Download Viral Hemorrhagic fever

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.
All types of VHF are characterized by fever and bleeding disorders
and all can progress to high fever, shock and death in many cases.
Arenaviridae :
Lassa virus , Junin virus, and Machupo virus (MACV) are associated
with hemorrhagic fever.
Epidemiology:
Lassa virus: West Africa.
Junin virus: Argentina.
Machupo virus: Bolivia.
Virology:
-These are round, pleomorphic, and enveloped with a diameter of
120 nm.
- Nucleocapsid with two single-stranded RNA circular segments.
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Viral reservoir:
Some Arenaviruses are zoonotic pathogens and are generally
associated with rodents transmitted disease.
Transmission:
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.
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Pathogenesis and clinical picture:
Incubation period: 10-14 days.
The viruses infect macrophages, carried to blood vessels ;
endothelial cells infection, T-cell mediated response,
vascular damage.
- Visceral hemorrhage.
- Liver and spleen necrosis.
-
hemorrhage shock and cardiac damage.
Death in 50% of cases.
Filoviridae:
Marburg virus and Ebola virus :
Epidemiology : Endemic in Africa.
1-Marburg virus (Zimbabwe and Kenya).
2-Ebola virus (Sudan and Zaire).
Reservoir:
African green Monkeys and Wild Monkeys.
Transmission:
- Monkeys-Human contact, human-human contact, and unknown
routes of transmission.
-The first infection was first detected among Laboratory workers in
Marburg, who had been exposed to tissue culture of cell line
prepared from Monkeys.
Virology:
-
Filoviruses have a Single stranded RNA, which encodes
seven proteins
Enveloped filamentous virus with Helical nucleocapsid
measuring 800 to as long as 14000 nm.
Pathogenesis and clinical picture:
-Eosinophilic cytoplasmic inclusions are seen in cells
infected with the virus.
-These virus infection disseminated with blood stream to
parenchymal cells of liver, spleen, lymph nodes, and lung.
-Widespread hemorrhage causes edema and hypovolemic
shock.
-Liver function tests:
SGPT, and alkaline phosphatase elevated.
- Spleen destruction and lymph node enlargements.
Bunyaviridae:
-Super-group of at least 200 different viruses.
-Most are Arboviruses.
Virology:
-
Enveloped, spherical virion with a diameter of 90-100 nm.
Single-stranded RNA nucleocapsids virus.
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Transmission: Vector-born infection
1-Phlebovirus:
2-Nairovirus:
3-Bunyavirus:
Sandfly , genus : Phlebotomus.
Ticks.
Mosquito.
Vertebrate host:
1-Phlebovirus:
2-Nairovirus:
3-Bunyavirus:
Sheep, cattle, others
cattle, goats
Rodents, small mammals, and birds.
Disease:
1-Rift Valley fever ; hemorrhagic fever, encephalitis.
2-Crimean-Congo -Hemorrhagic fever.
3-California encephalitis.
Pathogenesis and clinical picture:
-Primary viremia; flu-like symptoms, infection of vascular
endothelium and Macrophage of Reticuloendothelial
system ; secondary viremia.
1-Vascular endothelial damage; leakage of plasma and
erythrocytes, hemorrhagic fever.
2- Cerebral edema and encephalitis.
3- Kidney hemorrhagic necrosis.
Crimean-Congo -Hemorrhagic fever caused by Nairovirus:
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Flaviviridae:
Flaviviruses are Arboviruses transmitted to man by vector
(flavus (Latin term) means yellow).
Two types of Flaviviridae cause Hemorrhagic fever (H.F), and
Yellow fever:
1-Dengue virus: DHF: dengue H.F, and DSS: dengue shock syndrome.
2-Yellow fever virus: Yellow fever and Hepatitis.
Vector:
Mosquito of the genus Aedes.
Host: Human and Monkeys.(Zoonosis).
Distribution:
Dengue fever: Worldwide, especially tropics.
Yellow fever: Africa, and South America.
Virology:
- Positive Single-stranded RNA viruses.
- Enveloped, Icosahedral nucleocapsid.
- Size: 40-65 nm.
- Glycoprotein spikes (adhesion of virus to tissue).
-All Flaviviruses are
serologically related:
So Anti-Virus serotype
antibodies could be
used as prophylactic
vaccine for others.
Pathogenesis and clinical picture:
- Biting of the host skin by vector ( Female Mosquito).
, inoculation of small capillaries bloodstream by virus in
Saliva.
-The virus will be carried by dendritic cells throughout small
capillaries to the target tissue.
-Target tissue:
1-The endothelial cells of Capillaries.
2-The blood Macrophage and monocytes.
-Blood phagocytes will transfer the microbe to the
Reticuloendothelial system(RES).
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-
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.
2-Brain: Encephalitis.
3-Vasculature and skin: Hemorrhage and shock.
Pathogenesis of Flaviviruses:
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