ARBOVIRUSES

By: Dr. Malak El Hazmi Assistant Professor & Consultant Virologist College of Medicine &

KKUH

Viral Zoonoses

Non arthropod-borne zoonoses Arthropod-borne Vs

Mosquito-borne Vs –Yellow Fever V–Dengue V

Rabies V. Ebola V. Marburg V. Lassa V . Hantaviruses

Tick-borne Vs –Tick-borne encephalitis Vs–Colorado tick fever

Fly-borne Vs–Sandfly fever V.

Arboviruses: Def Etiology Epidemiology Diseases Dengue Yellow Fever Rift Valley Fever Dx. Rx Prevention

Arthropod –borne Viruses Arboviruses > 500 Vs Classification

–Togaviridae* –Flaviviridae* –Bunyaviridae*

–Reoviridae–Orthomyxoviridae–Rhabdoviridae

Characteristic Properties of Arboviruses

Property Toga Flavi Bunya Rhabdo Reo* Ortho

Symmetry Cubic Cubic Helical Bullet Cubic Cubic

Diameter (nm)

70 40-60 80-100 180 x 85 60-80 15-120

Nucleic acid

(+)ssRNA

(+)ssRNA

(-)ssRNA

(-) ssRNA

dsRNA

(-) ssRNA

No. of Vs 29 68 318 63 77 2

*Non-enveloped

Life cycle of arboviruses

Epidemiology: Reservoir: Wild birds & Mammals Vector: Mosquito, ticks& Sandfly

Transmission: bite of infected vector

Life cycle of arboviruses

Epidemiology:Natural cycles

1. Arthropod - bird cycle

West Nile Vs ,EEEV, WEEV

2. Arthropod -mammal cycle Venezuelan equine encephalitis

Epidemiology:Natural cycles

Epidemiology:Natural cycles

3. Human- Arthropod cycle Dengue & Urban yellow fever

Epidemiology: Natural cycles

2.Arthropod- mammal cycle

1. Arthropod - bird cycle

3. Human- arthropod cycle

Diseases

Asymptomatic Infections* Diseases

1) CNS disease ( encephalitis)

2) Fever, Rash & arthralgia

3) Hemorrhagic fever ± hepatitis

*ArboVs associated with CNS disease:Virus Vector Reservoir Distribution

Eastern equine encephalitis EEEV

Mosquito Birds America

Western equine encephalitis WEEV

Mosquito Birds America

Venezuelan equine encephalitis VEEV

Mosquito Rodent America

Japanese encephalitis V Mosquito Birds Pigs Orient

Murray Valley encephalitis V

Mosquito

Birds Australia

West Nile V Mosquito Birds Europe, AfricaMiddle East Asia, America

West Nile virus Flaviviridae Febrile illness encephalitis

Eastern equine encephalitis virusEEEV

TogaviridaeKilled vaccine for horses

Western equine encephalitis virus WEEV

Severe Encephalitis

EEEV &WEEV

less severe

Togaviridae Febrile illness

encephalitis

Venezuelan equine encephalitis virus VEEV

*ArboVs associated with Hemorrhagic Fever

Virus Vector Reservoir Distribution

Crimean Congo Virus Tick Mammals Africa , Asia & Europe

Rift Valley fever virus Mosquito Sheep cattle

Africa

Yellow Fever virus Mosquito Monkeys Man

Africa & South America

Dengue Virus Mosquito Man Entire tropical zone

*ArboVs associated with Fever-rash-arthralgia

Virus Vector Reservoir Distribution

West Nile virus Mosquito Birds Africa, Europe, America

Rift Valley Fever Virus Mosquito Sheep Cattle

Africa

Dengue Virus Mosquito Man Entire tropical zone

Sandfly fever Virus Sandfly Man Mediterranean

Yellow Fever Flaviviridae Asymptomatic to Jaundice + Fever ±

hemorrhage ± renal failure Epidemiology

Tropical Africa

& South America

1. Jungle Yellow Fever

2. Urban Yellow Fever

Jungle Yellow Fever: Vector: mosquito

Reservoir: Monkeys Accidental host:

humans It is a disease of

Monkeys

Urban Yellow Fever: Vector: mosquito Reservoir: human It is a disease of

humans

Dengue Virus Vector : Mosquito Reservoir : human Tropical parts of the world

Diseases

1. The classic dengue fever

2. Dengue Hemorrhagic Fever

Dengue Virus

1.The classic dengue fever Fever – rash – arthralgia Break bone fever Self-limiting

2.Dengue Hemorrhagic Fever Severe disease Mortality rate 15% C/F - F-R-A - Hemorrhage (GI, skin)

Rift Valley Fever

Bunyaviridae Sheep, Cattle , etc Spread

Mosquitoes Infected animal

blood or tissue Raw milk

Diseases Febrile disease* Retinitis Fulminant disease with Hge + Jaundice + Hepatitis Rarely: encephalitis

Reference Lab Lab. Methods :

A. Isolation (Good standard )

Samples: blood, CSF, Viscera . Cell culture CPE

Identify by IF

B - IgM -AB* - EIEA, IF: (most used)

C - Arbovirus RNA by RT-PCR

Dx.

Rx.Ribavirin (some bunyavirus & Togavirus)

Prevention 1. Vector Control:

Elimination of

vector breading sites using insecticides Avoidance contact

with vectors

( repellants , net )

2. Vaccines:

2- Vaccines:1. Yellow Fever vaccine

(LAV, 17D strain, one dose /10 yrs)

2. Tick-borne encephalitis vaccine (killed, 2 doses ,3rd doses after 1 yr.

booster every 3-5 yrs)

3. Japanese encephalitis (killed,

LAV)