Overview of West Nile Virus

West Nile Virus (WNV) is a Mosquito borne zoonotic abrovirus that belongs to Genus – Flavivirus and Family – Flaviviridae. This Virus is found in temperate and tropical region. It was first identified in 1937 in West Nile Sub Region in Eastern African Nation of Uganda .The mode of spread before 1990 was considered as minor risk. Certain cases of Encephalitis due to West Nile Virus were first observed in 1993 in Algeria. First large outbreak was observed in1996 in Romania. Globally the first case was identified in New York City in 1999.

Transmission of West Nile Virus

 The West Nile Virus is transmitted through the Female Mosquito, which is a prime vector. Different Species of Culex Mosquitoes transmit West Nile Virus in various geographical localities of World. Culex Pipiens transmit this virus in (Eastern U.S.), Culex Quinquefasciatus  transmit Western Nile virus in Southeast,  Culex Tarsalis transmit West Nile Virus  in Mid west  respectively.

• Reservoir Host.The Mosquito infect the bird; replication of virus takes place in the bird, mosquito suck blood meal from the infected bird and then transmits it to another bird the cycle continues, when threshold level of virus in the bird increases then it become fatal. In Crow and Robins the infection is fatal after 4 to 5 days. The epizootic viral amplification cycle when it reaches to 15 to 16 days, the massive population of birds dies out then the mosquito diverts toward less specific host and feed on human and horse to transmit the infection, illness develops  within 2-15 days of incubation period. Human and Horses are called as incidental Host, because they cannot continue the transmission cycle. In mammal the virus does not multiply as readily as it multiply in birds and make mammal as dead end host.
• Direct Human to Human Transmission. It is caused by occupational exposure or conjunctive exposure. West Nile Virus can be directly transmitted to the donor by blood transfusion, organ transplant, and breastfeeding respectively
• Vertical Transmission: Transmission of Virus from female species to her offspring is called enzootic transmission.

  

Diagnosis of West Nile Virus

• Preliminary diagnosis is  often based on the  patient  clinical symptoms ,places and  date of  travel if  the  patient  is  from  the  non endemic  country. Whereas epidemiological location of infection occurs with recent History of mosquito bite, acute febrile illness associated with neurological signs and symptoms will cause clinical suspicion of WNV.
• Laboratory Diagnosis is based on Serological testing of Blood Serum or Cerebrospinal Fluid (CSF). CSF fluid show increase in level of lymphocytes, elevated level of Proteins, Glucose, Lactic acid level and no erythrocytes respectively. Specific diagnosis /Confirmation of West Nile Virus is based on the detection of Virus Specific Antibody Immunoglobin M (IgM) and neutralizing antibodies.

Preventive Measures.  Preventive Measures can be discussed at Personal, Household, and Community /environmental level.

• Personal Protected Measures: Use of mosquito repellent,wear long sleeves, pants,  protection to be observed at times of high mosquito activity (dawn/dusk) or stay indoors.
•  At Household level:  Protect your house and yard, Strict Residential source reduction should be observed, (number of mosquitoes are reduce through eliminating the breeding places is called as resource reduction),   Use/ fix screens, Air-conditioning, Empty water (breeding sites).
• At Community level: Preventive and control of WestNile Virus Disease is  accomplished  most

effectively through a comprehensive intergrated mosquito management Programme which includes  monitoring,preventionand  production of new mosquitoes.Mosquito control can be  done  by destroying

1. The larvicidal stage: by  using   chemical agents Paris  green or  Copper acetoarsenite and  Synthetic compound, Organophosphorous compound.     Breeding  site of Larva can be filmed by application of  mineral oil which is  one  of  the oldest practice which is done  by application of  used diesal oil ,and  Kerosine oil which  kill, the Larva and  pupa in short time.
2. Biological Control: can be done  through use of  fish Gambusia affinis and  Lebsiter reticulatus biological application is  only effective only when it is used with other methods.
3. Anti Adult Measures: like  use  of  residual sprays ,Space sprays. Application of Ultra Low Volume (ULV) ,can be used by chemical Pyrethroids or  Organophosphates,Besides this  numerous  formulation of EPA-registered for  specfic mosquito control used in residential setting.

Monitoring and Control of West Nile Virus.

WNV  can be sampled from enviornment by poooling  of trap mosquitoes  via carbondioxide baited light traps and  gravid  trap.Testing  blood  sample  drawn from bird ,sentinel  chicken and  the  sample  should  be  tested for WNV antibodies.Control of  Mosquito is  through destruction  of breeding  site such as  abandom pool .Applying  larvicide to active breeding  side  and  trageting  adult population by aerial spray.Most of  the  enviornmentalists are of  the  opionion  that aerial sprays may be detrimental, Environmental friendly approached  should  be developed.

 Treatment of West Nile Virus

No specific treatment  is available for WestNile Virus.

Prognosis of West Nile Virus

The  patient takes  60-90days to recover from the disease if neuro invasive  symptoms  appears then the disease may prolong  to years.