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MICR 454L. Emerging and Re-Emerging Infectious Diseases Lecture 11: SARS, Hantavirus (Reading: Emerging Viruses) Dr. Nancy McQueen & Dr. Edith Porter. Brief history Morphology Genome Replication cycle Diseases Pathogenesis Diagnosis Treatment Prevention Threat. Overview. SARS

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micr 454l

MICR 454L

Emerging and Re-Emerging

Infectious Diseases

Lecture 11:

SARS, Hantavirus

(Reading: Emerging Viruses)

Dr. Nancy McQueen & Dr. Edith Porter

overview
Brief history

Morphology

Genome

Replication cycle

Diseases

Pathogenesis

Diagnosis

Treatment

Prevention

Threat

Overview
  • SARS
  • Hantavirus
sars brief history
SARS Brief History
  • 2003 - an epidemic of severe and often fatal pneumonia broke out in Southeast China, Hong Kong, and Vietnam.
  • The disease spread to Toronto, Canada.
  • Air travel by infected individuals quickly spread the disease to 32 countries resulting in the first pandemic in the twenty-first century.
  • Over a 6 month period there were 8,000 cases and 800 deaths
  • The disease was named severe acute respiratory syndrome (SARS).
  • The causative agent was quickly identified as a previously uncharacterized coronavirus
slide5
SARS
  • Family Coronaviridae
    • Coronaviruses - divided into 3 groups (I,II, and III) based on antigenic and genomic sequences
      • SARS does not fit into any groups
      • ? recombination between an ancestral group II mammalian and a group III avian virus.
      • Humans - from contact with palm civets (a cat-like mammal related to the mongoose)
      • Probably acquired during slaughter of the civet rather than from eating the civet.
      • Palm civets - not the natural reservoir, but rather an intermediate or amplifier host
        • Chinese horseshoe bats are the natural reservoir
    • Spherical, enveloped with glycoprotein spikes
    • Linear SS + RNA genome
replication cycle of sars
Replication cycle of SARS

Fusion at the plasma membrane

Direct translation of genomic RNA

mRNA synthesis and genome replication in cytoplasm

Budding into intracytoplasmic vesicles

sars disease
SARS Disease
  • Transmission
    • From contact with infected civet
    • Human to human transmission
      • Through eyes, nose , and mouth
        • Direct contact
        • Fecal-oral
        • Droplets produced by coughing and sneezing
        • ? Contact with blood
  • Mean incubation period: 6.4 days
  • Symptoms
    • Fever, dry cough, dyspnea (shortness of breath), headache,hypoxemia (low blood oxygen concentration)
    • Other general influenza-like symptoms, including chills, malaise, loss of appetite, and myalgia.
    • Gastrointestinal symptoms (less common), including diarrhea (27%), vomiting (14%), and abdominal pain (13%).
sars pathogenesis
SARS Pathogenesis
  • Virus initially infects ciliated epithelial cells
  • Next infects macrophages, and T lymphocytes
    • Immune cells bring the virus to pneumocytes and surface enterocytes of the small intestine as well as other organs
  • The typical clinical course:
    • improvement in symptoms during the first week of infection
    • worsening of symptoms during the second week.
      • may be due to combined effects of patient's immune responses (proinflammatory cytokines) and uncontrolled viral replication.
  • Death may result from progressive respiratory failure due to diffuse alveolar damage (DAD).
    • Pathologic lesions show inflammatory exudation in the alveoli and interstitial tissue with hyperplasia of fibrous tissue and fibrosis.
    • Fatality rate is 13.2% for patients younger than 60 years and 43.3% for patients aged 60 years or older.
slide10

Proposed Role of Immune Cells in SARS Pathogenesis

Dissemination to other organs

Infection of immune cells

SARS-CoV

Infection of epithelial cells of respiratory tract

(Transient)

Immunosuppression

ARDS

Injury to respiratory tract

sars lung pathology
SARSLung Pathology

Normal lung tissue

Diffuse alveolar damage pattern of lung injury in SARS patients. (a) Early exudative phase diffuse alveolar damage showing vascular congestion, with interstitial and airspace edema and inflammatory cell infiltrates (H&E, original magnification 200); (b) the same field showing fibrinous exudates by Martius scarlet blue stain (original magnification 200); (c, d) exudative phase diffuse alveolar damage, with hyaline membranes (c, H&E, original magnification 200; d, elastic trichrome, original magnification 200); (e, f) organizing phase diffuse alveolar damage (e, H&E, original magnification 100; f, elastic trichrome, original magnification 100).

http://www.nature.com/modpathol/journal/v18/n1/images/3800247f1.jpg

sars laboratory findings
SARS Laboratory Findings
  • Lymphopenia - due to infection and destruction of T cells
    • Extent of decrease correlates with severity of disease
  • Mildly elevated aminotransferase indicating liver damage
  • Histopathological changes in many organs
sars diagnosis
SARS Diagnosis
  • Diagnostic tests for coronavirus infection fall into two types:
    • Serological testing
      • indirect fluorescent antibody testing
      • ELISA
    • Molecular testing
      • RT-PCR
sars treatment
SARS Treatment
  • Antiviral drugs such as Ribavirin and interferon  have been used
    • There is no agreement that these antiviral drugs have been successful in treating SARS or any coronavirus infection.
    • Some studies suggest that these treatments cause more harm than good for the patient.
sars prevention
SARS Prevention
  • Currently there is no vaccine, but several different vaccines are under development
  • Isolation of infected individuals
    • Hospital personnel must wear masks
    • Wash hands
    • Decontaminate all infectious wastes
sars threats
SARS Threats
  • No current threats
  • However, because coronaviruses can undergo high rates of recombination, it is feared that other coronaviruses might cross the species barrier as a result of generation of recombinants containing both animal and human coronavirus genes.
  • ~5% of bats in the U.S. carry coronaviruses
take home message sars
Take Home Message SARS
  • SARS is a coronavirus which is enveloped and contains a SS +RNA genome
  • The natural host for SARS is a bat and the disease was originally transmitted to humans from infected civets
  • SARS is characterized by a fever, hypoxemia and a high mortality rate from respiratory failure.
  • Currently no effective treatment or vaccines
hantavirus brief history 1
Hantavirus: Brief History (1)
  • In 1993 in the four corners area of the United States, 24 cases of a severe influenza-like respiratory illness complicated by respiratory failure occurred in previously healthy young adults.
  • Death occurred in 50-60% of the cases.
  • A hantavirus was ultimately identified as the causative agent and transmission found to be from contact with infected rodents (deer mice) or their droppings.
  • Why did this happen in the Four Corners area? Simply because there was a "bumper crop" of rodents there, due to heavy rains during the spring of 1993, which produced an extra-plentiful supply of the foods that rodents eat.
hantavirus brief history 2
Hantavirus Brief History (2)
  • A new type of hantavirus disease.
  • Previously, hantavirus infections had been associated with hemorrhagic fevers, not respiratory disease.
    • Documented as early as 1,000 years ago in China.
  • Since the initial outbreak in the Four Corners Region, the disease has been confirmed in over half of the states in the US, with a total of nearly 500 people infected.
hantavirus classification
Hantavirus Classification
  • Hantavirus belongs to the family Bunyaviridae, genus Hantavirus
    • Hantavirus genus contains several viruses that infect humans
      • Some cause a severe hemorrhagic fever with renal syndrome (HFRS)
      • Some cause hantavirus pulmonary syndrome (HPS)
    • All are zoonotic viruses of wild rodents
    • Spherical, enveloped virus
    • Linear SS, segmented, - RNA genome
      • 3 segments - small, medium, and large
hantavirus replication cycle
Hantavirus Replication Cycle

Enter via receptor mediated endocytosis

Fusion with endosomal membrane - uncoating

mRNA synthesis and genome replication occur in cytoplasm

Budding into the Golgi complex

hfrs disease pathogenesis
HFRS Disease/Pathogenesis
  • Transmission via aerosols of viruses from rodent saliva, urine or feces
  • Disease divided into five phases
    • Acute febrile - fever, chills, headache, anorexia, vomiting, backache
    • Hypotensive
    • Oliguric
    • Diuretic - suggests improvement
    • Convalescent - may require 4 months
  • Viral antigens are detected in brain, spleen, kidneys and liver.

thrombocytopenia with hemorrhagic manifestations; kidney edema, proteinuria, renal failure; cardiovascular instability and shock

Death

hps transmission to humans
HPS Transmission to humans
  • Aerosols of viruses from rodent saliva
  • Rodent bites (rare)
  • Oral after touching or eating something that has been contaminated with rodent urine, droppings, or saliva
  • Human-to-human transmission via aerosols
hps disease pathogenesis
HPS Disease/Pathogenesis
  • Disease divided into four phases:
    • Prodromal - non-specific symptoms such as fatigue, fever, chills, myalgias
    • Cardiopulmonary - abrupt onset of respiratory failure which may proceed rapidly and lead to shock, non-cardiogenic pulmonary edema and hypotension.
      • Symptoms include coughing and shortness of breath, with the sensation of, as one survivor put it, a "...tight band around my chest and a pillow over my face" as the lungs fill with fluid.
      • 50% die in 24-48 hours
    • Diuretic - coincides with rapid clinical improvement
    • Convalescence - may last several months
hantavirus pathophysiology
Hantavirus Pathophysiology
  • Hantaviruses preferentially infect endothelial cells
  • Viruses target the pulmonary capillary walls (HPS) or the capillary walls in the kidney (HFRS) initiating a cascade of events culminating in a massive, pulmonary or kidney-specific inflammatory response endothelial damage and edema (TNF and IL-1)
  • The damage to pulmonary/kidney microvascular endothelium increases capillary permeability and leads to even more fulminant pulmonary/kidney edema.
  • In HFRS - DIC, and hemorrhagic manifestations may follow
hantavirus diagnosis
Hantavirus Diagnosis
  • Serology
    • ELISA
    • Western immunoblot
  • Immunohistochemistry
  • RT-PCR
hantavirus treatment
Hantavirus Treatment
  • Ribavirin may reduce mortality if given early in disease - May increase error rate of the RNA polymerase
  • Attentive and supportive therapy
  • HPS - if infected individuals are recognized early and receive medical care in an intensive care unit, they may do better.
    • In intensive care, patients are intubated and given oxygen therapy to help them through the period of severe respiratory distress.
hantavirus prevention
Hantavirus Prevention
  • Eliminate or minimize contact with rodents
  • Vaccines are in development
hantavirus threats
Hantavirus Threats
  • 60,000 to 150,000 are hospitalized/year due to HPS or HFRS
  • Genomic reassortment by RNA viruses with segmented genomes is well documented and has the potential to produce viruses with altered biological activity, host range, and disease potential.
  • Genomic reassortment among hantaviruses is known to occur in nature, but the precise role of genomic reassortment in the epidemiology of hantavirus infections is unknown.
  • HPS causing hantviruses have potential use as biological weapons
    • Aerosol infection
    • Highly lethal
take home message hantavirus
Take Home Message Hantavirus
  • Hantaviruses are enveloped and contain a segmented SS - RNA genome.
  • The natural host for hantaviruses is rodents and man usually acquires the disease via inhalation after contact with infected rodents or their droppings.
  • Hantaviruses cause two different types of disease -
    • Hemorrhagic fever with renal syndrome (HFRS) characterized by fever, renal failure, hemorrhaging and shock with a 5-10% mortality rate
    • Hantavirus pulmonary syndrome (HPS) characterized by flu symptoms, coughing, and shortness of breath as the lungs fill with fluid. The mortality rate is over 50%.
  • There is potential for new hantaviruses through shift and drift
resources
Resources
  • The Microbial Challenge, by Krasner, ASM Press, Washington DC, 2002.
  • Brock Biology of Microorganisms, by Madigan and Martinko, Pearson Prentice Hall, Upper Saddle River, NJ, 11th ed, 2006.
  • Microbiology: An Introduction, by Tortora, Funke and Case; Pearson Prentice Hall; 9th ed, 2007.
  • Fundamentals of Molecular Virology, by Nicholas Acheson; Wiley and Sons; 2007
  • Human Virology by Collier and Oxford, Oxford University Press; 2nd edition, 2000.
  • www.chinadaily.com.cn/english/doc/2004-06/28/xin_11060128103408705697.jpg
  • www.stanford.edu/~siegelr/RSA/civet.jpg
resources1
Resources
  • www.math.tu-berlin.de/aktMath/site/pics/SARS-Virus.jpg
  • www.savi-info.ca/SARS_Virus.JPG
  • www.cdc.gov
  • http://www.emedicine.com/emerg/topic861.htm
  • Samuel, Melanie A. and Michael S. Diamond (2006). Pathogenesis of West Nile Virus Infection: a Balance between Virulence, Innate and Adaptive Immunity, and Viral Evasion, J Virol. 80(19): 9349-9360.
  • Amy C. Simsa, Susan E. Burkett, Boyd Yount, Raymond J. Pickles (2008). SARS-CoV replication and pathogenesis in an in vitro model of the human conducting airway epithelium. Virus Research 133:33–44
  • Yong Guo, Christine Korteweg, Michael A. McNutt, Jiang Gu (2008). Review - Pathogenetic mechanisms of severe acute respiratory syndrome. Virus Research 133:4–12.
  • Colleen B. Jonsson, Brook G. Milligan, Jeffrey B. Arterburn (2005) Potential importance of error catastrophe to the development of antiviral strategies for hantaviruses. Virus Research 107:195–205