Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 591: Vector for transmission of sleeping sickness?

A. Sandfly
B. Black fly
C. Tse-tse fly (Correct Answer)
D. Hard tick

Explanation: ***Tse-tse fly*** - The **tsetse fly** (genus *Glossina*) is the exclusive biological vector for the transmission of **African trypanosomiasis**, also known as sleeping sickness. - The fly transmits the parasites (*Trypanosoma brucei*) to humans through its bite after becoming infected by feeding on an infected host. *Sandfly* - **Sandflies** (family Psychodidae) are vectors for diseases such as **leishmaniasis** and **Bartonellosis** (Carrion's disease), but not sleeping sickness. - They are typically smaller than tsetse flies and have distinct hairy bodies and wings. *Black fly* - **Black flies** (family Simuliidae) are vectors for **onchocerciasis** (river blindness), caused by the *Onchocerca volvulus* parasite. - They are characterized by their hump-backed appearance and prefer to breed in fast-flowing rivers. *Hard tick* - **Hard ticks** (family Ixodidae) are vectors for a variety of diseases, including **Lyme disease**, **Rocky Mountain spotted fever**, and **Crimean-Congo hemorrhagic fever**. - They are arachnids, not insects, and transmit pathogens through prolonged feeding.

Question 592: What is the PRIMARY indication for cholera vaccination according to WHO recommendations?

A. To control cholera outbreaks
B. For travelers to endemic regions
C. For individuals in endemic areas (Correct Answer)
D. For neonates at risk

Explanation: ***For individuals in endemic areas*** - **Cholera vaccination** is PRIMARY recommended by WHO for populations living in cholera-endemic areas as part of a comprehensive cholera prevention and control strategy. - This is the **most important indication** as it protects vulnerable populations with sustained high-risk exposure and can reduce disease burden in settings where cholera is a persistent public health problem. - WHO emphasizes integration with water, sanitation, and hygiene (WASH) improvements for maximum impact. *To control cholera outbreaks* - While cholera vaccination **can be used** during outbreaks (reactive vaccination), this is a secondary strategy. - The **primary outbreak control measures** remain: rapid case management, WASH interventions, surveillance, and contact tracing. - Vaccination during outbreaks faces logistical challenges and delayed protection (requires 2 doses, immunity takes time to develop). *For travelers to endemic regions* - Cholera vaccination **is recommended** for certain travelers to endemic areas, especially those with limited access to safe water/food. - However, this represents a **much smaller target population** compared to endemic area residents and is not the primary public health indication. - Most travelers have lower risk than residents and can protect themselves through food/water precautions. *For neonates at risk* - **Cholera vaccines are NOT recommended** for neonates (infants under 28 days). - Current oral cholera vaccines are only approved for children ≥1 year of age (varies by vaccine type). - Neonates have low cholera risk and are protected by maternal antibodies and caregiver hygiene practices.

Question 593: According to RNTCP guidelines, what should be done first in a TB suspect case?

A. Chest X-ray
B. Sputum culture
C. Sputum microscopy (Correct Answer)
D. Start short-course chemotherapy

Explanation: ***Sputum microscopy*** - Under the Revised National Tuberculosis Control Programme (RNTCP) guidelines, **sputum smear microscopy** is the initial and primary diagnostic tool for identifying pulmonary TB in suspect cases. - It is a **cost-effective and rapid method** for detecting **acid-fast bacilli (AFB)** directly from sputum samples. *Chest X-ray* - While a Chest X-ray can show abnormalities consistent with TB, it is often used as a **supplementary diagnostic tool** after initial sputum tests. - It is **less specific** than sputum microscopy for confirming active TB and requires further confirmation with microbiological tests. *Sputum culture* - Sputum culture is a **more sensitive diagnostic method** for TB compared to microscopy, but it takes **several weeks** for results. - It is typically used when smear microscopy results are negative but there is a strong clinical suspicion of TB, or for **drug susceptibility testing**. *Start short-course chemotherapy* - Initiating short-course chemotherapy **without confirming the diagnosis** is not recommended and can lead to antibiotic resistance and inappropriate treatment. - Treatment should only be started after a **confirmed diagnosis** of active TB through microbiological tests like sputum microscopy or culture.

Question 594: What is the primary causative vector of Vagabond disease?

A. Louse (Correct Answer)
B. Mite
C. Tick
D. Black Fly

Explanation: ***Louse*** - Vagabond disease is a term historically used to describe the chronic skin changes (such as **pigmentation**, **lichenification**, and **excoriations**) resulting from persistent **pediculosis corporis** (body lice infestation). - The **body louse** (*Pediculus humanus corporis*) is the causative agent responsible for these chronic dermatological changes through prolonged infestation. - Body lice are also vectors that can transmit other diseases like **epidemic typhus**, **louse-borne relapsing fever**, and **trench fever**, but vagabond disease itself is the direct result of chronic louse infestation rather than a transmitted pathogen. *Mite* - Mites are responsible for various conditions, such as **scabies** (caused by *Sarcoptes scabiei*) and serve as vectors for **scrub typhus** (transmitted by chiggers, the larval form of trombiculid mites). - However, they are not associated with vagabond disease or the chronic dermatological changes caused by body lice. *Tick* - Ticks are known vectors for a wide range of diseases, including **Lyme disease**, **Rocky Mountain spotted fever**, **anaplasmosis**, and **babesiosis**. - These diseases are transmitted through the bite of infected ticks, which are distinct from the louse-related conditions associated with vagabond disease. *Black Fly* - Black flies (*Simulium* species) are vectors for **onchocerciasis** (river blindness), caused by the parasitic nematode *Onchocerca volvulus*. - While they can cause itchy bites and transmit significant disease, they are not involved in the chronic skin condition known as vagabond disease.

Question 595: Which of the following is not a notifiable disease to the WHO?

A. Yellow fever
B. Cholera
C. Plague
D. Tuberculosis (Correct Answer)

Explanation: ***Tuberculosis*** - While a globally significant public health concern, **tuberculosis** is not one of the **three diseases** that were traditionally notifiable under the **International Health Regulations (IHR)**. - Under the **IHR 1969**, only **Cholera, Plague, and Yellow Fever** were designated as quarantinable diseases requiring mandatory notification to WHO. - The current **IHR 2005** uses a different algorithm-based approach, but TB remains outside the list of diseases requiring automatic notification. - TB reporting occurs primarily through national surveillance systems and WHO's Global TB Programme rather than as an IHR-mandated immediate alert. *Cholera* - **Cholera** was one of the **three quarantinable diseases** under the **IHR 1969** requiring mandatory notification to WHO. - Its potential for rapid international spread and epidemic potential necessitated immediate reporting for global public health security. *Plague* - **Plague** was also among the **three quarantinable diseases** under the **IHR 1969** requiring mandatory notification to WHO. - Its historical impact as a cause of devastating pandemics and potential for severe outbreaks made early detection and reporting crucial. *Yellow fever* - **Yellow fever** was the third disease on the list of **quarantinable infections** under the **IHR 1969** requiring mandatory notification to WHO. - Rapid reporting was vital due to its epidemic potential and the need for vaccination and vector control measures.

Question 596: Which virus is not sensitive to disinfection by chlorination?

A. Rotavirus
B. Norwalk virus (Correct Answer)
C. None of the options
D. Poliovirus

Explanation: ***Norwalk virus (Norovirus)*** - **Norovirus** is notably **resistant to standard chlorination** at typical water treatment concentrations. - Its **non-enveloped structure** and **small size** make it more resistant to chemical disinfection compared to many other enteric viruses. - The virus has an **extremely low infectious dose** (as few as 10-100 viral particles), meaning even minimal survival after chlorination can cause outbreaks. - **Higher chlorine concentrations** (>10 mg/L) and **longer contact times** are often required for effective inactivation. *Poliovirus* - Poliovirus is generally **susceptible to chlorination** when proper free chlorine residuals (0.5 mg/L) and contact time (30 minutes) are maintained. - While it is non-enveloped and somewhat robust, standard water treatment chlorination protocols effectively inactivate poliovirus. - Historical **polio eradication efforts** have successfully used chlorination as part of water safety measures. *Rotavirus* - **Rotavirus** is **susceptible to inactivation by adequate chlorination** at concentrations typically used in water treatment. - It is effectively controlled through optimized disinfection protocols in municipal water systems. - While it causes gastroenteritis, proper chlorination significantly reduces transmission through water. *None of the options* - This option is incorrect because **Norwalk virus (Norovirus)** is indeed known to be **resistant to standard chlorination**, making it the most appropriate answer among the choices provided. - Among enteric viruses, Norovirus shows notable resistance to chlorine disinfection compared to poliovirus and rotavirus.

Question 597: Which of the following statements is true regarding carriers of infectious diseases?

A. Carriers never show any clinical symptoms.
B. Carriers can transmit the infection to others. (Correct Answer)
C. Carriers are always more infectious than symptomatic cases.
D. Carriers pose a lower risk of transmission than symptomatic cases.

Explanation: ***Carriers can transmit the infection to others.*** - **Carriers** harbor a pathogen without showing symptoms, but they can still shed the pathogen and infect others. - This ability to transmit disease makes carriers a significant public health concern, contributing to the silent spread of infections. *Carriers never show any clinical symptoms.* - While many carriers are **asymptomatic**, some may experience mild, non-specific symptoms that are not severe enough to be recognized as the full-blown disease. - The definition of a carrier primarily focuses on the ability to harbor and transmit a pathogen in the absence of obvious, diagnostically significant symptoms. *Carriers are always more infectious than symptomatic cases.* - The **infectiousness of carriers** varies widely depending on the pathogen, the stage of infection, and individual factors. - In many cases, symptomatic individuals, particularly during acute phases of illness, shed higher viral or bacterial loads and are more infectious due to overt symptoms like coughing and sneezing. *Carriers pose a lower risk of transmission than symptomatic cases.* - The risk of transmission from carriers is complex; while the *per-contact transmission rate* might be lower than a highly symptomatic individual, their lack of symptoms means they are less likely to isolate. - This leads to increased exposure of others over time, potentially resulting in a higher overall number of transmissions, making them a significant epidemiological challenge.

Question 598: Which of the following statements about measles is false?

A. Infectivity is low (Correct Answer)
B. Measles commonly affects individuals of any age who are not immune.
C. Koplik's spots are pathognomonic
D. The source of infection is typically an infected person

Explanation: ***Infectivity is low*** - Measles is highly contagious, with an **R0 (basic reproduction number)** typically between 12 and 18, making it one of the most infectious human diseases. - Its high infectivity is why **herd immunity** requires a very high vaccination coverage rate (around 95%) to prevent outbreaks. *Koplik's spots is pathognomonic* - **Koplik's spots** are indeed considered **pathognomonic** for measles, appearing as small, white, bluish-white, or grayish lesions on the buccal mucosa opposite the molars. - These spots typically emerge 2-3 days before the characteristic rash and fade as the rash develops. *Measles commonly affects individuals of any age who are not immune.* - Lack of immunity, either through vaccination or previous infection, makes an individual susceptible to measles **regardless of age**. - In developed countries, outbreaks often occur in unvaccinated populations or those with waning immunity, as seen in adults who may not have received measles vaccines or caught the infection as children. *The source of infection is typically an infected person* - Measles is an **airborne disease** spread through respiratory droplets from an infected person's coughing and sneezing. - The virus can live for up to two hours in the air or on surfaces, making direct contact with an infected individual or their respiratory secretions the primary mode of transmission.

Question 599: Polio is said to be eradicated if no case of polio by wild poliovirus occurs in an area for ?

A. 1 year
B. 2 years
C. 3 years (Correct Answer)
D. 4 years

Explanation: ***3 years*** - The World Health Organization (WHO) certification criteria for **polio eradication** requires that no new cases of wild poliovirus-caused poliomyelitis be recorded for a minimum of **three consecutive years** in a defined geographical area. - This timeframe is chosen to ensure that all possible chains of transmission have been interrupted and that the virus is no longer circulating in the population. *1 year* - While one year without cases is a positive sign, it is generally considered **insufficient** to declare eradication due to the possibility of **undetected transmission** or a long incubation period for some cases. - Many infectious diseases require a longer period of surveillance to confirm eradication definitively. *2 years* - Similar to one year, a two-year period is often considered **too short** to confidently declare polio eradicated. - The risk of **re-emergence** from undetected or imported cases is still significant in this timeframe. *4 years* - While a four-year period would provide even greater assurance, the standard and internationally accepted criterion for declaring polio eradication is **three years**. - This duration balances the need for robust confirmation with the practicality of ongoing surveillance efforts.

Question 600: Post exposure prophylaxis is not indicated in which of the following conditions?

A. Rabies
B. Chickenpox
C. Measles
D. Typhoid (Correct Answer)

Explanation: ***Typhoid*** - **Post-exposure prophylaxis (PEP)** is generally **not indicated** for typhoid fever, as **antibiotic treatment** is highly effective once symptoms develop. - Prevention primarily involves **vaccination** and ensuring **safe food and water hygiene**, not medication after exposure. *Rabies* - **PEP is crucial** for rabies due to its nearly 100% fatality rate once symptoms appear, involving **vaccine** and **immunoglobulin** administration. - Exposure typically occurs through bites or scratches from **rabid animals**. *Chickenpox* - **PEP** with **VariZIG (varicella zoster immune globulin)** or **antiviral medications** may be indicated for high-risk individuals after exposure. - This is primarily to prevent severe disease in **immunocompromised individuals** or pregnant women without immunity. *Measles* - **PEP** with the **measles vaccine** or **immunoglobulin (IG)** is recommended for susceptible individuals exposed to measles. - This intervention can **prevent or modify the course** of the disease, especially in unvaccinated contacts.

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