Innovations in Biotechnology and Medical Sciences

West Nile Fever Outbreak in Kerala 


From UPSC perspective, the following things are important :

Prelims level: West Nile Virus, Its host, Transmission;

Mains level: NA

Why in the news?

  • The Kerala government disclosed the re-emergence of West Nile fever cases in Thrissur, Malappuram, and Kozhikode districts.
  • West Nile fever was first detected in Kerala in 2011, with a fatal case recorded in 2019 involving a six-year-old from Malappuram.

What is West Nile Fever?

  • West Nile fever is caused by a West Nile Virus (WNV) transmitted through bites from infected Culex mosquitoes.
  • The WNV is a mosquito-borne, single-stranded RNA virus.
  • According to the WHO, it is a member of the flavi-virus genus and belongs to the Japanese Encephalitis antigenic complex of the family Flaviviridae.

How does it spread?

  • It is transmitted by infected mosquitoes between and among humans and animals, including birds, which are the reservoir host of the virus.
  • Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days.
  • The virus eventually gets into the mosquito’s salivary glands.
  • During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness.
  • WNV can also spread through blood transfusion, from an infected mother to her child, or through exposure to the virus in laboratories.
  • It is not known to spread by contact with infected humans or animals.

Symptoms of WNV infection:

  • The disease is asymptomatic in 80% of the infected people.
  • The rest develop what is called the West Nile fever or severe West Nile disease.
  • In these 20% cases, the symptoms include fever, headache, fatigue, body aches, nausea, rash, and swollen glands.


[2017] Consider the following statements:

1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue.

2. Sexual transmission of Zika virus disease is possible.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2


Back2Basics: Type of Viruses 

Subtypes Description Examples
DNA Viruses Herpesviruses DNA viruses with a complex structure causing various diseases including cold sores, chickenpox, and mononucleosis. HSV-1, HSV-2, VZV, EBV
Papillomaviruses DNA viruses associated with warts and certain cancers. HPV
Adenoviruses DNA viruses causing a wide range of infections in humans. Adenovirus types causing respiratory, gastrointestinal, and ocular infections
Poxviruses Large, complex DNA viruses responsible for diseases like smallpox. Variola virus (smallpox), Vaccinia virus
RNA Viruses Positive-Sense RNA Viruses RNA viruses with genomes that can directly serve as mRNA, causing diseases like the common cold, Zika, and COVID-19. Picornaviruses, Flaviviruses, Coronaviruses
Negative-Sense RNA Viruses RNA viruses requiring transcription into positive-sense RNA before translation, causing diseases like influenza and rabies. Orthomyxoviruses, Paramyxoviruses, Rhabdoviruses
Retroviruses RNA viruses that use reverse transcriptase to integrate their genome into the host cell’s DNA. HIV, HTLV
Double-Stranded RNA (dsRNA) Viruses RNA viruses with double-stranded RNA genomes causing gastroenteritis and other infections. Reoviruses
Single-Stranded RNA (ssRNA) Viruses with Ambisense Genome RNA viruses with genomes containing both positive-sense and negative-sense RNA regions. Arenaviruses, Bunyaviruses
Single-Stranded RNA (ssRNA) Viruses with Segmented Genome RNA viruses with genomes consisting of multiple segments, causing diseases like influenza and hemorrhagic fevers. Orthomyxoviruses, Bunyaviruses
Single-Stranded RNA (ssRNA) Viruses with Circular Genome Satellite viruses with a circular RNA genome requiring helper viruses for replication. Hepatitis Delta Virus (HDV)
Enveloped Viruses Influenza Viruses RNA viruses surrounded by a lipid envelope causing seasonal flu outbreaks. Influenza A, B, C viruses
Herpesviruses Enveloped DNA viruses causing diseases like cold sores, chickenpox, and mononucleosis. HSV-1, HSV-2, VZV, CMV
Coronaviruses Enveloped RNA viruses causing diseases like severe acute respiratory syndrome (SARS) and COVID-19. SARS-CoV, MERS-CoV, SARS-CoV-2
HIV Enveloped retroviruses responsible for acquired immunodeficiency syndrome (AIDS). Human immunodeficiency virus
Ebola Virus Enveloped RNA virus causing severe hemorrhagic fever in humans. Ebola virus
Non-enveloped Viruses Adenoviruses DNA viruses lacking a lipid envelope, causing various infections in humans. Adenovirus types causing respiratory, gastrointestinal, and ocular infections
Papillomaviruses DNA viruses associated with warts and certain cancers, lacking an envelope. HPV
Noroviruses RNA viruses causing gastroenteritis, lacking an envelope. Norovirus
Rotaviruses RNA viruses causing severe gastroenteritis in infants and young children, lacking an envelope. Rotavirus
Bacteriophages T4 Bacteriophage Viruses that infect bacteria, with a complex structure and lifecycle. T4 bacteriophage
Lambda Phage Temperate bacteriophage capable of lysogenic and lytic cycles in E. coli. Lambda phage

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