Viral hemorrhagic fever
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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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Viral hemorrhagic fever

Viral Hemorrhagic fever:

The viral hemorrhagicfevers (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

Arenaviridae:

Lassavirus, Juninvirus, 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.


Viral hemorrhagic fever

N

Viral reservoir:

Some Arenavirusesare zoonotic pathogens and are generally associated with rodentstransmitted 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.


Viral hemorrhagic fever

n

Pathogenesis and clinical picture:

Incubation period: 10-14 days.

The viruses infect macrophages, carried to bloodvessels ; endothelialcells infection, T-cell mediated response,

vascular damage.

Visceral hemorrhage.

Liver and spleen necrosis.

hemorrhage shock and cardiac damage.

Deathin 50% of cases.


Filoviridae

Filoviridae:

Marburg virus and Ebola virus :

Epidemiology : Endemic in Africa.

1-Marburgvirus (Zimbabwe and Kenya).

2-Ebolavirus (Sudan and Zaire).

Reservoir:

African green Monkeysand Wild Monkeys.

Transmission:

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.


Virology

Virology:

Filoviruses have a Single stranded RNA, which encodes

seven proteins

Envelopedfilamentous virus with Helicalnucleocapsid

measuring 800 to as long as 14000nm.


Pathogenesis and clinical picture

Pathogenesis and clinical picture:

-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

shock.

-Liverfunctiontests:

SGPT, and alkaline phosphatase elevated.

- Spleen destruction and lymph node enlargements.


Bunyaviridae

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.


Viral hemorrhagic fever

N

Transmission: Vector-born infection

1-Phlebovirus: Sandfly, genus : Phlebotomus.

2-Nairovirus: Ticks.

3-Bunyavirus: Mosquito.

Vertebrate host:

1-Phlebovirus: Sheep, cattle, others

2-Nairovirus: cattle, goats

3-Bunyavirus: Rodents, small mammals, and birds.

Disease:

1-Rift Valley fever ; hemorrhagic fever, encephalitis.

2-Crimean-Congo -Hemorrhagic fever.

3-California encephalitis.


Pathogenesis and clinical picture1

Pathogenesis and clinical picture:

-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.


Crimean congo hemorrhagic fever caused by nairovirus

Crimean-Congo -Hemorrhagic fever caused by Nairovirus:

N


Flaviviridae

Flaviviridae:

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.

Vector:

Mosquito of the genus Aedes.

Host: Human and Monkeys.(Zoonosis).

Distribution:

Dengue fever: Worldwide, especially tropics.

Yellow fever: Africa, and South America.


Virology1

Virology:

- Positive Single-strandedRNA viruses.

- Enveloped, Icosahedralnucleocapsid.

- Size: 40-65 nm.

Glycoprotein spikes (adhesion of virus to tissue).

-All Flavivirusesare

serologically related:

SoAnti-Virus serotype

antibodies could be

used as prophylactic

vaccine for others.


Pathogenesis and clinical picture2

Pathogenesis and clinical picture:

- Biting of the host skin by vector ( FemaleMosquito).

, inoculation of smallcapillariesbloodstream by virus in

Saliva.

-The virus will be carried by dendriticcells throughout small

capillaries to the targettissue.

-Target tissue:

1-The endothelial cells of Capillaries.

2-The blood Macrophage and monocytes.

-Blood phagocytes will transfer the microbe to the

Reticuloendothelialsystem(RES).


Viral hemorrhagic fever

N

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

Pathogenesis of Flaviviruses:

N


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