Marburg and Ebola viruses

Lethal beyond imagination!!!!!!!

PANKAJ DHAKAPh.D Scholar, VPH, I.V.R.Ipankaj.dhaka2@gmail.com

Taxonomy

Order: Mononegavirales Family: Filoviridae Genus: Ebola like viruses Species: Ebola

Subtypes – Ebola-Zaire, Ebola-Sudan,

Ebola-Ivory Coast• disease in humans

– Ebola-Reston • disease in nonhuman primates

The Media and Public Perception

Ebola outbreak- 2014• World's worst outbreak of the Ebola virus, killing 3,338 people

…..and continue…

• Location: West Africa, caused by the Zaire species of the virus

• Although most previous Ebola outbreaks occurred in Central Africa, this outbreak started in the West African nation of Guinea in late 2013

• “On 8 August 2014, the WHO declared the epidemic to be an international public health emergency”

• General concepts- Ebola and Marburg viruses are– Non-segmented– Negative-sense– ss RNA viruses that resemble rhabdoviruses and paramyxoviruses in

their genome organization and replication mechanisms – Together, they make up the family Filoviridae.

• Latin "filum," meaning thread-like, based upon their filamentous structure

• Also classified as "hemorrhagic fever viruses" based on their clinical manifestations, which include coagulation defects, a capillary leak syndrome, and shock [Bray, 2005]

An Introduction

Viral structure:

• Mature filoviral particles take on a variety of forms from circular or “6”-shaped to straight filaments

• Length of the virions is variable with Marburg particles averaging close to 800 nm, and Ebola virions measuring about 1 μm

• The diameter of all filovirus particles uniformly measures- 80 nm.

Marburg virus

• All isolates of Marburg virus are currently considered to be members of a single species– First outbreak (Marburg, Germany, 1967)– laboratory workers infected by monkeys

• They may vary in their pathogenicity for humans

• Overall fatality rate in the 1967 outbreak in Europe was 21 %, whereas mortality among identified cases in 2000 in the Democratic Republic of Congo (DRC) and in 2005 in Angola was in the range of 80-90%

• Alternatively, the striking difference in outcome may reflect the paucity of medical resources where the latter outbreaks took place

[Bausch et. Al., 2003]

(African Hemorrhagic Fever, Green Monkey Disease, Marburg Fever)

The name ‘Ebola’

Aug 26, 1976 in Yambuku, town of Zaïre

-44 year-old school teacher, went to the doctor for his high fever, they gave him a quinine shot which is good against malaria

-A week later, uncontrolled vomiting, bloody diarrhea, trouble breathing and then bleeding from his nose, mouth, and anus

-He died ~14 days after the onset of symptoms

He started an epidemic that killed 280 of the 313 infected persons (88%)

& still To be continued to ….the deadliest outbreak of Ebola in history

A glimpse of Ebola virus assault:

• Five species- Zaire, Sudan, Ivory Coast, Bundibugyo & Reston

• The Zaire virus: 1st appearance in 1976, caused multiple large outbreaks with mortality rates of 55 to 88 %

• The Sudan virus: 50 % case-fatality rate in four known epidemics: two in Sudan in the 1970s, one in Uganda in 2000, and Sudan in 2004.

• The Ivory Coast virus: Identified as the causative agent in an ethologist performed a necropsy on a chimpanzee in the Tai Forest. The case survived

• The Bundibugyo virus: Emerged in Uganda in 2007, lower case-fatality rate (30%)

• The Reston virus: Apparently maintained in an animal reservoir in the Philippines , not been found in Africa.

• 1st recognized in an outbreak of lethal infection in macaques imported into the U.S in 1989. This episode brought the filoviruses to worldwide attention through the publication of Richard Preston's book, The Hot Zone.

Major outbreaks:

2014

Death toll of Ebola…..

RNA

L

NP

VP35

VP40 VP30

Membrane

VP24

GP1,2

?

Molecular Biology

OR

GP VP30

IRIR

VP40

3‘-HO

NP VP35

IR

l

IR1IR

t

19,104

P -5‘

LVP24

The virions contain the ~ 19 kb non-infectious genome that encodes seven structural proteins with a gene order of: 3' leader, nucleoprotein (NP), virion protein (VP) 35 (VP35), VP40, glycoprotein (GP), VP30, VP24, polymerase L protein, and 5' trailer.

Pathogenesis of Ebola and Marburg virus infection

Impairment of adaptive immunity

Through impaired dendritic cell function and lymphocyte apoptosis

• Act both directly and indirectly to disable antigen-specific immune responses– Dendritic cells, which have primary responsibility for the initiation of adaptive immune responses,

are a major site of filoviral replication. – Infected cells fail to undergo maturation and are unable to present antigens to naive lymphocytes-

Explaining why patients dying from Ebola hemorrhagic fever do not develop antibodies to the virus

• Adaptive immunity is also impaired by the massive loss of lymphocytes that accompanies lethal Ebola virus infection.

– Lymphocytes remain uninfected, but undergo "bystander" apoptosis, presumably induced by inflammatory mediators and/or the loss of support signals from dendritic cells, resembles phenomenon of septic shock

(Geisbert et. al., 2003)

The infections are characterized by “crashing” patients with liquefying organs; patients die from extensive blood loss

How it works

Threadlike Ebola virions bud from a cell, Ebola virus disables a cell's tetherin protein.

Tetherin: A human cellular protein which inhibits retrovirus infection by preventing the diffusion of virus particles after budding from infected cells

PATHOGENESIS

• Endothelial cells, phagocytes and hepatocytes are main target of the infection.

• After infection a secreted glycoprotien (sGP) is synthesized.• sGP forms the trimeric complex, which binds the virus to

endothelial cell. Also inhibits the early steps of neutrophil activation.

• The presence of viral particles and cell damage resulting from budding leads to release of cytokines TNF , IL-6 and IL-8.The cytopathic effect from infection in endothelial cells result in loss of vascular integrity (Onyango et. al., 2007)

Where does Ebola hide?

• 2002- Fruit Bats showed antibodies against Ebola

• Isolated from liver and spleen

• Fruit bats do not show any symptoms, hence best candidate to be the reservoir

• More research needs to be done

Towards detecting the natural host of the virus

Ecology of virus

The virus kills gorillas and chimpanzees and other monkeys. in such high percentage – they are not likely to be its natural host

TRANSMISSION:

• Close contact with blood, secretion, organs or other body fluid of infected animals

• Handling of infected monkeys, chimpanzees & fruit bats

• Human to human transmission- vomiting from direct contact with the blood, secretion, organs or body fluid like saliva or semen

• Burial ceremonies in which mourners have direct contact with the body of deceased person can play role in transmission

• It can spread through semen for up to 7weeks after recovery from illness

Clinical symptoms:

• I.P: 2-21 days • Abrupt illness with fever, severe frontal

headache, red eyes, malaise, lumbar myalgia, vomiting, nausea and diarrhoea.

• Maculopapular rash begins 5-7 days later on trunk and upper arms.

• GI haemorrhage as the severity of illness increases.

• Marked leucopenia, necrosis of granulocytes, DIC and thrombocytopenia

• In fatal case patient become hypotensive, develop impaired liver and kidney functions and lapse into coma.

DIAGNOSIS:

• Ruled out- malaria, typhoid, shigellosis, cholera, leptospirosis, plague, rickettsia, relapsing fever, meningitis, hepatitis and other viral hemorrhagic fever

• If there is strong suspicion and reason to consider Ebola HF, patient should be isolated & following that samples should be collected and tested to confirm

• Diagnostic test available are:– Antigen Capture ELISA– Antibody capture ELISA (IgM & IgG)– RT PCR Assay– Virus isolation & immunohistochemistry

testing

TREATMENT:

• No specific treatment is available, supportive management can be done

• Therapeutic principle: Reversal of dehydration, hemoconcentration, renal failure, protein, electrolyte loss or blood loss

• Transfusion of fresh blood & platelets are frequently given to combat DIC & haemmorhagic manifestation. Successful management may require renal dialysis.

• Drug Zmapp: Like i/v immunoglobulin therapy, ZMapp contains neutralizing antibodies that provide passive immunity to the virus by directly and specifically reacting with it in a "lock and key" fashion, experimental treatment was used in humans in present outbreak.

Preventive measures during epidemic

• Hospitalization and Isolation of patients

• Quarantine areas if Necessary

• Protective measures (Gloves, gowns, face shields, masks, eye Protection)

• Disinfect bedding, utensils, excreta (heat or chemicals)

• Burn used articles

Isolation Criteria

Based upon 4 main factors: 1. Potential harm to life 2. Potential harm to critical systems 3. Potential harm to property 4.Topography & meteorological

considerations

Direct Contact with infected blood, body fluids to be avoided

Airborne transmission rare, but cannot be conclusively excluded- negative pressure room and HEPA respirator

Laboratory Precautions- BSL 4

Personal Protective Equipment

Post-Mortem Practices

Protection tips for authority:

Challenges:

• Finding the Reservoir

• How different strains with different mortility!!!!1

• Need to know more about Transmission – From animal to man– Ways of putting it into food

• Aerosolization– Possible ???

Bioweapon !!!!!

– Rates of fatality

– Deaths• Terror of dying

• Ignorance of the general public– Think that they can die by being in same room with

person– Much not known by general physicians and scientist

“Adopt the pace of nature: her secret is patience” - R. Emerson