Arboviruses = Arthropod born viruses .These viruses require the presence of vertebrate host and arthropod vector usually mosquitoes , ticks or sand flies .In the natural environment the virus is maintained in a cycle that involves the vertebrate host and the vector .
These viruses multiply inside the vertebrate host as well as the vector .The vector transmits the disease to human and other mammals , through the bite .Man generally plays no role in the natural history of arboviruses .Humans are not the natural reservoir for the virus .
There are hundreds of arboviruses, many of which are not pathogens to human .Human pathogens arboviruses are grouped into three viral families :1- Togaviridae .2- Bunyaviridae .3- Flaviviridae . Arboviruses are enveloped, with ss-RNA genome .
Humans are infected through the bite of infected vector , or when they come into contact with infected host .Vector : Mosquitoes, ticks or sand flies .Vertebrate host : Mammals and birds.
1- Hemorrhagic fever .2- Encephalitis .3- Fever with rash and arthralgia .
1- Dengue virus . 1- Dengue virus . Family: Flaviviridae .2- Yellow fever virus . family : Flaviviridae .3- Rift valley fever virus . Family : Bunyaviridae .4- Crimean congo hemorrhagic fever virus . Family : Bunyaviridae .
Enveloped , icosahedral particle .About 40 -60 nm in diameter .The viral genome is ss-RNA , with positive polarity .Flavi = Yellow .
Enveloped with helical symmetryAbout 90 – 100 nm in diameter .The viral genome consists of three segments of ss- RNA (large , medium and small ) , with negative polarity .
1- Dengue fever ( break bone fever ) :Geographical distribution : Asia, Middle east , Africa & South America .Vector: Mosquitoes .Vertebrate host : human .Diseases : 1-Most cases are mild or asymptomatic . 2- Dengue hemorrhagic shock syndrome .
2- yellow fever :Geographical distribution : Africa and South America .Vector : Mosquitoes .Vertebrate host : Human , monkeys.Symptoms: Most cases are mild or asymptomatic .The severe form of the disease is characterized by fever, myalgia, arthralgia, nausea, vomiting, jaundice, mucosal bleeding, bleeding under the skin, vomiting blood, seizures and coma .
1- Jungle yellow fever :Involves transmission between mosquitoes and non-human primate, with human as accidental host.2- Urban yellow fever :
3- Rift valley fever :Geographical distribution : Africa and Asia .Vector : Mosquitoes .Vertebrate host :Sheep, goats and cattle , camels and human .Diseases 1-Most cases are mild or asymptomatic .2- Hemorrhagic form : are characterized by fever, headache, myalgia, arthralgia, nausea, mucosal bleeding and bleeding under the skin .
3- Meningoencephalitis : fever, severe headache, stiffness of neck, back pain, hallucination. Mental confusion, lack of coordination, convulsions and coma . Transmission :By direct contact with infected animal blood or tissue .Through the bite of mosquitoes.Human to human transmission has not been documented..
4- Crimean Congo H F :Geog. Dist. : Africa, Asia and middle east .Vector : Ticks .Vertebrate host : Sheep, goats , cattle and human .Symptoms : Most cases are mild or asymptomatic .In severe cases, the symptoms are : fever, headache, myalgia, artheralgia, nausea, vomiting, mucosal bleeding and bleeding under the skin .
Through the bite of infected ticks . Through the bite of infected ticks . By direct contact with infected animal blood.Human to human transmission occurs through direct contact with infected blood or body fluids.
1- West Nile Encephalitis (WNE ) .Family : Flaviviridae .2- Eastern Equine Encephalitis ( EEE ) .Family : Togaviridae .3-Westwrn Equine Encephalitis (WEE ). .Family : Togaviridae .4-Venezuelan Equine Encephalitis (VEE ). .Family : Togaviridae .
Enveloped , icosahedral particle .About 75- nm in diameter .The viral genome is ss-RNA , with positive polarity .
1- West Nile Encephalitis .Family: Flaviviridae.Geog. Dist. : Africa, Asia. Middle East, North America .Vector : Mosquitoes .Vertebrate host : Birds, horses, dogs, cats and human .Diseases :Most cases are mild or asymptomatic . 2- Encephalitis .
Through the bite of infected mosquitoes.Human to human transmission has not been documented .Can be transmitted through blood transfusion and organ transplantation .
2- Eastern equine encephalitis :Family : Togaviridae .Geog. Dist ; America .Vector : mosquitoes . Vertebrate host : Birds, horses and human .Diseases :1- Most cases are mild or asymptomatic . 2- Encephalitis .
Transmission : Through the bite of infected mosquitoes .
3- Western equine encephalitis :Family: Togaviridae.Geog dist : America .Vector : Mosquitoes .Vertebrate host : Birds, horses and human .Diseases :1-Most cases are mild or asymptomatic .2- Encephalitis .
Transmission : Through the bite of infected mosquitoes .
4- Venezuelan equine encephalitis :Family : Togaviridae .Geog, dist : America .Vector : Mosquitoes .Vertebrate host : Rodents, horses and human .Diseases :1-Most cases are mild or asymptomatic .2- Encephalitis .
Transmission : Through the bite of infected mosquitoes .
Restricted to reference laboratories , with facilities for high level containment .The most commonly lab. Methods are :2- Isolation of the virus in tissue culture, followed by identification of the isolated virus .3- Detection of IgM antibody .
The only vaccine available is for yellow fever .It is a live attenuated vaccine .The vaccine is known as 17 – D strain .The vaccine is administered in one dose , with a booster dose every 10 years .The vaccine is recommended to travelers to endemic areas.Should not be given to children less than 9-months.
Elimination of vector breading sites .Elimination of vectors using suitable insecticides.Avoidance contact with mosquitoes and ticks .
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