Question 1: Consider the following statements regarding dengue virus :
1. It has four distinct serotypes.
2. Infection with any one serotype confers lifelong immunity for that virus serotype.
3. Secondary infection with dengue serotype 2 leads to severe form of dengue. Which of the statements given above are correct?
- A. 1 and 2 only (Correct Answer)
- B. 2 and 3 only
- C. 1 and 3 only
- D. 1, 2 and 3
Explanation: ***1 and 2 only***
- Dengue virus indeed has **four distinct serotypes (DENV-1, DENV-2, DENV-3, DENV-4)**, explaining different epidemiological patterns and reinfections.
- Infection with one serotype provides **lifelong homologous immunity** against that specific serotype, meaning a person will not get sick again from the same serotype.
*2 and 3 only*
- While statement 2 is correct, statement 3 is not universally true, as severe dengue can occur with secondary infection of any serotype, although **DENV-2** and **DENV-3** are more frequently implicated.
- This option incorrectly excludes the fact that dengue has four distinct serotypes, which is a fundamental aspect of its biology and epidemiology.
*1 and 3 only*
- While statement 1 is correct, statement 3 is a simplification; severe dengue in secondary infections is due to **antibody-dependent enhancement (ADE)**, which can happen with various heterologous serotypes, not exclusively DENV-2.
- This option incorrectly implies that infection with one serotype does not confer lifelong immunity to that specific serotype, which is a key characteristic of dengue immunity.
*1, 2 and 3*
- This option is incorrect because statement 3, while partially true, is too absolute. Severe dengue can be linked to **DENV-2** or **DENV-3** in secondary infections but isn't exclusive to DENV-2.
- The risk of severe dengue is due to a **secondary infection** with a **heterologous serotype**, not specifically serotype 2, though DENV-2 often causes more severe illness in secondary infections.
Question 2: Monkeypox, a viral zoonotic disease, is caused by
- A. a single-stranded RNA virus
- B. a single-stranded DNA virus
- C. a double-stranded DNA virus (Correct Answer)
- D. a double-stranded RNA virus
Explanation: ***a double-stranded DNA virus***
- Monkeypox is caused by the **monkeypox virus (MPXV)**, which belongs to the **Poxviridae family**.
- Viruses in the Poxviridae family are known for having a **double-stranded DNA genome**.
*a single-stranded RNA virus*
- Many common viruses, such as **SARS-CoV-2 (COVID-19)**, **influenza virus**, and **HIV**, are single-stranded RNA viruses.
- This genomic structure is fundamentally different from that of the monkeypox virus.
*a single-stranded DNA virus*
- Viruses like **Parvovirus B19** are single-stranded DNA viruses.
- This type of genome is less common in human pathogens compared to double-stranded DNA or RNA viruses.
*a double-stranded RNA virus*
- Viruses such as **rotaviruses**, which cause gastroenteritis, are double-stranded RNA viruses.
- While also double-stranded, its RNA nature distinguishes it from the DNA genome of monkeypox virus.