West Nile fever is an infection by the West Nile virus, which is typically spread by mosquitoes. It causes disease in humans, horses, and several species of birds

1. West Nile Fever
MD. Abdul Karim Mia
MS in Microbiology
ID: 192-033-061
Department of Microbiology
Primeasia University
Department of Microbiology, Primeasia University

2. West Nile fever
West Nile fever is an infection by the West Nile virus, which
is typically spread by mosquitoes. It causes disease in
humans, horses, and several species of birds. In about 80%
of infections people have few or no symptoms. About 20% of
people develop a fever, headache, vomiting, or a rash. In less
than 1% of people, encephalitis or meningitis occurs, with
associated neck stiffness, confusion, or seizures. Recovery
may take weeks to months. The risk of death among those in
whom the nervous system is affected is about 10%.
Department of Microbiology, Primeasia University

3. West Nile virus (WNV)
Flaviviridae
Flavivirus
Single stranded RNA virus
2 genetic lineages
Linage 1
3 clades (1a, 1b, 1c)
Infects humans, birds, mosquitoes, horses,
and other mammals
Department of Microbiology, Primeasia University

4. History
1937: West Nile District, Uganda
First isolated
1950: Egypt
Ecology studied
Additional outbreaks
1951-54, 1957, Israel
1962, 2000: France
1973-74: South Africa
1996: Romania, 1998: Italy
Department of Microbiology, Primeasia University

5. Transmission
 Primary mosquito vector
Culex spp.
 Tick vectors
Asia, Russia
Role in transmission not clear
 Overwintering of mosquitoes
 Transovarial transmission
 Birds
Contact
Migratory transport
Department of Microbiology, Primeasia University

6. Human Transmission
 Direct contact
Infected birds, tissues
 Laboratory acquired
 Blood transfusions
Screening implemented in 2003
 Organ transplants
 Transplacental transmission
 Breast feeding
Department of Microbiology, Primeasia University

7. Department of Microbiology, Primeasia University
Transmission Cycle of West Nile Virus

8. Horses Black Bear Bats
Goats Wolf Llama
Sheep Alpaca Cattle
Dog Mountain Goat Seal
Rabbit Alligator Cat
Chipmunk Gray Squirrels Deer
Skunk
Crocodile
Species Affected By West Nile Virus
Department of Microbiology, Primeasia University

9. Clinical Signs
Many asymptomatic
Anorexia
Ataxia
Weakness
Teeth grinding
Convulsions
Circling
Tremors
Difficulty swallowing
Attitudinal changes
Facial edema
Colic
Urinary dysfunction
Complications
Mortality
Many euthanized
Department of Microbiology, Primeasia University

10. Diagnosis In Human
Serology
Serum or CSF
IgM capture ELISA
Cross reactions possible
Plaque neutralization test
Detection of virus, antigen, or nucleic acids
RT-PCR
Immunohistochemistry
Department of Microbiology, Primeasia University

11. Treatment
No specific therapy
Supportive care
Therapies in clinical trials
Interferon
Antisense nucleotides
IV immunoglobulin
Antiviral drugs
Department of Microbiology, Primeasia University

12. Vaccination
 Several commercial vaccines available for horses
 Consult label for instructions
 Usually 2 doses, 3 to 6 weeks apart
 Annual revaccination
 Vaccines sometimes used off-label to protect birds
Prevention and Control
Mosquito Management
 Surveillance
 Source reduction
 Personal protection
 Biological control
 Larvicide & Adulticide
Department of Microbiology, Primeasia University

13. Surveillance
 Dead bird testing
 Sentinel chicken flocks
 Mosquito collection
 Test for pathogens
 Account for species
 Larval and adult mosquitoes
 Map habitats
 Record keeping
Mosquito Management
Source Reduction
 Eliminating larval habitats
 Tires, bird baths, containers,
rain gutters, unused swimming
pools
 Making habitats unsuitable for
larval development
 Public education
 Marsh water management
 Drain, fish access, gated
Personal Protection
 Reduce time outdoors
 Especially evening hours
 Long pants and sleeves
 Use mosquito repellent
 35% DEET
 Do not use DEET on
animals
 Keep window screens
intact
 Use yellow “bug” light
bulbs in outdoor light
fixtures
Department of Microbiology, Primeasia University

14. Biological Control
 Utilizes predators, both natural and
introduced, to eat larvae and
pupae
 Mosquito fish
Gambusia affinis, G.
holbrooki most
common
Fundulus spp.,
Rivulus spp., killifish
 Other agents have been used but
are not readily available
 Fungus, protozoa, nematodes
 Copepods
Larvicides
 Use when source reduction
and biological control not
feasible
 More effective and target-
specific
 Less controversial than
adulticides
 Applied to smaller
geographic areas
 Larvae concentrate in
specific locations
Adulticides
 When other control
measures unsuccessful
 Least efficient
 Proper type and time of
application helps efficacy
 Ultra Low Volume foggers
 1 ounce per acre
 Small droplets contact and
kill adults
Mosquito Management
Department of Microbiology, Primeasia University