are viruses that can be transmitted to man by arthropod vectors. Humans are usually not the natural...
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Transcript of are viruses that can be transmitted to man by arthropod vectors. Humans are usually not the natural...
Arthropod-borne viruses (arboviruses)
Arthropod-borne viruses
(arboviruses)
are viruses that can be transmitted to man
by arthropod vectors.
Humans are usually not the natural reservoir for the virus.
Arthropod-borne viruses
(arboviruses)Human pathogens arboviruses are
grouped into three viral families:
1- Togaviridae
2- Bunyaviridae
3- Flaviviridae
ArbovirusesThere are hundreds of arboviruses, many of which are not pathogens to human .Arboviruses are enveloped, with ss-RNA genome.
Family: Togaviridae 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 .
Family: Flaviviridae
Family : Bunyaviridae 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.)
Diseases Caused
Fever and rash - this is usually a non-specific illness resembling a number of viral illnesses.
Diseases CausedHaemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo haemorrhagic fever.
Diseases CausedEncephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis.
1- Arboviruses associated with hemorrhagic fever
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
2- Arboviruses associated with encephalitis .
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
Arboviruses transmission Cycles
Man-Arthropod-Man Cycle
Animal-Arthropod-Man Cycle
Arboviruses transmission Cycles
Transmission Cycles
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.
Arthropod Vectors
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.
Animal Reservoirs
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
Diagnosis
Serology - usually used to make a diagnosis of arbovirus infections.
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.
Prevention
Surveillance - of disease and vector populations
Control of vector - pesticides, elimination of breeding grounds
Prevention
Personal protection - screening of houses, bed nets, insect repellants
Vaccination - available for a number of arboviral infections e.g. Yellow fever, Japanese encephalitis, Russian tick-borne encephalitis
1- Arboviruses associated with hemorrhagic fever
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
Crimean Congo hemorrhagic fever
In Africa, Asia and middle east
Vector : Ticks
Vertebrate host : Sheep, goats , cattle, rodents and human
Crimean Congo hemorrhagic fever(Clinical findings)
Most cases are mild or asymptomatic
In severe cases: fever, headache, myalgia, artheralgia, nausea, vomiting, mucosal bleeding and bleeding under the skin
Yellow FeverMainly 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.
Nonhuman primates are the main reservoir transmitted by forest mosquitoes. Man may become incidentally infected on venturing into jungle areas.
Yellow fever cycle
DengueDengue 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.
Dengue cycle
Aedes mosquitoes which reside in water-filled containers
Dengue (clinical findings)
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%.
Rift valley feverGeographical 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
Arboviruses associated with encephalitis .
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 .
Arboviruses associated with 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 .
Eastern Equine Encephalitis