Orthomyxovirus Paramyxoviruses

EDWARD-BENGIE L. MAGSOMBOL, MDFPCP, FPCC, DASNC

Associate Professor, Department of MicrobiologyFatima College of Medicine

A 22-year old man suddenly experienced headache, myalgia, malaise, dry cough, and fever. He basically felt “lousy”. After a couple of days, he had a sore throat, his cough had worsened, and he started to feel nauseated and vomited. Several of his family members had experienced similar symptoms during the previous two weeks.

Characteristics:

• Influenza A, B and C the only members• Enveloped virion; inactivated by

detergents• Segmented negative-sense RNA genome

with eight nucleocapsid segments• Genetic instability responsible for annual

epidemics (mutation:drift) and periodic pandemics (reassortment: shift)

Structure & Replication:

• Envelope with two group-specific glycoproteins:1. Hemagglutinin (HA)

Functions:a. Viral attachment protein – bind to

sialic acid on epithelial cell surface receptors

b. Promotes fusion of the envelope to the cell membrane

c. Hemagglutinates human, chicken and guinea pig rbc

d. Elicits protective neutralizing antibody response

Structure & Replication:

• Envelope with two group-specific glycoproteins:2. Neuraminidase (NA)

With enzyme activity Cleaves the sialic acid on glycoproteins,

including the cell receptor prevents clumping & facilitates release of virus from infected cells

Target for two antiviral drugs: zanamivir (Relenza) and oseltamivir (Tamiflu)

Structure & Replication:

• Type-specific proteins: used to differentiate among influenza A, B, and C viruses1. Matrix protein (M1)

Viral structural protein Interacts with nucleocapsid & envelope

promotes assembly2. Membrane protein (M2)

Forms membrane channel Facilitates uncoating & HA production Target for amantadine

3. Nucleocapsid proteins (NP)

Structure & Replication:

• Transcribes and replicates its genome in the target cell nucleus

• Assembles and buds from the plasma membrane

Pathogenesis & Immunity:

• Virus first targets & kills mucus-secreting, ciliated, and other epithelial cells loss of primary defense system

• Cleavage of sialic acid residues of mucus by NA provide access to tissues

• Preferential release of the virus at the apical surface of epithelial cells and into the lungs promote cell-to-cell spread & transmission to other hosts

Pathogenesis & Immunity:

• Spread to lower respiratory tract shedding of bronchial or alveolar epithelium

• Promotes bacterial adhesion to the epithelial cells pneumonia

• Histologic: inflammatory response of mucosal membrane (primarily monocytes & lymphocytes) with submucosal edema

Pathogenesis & Immunity:

• Systemic symptoms due to the interferon and lymphokine response to the virus

• Local symptoms due to epithelial cell damage

• Interferon & CMI responses (NK & T cell) important for immune resolution and immunopathogenesis classic symptoms associated with interferon induction

• Antibody important for future protection against infection

Pneumonia Secondary bacterial pneumonia

Primary viral pneumonia

CNS/muscle involvement

Antibody

T-cell response

Future protection

Interferon induction

Aerosol inoculation

of virus

Replication in resp. tract

Desquamation of mucus-

secreting and ciliated cells

Influenza syndrome

Major contributors to pathogenesis

Immune response

Less frequent outcomes

Why is influenza difficult to control even when there is

vaccination available?

Antigenic Changes:

1. Antigenic drift• Minor change• Mutation of the HA and NA genes• Occurs every 2 to 3 years• Cause local outbreaks of influenza A & B

2. Antigenic shift• Major change• Result from re-assortment of genomes

among different strains, including animal strains

• Associated with pandemics• Occurs only with influenza A

Lung cell

Human influenza

virus

Chicken influenza

virus

Re-assortment of RNA genome segments

New strain of influenza virus

How is the virus transmitted?

• Virus is spread by inhalation of aerosol droplets expelled during talking, breathing, and coughing.

• Virus likes cool, less humid atmosphere

• Virus is extensively spread by school children.

Who is at risk?

Seronegative people.Adults: classic “flu” syndromeChildren: asymptomatic to severe respiratory

tract infection

High-risk Groups: Elderly Immunocompromised people People with underlying cardiac or

respiratory problems (including people with asthma and smokers)

What are the clinical syndromes associated with

the virus? What are the possible complications?

Diseases Associated with Influenza Virus Infections

Disorder Symptoms

Acute infection in adults Rapid onset of fever, malaise, myalgia, sore throat, and non-productive cough

Acute infection in children

Acute disease similar to that in adults but with higher fever, gastrointestinal tract symptoms (abdominal pain, vomiting), otitis media, myositis, and more frequent croup

Complications Primary viral pneumoniaSecondary bacterial pneumoniaMyositis & cardiac involvementNeurologic syndromes: Guillain-Barre syndrome Encephalopathy Encephalitis Reye’s syndrome

How would the diagnosis of influenza

be confirmed?

Laboratory Diagnosis of Influenza Virus Infection

Test Detects

Cell culture

Hemadsorption to infected cellsHemagglutination Hemagglutination inhi- bitionAntibody inhibition of hemadsorptionImmunofluorescence, ELISASerology: HI, headsorp- tion inhibition, ELISA, immunofluorescence, complement fixation

Presence of virus, limited cytopathologic effectsPresence of HA protein on cell surface

Presence of virus in secretionsType and strain of influenza virus or specificity of antibodyIdentification of influenza type and strain

Influenza virus antigens in respiratory secretions or tissue cultureSeroepidemiology

Which antiviral drugs are effective for the treatment of

influenza virus infection? What are the targets & mechanisms

of action of these drugs?

Amantadine, Rimantadine• Target: M2 protein inhibit an uncoating

step • Do not affect influenza B or C virus

Zanamivir (Relenza) & Oseltamivir (Tamiflu)• Target: neuraminidase prevent release

of virus from infected cells• Inhibit both influenza A and B• Effective for prophylaxis and for treatment

during the first 24 to 48 hours after the onset of influenza A illness

What is the best way to control the virus?

The best way to control the virus is through IMMUNIZATION!

• Killed vaccine representing the “strains of the year”o Killed (formalin-inactivated) whole-virus

vaccineo Detergent-treated virion preparations and

HA- and NA-containing detergent extracts of virus

• Vaccination routinely recommended for the elderly and people with chronic pulmonary or heart disease.

PARAMYXOVIRUSES

Properties of Orthomyxoviruses and Paramyxoviruses

Property Orthomyxoviruses Paramyxoviruses

Viruses Influenza A, B, and C Measles, mumps, RSV, and parainfluenza viruses

Genome Segmented (8 pieces) ssRNA of negative polarity

Non-segmented ssRNA of negative polarity

Virion RNA polymerase

Yes Yes

Capsid Helical Helical

Envelope Yes Yes

Size Smaller (110 nm) Larger (150 nm)

Surface spikes HA and NA on different spikes

Hemagglutinin & neuraminidase on same spikes

Giant cell formation

No Yes

Members of the Family Paramyxoviridae

Genus Human pathogens

MorbillivirusParamyxovirus

Pneumovirus

Measles virusParainfluenza viruses 1 to 4Mumps virusRespiratory syncytial virusNipah virus (1998, Malaysia and Singapore)Hendra virus (1994, Australia)

Members of the Family Paramyxoviridae

Unique Features of the Paramyxoviridae

• Large virion with helical nucleocapsid• Negative RNA genome• Envelope containing viral attachment protein

(HN, paramyxovirus and mumps virus; H, measles virus, and G, RSV) and a fusion protein (F)o HN with hemagglutinin & neuraminidase activity o H with hemagglutinin activityo G without hemagglutinin or neuraminidase

acvitity• Replicates in cytoplasm• Penetrate the cell by fusion with and exit by

budding from the plasma membrane• Induce cell-to-cell fusion multinucleated giant

cells

Envelope Spikes of Paramyxoviruses

Virus Hemagglutinin

Neuraminidase

Fusion protein1

Measles virus + - +

Mumps virus2 + + +

Respiratory syncytial virus

- - +

Parainfluenza virus2

+ + +

1The measles and mumps fusion proteins are also hemolysins.2In mumps and parainfluenza viruses, the hemagglutinin and neuraminidase are on the same spike and the fusion protein is on a different spike.

An 18-year old college freshman complained of a cough, runny nose, and conjunctivitis. The physician in the campus health center noticed small white lesions inside the patient’s mouth. The next day, a confluent red rash covered his face and neck.

• How is the disease transmitted?

• What clinical characteristics of this case were diagnostic for measles?

• When was the patient contagious?

Transmission:• Inhalation of large-droplet aerosols

Disease Mechanisms:• Infect epithelial cells of respiratory tract• Spread systemically in lymphocytes

and by viremia• Replicate in cells of conjunctivae,

respiratory tract, lymphatic system, blood vessels, and CNS

• Characteristic rash caused by immune T cells targeted to measles-infected endothelial cells lining small blood vessels

Mechanisms of spread and pathogenesis of measles

Inoculation of respiratory tract

Local replication in respiratory

tract

Lymphatic spread

Viremia

Wide dissemination

ConjunctivaeRespiratory tractUrinary tractSmall blood vesselsLymphatic systemCNS

Virus-infected cell + immune

T cellsRASH

Recovery (lifelong

immunity)

Post-infectious encephalitis

(immunopathological;etiology)

Subacute sclerosing panencephalitis

(defective measles virus infection of CNS)

No resolution of acute infection due to defective CMI

(frequently fatal outcome)

• Incubation period: 7 to 13 days

• Prodrome: high fever + 3C’s + P most infectious

• Koplik’s spots after 2 days of illness last 24 to 48 hours

• Appearance of exanthem within 12 to 24 hours of the appearance of Koplik’s spots

• Rashes undergo brawny desquamation

Clinical Consequences of Measles Virus Infection

Disorder Symptoms

Measles Characteristic maculopapular rash, cough, conjunctivitis, coryza, photophobia, Koplik’s spotsComplications: otitis media, croup, bronchopneumonia, and encephalitis

Atypical measles Rash (most prominent in distal areas); possible vesicles, petechiae, purpura, or urticaria

SSPE CNS manifestations (e.g. Personality, behavior, and memory changes; myoclonic jerks; spasticity; and blindness)

How can the infection be prevented?

Post-exposure: Immune serum globulin given within six days of exposure

Pre-exposure:1. Live, attenuated vaccine2. MMR

• Composition: a. Measles – Schwartz or Moraten substrains

of Edmonton B strainb. Mumps – Jeryl Lynn strainc. Rubella – RA/27-3 strain

• Schedule: at 15-24 months and at 4-6 years

• Efficacy: 95% lifelong immunization with a single dose

A 13-month-old child had a runny nose, mild cough, and low-grade fever for several days. The cough got worse and sounded like “barking.” The child made a wheezing sound when agitated. The child appeared well except for the cough. A lateral radiograph of the neck showed a sub-glottic narrowing.

What is the specific and common name for these

symptoms?

What other agents would cause a similar clinical

presentation (differential diagnosis)?

What is the most common cause?

How was the virus transmitted?

Answer: Droplet inhalation

Parainfluenza Viruses

Characteristics:

• Four serotypes

• Infection limited to upper respiratory tract Upper respiratory tract disease most

common, but significant disease can occur with lower respiratory tract infection

• Not systemic and do not cause viremia

• Infection induces protective immunity of short duration

Parainfluenza Viruses

Four serologic types

• Types 1, 2, and 3 Second only to RSV as important causes of

severe lower respiratory tract infection in infants and young children

Cause respiratory tract syndromes ranging from a mild cold-like URTI to bronchiolitis to pneumonia

Especially associated with croup

• Type 4 Mild upper respiratory tract infection in

children and adults

Parainfluenza Viruses

• Clinical:

• Main cause of croup in children < 5 y/o

• Characterized by harsh cough (“seal bark cough” and hoarseness due to subglottal swelling

• Other clinical conditions: common cold, pharyngitis, otitis media, bronchitis, and pneumonia

Respiratory Syncytial Virus

• Most important cause of pneumonia and bronchiolitis in infants

• Fusion protein causes formation of multinucleated giant cells syncytia

• Humans and chimpanzees are the natural hosts

• Two serotypes – subgroup A and B

Respiratory Syncytial Virus

• MOT:1. Respiratory droplets2. Direct contact of contaminated hands with the

nose or mouth

• Infection in infants more severe and usually involves lower respiratory tract than in older children and adults

• No viremia occurs

Respiratory Syncytial Virus

• Severe disease in infants with immunopathogenic mechanismo Maternal antibody passed to infant react

with the virus form immune complexes damage respiratory tract cells

• Most individuals with multiple infections indicate incomplete immunity

• IgA respiratory antibody reduces the frequency of infection as a person ages

Respiratory Syncytial Virus

• Clinical:

1. Bronchiolitis

2. Pneumonia

3. Otitis media in young children

4. Croup

5. Upper respiratory tract infection similar to common cold in older children and adults

Respiratory Syncytial Virus

• Treatment:

Aerosolized ribavirin (Virazole) for severely ill hospitalized infants

Combination ribavirin + hyperimmune globulin may be more effective

A 7 year-old boy developed fever, body malaise, and loss of appetite. This was followed by tender swelling around the right mandibular area, with increase in the pain everytime he drinks calamansi juice. The condition spontaneously resolved after one week.

Mumps Virus

• Two types of envelope spikes:1. With both hemagglutinin and

neuraminidase activities 2. With cell-fusing and hemolytic activities

• Only one serotype

• Neutralizing antibodies directed against the hemagglutinin

• Humans are natural hosts

Mumps Virus

• MOT: respiratory droplets

• Infects both upper and lower respiratory tracts spread through blood parotid glands, testes, ovaries, pancreas, and in some cases, meninges

• Occurs only once subsequent cases may be caused by parainfluenza viruses, bacteria, and by duct stones

Mumps Virus

Mumps Virus

Mumps Virus

• Complications:

1. Orchitis in post-pubertal males may lead to sterility if bilateral

2. Meningitis – usually benign, self-limited, and without sequelae

Mumps Virus

• Prevention:

Live, attenuated vaccine given subcutaneously to children at 15 months of age (MMR)

Immune globulin not useful for preventing or mitigating mumps orchitis.

The End