Microbiology Viruses lesson 1

What are viruses made of

Nucleic acid( either RNA or DNA…never both!)

• • surrounded by protein shell(capsid)

• • Attach, inject nucleic acid(penetration), highjack synthetic processes inside cells to make more viruses

• Require living cells for growth and replication

• surface antigens 

What are the steps for replication of viruses

1) Adsorption

2) penetration and uncoating

3) Nucleic Acid and protein synthesis 

4) Assembly and Maturation

5) Release

How do we detect viral infections

1) detect the viruses itself

2) detect immune response… antibodies against the viruses(indirect Elisa) 

3) focus of unique symptoms 

What are the different ways of Viral Diagnosis 

 1. Visualisation by Electron microscopy

 2. Cell culture (cytopathic effects, hemagglutination, immunofluorescence)

3. Detection of patient’s immune responses

– IMMUNITY TEST

– DIAGNOSTIC TEST

What is cytopathic effects

are spots that are holes or plaques in the cell culture

they show how many viruses you have

destroy the cell its growing in after releasing

hemagglutination

is when the virus binds and clumps with red blood cells

Immunofluorescence

does not destroy cell but leaves it intact

Immunity Test

see if the patient has an antibody

Diagnostic test

How much antibody concentration

What are the two types of Influenza Viruses

Influenza virus type A: major epidemics

• Influenza virus type B: milder disease

What is its way to diagnose 

if it Produces haemagglutinin (diagnostic)( can bind to red blood cells)

What are its three components

• Frequent recombination

• High antigenic variability

• Pandemics

What are some of its clinical manesfestations

• fever, variable respiratory symptoms

• Infants and elderly more susceptible

how to obtain culture

• Throat washings, naso-pharyngeal aspirate inoculated into cell culture

• Serum:

• Paired sera (acute and convalescent stage)( take blood sample when sick and healthy and compare them) 

what are some preventative measure

– Annual vaccination

especially for high risk groups

What age group does parainfluenza viruses affect 

Infants and young children( 5-12) 

What is the major defining symptom of this virus

• Croup (barking cough, high pitch sound on

inhalation)

is there a vaccine

no

What age group does Respiratory syncytial virus affect 

Major respiratory pathogen for children < 2 or 5 years

What are its symptoms and is there a vaccine/ treatment

Pneumonia and bronchiolitis; occasionally fatal

• Epidemics

• Vaccine available

• Antiviral

What is rhinovirus considered

Common colds

• > 100 serotypes; no cross-immunity

• Repeated infections

What Is unique about coronavirus

• it is an RNA virus 

• has a unique antigen that is called the spike protein 

• its a respiratory virus that causes problems to every part of your body 

how does it spread

Most people are being infected from other people

people can get infected when these droplets enter the nose, eyes or mouth 

Enteric Viruses

• Infect intestinal / lymphoid cells

• Multiply in GI tract, but RARELY cause gastro-enteritis

• Infection via respiratory or GI tract (peyer’s patches)

• Spread to other target organs in body

Poliovirus

Humans are the ONLY natural host

• Types 1, 2 and 3

• Causes poliomyelitis

– Highly infectious, invades the host nervous system and can cause total paralysis in as little as a few hours- cytoplastic  effect 

Where is polio mostly found

Currently polio is only found in parts of Africa and South Asia (Nigeria, India, Pakistan, Afghanistan)

How to diagnose polio

Isolation from stool samples (up to 5-6 weeks after infection), CSF and pericardial fluid

• Serology: acute and convalescent phases

Polio Prevention

Salk vaccine (Jonas Salk)

• Killed/inactivated vaccine; does not produce local immunity in GI of host (IgA); Virus can still colonize host GI tract and SPREAD to the community!!!

• used for immunocompromised

– Sabin vaccine (most common; Albert

Sabin)

• Live attenuated; host will produce IgA and IgG, so is protected against intestinal colonization and virus can NOT replicate and spread

• Oral administration

Coxsackieviruses

Groups A and B

• Seasonal variation

• Diagnosis by stool sample and paired sera (same as polio)

• NO VACCINE

What are some symptoms

Minor Respiratory illnesss

aseptic meningitis

Herpangina and hand-foot-and mouth disease 

pleurodynia pericarditis and myocarditis 

Rotavirus

Found in young people (17 years or less)

replication in small intestine 

vomitting, diarrhea- Acute gastroenteritis fever 

highly infectious 

How to diagnose 

• EM or immunological testing of virus from stool samples (within 3 days)

• Short incubation (2-3days)

• Fecal-oral route, aerosols (explosive diarrhea), fomites

• Outbreaks in daycare centres, children’s hospitals

Prevention

– Rapid diagnosis and isolation of patient

– Proper handwashing

– Vaccine available

how is Norovirus different from Rotavirus

Outbreaks of gastroenteritis in older children and adults( 18 years and older) 

How to diagnose and treat

• Diagnosis: first exclude bacterial cause, then can be differentiated from bacterial gastroenteritis

• Epidemiology: VERY CONTAGIOUS; survives well on objects/environment

– Fecal-oral route; food-borneoutbreaks

• Prevention: no vaccine; handwashing and isolation of infected individuals

Measles 

One of the highest infectivity rates

• Clinical: rash first appears behind ears, forehead and nostrils then spreads to whole body;

BLOTCHY appearance

• Lifelong immunity after natural infection

• Complications: secondary bacterial infections, e.g., bronchopneumonia

– Encephalitis (rare)

– Exacerbation of TB and leukemia

What are the three manifestations of messages 

• cough 

• coryza

• conjunctivitis 

How to diagnose

• IgM Ab in single blood specimen against measles OR a rising

• IgG Ab titer against measles in paired blood- immunity

– Immune status

• Circulating measles specific Ab IgG

How to prevent it

• Immunoglobulin: can suppress disease if given within 5 days of contact with virus

– Live attenuated vaccine: very effective, widely used.

Administer after 12 months of age

• MMR

Rubella

(German Measles; 3-day measles)

VERY dangerous for non-immune pregnant

women birth defects

• Birth defects:

– General: abortion, death of newborn

– Localized: cataracts

• deafness

• heart defects

Other: low birth weight, cleft palate, intellectual

deficiency

How to diagnose it

Clinical: similar to measles but milder; life- long immunity

• pre-vaccine era, seen in school children during winter in spring, outbreaks lead to life-long immunity

Lab Diagnosis:

– Suspected cases: detection of rubella specific IgM or rising Ab titer in paired sera

– Immunity status: detection of circulating Rubella Ab (IgG)

How to prevent it

• Check immune status of women of childbearing age

•  Diagnosis in hospitals

• Rubella serology screening of men and women starting work in hospitals

• Vaccination-live attenuated vaccine

– Do NOT give vaccine to women who are already pregnant!

What are the two types of Varicella

Chickenpox: Varicella

Herpes Zoster (Shingles)

What are their manifestations

Chickenpox: Varicella

• Clinical: childhood febrile illness with characteristic rash

– In non-immune adults, occasional pneumonia, may be fatal

Herpes Zoster (Shingles)

– LIMITED rash, along trajectory of ONE nerve

– Late recurrence of latent VZV (chicken pox) infection

• Diagnosis: ID of virus particles in pustules by EM or immuno methods, followed by cell culture

how to prevent it 

Prevention: vaccine; detection of susceptible

persons by serological methods

what are the two types of Herpes Simplex Virus (HSV) and what do they do

– HSV1: “cold sores” oral and ocular lesions;

transmitted via oral and respiratory secretions

– HSV2: “herpes genitalis” associated with genital tract; infected females can transmit to the newborn

• Diagnosis: ID of virus particles by EM or immuno methods; cell cultures; Serology NOT useful

can also cause ulceration of cornea and blindness

What are some treatments and preventions

• antivirals; C-section for symptomatic mothers; Vaccines coming soon

Papilloma Viruses 

• Genital warts: sexual transmission, asymptomatic carriers

•  Some types associated with cancer: cervix, vulva, penis

How to diagnose it and treat it 

Diagnosis: immuno techniques and DNA

hybridization techniques; no cell cultures available

• Prevention: Vaccine now available (Gardasil)