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 symmetry About 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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