Viral Hemorrhagic fever: . The viral hemorrhagic fevers ( VHFs ) are a diverse group of animal and human illnesses that are caused by four different families of RNA viruses: 1- Arenaviridae . 2- Filoviridae . 3- Bunyaviridae . 4- Flaviviridae .
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The viral hemorrhagicfevers (VHFs) are a diverse group of animal and human illnesses that are caused by four different families of RNA viruses:
All types of VHF are characterized by fever and bleeding disorders and all can progress to high fever, shock and death in many cases.
Lassavirus, Juninvirus, and Machupo virus (MACV) are associated with hemorrhagic fever.
Lassa virus: West Africa.
Junin virus: Argentina.
Machupo virus: Bolivia.
-These are round, pleomorphic, and enveloped with a diameter of
- Nucleocapsid with two single-stranded RNA circular segments.
Some Arenavirusesare zoonotic pathogens and are generally associated with rodentstransmitted disease.
Humans could be infected through mucosal exposure to aerosols, or by direct contact of broken skin with the infectious material, derived from infected rodents.
Ingestion of contaminated food, person-to-person contact is incriminated with transmission of the virus in some cases.
Pathogenesis and clinical picture:
Incubation period: 10-14 days.
The viruses infect macrophages, carried to bloodvessels ; endothelialcells infection, T-cell mediated response,
Liver and spleen necrosis.
hemorrhage shock and cardiac damage.
Deathin 50% of cases.
Marburg virus and Ebola virus :
Epidemiology : Endemic in Africa.
1-Marburgvirus (Zimbabwe and Kenya).
2-Ebolavirus (Sudan and Zaire).
African green Monkeysand Wild Monkeys.
Monkeys-Human contact, human-human contact, and unknown
routes of transmission.
-The first infection was first detected among Laboratory workersin
Marburg, who had been exposed to tissue culture of cell line
prepared from Monkeys.
Filoviruses have a Single stranded RNA, which encodes
Envelopedfilamentous virus with Helicalnucleocapsid
measuring 800 to as long as 14000nm.
-Eosinophiliccytoplasmicinclusions are seen in cells
infected with the virus.
-These virus infection disseminated with blood stream to
parenchymalcells of liver, spleen, lymphnodes, and lung.
-Widespread hemorrhage causes edema and hypovolemic
SGPT, and alkaline phosphatase elevated.
- Spleen destruction and lymph node enlargements.
-Super-group of at least 200 different viruses.
-Most are Arboviruses.
Enveloped, spherical virion with a diameter of 90-100 nm.
Single-stranded RNA nucleocapsids virus.
Transmission: Vector-born infection
1-Phlebovirus: Sandfly, genus : Phlebotomus.
1-Phlebovirus: Sheep, cattle, others
2-Nairovirus: cattle, goats
3-Bunyavirus: Rodents, small mammals, and birds.
1-Rift Valley fever ; hemorrhagic fever, encephalitis.
2-Crimean-Congo -Hemorrhagic fever.
-Primaryviremia; flu-like symptoms, infection of vascular
endotheliumand Macrophageof Reticuloendothelial
system ; secondary viremia.
1-Vascular endothelial damage; leakage of plasma and
erythrocytes, hemorrhagic fever.
2- Cerebral edema and encephalitis.
3- Kidney hemorrhagic necrosis.
Flavivirusesare Arboviruses transmitted to man by vector (flavus (Latin term)means yellow).
Two types of Flaviviridaecause Hemorrhagicfever (H.F), and Yellowfever:
1-Dengue virus: DHF: dengue H.F, and DSS: dengue shock syndrome.
2-Yellow fever virus: Yellow fever and Hepatitis.
Mosquito of the genus Aedes.
Host: Human and Monkeys.(Zoonosis).
Dengue fever: Worldwide, especially tropics.
Yellow fever: Africa, and South America.
- Positive Single-strandedRNA viruses.
- Enveloped, Icosahedralnucleocapsid.
- Size: 40-65 nm.
Glycoprotein spikes (adhesion of virus to tissue).
antibodies could be
used as prophylactic
vaccine for others.
- Biting of the host skin by vector ( FemaleMosquito).
, inoculation of smallcapillariesbloodstream by virus in
-The virus will be carried by dendriticcells throughout small
capillaries to the targettissue.
1-The endothelial cells of Capillaries.
2-The blood Macrophage and monocytes.
-Blood phagocytes will transfer the microbe to the
This will initiate Primary Viremia (fever, chill, headaches, and flu-like symptoms within 3-7 days).
Secondary Viremia is associated with efficient replication of
virus in RES.
-This viremia can produce sufficient virus to infect:
1-Liver: Hepatitis, and Jaundice; yellow fever.
3-Vasculature and skin: Hemorrhage and shock.