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Hemorrhagic fever viruses

Hemorrhagic fever viruses. By Dr. Marwa Salah. Hemorrhagic fever viruses. Arboviruses : Dengue fever virus (Flaviviridae) Rift Valley fever virus ( Bunyaviridae ) Yellow fever virus (Flaviviridae) Roboviruses: Hantaan virus ( Bunyaviridae ) Marburg & Ebola viruses ( Filoviridae )

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Hemorrhagic fever viruses

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  1. Hemorrhagic fever viruses By Dr. MarwaSalah

  2. Hemorrhagic fever viruses • Arboviruses: • Dengue fever virus (Flaviviridae) • Rift Valley fever virus (Bunyaviridae) • Yellow fever virus (Flaviviridae) • Roboviruses: • Hantaan virus (Bunyaviridae) • Marburg & Ebola viruses (Filoviridae) • Lassa fever virus (Arenaviridae) • Junin & Muchupo(Arenaviridae)

  3. OHF virus (OMSK hemorrhagic fever) (Flaviviridae) • KFD virus (Kyasanur forest disease) (Flaviviridae) • CCHF virus (Crimean-Congohemorragic fever) (Bunyaviridae

  4. Arboviruses & Roboviruses • “Arbo” is derived from arthropod-born viruses • they do not cause disease in arthropods. • They are enveloped (sensitive) viruses, they need intimate contact or insect bite to be transmitted. • No man to man transmission except in yellow fever and dengue. • Various animal, rodents and birds are reservoirs of infection.

  5. Roboviruses are not transmitted by arthropods but maintained within the rodent reservoir. • Man to man transmission occurs.

  6. Dengue fever • Flaviviridae, Arbovirus, icosahedral enveloped (+) ss RNA • Replication • In the cytoplasm • Released by budding

  7. Replication of Dengue virus

  8. Transmission & Pathogenesis of Dengue fever • Four serotypes • Reservoir probably monkey • Vector mosquito; Aedesegypti • High Viremia, so man to man transmission occurs Female Aedesaegypti mosquito

  9. I.P.: 5-6 daysEpidemiology • Dengue fever 1st reported epidemics in 1779-80 • In Africa, South East Asia & South America • KSA in 2006, 1544 cases (461 children <14 yrs.) Clinical forms • Asymptomatic • Classic Dengue Fever (Break bone fever ):fever, headache, myalgia, arthralgia, nausea, vomiting, macular rash • Dengue Hemorrhagic fever • Dengue Shock Syndrome

  10. Dengue hemorrhagic fever • Mainly in children • Acute onset of fever, hematemesis, melena renal involvement and shock with 50% mortality • It needs biosafety level 2

  11. Hemorrhagic conjunctivitis A large subcutaneous hemorrhage on upper arm in Patient with dengue hemorrhagic fever

  12. Pathogenesis of Dengue HF • Primary infection with one serotype produces antibodies specific to that serotype. • Secondary infection with another serotype is followed by formation of immune complexes between the second serotype and antibodies to the first one. • These antibodies not only fail to neutralize the virus but also enhances its ability to infect higher number of monocytes & release of cytokines, & vasoactive mediators leading to DIC, Hemorrhage, shock & death.

  13. Pathogenesis of Dengue HF

  14. Rift Valley fever • Bunyaviridae: Helical enveloped (-) ss RNA segmented • Single serotype • Replication • Transmission: • mosquito bite • contact with tissues, blood or body fluids of infected animals

  15. Epidemiology • In Africa, Yemen & KSA • 1st reported in Kenya 1931 • KSA in 2000-01, 77 died • Epizootics in sheep & cattle in Sudan, Egypt & South Africa. • In 1977, an outbreak occurred in Egypt with many deaths in animals and 600 human deaths

  16. Pathogenesis of RFV infection • Virus spreads to regional lymph nodes, liver and spleen & infects tissue macrophages • Soluble mediators & cytokines recruit more cells , to be infected leading to virus amplification • Infection of hepatocytes impairs synthesis of clotting factors • Reduced synthesis of albumin by hepatocytes reduced plasma osmotic pressure causing edema. • Infected adrenal cortical cells impairs secretion of steroid-synthesizing enzymes leading to hypotension and hypovolemia.

  17. C/P: 1. Mild: most cases, inapparent or flu-like e.g. fever, headache, myalgia, nausea, vomiting. Recovery in 4-7 days 2. Severe: • i. Ocular retinopathy • ii. Meningoencephalitis • iii. Hemorrhagic fever • It requires Biosafety level 3

  18. Laboratory Diagnosis of HFVs • Direct virus isolation on tissue culture. • Detection of viral antigens or antibody by immunofluorescence. • Detection of viral nucleic acid by PCR.

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