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)