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Veterinary &

Animal Sciences

University

Bangladesh

Risk Analysis on West Nile

Virus infection in Bangladesh

Dr. Md. Abu Sayeed

Course: Risk Analysis and Policy Making

Roll: 0214/04; Regi no: 212

Session: 2014-15

MS in Epidemiology (Fellow)

Dept of Medicine & Surgery

Chittagong Veterinary & Animal Sciences University

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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.

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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.

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Distribution of WNV

Source: http://ecdc.europa.eu/en/healthtopics/west_nile_fever/West-Nile-fever-maps/Pages/index.aspx

Russia

Eastern

EuropeMiddle East

North America

Africa

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Vector

• 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

Host

• Reservoir Hosts– migratory Passeriformes

(perching birds/songbirds)

– Strigiformes (owls)

– Falconiformes (hawks)

– Charadriiformes(shorebirds)

– Alligators and Lake Frogs

• Incidental Hosts– Horse

– Human

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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).

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Transmission Cycle

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Pathogenesis in Incidental Host

Inoculation into the skin Langerhans cells lymph nodes

LymphaticsDifferent tissues

Thoracic duct

Bloodstream

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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

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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.

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Diagnosis

ELISA Neutralization assays

Virus isolation by cell culture

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Treatment

Hospitalization Intravenous fluids

Respiratory supportAntibiotics

Supportive

Therapy

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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?

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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

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Key starting assumptions

• Undisclosed infection may be present in liveequidae that may be imported to Bangladesh vialegal trade or illegal movements from the currentlyknown affected areas;

• The virus may also enter in Bangladesh viamigratory wild birds or by infected vectors beingbrought in by prevailing winds or some othermeans;

• Favorable ecological conditions may exist inBangladesh and would support the establishmentand further spread of the virus should it beintroduced.

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Risk Pathway

Migratory

Birds

Legal and illegal

movement from

affected countries

Accidental import

of biological

vectors

Live

equidae

Live poultry /

captive birds

Non-Avian

non-Equidae

species

Research

SamplesTourists

No riskIntroduction of disease into

human population of Bangladesh

Possible conceptual pathways for the introduction of WN

virus in Bangladesh from the currently known affected areas

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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

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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

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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

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Risk Management

• Surveillance activities– Human: passive surveillance

– Veterinary: passive surveillance for horses and migratory birds withvector control strategy

• Suggested public health actions and interventions• Health sector

– Increase awareness amongst healthcare professionals about WNV soas it will be considered in the differential diagnosis of travelers returningfrom affected areas.

• Education of travelers to affected areas on how to reduce the risk.

• Ensure there are laboratory capabilities within the country fordiagnosis.

• Ensure Gov. and others donation authorities have implementedmeasures to prevent transmission through travelers returning fromaffected areas

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Risk communication

• Communicating risk assessment results and

explanation of the risk management measures

• Health care professionals and Veterinarians

• Local Law enforcing authority

• Mass media

• Government and Non-Government disease

control authority

• CDC, USA

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Conclusion

• The release and exposure of WNV in

Bangladesh is negligible. So, don’t need to

drop it or take it seriously. Only sincere

activities should develop for preventing

this infection in our country.

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Acknowledgement

• My supervisor

– (Prof. Ahasanul Hoque, Dean FVM)

• All Epi members CVASU

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References

• http://ecdc.europa.eu/en/healthtopics/west_nile_fever/risk-assessment-tool/Pages/risk-assessment-tool.aspx

• http://ecdc.europa.eu/en/healthtopics/west_nile_fever/risk-assessment-tool/Pages/risk-assessment-tool.aspx

• http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1437&context=etd

• Mainali et al. Journal of Medical Case Reports 2011,5:204http://www.jmedicalcasereports.com/content/5/1/204

• http://www.who.int/mediacentre/factsheets/fs354/en/

• https://www.michigan.gov/documents/Cooleywnvinwildlife_77045_7.pdf

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