fresh water collections. - It is not typically associated with the spread of malaria in densely populated urban settings, unlike *Anopheles stephensi*.

Q: The natural life cycle of the Japanese encephalitis (JE) virus occurs between which of the following?

Pigs and Mosquitoes. ***Pigs and Mosquitoes*** - The primary **enzootic cycle** of Japanese encephalitis virus (JEV) occurs between **pigs** (amplifying hosts) and **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*). - **Pigs** develop high levels of viremia (up to 10^5-10^7 infectious units/mL) without showing severe clinical signs, making them the most important **amplifying hosts**. - **Mosquitoes** acquire the virus after feeding on infected pigs and then transmit it to other pigs, humans, and incidental hosts, maintaining the transmission cycle in endemic areas. - While birds serve as **reservoir hosts**, the **pig-mosquito cycle** is the predominant pathway for viral amplification and human exposure. *Pigs and Humans* - Humans are **dead-end hosts** who typically do not develop viremia levels high enough (usually <10^5 infectious units/mL) to infect feeding mosquitoes. - There is **no direct human-to-human or pig-to-human transmission** without the mosquito vector. - The natural life cycle does not occur between pigs and humans alone. *Cattle and Birds* - **Birds** (particularly wading birds like herons and egrets) serve as **reservoir hosts** and can maintain the virus in nature, but they are not the primary amplifying hosts. - **Cattle** are generally not significant hosts or reservoirs for JEV transmission and do not develop sufficient viremia to contribute to the cycle. *Birds and Pigs* - While both birds and pigs can be infected, the transmission between them still requires a **mosquito vector** to complete the natural cycle. - The question asks about what the cycle occurs "between," which refers to the **direct transmission pair**: mosquitoes and pigs, not the broader ecological network.

Q: True regarding Japanese encephalitis is except -

Mortality is 80-90%.. ***Mortality is 80-90%.*** - The **mortality rate** for Japanese encephalitis is generally reported between **20-30%** among symptomatic cases, particularly in children. - A mortality rate of 80-90% is excessively high and **inaccurate** for Japanese encephalitis. *The iceberg phenomenon is observed.* - The **iceberg phenomenon** is characteristic of Japanese encephalitis, meaning that for every symptomatic case, there are many **asymptomatic infections** that go undetected. - Only a small proportion of infected individuals develop severe neurological disease, while the majority remain subclinical. *Human-to-human transmission is not reported.* - Japanese encephalitis is a **vector-borne disease** transmitted primarily by mosquitoes; it is **not transmitted directly** from person to person. - The virus circulates between mosquitoes, amplifying hosts (like pigs), and humans are typically dead-end hosts. *Culicine mosquitoes are zoophilic.* - **Culicine mosquitoes**, particularly *Culex tritaeniorhynchus*, are the primary vectors and are indeed **zoophilic**, meaning they prefer to feed on animals (like pigs and wading birds). - This zoophilic nature contributes to the amplification cycle of the virus in animal reservoirs before humans are incidentally bitten.

Q: Healthy carriers are not seen in

Measles virus. ***Measles virus*** - Measles infection does not typically lead to a **chronic carrier state**; individuals either recover completely or succumb to the disease. - The virus is eliminated from the host after the acute phase, and **lifelong immunity** usually develops. *Vibrio cholerae* - Individuals can be **asymptomatic carriers** and shed the bacteria in their feces, contributing to the spread of cholera. - This carrier state can persist for weeks after recovery from acute infection. *Salmonella typhi* - **Chronic carriers** of *Salmonella typhi* can excrete the bacteria for years, often harboring it in the **gallbladder**. - These carriers are a significant source of infection for others, famously exemplified by "Typhoid Mary." *Corynebacterium diphtheriae* - Asymptomatic carriers can harbor *C. diphtheriae* in their **nasopharynx** and transmit the bacteria to susceptible individuals. - This carrier state can persist for extended periods, even in the absence of overt disease symptoms.

Q: True about chicken pox -

Caused by varicella-zoster virus. ***Caused by varicella-zoster virus*** - Chickenpox, also known as varicella, is definitively caused by the **varicella-zoster virus (VZV)**, a member of the herpesvirus family. - VZV is highly contagious and responsible for both primary infection (chickenpox) and latent infection (shingles). *Rash is deep seated* - The rash of chickenpox is characteristically **superficial**, appearing as vesicles on the epidermis and upper dermis, often described as "dewdrops on a rose petal." - Deep-seated lesions are more characteristic of diseases like **smallpox**, which results in deeper scarring. *SAR is 70%* - The **secondary attack rate (SAR)** for chickenpox in susceptible household contacts is much higher than 70%, typically ranging from **80% to 90%**, highlighting its extreme contagiousness. - This high SAR means that most unvaccinated individuals living with an infected person will contract the disease. *Scab is infective* - While scabs contain the virus, the **infectivity significantly decreases** once the lesions have crusted over and formed scabs. - The most infective stages are typically from 1-2 days before the rash appears until all lesions have crusted.

Q: Mass treatment of trachoma is undertaken if the prevalence of active trachoma (TF), in children aged 1-9 years, is:

5%. ***5%*** - Mass treatment (antibiotic distribution) for trachoma is recommended when the prevalence of **TF (trachomatous inflammation—follicular)** in children aged 1-9 years is **≥5%**. - This threshold is part of the **WHO SAFE strategy** (Surgery, Antibiotics, Facial cleanliness, Environmental improvement) for trachoma elimination. - At this prevalence level, **community-wide mass drug administration (MDA)** with azithromycin is indicated. *6%* - While 6% would definitely trigger mass treatment, the **minimum threshold** established by WHO for initiating antibiotic MDA is **5%**. - This option is above the action threshold but not the specific lower limit defined in guidelines. *3%* - A prevalence of 3% is **below the WHO threshold** for implementing mass antibiotic treatment. - At this level, other components of the **SAFE strategy** (facial cleanliness, environmental improvements) are emphasized, with targeted rather than mass treatment. *10%* - A 10% prevalence is well above the required threshold and would definitely warrant mass treatment, but the question asks for the **minimum threshold**, which is **5%**. - This indicates a **high disease burden** requiring intensive intervention beyond the minimum cutoff.

Question 1

The infectivity of a convalescent case of cholera lasts for

Accepted Answer

7-14 days

Answer

14-21 days

Answer

21-28 days

Answer

Less than 7 days

Question 2

In Guinea worm prophylaxis, all are true, except -

Accepted Answer

Mass treatment with anti-helminthic drugs

Answer

Identification of carriers

Answer

Acute search of new cases

Answer

Health education to people to use a sieve for straining drinking water

Question 3

Which of the following is a mosquito-borne infection?

Accepted Answer

Japanese encephalitis

Answer

HIV

Answer

Plague

Answer

Leprosy

Question 4

Urban malaria is spread by

Accepted Answer

Anopheles stephensi

Answer

Culex fatigans

Answer

Anopheles gambiae

Answer

Anopheles culicifacies

Question 5

The natural life cycle of the Japanese encephalitis (JE) virus occurs between which of the following?

Accepted Answer

Pigs and Mosquitoes

Answer

Pigs and Humans

Answer

Cattle and Birds

Answer

Birds and Pigs

Question 6

Which of the following strategies are part of the National Leprosy Control Programme?

Accepted Answer

Early detection of cases and short course multi-drug therapy

Answer

Chemoprophylaxis with dapsone and rehabilitation

Answer

Short course multi-drug therapy and chemoprophylaxis

Answer

Rehabilitation and early detection of cases

Question 7

True regarding Japanese encephalitis is except -

Accepted Answer

Mortality is 80-90%.

Answer

The iceberg phenomenon is observed.

Answer

Human-to-human transmission is not reported.

Answer

Culicine mosquitoes are zoophilic.

Question 8

Healthy carriers are not seen in

Accepted Answer

Measles virus

Answer

Vibrio cholerae

Answer

Salmonella typhi

Answer

Corynebacterium diphtheriae

Question 9

True about chicken pox -

Accepted Answer

Caused by varicella-zoster virus

Answer

Rash is deep seated

Answer

SAR is 70%

Answer

Scab is infective

Question 10

Mass treatment of trachoma is undertaken if the prevalence of active trachoma (TF), in children aged 1-9 years, is:

Accepted Answer

5%

Answer

6%

Answer

3%

Answer

10%

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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