1. Risk Analysis on West Nile Virus infection in Bangladesh
Course: Risk Analysis and Policy Making
Roll: 0214/04; Regi no: 212
Session:
MS in Epidemiology
Dept of Medicine & Surgery
Chittagong Veterinary & Animal Sciences University

2. West Nile Virus
West Nile virus (WNV) is an arthropod-borne flavivirus transmitted to humans and horses by the bite of an infected mosquito. West Nile Virus (WNV) is also belongs to the Japanese encephalitis antigenic complex of the family Flaviviridae.

3. Discovery
In 1937; West Nile virus was first isolated from the blood of a febrile woman from the West Nile region of Uganda (Smithburn et al, 1940).
In 1950; WNV isolates were obtained from the blood of three apparently healthy children in Egypt (Melnick et al, 1951).
In the summer of 1999; West Nile virus was recognized in the western hemisphere for the first time when it caused an epidemic of encephalitis and meningitis in the metropolitan area of New York City, NY, USA.

4. Distribution of WNV Eastern Europe Russia Middle East North America
Africa
Source:

5. Vector Host WNV has been isolated from more than 40 mosquito species
Culex antennatus, Culex univittatus, Culex pipiens, Culex nigripalpus, Culex salinarius, Culex restuans and Culex quinquefasciatus
Reservoir Hosts
migratory Passeriformes (perching birds/songbirds)
Strigiformes (owls)
Falconiformes (hawks)
Charadriiformes (shorebirds)
Alligators and Lake Frogs
Incidental Hosts
Horse
Human

6. Mode of Transmission Direct biting by mosquito
Additional transmission routes
trans-placental and breast milk transmission
infected blood transfusion and organ transplantation
urinary excretion of the virus (human)
experimental oral transmission (birds)
(King et al, 2007).

7. Transmission Cycle

8. Pathogenesis in Incidental Host
Inoculation into the skin
Langerhans cells
lymph nodes
Thoracic duct
Bloodstream
Lymphatics
Different tissues

9. Encephalitis form
The exact mechanism by which encephalitic flaviviruses enter the central nervous system (CNS) is unclear.
High viremia, development of brain infection and appearance of viral antigen in nervous tissue leads to the hematogenous spread into the CNS.
Artificial disruption of the blood-brain barrier (by underlying infection) may also lead to encephalitis and neuroinvasion. Mainly olfactory neuronal infection has also been suggested as a route of neuroinvasion.
The incubation period is usually 3 to 14 days

10. Signs and symptoms
About 80% cases infection with WNV is either asymptomatic (no symptoms) or severe West Nile disease.
About 20% cases will develop West Nile fever. Symptoms include
fever
vomiting
occasionally skin rash with swollen lymph glands.
The symptoms of as West Nile encephalitis include
high fever
neck stiffness followed by disorientation
coma, tremors, convulsions, muscle weakness, and paralysis.
In case of human, serious illness can occur in any age, however people over the age of 50 and some immunocompromised persons are at the highest risk.
Approximately 1 in 150 persons infected with the West Nile virus will develop West Nile encephalitis.

11. Diagnosis
ELISA
Neutralization assays
Virus isolation by cell culture

12. Treatment Supportive Therapy Hospitalization Intravenous fluids
Respiratory support
Antibiotics
Supportive
Therapy

13. Risk Question
What is the probability of introducing West Nile virus in Bangladesh through an infected host (mammal, avian or insect) from current affected countries?
What is the probability of West Nile virus becoming established in Bangladesh in the local mosquito and avian population?
What is the probability of a Bangladeshi resident horse becoming infected with West Nile virus given contact with an infected host?

14. Risk Assessment Indicators
Presence of the vector species
Abundance and dynamics of vector and reservoir hosts population
Detection and/or isolation of the virus and mosquito infection rate
Characterization of viral strains by sequencing
Identifying the larval habitats, adult resting places and flight activity of the detected vector species

15. Key starting assumptions
Undisclosed infection may be present in live equidae that may be imported to Bangladesh via legal trade or illegal movements from the currently known affected areas;
The virus may also enter in Bangladesh via migratory wild birds or by infected vectors being brought in by prevailing winds or some other means;
Favorable ecological conditions may exist in Bangladesh and would support the establishment and further spread of the virus should it be introduced.

16. Introduction of disease into human population of Bangladesh
Risk Pathway
Possible conceptual pathways for the introduction of WN virus in Bangladesh from the currently known affected areas
Migratory Birds
Legal and illegal
movement from
affected countries
Accidental import
of biological vectors
Live
equidae
Non-Avian
non-Equidae
species
Tourists
Live poultry /
captive birds
Research
Samples No
Yes
Introduction of disease into human population of Bangladesh
No risk

17. Not act as reservoir host for WNV (CDC: 99-12)
Release Assessment
Major birds are water birds like Black faced spoon bill and Spoonbilled Sandpiper
Not act as reservoir host for WNV (CDC: 99-12)
Negligible
Good quarantine facility and less importation of horses
Presence of good Vector (Mosquitoes) control strategy and less horse population
East Asia Australasia Flyway

18. Exposure Assessment
Horses and humans are dead-end hosts with very low short lived viremia and therefore even if an infected horse or human arrive in Bangladesh, it would not be involved in onward transmission.
An infected wild bird arrive in Bangladesh, the potential for WNV transmission to a competent vector in Bangladesh would be determined by potential for contact with and the abundance of competent vectors.
WNV competent vectors of several Culex spp. are not available in Bangladesh

19. Consequence Assessment
Therefore a good quarantine system of Bangladesh with low horse population in the area as well as lack of competent migratory birds and vectors lead the introduction of WNV is in negligible condition.
Release status= Negligible
Exposure status=Negligible
Probability (P)= Release × Exposure
= Negligible × Negligible
= Negligible

20. Risk Management Surveillance activities
Human: passive surveillance
Veterinary: passive surveillance for horses and migratory birds with vector control strategy
Suggested public health actions and interventions
Health sector
Increase awareness amongst healthcare professionals about WNV so as it will be considered in the differential diagnosis of travelers returning from affected areas.
Education of travelers to affected areas on how to reduce the risk.
Ensure there are laboratory capabilities within the country for diagnosis.
Ensure Gov. and others donation authorities have implemented measures to prevent transmission through travelers returning from affected areas

21. Risk communication Health care professionals and Veterinarians
Local Law enforcing authority
Mass media
Government and Non-Government disease control authority
CDC, USA

22. Thanks for patience