Infectious Diseases Practice Questions

Q: Pediculosis is caused by?

Louse. ***Louse*** - **Pediculosis** is a parasitic infestation of the skin by blood-feeding insects called **lice**. - There are different types of lice, including head lice (Pediculus humanus capitis), body lice (Pediculus humanus humanus), and pubic lice (Pthirus pubis), all of which cause pediculosis. *Mite* - **Mites** are responsible for infestations like **scabies**, which is caused by Sarcoptes scabiei. - While both lice and mites are arthropods, they cause distinct parasitic conditions with different clinical presentations and treatments. *Tick* - **Ticks** are known vectors for various diseases, including **Lyme disease** (Borrelia burgdorferi), **Rocky Mountain spotted fever** (Rickettsia rickettsii), and **tick-borne encephalitis**. - Ticks are arachnids, not insects, and their bites can cause localized reactions but not pediculosis. *Black Fly* - **Black flies** (Simulium species) are vectors for **onchocerciasis** (river blindness), caused by the parasitic nematode Onchocerca volvulus. - Their bites are typically painful and can cause localized swelling and allergic reactions, but they do not transmit pediculosis.

Q: According to WHO guidelines for yellow fever vector control, what Aedes aegypti index threshold is generally recommended to minimize yellow fever transmission risk?

Less than 1%. ***Less than 1%*** - The **WHO guidelines** for yellow fever vector control recommend maintaining **Aedes aegypti indices** (particularly the **House Index or Container Index**) at **very low levels, ideally below 1%**, to effectively minimize yellow fever transmission risk. - Yellow fever requires more stringent vector control than dengue, as even low vector densities can sustain transmission in susceptible populations. - A threshold **below 1%** indicates minimal mosquito breeding sites and significantly reduces the risk of epidemic transmission. - This represents the **target level for effective prevention** in yellow fever-endemic areas. *2% or more* - An **Aedes aegypti index of 2% or more** indicates increased mosquito breeding activity. - At this level, there is a **moderate risk of transmission**, particularly if the population has low immunity. - This threshold requires enhanced surveillance and vector control interventions. *3% or more* - An index of **3% or more** suggests substantial vector presence and breeding sites. - This level is associated with an **elevated risk of yellow fever outbreaks**, especially in areas with susceptible populations. - Urgent intensification of vector control measures is needed at this threshold. *5% or more* - An index of **5% or more** indicates widespread **Aedes aegypti** presence. - This level carries a **high risk of epidemic yellow fever transmission** and may indicate inadequate vector control. - At this threshold, emergency vector control and potential vaccination campaigns are required. **Note:** For yellow fever specifically, WHO recommends more stringent control (indices <1%) compared to dengue (Breteau Index <5), given yellow fever's epidemic potential and severity.

Q: What is the recommended number of openings per square inch for a standard mosquito net to ensure effective mosquito control?

150 openings. ***150 openings*** - A minimum of **150-156 openings per square inch** is the **WHO-recommended standard** for mosquito nets to effectively prevent mosquito penetration while maintaining adequate ventilation. - This mesh size corresponds to approximately **1.2-1.5 mm** aperture, which blocks all medically important mosquito species including *Anopheles*, *Aedes*, and *Culex*. - This specification is fine enough to provide reliable protection against vector-borne diseases like malaria, dengue, and filariasis. *100 openings* - This mesh size is **too coarse** and would allow smaller mosquitoes to pass through, significantly reducing the net's effectiveness. - It does not meet public health standards and would not provide adequate protection against disease-transmitting mosquito species. *175 openings* - While this would provide effective mosquito exclusion, it is **not the standard recommendation** and represents an unnecessarily fine mesh. - The additional fineness provides minimal benefit over the standard 150-156 openings while potentially reducing airflow slightly. *250 openings* - This mesh is **excessively fine** and significantly **reduces airflow and ventilation**, making the net uncomfortable for users, especially in hot, humid climates. - The very fine mesh accumulates dust and debris more rapidly, requiring frequent cleaning without providing meaningful additional protection over the standard mesh size. - Poor ventilation may reduce user compliance and acceptance of bed net use.

Q: Which of the following conditions has an effective control strategy to prevent blindness?

Trachoma. ***Trachoma*** - **Trachoma** is a bacterial infection caused by *Chlamydia trachomatis* that is a leading cause of preventable blindness worldwide. - The World Health Organization (WHO) promotes a highly **specific and structured strategy** called **SAFE** (Surgery, Antibiotics, Facial cleanliness, Environmental improvement) for its effective control and elimination. - SAFE is a **disease-specific control program** with clear targets for trachoma elimination as a public health problem. *Conjunctivitis* - While some severe forms of **conjunctivitis** (bacterial, viral, or allergic) can cause complications, most cases are self-limiting or easily treated. - There is no specific, structured public health control strategy comparable to SAFE for trachoma, as conjunctivitis encompasses many different etiologies with varying outcomes. *Refractive error* - **Uncorrected refractive errors** are actually the **second leading cause of visual impairment and blindness globally** after cataracts. - While WHO's **VISION 2020** initiative includes refractive error services as a key component for preventing avoidable blindness, and effective interventions exist (screening programs, affordable spectacles, refraction services), this is a **broad service delivery approach** rather than a disease-specific control strategy. - However, trachoma has a more **specific, structured, and targeted control program (SAFE)** making it the best answer in this context. *Ocular trauma* - **Ocular trauma** can cause severe and permanent vision loss or blindness, but it is an acute injury. - Prevention strategies focus on safety measures and protective eyewear, but this differs from a systematic disease control program designed to eradicate a public health burden of blindness like the SAFE strategy for trachoma.

Q: Which of the following is the least common mode of transmission of HIV?

Transfusion of blood products. ***Transfusion of blood products*** - In countries with robust screening, **blood product transfusions** have become an extremely rare source of HIV transmission due to meticulous testing of donated blood [2]. - While historically a significant route, advancements in blood screening and donor selection have nearly eliminated this risk, making it the **least common** mode in many regions [2]. *Homosexual contact* - **Unprotected anal intercourse** between men has been, and remains, a predominant mode of HIV transmission globally, particularly in developed countries [1]. - The risk is high due to the **fragility of rectal mucosa** and the potential for trauma during intercourse. *Heterosexual contact* - **Unprotected heterosexual intercourse** is the most common mode of HIV transmission globally, especially in sub-Saharan Africa [1]. - The risk is influenced by the presence of **other sexually transmitted infections** (STIs) and viral load of the infected partner. *Intravenous drug use* - **Sharing contaminated needles and syringes** among intravenous drug users is a highly efficient way to transmit HIV [1]. - This mode facilitates direct transfer of infected blood from one individual to another.

Q: Polio is transmitted by:

Fecal-oral. **Fecal-oral** - **Polioviruses** are transmitted primarily through the ingestion of material contaminated with the feces of an infected person. - This route facilitates the virus's entry into the **gastrointestinal tract**, where it replicates and can then spread. - This is the **primary mode of transmission**, especially in areas with poor sanitation and hygiene. *Blood* - While it's theoretically possible for polio to be transmitted via blood transfusions if a donor is acutely viremic, it is **not a primary or common route** of transmission. - Bloodborne transmission is **not the main mechanism** for the spread of polio in populations. *Skin contact* - **Direct skin contact** does not typically facilitate the transmission of poliovirus. - Poliovirus requires entry into the body via the **mucous membranes**, primarily the mouth, which is not achieved through simple skin contact. *Inhalational* - **Inhalational transmission** through respiratory droplets or aerosols is not the primary mode of poliovirus spread. - While some viruses can spread this way, polio's primary entry point is the **gastrointestinal system** via the fecal-oral route.

Q: Which of the following is not a vector-borne disease?

Brucella. ***Brucella*** - **Brucellosis** is primarily transmitted through the consumption of infected, unpasteurized dairy products or direct contact with infected animal tissues, making it a **food-borne** or **contact-borne** disease, not vector-borne. - The bacteria can also be acquired through inhalation of aerosols in occupational settings, but a biological vector is not involved in its transmission to humans. *KFD* - **Kyasanur Forest Disease** (KFD) is a **tick-borne viral hemorrhagic fever** endemic to India. - It is transmitted to humans through the bite of infected ticks, making it a classic example of a **vector-borne disease**. *JE* - **Japanese Encephalitis** (JE) is a **mosquito-borne flaviviral infection** and is the most important cause of viral encephalitis in Asia. - It is transmitted by **Culex mosquitoes**, particularly *Culex tritaeniorhynchus*, confirming its vector-borne nature. *Plague* - **Plague** is a severe bacterial infection caused by *Yersinia pestis*, primarily transmitted to humans through the bites of **infected fleas** (a type of vector). - These fleas often carry the bacteria from infected rodents, making it a definitive **vector-borne disease**.

Q: Which disease is NOT primarily transmitted by hard ticks?

Relapsing fever. ***Relapsing fever*** - Relapsing fever, particularly **epidemic louse-borne relapsing fever**, is primarily transmitted by the human body louse (*Pediculus humanus humanus*), not hard ticks. - While some forms of relapsing fever (endemic relapsing fever) *can* be transmitted by soft ticks, the most common association for public health concern regarding relapsing fever is with lice. *KFD* - **Kyasanur Forest Disease (KFD)** is a viral hemorrhagic fever transmitted by the bite of **hard ticks**, primarily *Haemaphysalis spinigera*. - The disease is endemic to certain regions of India and is a classic example of a hard tick-borne illness. *Indian tick typhus* - **Indian tick typhus** is a form of **spotted fever group rickettsiosis** caused by *Rickettsia conorii*, which is transmitted by **hard ticks**, including *Rhipicephalus sanguineus* (brown dog tick). - It is a well-known tick-borne disease in tropical and subtropical regions. *Tularemia* - While tularemia can be transmitted by various routes, **hard ticks** such as *Dermacentor* (dog ticks) and *Amblyomma* (lone star ticks) are important vectors for transmitting *Francisella tularensis*. - Tick bites are a significant mode of transmission for the **ulceroglandular form** of tularemia.

Q: Which of the following statements about leptospirosis is true?

Rats are prime reservoirs. ***Rats are prime reservoirs*** - **Rats** and other wild and domestic animals (e.g., cattle, pigs, dogs, rodents) are the primary **reservoir hosts** for *Leptospira* bacteria, shedding the bacteria in their urine. - Humans become infected through contact with contaminated water or soil, or infected animal tissues/urine. *Fluoroquinolones are the drug of choice* - **Fluoroquinolones** are generally not the drug of choice for leptospirosis. - First-line treatment typically involves **doxycycline** for mild cases and **intravenous penicillin G** or **ceftriaxone** for severe disease. *Person to person Transmission is common* - **Person-to-person transmission** of leptospirosis is extremely rare and not considered a common route of infection. - The disease is usually acquired through environmental exposure to contaminated animal urine. *Hepatorenal syndrome may occur in severe cases.* - While **hepatic** (liver) and **renal** (kidney) dysfunction are characteristic of severe leptospirosis (Weil's disease), the term **hepatorenal syndrome** is a specific diagnosis describing acute kidney injury in patients with advanced liver cirrhosis. - The kidney and liver damage in leptospirosis are direct effects of the bacterial infection, rather than a secondary complication of liver cirrhosis.

Question 1

Pediculosis is caused by?

Accepted Answer

Louse

Answer

Mite

Answer

Tick

Answer

Black Fly

Question 2

Which of the following is not an indicator for malaria surveillance in a population?

Accepted Answer

Hemoglobin level

Answer

Annual parasite index

Answer

Annual parasite incidence

Answer

Annual falciparum incidence

Question 3

According to WHO guidelines for yellow fever vector control, what Aedes aegypti index threshold is generally recommended to minimize yellow fever transmission risk?

Accepted Answer

Less than 1%

Answer

2% or more

Answer

3% or more

Answer

5% or more

Question 4

What is the recommended number of openings per square inch for a standard mosquito net to ensure effective mosquito control?

Accepted Answer

150 openings

Answer

100 openings

Answer

250 openings

Answer

175 openings

Question 5

Which of the following conditions has an effective control strategy to prevent blindness?

Accepted Answer

Trachoma

Answer

Conjunctivitis

Answer

Refractive error

Answer

Ocular trauma

Question 6

Which of the following is the least common mode of transmission of HIV?

Accepted Answer

Transfusion of blood products

Answer

Homosexual contact

Answer

Heterosexual contact

Answer

Intravenous drug use

Question 7

Polio is transmitted by:

Accepted Answer

Fecal-oral

Answer

Blood

Answer

Skin contact

Answer

Inhalational

Question 8

Which of the following is not a vector-borne disease?

Accepted Answer

Brucella

Answer

KFD

Answer

JE

Answer

Plague

Question 9

Which disease is NOT primarily transmitted by hard ticks?

Accepted Answer

Relapsing fever

Answer

KFD

Answer

Indian tick typhus

Answer

Tularemia

Question 10

Which of the following statements about leptospirosis is true?

Accepted Answer

Rats are prime reservoirs

Answer

Fluoroquinolones are the drug of choice

Answer

Person to person Transmission is common

Answer

Hepatorenal syndrome may occur in severe cases

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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