## Epidemiology and Transmission of Arboviral Infections ### Correct Statements (True — Not the Answer) **Key Point:** Dengue virus is transmitted by *Aedes aegypti* mosquitoes, which are predominantly diurnal feeders with peak biting activity during early morning and late afternoon. This is a well-established epidemiological fact. [Park's Textbook of Preventive and Social Medicine, 26e] **Key Point:** Chikungunya virus can be transmitted vertically from mother to fetus, with the highest risk occurring during the **third trimester** (intrapartum transmission rates of 30–50% documented). This is consistent with published literature. [Harrison's Principles of Internal Medicine, 21e, Ch 297] **Key Point:** Zika virus is transmitted by **both *Aedes aegypti* AND *Aedes albopictus*** mosquitoes. More importantly, Zika has well-documented **human-to-human transmission** routes including sexual transmission (virus isolated from semen), perinatal/vertical transmission (causing congenital Zika syndrome with microcephaly), and blood transfusion. Option C is therefore also incorrect, but Option D contains a more fundamental taxonomic error. ### Incorrect Statement (The Answer — Option D) **High-Yield:** Option D states that **all three viruses belong to the Flaviviridae family**. This is **factually incorrect**: | Virus | Family | Genus | |---|---|---| | Dengue | **Flaviviridae** | *Flavivirus* | | Zika | **Flaviviridae** | *Flavivirus* | | Chikungunya | **Togaviridae** | *Alphavirus* | Chikungunya virus belongs to the **Togaviridae** family, genus *Alphavirus* — NOT Flaviviridae. Dengue and Zika are both Flaviviruses (Flaviviridae), but chikungunya is an Alphavirus. This is a fundamental taxonomic distinction tested repeatedly in NEET PG / INI-CET examinations. **Clinical Pearl:** The Togaviridae family (chikungunya, rubella) and Flaviviridae family (dengue, Zika, yellow fever, Japanese encephalitis) are distinct. All are enveloped, single-stranded positive-sense RNA viruses, but their family classification differs. Confusing chikungunya with Flaviviridae is a classic distractor. [Robbins Basic Pathology, 10e, Ch 8; Murray's Medical Microbiology] ### Why Option C is Also Partially Incorrect (But Not the Best Answer) Option C contains two errors: (1) Zika is transmitted by *both* Aedes aegypti and Aedes albopictus, not primarily albopictus; and (2) Zika has documented human-to-human transmission (sexual, perinatal, transfusion). However, Option D's error — misclassifying chikungunya's viral family — is a more absolute and unambiguous factual error, making D the single best answer in an "EXCEPT" question format.
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