are viruses that can be transmitted to man by arthropod vectors. Humans are usually not the natural reservoir for the virus.

Human pathogens arboviruses are grouped into three viral families: 1- Togaviridae 2- Bunyaviridae 3- Flaviviridae Arboviruses There are hundreds of arboviruses, many of which are not pathogens to human .

Arboviruses are enveloped, with ss-RNA genome.

Enveloped , icosahedral particle .

About 75- nm in diameter .

The viral genome is ss-RNA , with positive polarity .

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 .

For some genera the S segment is ambisense .

(Ambisense means that some of the genes on the RNA strand are negative sense and others are positive sense.)

Fever and rash - this is usually a non-specific illness resembling a number of viral illnesses.

Haemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo haemorrhagic fever.

Encephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis.

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

1- West Nile Encephalitis (WNE ) Family : Flaviviridae .

2- Eastern Equine Encephalitis ( EEE ) Family : Togaviridae .

3-Western Equine Encephalitis (WEE ) Family : Togaviridae .

4-Venezuelan Equine Encephalitis (VEE ) Family : Togaviridae

Man-Arthropod-Man

Cycle

Animal-Arthropod-Man Cycle

Man - arthropod -man e.g. dengue, urban yellow fever.

Reservoir may be in either man or arthropod vector.

In the latter transovarial transmission may take place.

Animal – arthropod - man e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever.

The reservoir is in an animal.

The virus is maintained in nature in a transmission cycle involving the arthropod vector and animal. Man becomes infected incidentally.

Mosquitoes Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis, EEE, WEE, VEE etc.

Ticks Crimean-Congo haemorrhagic fever, various tick-borne encephalitides etc.

Sandflies Sicilian sandfly fever, Rift valley fever.

In many cases, the actual reservoir is not known. The following animals are implicated as reservoirs Birds Japanese encephalitis, St Louis encephalitis, EEE, WEE Pigs Japanese encephalitis Monkeys Yellow Fever Rodents VEE, Russian Spring-Summer encephalitis

Serology infections.

- usually used to make a diagnosis of arbovirus Culture - a number of cell lines may be used, including mosquito cell lines. However, it is rarely carried out.

Direct detection tests - e.g detection of antigen and nucleic acids are available but there are safety issues.

Surveillance - of disease and vector populations Control of vector grounds - pesticides, elimination of breeding

Personal protection repellants - screening of houses, bed nets, insect Vaccination - available for a number of arboviral infections e.g.

Yellow fever, Japanese encephalitis, Russian tick-borne encephalitis

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

In Africa, Asia and middle east Vector : Ticks Vertebrate host : Sheep, goats , cattle, rodents and human

Most cases are mild or asymptomatic In severe cases: fever, headache, myalgia, artheralgia, nausea, vomiting, mucosal bleeding and bleeding under the skin

Mainly found in West Africa and S America Most cases are mild or asymptomatic.

The severe form of the disease may be caused after 3-4 days characterized by fever, myalgia, arthralgia, nausea, vomiting, jaundice, mucosal bleeding, bleeding under the skin, vomiting blood, seizure and coma.

Yellow fever occurs in 2 major forms: Urban and jungle (sylvatic) yellow fever.

N

onhuman primates are the main reservoir transmitted by forest mosquitoes. Man may become incidentally infected on venturing into jungle areas.

Dengue is the biggest arbovirus problem in the world today with over 2 million cases per year. Dengue is found in SE Asia, Africa and the Caribbean and S America.

Aedes mosquitoes which reside in water-filled containers

High fever, lymphadenopathy, myalgia, bone and joint pains, headache, and a maculopapular rash.

Severe cases may present with haemorrhagic fever and shock with a mortality of 5-10%.

Geographical distribution : Africa and Asia Vector: Sandflies Vertebrate host :Sheep, goats and cattle , camels and human Diseases: 1-Most cases are mild or asymptomatic 2- Hemorrhagic form: characterized by fever, headache, myalgia, arthralgia, nausea, mucosal bleeding and bleeding under the skin .

3- Meningoencephalitis

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 .

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 .