Othomyxo and paramyxoviruses

Kaveh HaratianPhD. Medical Virologist

Department of Microbiology and ImmunologySchool of Medicine

1

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.

2

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)

3

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

4


• 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)

5


• Type-specific proteins: used to differentiate

among influenza A, B, and C viruses

1. Matrix protein (M1)

Viral structural protein

Interacts with nucleocapsid & envelope

promotes assembly

2. Membrane protein (M2)

Forms membrane channel

Facilitates uncoating & HA production

Target for amantadine

3. Nucleocapsid proteins (NP)

6


• Transcribes and replicates its genome in the

target cell nucleus

• Assembles and buds from the plasma

membrane

7

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

8


• 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

9


• 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

10

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

11

Why is influenza difficult to

control even when there is

vaccination available?

12

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 A13

Lung cell

Human

influenza

virus

Chicken

influenza

virus

Re-assortment of RNA

genome segments

New strain of influenza

virus

14

How is the virus

transmitted?

15

• 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.

16

Who is at risk?

17

Seronegative people.

Adults: classic “flu” syndrome

Children: 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)

18

What are the clinical

syndromes associated with

the virus? What are the

possible complications?

19

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 pneumonia

Secondary bacterial pneumonia

Myositis & cardiac involvement

Neurologic syndromes:

Guillain-Barre syndrome

Encephalopathy

Encephalitis

Reye’s syndrome20

How would the

diagnosis of influenza

be confirmed?

21

Laboratory Diagnosis of Influenza Virus Infection

Test Detects

Cell culture

Hemadsorption to

infected cells

Hemagglutination

Hemagglutination inhi-

bition

Antibody inhibition of

hemadsorption

Immunofluorescence,

ELISA

Serology: HI, headsorp-

tion inhibition, ELISA,

immunofluorescence,

complement fixation

Presence of virus, limited cytopathologic

effects

Presence of HA protein on cell surface

Presence of virus in secretions

Type and strain of influenza virus or

specificity of antibody

Identification of influenza type and strain

Influenza virus antigens in respiratory

secretions or tissue culture

Seroepidemiology

22

Which antiviral drugs are

effective for the treatment of

influenza virus infection? What

are the targets & mechanisms of

action of these drugs?

23

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

24

What is the best way to

control the virus?

25

The best way to control the virus is through

IMMUNIZATION!

• Killed vaccine representing the “strains of the

year”

o Killed (formalin-inactivated) whole-virus

vaccine

o 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.26

27

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

28

Members of the Family Paramyxoviridae

Genus Human pathogens

MorbillivirusParamyxovirus

Pneumovirus

Measles virus

Parainfluenza viruses 1 to 4

Mumps virus

Respiratory syncytial virus

Nipah virus (1998, Malaysia and

Singapore)

Hendra virus (1994, Australia)

29

Members of the Family Paramyxoviridae

30

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 activity

o 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

31

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.

32

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.

33

• How is the disease

transmitted?

• What clinical characteristics

of this case were diagnostic

for measles?

• When was the patient

contagious?

34

35

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

36

Mechanisms of spread and pathogenesis of measles

Inoculation of

respiratory tract

Local replication

in respiratory

tract

Lymphatic

spreadViremia

Wide

dissemination

Conjunctivae

Respiratory tract

Urinary tract

Small blood vessels

Lymphatic system

CNS

Virus-infected

cell + immune

T cells

RASH

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)

37

• 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

38

39

40

Clinical Consequences of Measles Virus Infection

Disorder Symptoms

Measles Characteristic maculopapular rash, cough,

conjunctivitis, coryza, photophobia,

Koplik’s spots

Complications: 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)

41

How can the

infection be

prevented?

42

Post-exposure: Immune serum globulin given

within six days of exposure

Pre-exposure:

1. Live, attenuated vaccine

2. MMR• Composition:

a. Measles – Schwartz or Moraten substrains of

Edmonton B strain

b. Mumps – Jeryl Lynn strain

c. Rubella – RA/27-3 strain

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

• Efficacy: 95% lifelong immunization with a

single dose

43

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.

44

What is the specific and

common name for these

symptoms?

45

What other agents would cause

a similar clinical presentation

(differential diagnosis)?

What is the most common

cause?

46

How was the virus

transmitted?

Answer: Droplet inhalation

47

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

48


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

49


• 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

50

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

51


• MOT:1. Respiratory droplets

2. 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

52


• 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

53


• 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

54


• Treatment:

Aerosolized ribavirin (Virazole) for

severely ill hospitalized infants

Combination ribavirin + hyperimmune

globulin may be more effective

55

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.

56

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

57

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

58

Mumps Virus

59

Mumps Virus

60

Mumps Virus

• Complications:

1. Orchitis in post-pubertal males may lead to

sterility if bilateral

2. Meningitis – usually benign, self-limited, and

without sequelae

61

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.

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Health & Medicine

Othomyxo and paramyxoviruses