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
- 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.
- 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.
- 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.