The causal organism of dengue fever is a mosquito-borne virus which belongs to which one among the following categories?
Flavi-ribo virus
The correct classification of the dengue virus is Flavi-ribo virus, which refers to viruses in the Flavivirus genus of the Flaviviridae family that possess a single-stranded, positive-sense RNA genome. Dengue virus (DENV) falls into this category and is responsible for causing dengue fever, a rapidly spreading mosquito-borne viral disease. The transmission occurs primarily through the bite of infected Aedes aegypti mosquitoes, which are day-biting mosquitoes commonly found in tropical and subtropical regions.
Virology and Structure
The dengue virus is an enveloped virus with an icosahedral capsid. It contains RNA as its genetic material—this is where the "ribo" part of the name comes from. The term “Flavi” refers to the viral genus Flavivirus, which includes other notable viruses such as Zika, Yellow Fever, and West Nile Virus.
| Feature | Description |
|---|---|
| Virus Family | Flaviviridae |
| Genus | Flavivirus |
| Genome Type | Single-stranded positive-sense RNA |
| Serotypes | DENV-1, DENV-2, DENV-3, DENV-4 |
| Capsid | Enveloped, icosahedral |
| Replication Site | Cytoplasm |
- These four serotypes can all cause dengue, and infection with one does not provide lasting immunity against the others. In fact, secondary infection with a different serotype increases the risk of severe dengue due to a phenomenon known as antibody-dependent enhancement (ADE).
Clinical Features and Disease Progression
- Dengue infection presents a wide clinical spectrum, ranging from mild flu-like symptoms to severe complications like Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). Initial symptoms typically begin 4–10 days after the mosquito bite and include:
- High fever
- Severe headache
- Retro-orbital pain (pain behind the eyes)
- Joint and muscle pain
- Skin rash
- Mild bleeding (e.g., nose or gum bleed)
- In severe cases, there may be plasma leakage, fluid accumulation, respiratory distress, and even organ impairment.
Lifecycle and Transmission
The mosquito becomes infected when it feeds on a person already infected with dengue virus. After an extrinsic incubation period (usually 8–12 days), the virus replicates in the mosquito’s salivary glands, and the mosquito becomes capable of transmitting the virus for life.
| Stage | Action |
|---|---|
| Human with dengue virus | Bitten by Aedes mosquito → mosquito ingests virus |
| Virus incubation in mosquito | 8–12 days for replication in midgut and salivary glands |
| Infected mosquito bites new host | Virus enters bloodstream and infects host cells |
Comparison with Other Viruses
Other viruses listed in the options differ significantly in terms of their structure, transmission, and the diseases they cause.
| Virus | Family | Genome Type | Transmission Mode | Disease |
|---|---|---|---|---|
| Adenovirus | Adenoviridae | Double-stranded DNA | Respiratory droplets, fecal-oral | Respiratory illnesses, conjunctivitis |
| Vaccinia | Poxviridae | Double-stranded DNA | Contact (used in vaccine) | Used to vaccinate against smallpox |
| Nipah Virus | Paramyxoviridae | ssRNA (-) | Bat → animal → human | Encephalitis, respiratory failure |
None of these are mosquito-borne RNA viruses from the Flaviviridae family, making them incorrect choices.
Global Impact and Prevention
- Dengue has seen a dramatic global increase in incidence over recent decades, with an estimated 390 million infections annually. It is endemic in over 100 countries, particularly in Southeast Asia, South America, and sub-Saharan Africa. Urbanization, poor sanitation, and climate change contribute to the growing spread of Aedes mosquitoes.
- Efforts to prevent dengue focus primarily on mosquito control:
- Removing standing water to prevent breeding
- Using mosquito nets and repellents
- Community fogging operations
- Educating the public on preventive practices
- Although a vaccine (Dengvaxia) exists, its use is limited to certain age groups and individuals who have had previous dengue infections due to concerns over increased risk of severe disease in seronegative individuals.
In summary, the dengue virus is an RNA virus from the Flavivirus genus, making Flavi-ribo virus the correct classification. Its transmission by Aedes mosquitoes, broad clinical spectrum, and expanding global footprint make it a significant public health concern.
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