**Question:** All are caused by common vectors, except -

A. Dengue
B. Malaria
C. Chikungunya
D. Japanese Encephalitis

**Core Concept:** Vector-borne diseases are infectious diseases caused by pathogens transmitted to humans through the bite of an infected arthropod vector, such as mosquitoes, ticks, or sandflies. Common vectors include mosquitoes (e.g., Anopheles for malaria), ticks (e.g., Ixodes for Lyme disease), and sandflies (e.g., Phlebotomus for Leishmaniasis).

**Why the Correct Answer is Right:**

Option A (Dengue) is caused by a virus (Dengue virus) transmitted through the bite of an infected Aedes mosquito. Dengue is not directly caused by a vector, but rather by the virus transmitted by the vector, which leads to the disease.

Option B (Malaria) is caused by a protozoan parasite (Plasmodium species) transmitted through the bite of an infected female Anopheles mosquito. Malaria is also not caused by a vector, but by the parasite transmitted by the vector, leading to the disease.

Option C (Chikungunha) is caused by a virus (Chikungunha virus) transmitted through the bite of an infected Aedes mosquito. Similar to Dengue, Chikungunha is not caused by a vector, but by the virus transmitted by the vector, resulting in the disease.

**Why Each Wrong Option is Incorrect:**

Option D (Japanese Encephalitis) is caused by a virus (Japanese Encephalitis virus) transmitted through the bite of an infected Culex mosquito. Like Dengue, Chikungunha, and Malaria, Japanese Encephalitis is not caused by a vector, but by the virus transmitted by the vector, resulting in the disease.

**Core Concept:**

The question is testing the understanding of whether a specific disease is caused by a vector (arthropod) or the pathogen (virus, bacteria, or parasite) transmitted by the vector.

**Clinical Pearls:**

1. Dengue, Chikungunha, Malaria, and Japanese Encephalitis are vector-borne diseases caused by viruses transmitted by mosquitoes.
2. Understanding the difference between vector-borne diseases and diseases caused by pathogens transmitted by vectors is crucial for practicing clinicians to diagnose, treat, and prevent these infections accurately.
3. Vectors are not the direct cause of these diseases; instead, they act as vectors for pathogens, which lead to the diseases.

**Why Each Wrong Option is Incorrect:**

A. Dengue, Chikungunha, Malaria, and Japanese Encephalitis are all transmitted through the bite of infected mosquitoes.
B. While some diseases are transmitted by vectors, others (e.g., Lyme disease) are caused by bacteria transmitted by ticks.
C. Vectors are not the causative agents of these diseases; rather, they carry and transmit pathogens that cause these diseases.