HSS1100 Immunology - Lectures 8, 9, 10

Viruses, Nosocomial infections, and Disinfection

What are the general characteristics of viruses?

- Grow only in living cells;
- Possess only one type of nucleic acid (either DNA or RNA);
- Multiply by separate synthesis of nucleic acid and protein that are then assembled to form virus particles;
- Viruses DO NOT DIVIDE;
- Do not have their own metabolism;
- Vary in size from 10-300 nm.

What are the basic structural components of virions?

1. Nucleic acid core: carries the genetic code;
2. Protein coat: protects the core and carries the antigens.

Some protein coats (capsids) contain carbohydrates or lipids.

What are the three methods by which viruses can be grown?

1. Cell cultures;

2. Embryonated eggs;

3. Living animals.

NOT ALL VIRUSES GROW IN ALL THREE.

What are the 5 general steps of replication?

1. Adsorption;

2. Penetration and uncoating;

3. Synthesis of nucleic acid and protein;

4. Assembly-Maturation;

5. Release.

What occurs during the adsorption step of viral replication?

Viruses adsorb to receptors on the cell surface.

What occurs during the penetration and uncoating step of viral replication?

The virus enters the cell, the protein coat is lost and the nucleic acid is release.

The nucleic acid becomes undetectable (eclipse).

What occurs during the synthesis of nucleic acid and protein step of viral replication?

The viral nucleic acid redirects the cell metabolism to produce viral protein and nucleic acid.

What occurs during the assembly-maturation step of viral replication?

Viral components are assembled to form mature (infective) virus particles.

What occurs during the release step of viral replication?

Newly formed virus particles are released by either lysis (destruction) of the cell or budding through the cell membrane.

What is the golden rule for detection of viruses in a laboratory?

The golden rule is that viruses DIE OUT QUICKLY in clinical specimens. They must be examined and inoculated in the laboratory within hours after collection.

Use viral transport media and courier services, no room for the postal services. DO NOT FREEZE but keep refrigerated.

What are the two main approaches for viral diagnosis?

1. Detection of viruses in clinical specimens.

2. Detection of the immune reactions triggered by the virus in the patient (i.e., detection of antibodies in the patient's blood.

What are the steps for detection of viruses in clinical specimens?

1. Visualization by electron microscopy, high magnification required.

2. Effects after inoculation into the cell cultures require time to wait for multiplication.

3. Direct detection of viral antigens in clinical specimens themselves by immunological methods.

What are the effects that occur after inoculation of virus into a cell culture?

- Cytopathic effect (visible modification of infected cells).

- Hemagglutination (some cells agglutinate red blood cells).

- Immunofluorescence and other serological methods reveal the presence of viral antigenic material (even when there is no visible damage by multiplying virus).

What are the steps for detecting the immune reactions triggered in a patient's immune system by a virus?

1. Presence or absence of antibody against a given virus (immunity tests).

2. Rise in antibody or high antibody titer against a given virus (evidence that the virus caused a viral illness, diagnostic tests).

What are respiratory viruses?

A group of viruses which are found mainly in the respiratory tract and produce respiratory tract diseases.

They belong to different virus families.

What five virus groups are included in the respiratory virus category?

1. Influenza viruses;

2. Parainfluenza viruses;

3. Respiratory syncytial viruses;

4. Rhinoviruses;

5. Coronaviruses.

What are the two main types of influenza virus?

- Influenza A (MAJOR EPIDEMICS);

- Influenza B (milder diseases);

What are the general characteristics of influenza viruses?

- Grow easily in certain cell cultures;
- Produce a haemagglutinin.
- Nucleic acid made of separate but connected segments (high frequency of recombination);
- Antigenic variability explains reappearance of new types of influenza that cause "pandemics".

What are the clinical symptoms of influenza?

- Acute febrile illness with variable respiratory symptoms.
- Extreme age groups are sensitive to both disease and complications.

What are the two methods for diagnosing influenza?

1. Throat washing (naso-pharyngeal aspirate);

2. Serum samples.

What is throat washing (naso-pharyngeal aspirate)? How is it used to diagnose influenza?

Taken within 3 days after onset and inoculated immediately in cell cultures. If delayed, use transport medium.

How are serum samples used to diagnose influenza?

Two blood samples (acute and convalescent phase) taken at 2-3 weeks interval are investigated for antibodies. Acute sample needs to be collected as soon as onset.

What is serum?

The liquid portion (containing antibodies) of whole blood when cells are removed. If the only test possible is detection of specific IgG or total antibody, then paired sera are required.

Sera is taken 14-21 days apart and tested at the same time. A rise in amount of antibody indicates a current infection. A significant rise or decrease or seroconversion in titer indicates a current infection.

How is influenza infection prevented?

- Vaccines against both types are available, but use is hampered by antigenic changes.
- Antibodies against one strain protect only partially or not at all against new strains.
- Vaccines are administered to high risk groups (elderly, heart diseases, health workers).
- Some antiviral drugs (amantidine) are available but are only active against type A.

What are the main characteristics of parainfluenza viruses?

- Frequent in infants and small children.
- Cause respiratory disease that may result in serious complications.
- Cause Laryngotracheobronchitis (croup), bronchiolitis, and bronchopneumonia.

No vaccine available.

What are the main characteristics for respiratory syncytial virus?

- Major respiratory pathogen in children under 2 years.
- Bronchiolitis and pneumonia can occasionally be fatal.
- Can cause epidemics;
- NO VACCINE available;
- Antiviral treatment with ribavizine.

What are the main characteristics of rhinoviruses?

- Main cause of the common cold;
- Over 100 different serological types with no cross immunity;
- Repeated infections are common.

What are the main characteristics of coronaviruses?

A virus causing coronavirus disease 2019 (COVID-19) discovered in 2020 in Wuhan china.

Spreads from infected person to person through:
- Close contact;
- Respiratory droplets;
- Contaminated surfaces;
- Touching objects (fomites);
- Common greetings.

How do laboratories detect respiratory viruses?

1. Fastest approach is direct detection of viral antigens by immunofluorescence or other immunological methods (combined with inoculation in cells).

2. Clinical specimens, by order of decreasing usefulness:
- Naso-pharyngeal aspirates;
- Throat washings;
- Throat and nasal swabs.

3. Chances of detecting the virus decrease rapidly after a few days illness.

How are respiratory viruses serologically diagnosed?

- Less useful and usually retrospective.
- Dates of paired sera in relation to illness are important for the lab.
- Labs test for series of respiratory agents, since symptoms are rarely typical for a given virus.

What are some public health measures for respiratory viruses?

1. Detection of circulating strains and antigenic make-up influenza strains in the community.

2. Decide if amantadine is useful (active against influenza A only).

3. Restricting admissions/ closing of nursing homes, hospitals, etc...

What are some methods of managing patients with respiratory viruses?

1. Cohorting in pediatric facilities for RSV and croup.

2. Restrictive use of antivirals (amantadine for influenza A, ribavirine for RSV).

3. Special care for debilitated patients.

What viruses are included in the enteric virus category?

1. Polioviruses;

2. Coxsackieviruses;

3. Echoviruses.

What are enteroviruses?

Viruses that multiply mainly in the gastro-intestinal tract, but, as a rule, DO NOT CAUSE GASTRO-ENTERITIS.

They can reach other organs as a results of viremia (virus in blood) and cause severe damage. Usually causes damage in the central nervous system.

What are the common characteristics of enteroviruses?

- Infection acquired through the respiratory tract (naso-pharynx) and/or gastro-intestinal tract.

- Infection with enteroviruses is 95% inapparent (multiples up to 5-6 weeks without symptoms.

- Infection causes minor illness in 4-5% of cases (fever, pharyngitis).

- Infection causes major illness in

What are the types of poliovirus?

There are three immunological types of polioviruses:
- Type 1;
- Type 2;
- Type 3.

Man is the only natural host for poliovirus.

How are polioviruses diagnosed clinically?

1. Isolation of virus from stool specimens (in stools after 5-6 weeks), CSF, pericardial fluid, after inoculation in cell cultures.

2. Serology:
- Two specimens (acute and convalescent phase) are necessary.
- Acute specimen immediately after onset.
- Convalescent specimen 2-3 weeks later is usually collected.

What is the epidemiology of poliovirus infections?

The most important factor that favours the spread of the disease is the large number of INAPPARENT infections.

People infected with enteroviruses show no sign of disease, but spread the virus to other susceptible persons.

How is poliovirus infection prevented?

Two types of highly effective vaccines are used:

1. Killed (inactivated) polio vaccine - SALK, trivalent.

2. Live attenuated polio vaccine - SABIN, trivalent.

What are the characteristics of the Salk, killed polio vaccine?

- Does not produce local immunity (IgA) in the GI tract.
- The virus can still multiply in GI tract and spread in the community.
- Vaccine is superseded by the live attenuated vaccine.
- Killed vaccine is used in immunocompromised individuals and adults with no previous immunizations against poliomyelitis.

What are the characteristics of the Sabin, live attenuated polio vaccine?

- Easy to administer by mouth;
- Produces IgA and IgG antibodies;
- Produces GI tract resistance to infections;
- Prevents wild spread of virus in the community.
- Should not be administered to immunocompromised patients or adults who have never been vaccinated against polio before.

What are the two types of Coxsackieviruses?

Type A - several types;

Type B - several types.

What are the clinical symptoms of the Coxsackieviruses?

* Aseptic meningitis (Group A, B);


* Herpangina and hand-foot-mouth disease (group A);
* Minor respiratory illness (Group B);
* Pleurodynia, pericarditis and myocarditis (group B).

What is the epidemiology of Coxsackieviruses?

- Seasonal variation (summer and fall);
- Prevalent type varies every few years.

How are Coxsackieviruses diagnosed?

Most group A coxsackieviruses can be isolated only by mouse inoculation.

Other diagnostic methods include:

1. Isolation of virus from stool specimens (in stools after 5-6 weeks), CSF, pericardial fluid, after inoculation in cell cultures.

2. Serology:
- Two specimens (acute and convalescent phase) are necessary.
- Acute specimen immediately after onset.
- Convalescent specimen 2-3 weeks later is usually collected.

What are the preventative methods for Coxsackieviruses?

None, there are no vaccines or preventative measures for Coxsackieviruses.

What are echoviruses and their general characteristics?

ECHO = Enteric cytopathic human orphan viruses.

Named because, when first isolated in cell cultures, no relation to disease was evidence.

There are several types of viruses.

What are the clinical symptoms of echoviruses?

- Minor respiratory illness.
- Aseptic meningitis.

How are echoviruses diagnosed in the laboratory?

1. Isolation of virus from stool specimens (in stools after 5-6 weeks), CSF, pericardial fluid, after inoculation in cell cultures.

2. Serology:
- Two specimens (acute and convalescent phase) are necessary.
- Acute specimen immediately after onset.
- Convalescent specimen 2-3 weeks later is usually collected.

What are the preventative methods for echoviruses?

None, there are no vaccines or preventative measures.

What are four examples of viruses that causing diarrhea?

1. Rotavirus;

2. Norovirus;

3. Adenovirus;

4. Calici- and astroviruses

What are Rotaviruses and their general characteristics?

A virus causing epidemics of diarrhea of infants, during winter months. The virus multiplies in the small intestine, producing a loss of fluids and electrolytes.

Transient malabsorption of fats and sugars.

What are the clinical symptoms of rotavirus infection?

- Acute gastroenteritis in infants and young children (6mo - 2 years).
- Diarrhea;
- Vomiting;
- Fever;
- Dehydration.

Rotaviruses are found in enormous numbers in stool, diapers, on hands, surfaces, and are HIGHLY INFECTIOUS.

How is a rotavirus infection diagnosed?

- Identification of virus present in stools by electron microscopy or immunological techniques.

- Cell cultures have no practical value;

- Examine stools within 3 days.

What is the epidemiology of rotavirus infections?

Short incubation period: 2-3 days.

Transmission from infants with explosive diarrhea by the fecal-oral route, via aerosols and fomites.

Nosocomial outbreaks occur in nurseries, day care centers and children's hospitals.

Most older children and adults are immune.

What are preventive measures for rotavirus infections?

Treat at home when possible.

In hospitals:
- Rapid viral diagnosis;
- Proper isolation procedures;
- Strict adherence to hand washing and gowning procedures to prevent nosocomial infections.
- Early discharge from hospitals;
- VACCINE.

What are the general characteristics of norovirus infections?

Noroviruses are the cause of outbreaks of gastroenteritis in older children and adults, in any season.

How are norovirus infections diagnosed?

Diagnosis is important in nursing homes, hospitals to differentiate it from bacteria gastroenteritis. Diagnosis is arrived at by first excluding a bacterial cause.

What is the epidemiology of a norovirus infection?

Similar to rotavirus, but just as contagious.

Fecal-oral route of transmission; foodborne outbreaks have been reported from water, and shell-fish.

Acquisition of immunity is slower than rotavirus, hence disease in older age groups.

How are norovirus infections prevented?

No vaccine.

Treat at home when possible.

In hospitals:
- Rapid viral diagnosis;
- Proper isolation procedures;
- Strict adherence to hand washing and gowning procedures to prevent nosocomial infections.
- Early discharge from hospitals;

PROBLEM:
- Isolation and cohorting is more difficult and complicated by the presence of cases among staff.

What are the general characteristics of adenoviruses?

- Some types cause gastroenteritis in young children;
- The types causing gastroenteritis cannot be cultivated in cell cultures;
- Diagnosed by ELECTRON MICROSCOPY and Immunology methods.

What are the general characteristics of Calici- and astroviruses?

- Poorly characterized viruses causing sporadic gastroenteritis in infants and children;
- Diagnosed by ELECTRON MICROSCOPY.
- Transmission by the fecal-oral route.

Provide a general summary of the viruses causing gastroenteritis in terms of epidemiology, age, transmission, diagnosis, and vaccines.

What is the practical importance of rapid laboratory diagnosis of gastroenteritis viruses?

- Rotavirus and norovirus are extremely contagious;
- Isolate and/or cohort ASAP;
- Laboratory not useful for "clearing out" patients (in contract to bacterial gastroenteritis).

What are the five viruses that cause Exanthems (rashes)?

1. Measles;

2. Rubella (German Measles);

3. Varicella (chickenpox);

4. Herpes simplex virus (HSV);

5. Papilloma viruses.

What are the common epidemiological features of viruses causing exanthams (rashes)?

1) Humans are the SOLE reservoir;

2) They are HIGHLY contagious.

What are the clinical symptoms of measles infection?

- Nasal and ocular catarrh (redness) preceding the rash;
- High fever;
- Koplik spots;
- Rash appears behind the ears, forehead, and around the nostrils (spread to the whole body);
- Natural disease produces lifelong immunity.

What are the complications associated with measles infection?

- Secondary bacterial infections (e.g., broncho-pneumonia, otitis);
- Encephalitis;
- Sclerosing panencephalitis (SSPE);
- Exacerbation of tuberculosis and leukemias.

How is measles diagnosed?

Serological diagnosis of suspected cases and determination of immune status of contacts.

Why is laboratory diagnosis of measles important?

1. Allows to detect the first index case of a potential epidemic;

2. Allows to detect which individuals are immune.

How are suspected measles cases serologically determined?

The demonstration of IgM antibody against measles in a single blood specimen or of a rising antibody titer against measles (IgG) in paired blood samples.

OR

Demonstration of circulating measles specific antibody (IgG) in close contacts.

What are the two methods for which we prevent measles infections?

1) Immunoglobulin treatment administered within 5 days of contact with a measles case (suppresses or attenuates the disease).

2) Live attenuated vaccination, administered after 12 months of age.

GIVEN AS MMR (Measles, Mumps, Rubella vaccine).

What are the general characteristics of Rubella (German Measles)?

Causes mild disease, but is extremely dangerous in non-immune pregnant women because it can produce BIRTH DEFECTS in the offspring.

What are the clinical symptoms of rubella?

- Similar to measles but milder;
- Causes enlargement of cervical, retro-auricular (behind ears), and sub-occipital lymph nodes;
- Results in lifelong immunity.

PARTICULARLY DANGEROUS IN THE FIRST TRIMESTER IN SUSCEPTIBLE PREGNANT WOMEN.

After the third trimester, the risk is lower, but damage can still be traced up to the 6th month.

What are the risks to the fetus from contracting rubella at each trimester?

1st Trimester (0-4 weeks):
- 50%

2nd Trimester (5-8 weeks):
- 20%

3rd Trimester (9-12 weeks):
- 7%

After the third trimester, the risk is lower, but damage can still be traced up to the 6th month.

What are the principal birth defects associated with rubella?

Generalized:
- Abortion;
- Early death of newborn.

Localized:
- Cataracts (infection at 6th week);
- Deafness (infection at 9th week);
- Hear defects (infection from 5-10th week).

Others:
- Low birth weight;
- Cleft palate;
- Dental abnormalities;
- Mental deficiency.

How long do congenital rubella cases last?

Virus can persist up to 18 months in urine and therefore presents a hazard for susceptible personnel and family contacts.

What is the epidemiology of rubella infections?

Pre-vaccine era:
- Cases occurred in school-age children;
- Winter and spring;
- Major epidemics every 7-10 years;
- Lifelong immunity in 80% of young adults.

NOW:
- 60% of cases are in those 15 years+;
- Symptoms cannot be atypical.

How are rubella cases diagnosed?

By serological methods:

1. Suspected cases (acquired or congenital) -- detection of rubella specific IgM antibody or rising antibody titer against rubella in paired sera.

2. Immunity status -- detecting of circulating antibody against rubella (IgG) in single serum).

Several methods have now replaced the old hemagglutination inhibition test (HAI).

Why is it important for laboratory diagnosis of rubella?

Atypical cases may spread to susceptible pregnant women and trigger an epidemic.
- Confirmation of cases during early pregnancy allows informed decisions concerning abortion.
- Confirmation of a case in a newborn can prevent spread to non-immune nurses who are pregnant.
- Determination of immune status of contacts is important.

How is rubella infection prevented?

1. Check the immune status of women in child-bearing age (presence of IgG antibody to indicate immunity).

2. Diagnosis of congenital rubella syndrome in hospitals (Risk to non-immune staff).

3. Rubella serology screening in women and men starting work in hospitals, clinics, etc...

4. Vaccination of the non-immune with LIVE ATTENUATED vaccines.

5. Strict isolation of congenital rubella cases in hospital.

What are the vaccination policies of rubella?

Vaccinate with live attenuated vaccine:

1. Vaccination of babies (MMR) after 12 months.

2. Vaccination of pre-pubertal girls, if not immune.

3. Vaccination in the post-partum, if not immune.

4. Vaccination of hospital personnel, women and men, if not immune.

Immunity induced by the live vaccines appears to be long-lasting.

What is Varicella (chickenpox) caused by?

It is caused by the varicella/zoster virus (VZV), a member of the herpes group.

What are the clinical symptoms of varicella?

- Mild childhood febrile illness with characteristic vesicular rash;
- Successive crops of fresh vesicles appear within 3-4 days after the onset of the rash;
- Papule, vesicles, and crusts are present.

What are complications associated with varicella infection?

* In non-immune adults, pneumonia can be fatal;
* Chickenpox can be transmitted to the newborn if infection occurs close to the end of pregnancy.
* Shingles (Herpes Zoster)

What is Shingles (Herpes Zoster)?

A limited rash, along the traject of one nerve (often intercostal) accompanied by pain. The disease is mainly found in adults and represents a late recurrence of latent varicella infection in the partially immune.

Cases of zoster may be at the origin of outbreaks of varicella.

How is varicella infection diagnosed?

Identification of viral particles in vesicles or pustules by electron microscopy or immunological methods, followed by cell cultures.

How is varicella infection prevented?

- Vaccination;
- Detection of susceptible individuals in hospital personnel by serology;
- Passive immunization with zoster immuno-globulins (ZIG);
- Treatment with antivirals.

What is Herpes Simplex virus (HSV)?

A widely dissemination virus and infections that occur in early childhood, most often inapparent. After initial infection, the virus may persist as a latent infection with reapparance of lesions (clusters of vesicles) "cold sores" triggered by factors like:
- Fever;
- Exposure to the sun;
- Change in temperatures.

The spread of infection is difficult to control because of the high percent of inapparent infection and because it can be transmitted sexually.

What are the two types of herpes simplex virus?

- Type 1 (HSV1);
- Type 2 (HSV2).

What is type 1 herpes simplex virus?

Primarily associated with oral and ocular lesions and transmitted through oral and respiratory secretions: "cold sores".

Type 1 can also be transmitted sexually, but some protection is afforded by previous Type 1 infections.

What is type 2 herpes simplex virus?

Herpes genitalis -- Associated with genital tract and transmitted mainly venereally. Infection in females can be transmitted to newborns.

Type 1 can also be transmitted sexually, but some protection is afforded by previous Type 1 infections.

What is recurrent herpes? Which type of HSV does it occur with?

Occurs with both types of herpes simplex virus, and usually in the same region(s) as the primary lesion.

How is herpes simplex virus diagnosed?

1. Identification of virus particles by EM or immunological methods in clinical specimens.

2. Virus grows easily in cell cultures (usually within 24-48 hours);

3. Serology of very little use.

What are the clinical symptoms apart from cold sores associated with herpes simplex virus?

- Genital infections;
- Herpetic encephalitis;
- Neonatal herpes;
- Herpetic whitlow;
- Corneal and conjunctival infection;
- Relationship to carcinoma of the cervix (unproven).

What are genital infections associated with HSV?

Primary infections that cause recurrences in both sexes.

What is herpetic encephalitis?

Encephalitis in young adults as a result of a latent herpetic infection since the primary infection in childhood.

Rare but very serious, affects the nervous system.

What is neonatal herpes?

Usually acquired during the passage in the birth canal from an asymptomatic mother affected with either type 1 or type 2 herpes.

Difficult to prevent. Severity varies from a few vesicles to a fulminant generalized infection.
- Death or severe sequelae.

What is herpetic whitlow?

Herpetic infection affecting the fingers, occupation hazard of health care personnel.

Leads to nosocomial infections of newborns in nurseries.

What are corneal and conjunctival infections caused by HSV?

Infections that lead to ulceration of the cornea and blindness.