PHA 6114 LEC — VIRUSES 1.2

vertical transmission

- most common way of transmission in viral infections

- through generations

- from pregnant mother to embryo or from mother to baby via breastmilk

horizontal transmission

- way of transmission in viral infections

- from one individual to another of the same species and they are not in a parent-child relationship

via droplet nuclei

- modes of transmission

- particles expelled into the atmosphere during sneezing, coughing, or talking

• mucus-coated droplet

• ease of transmission is dependent on humidity

influenza, common cold, measles, & other viruses infecting the respiratory system

examples of infections that spread via droplet nuclei

low humidity

mucus rapidly dries so the aerosolized particle becomes lighter and remains suspended in the air for longer — becoming airborne

will remain in droplet form

if there is high humidity, what will happen to a droplet nuclei?

fecal-oral route

common means of transmission for viruses whose primary infection site is the gastrointestinal tract associated organs

hepatitis A & polio

examples of infections that spread through fecal-oral route; they also multiply in the intestinal core

HIV/AIDS, hepatitis B, genital herpes, & cervical cancer

examples of infections that spread through sexual intercourse

dengue fever virus, West Nile disease, & tickborne encephalities

examples of infections that spread through insect vectors

direct contact with infected patients or contaminated objects

- mode of transmission in viral infections

- introduction onto the skin

- examples: warts & verrucae

- into the blood stream by skin damage following scratching (e.g. pox viruses)

when the infection is almost gone

when is the most infectious stage when it comes to direct contact with infected patients or contaminated objects?

direct introduction into the blood stream

- mode of transmission in viral infections

- hepatitis B from contaminated syringes and needles

- rabies following animal bites

viruses' characteristics

- cannot reproduce on their own

- no metabolism

- cannot synthesize their own proteins, lipids, or nucleic acids

true intracellular parasites

- grow within living cells

- use their energy & synthetic machinery to produce viral components

viruses' characteristics

- production & excision from the host cell will result in cell death (not immediate)

- replication of one virus will result to hundreds of new viruses (virus progeny/virions)

viral disease

propagation from one infected cell to new cells & the subsequent destruction of tissue or cells

1. multiplication of the virus & destruction of the host cell upon release of the viral progeny

2. multiplication of the virus and release of the virions without the immediate destruction of the host cell

3. survival of the virus in a latent stage without noticeable changes to the infected cell

4. survival of the infected cell in a dramatically altered/transferred state

5. incorporation of the viral nucleic acid in the host cell genome without noticeable changes to the infected cell

5 interactions in virus-host cell

asymptomatic & silent

- viral infection characteristic

- cytomegalovirus in children

- pregnant women should be protected from this

mild symptoms

- viral infection characteristic

- rhinoviruses

kill the host

- viral infection characteristic

- Ebola virus

range of symptoms

- viral infection characteristic

- SARS-Cov-2 virus

not cause immediate symptoms but will lead to an incurable disease

- viral infection characteristic

- HIV

attachment to host cell

- 1st multiplication of human viruses step

- has viral receptors/glycoproteins

1. initial contact dependent on Brownian motion

2. reversible phase during which electrostatic repulsion is reduced

3. irreversible changes in virus-receptor-host-receptor configuration that initiates viral penetration through the cell membrane

viral receptors/glycoproteins

- recognize & bind receptors on the host cell

- provide the virus with its high specificity

penetration of viral particle

- 2nd multiplication of human viruses step

1. endocytosis

2. fusion

3. injection

endocytosis

- step in penetration of viral particle

- virus-host-receptor interaction triggers cell

membrane to engulf virus particle forming a cystosolic vacuole

- true for non-enveloped but with few enveloped viruses

fusion

- step in penetration of viral particle

- what envelope does w host-cell membrane, liberating viral capsid within cell cytoplasm

- enveloped viruses

injection

- step in penetration of viral particle

- bacteriophages

uncoating of viral particle

- 3rd multiplication of human viruses step

- release of the nucleic acid from the capsid

- endocytosis; acidification of the cytosolic vacuoles

following endosome fusion — induces a conformational

change in the capsid & the release of viral nucleocapsid (helper proteins + nucleic acid) into the cytoplasm

- partial uncoating (reovirus) might also happen

replication of nucleic acids & translation of genome

- 4th multiplication of human viruses step

- viral replication ensuring

- mechanisms: transcription of viral genes into viral mRNA, translation of the viral genome into proteins, & replication of the viral genome

- transcription & translation

- replication depends on the type of nucleic acid carried by the virus

1) host cell synthesis machinery is taken over by the virus & that 2) the viral genome is replicated

what does viral replication ensure in replication of the nucleic acids & translation of the genome?

transcription & translation

- occur immediately after the release of nucleocapsid in

to the cytoplasm

- ensures production of early proteins such as viral polymerases, and the hijacking of the cell synthesis machinery

viral mRNA

- polycistronic; several distinct proteins are encoded within a single piece of mRNA

- needs to use a virus-specific protease to cut at the correct place the polyprotein produced by translation to restore the functionality of viral proteins

positive strand RNA; poliovirus

can be used directly as mRNA following the acquisition of a terminal sequence from the host cell; translated to proteins

negative strand RNA; influenza virus

transcribed into a positive RNA using an RNA-dependent RNA polymerase carried by the virus

ds DNA viruses; adenoviruses

the nucleic acid passes into the nucleus where it is usually transcribed by a host DNA-dependent RNA polymerase; to positive RNA

poxvirus

the enzyme is contained within the virus allowing the replication in the cytoplasm

ss RNA

reverse transcribed to a ss proviral DNA by reverse transcriptase

reverse transcriptase

- acts both as an RNA- and DNA-directed DNA polymerase

- has RNAase activity

- proviral DNA can be transported to the cell nucleus where it can be integrated within the cell host genome by a viral integrase

FALSE: it will always end up as positive RNA

T or F: whatever/wherever the replication started, it will always end up as a negative RNA

maturation/assembly of virions

- 5th multiplication of human viruses step

- viral capsid starts to form from individual structural proteins

- replicated viral genome and some viral proteins become packaged within the capsid; occuring within the cytoplasm/in the cell nucleus

- enveloped; envelope originates from the host

- presence of chaperone proteins may play an important role in the interaction of the nucleic acid and the structural proteins

release of virions into surrounding environment

- 6th multiplication of human viruses step

- mature virions are released from the host cell

- enveloped; released by a budding process

- host cell will die following damage to its metabolism and housekeeping functions during viral replication

- non-enveloped; virus progeny accumulates within the host cell cytoplasm & is released following cell lysis

steps in non-enveloped virus pyrogeny accumulation followed by cell lysis

1. bacteriophages produce a lytic enzyme/peptide/proteases to lyse the host enabling release of infectious particles

2. host self-disintegrates as it cannot maintain normal housekeeping functions during viral infection

primary cell culture

- diploid cell lines

- derived directly from an intact tissue such as human embryo/monkey kidney

- have contact inhibition

once end of petri dish is touched

when will a virus stop replicating in a petri dish?

secondary cell culture

- diploid cell lines

- derived from primary cultures, usually those arising from embryonic tissue

- more homogenous, better characterized, but might not be as susceptible to viral infection as primary cell lines

- limited subcultures can be performed up to a maximum of about 50 before cells degenerate

continuous cell culture

- derived from malignant tissue; Hela cells derived from a cervical carcinoma

- have the capacity to multiply indefinitely in vitro

- no contact inhibition

vaccine production

- obtained from an approved cell bank

- need to be checked for infectious agents & tumorigenicity (in the case of live vaccines)

chick embryo

- fertile chicken eggs

- used as a convenient cell system to grow human pathogenic viruses

- there are many types of different tissues found on eggs, will support growth of different viruses

9-11 days old

how many days old would a fertile chicken egg be?

expensive

Chick embryo are ____

specific pathogens ; healthy flocks

Chick embryo should be free from _____ and originate from _____

aseptic ; infectious

The processing of fertilized egg must be conducted under ____ conditions in area where no other ____ agents are handled at the same time

rodents and primates

What are the animals used in animal inoculation?

antiviral and vaccine effectiveness

Animal inoculation is used to study what? (2)

animal inoculation

What is the source of cell lines for cell culture?

ethical ; expensive

Animal inoculation follows strict ____ guidelines and is extremely ____

diseases

When inoculating animals, what must they be free from?

growth of virus

In animal inoculation, what is indicated by signs of disease or death?

Fertilized hen's eggs - membrane bounding amniotic activity

In the cultivation for vaccine production, Influenza virus is cultivated with?

Fertilized hen's eggs - chorioallantoic membrane

In the cultivation for vaccine production, smallpox virus is cultivated with?

Measles and mumps, Tick-borne encephalitis virus, Yellow fever virus

What viruses are cultivated by chick embryo cells? (3)

Varicella Zoster Virus, Rubella, Hepatitis A, Human herpesvirus 3 (shingles, herpes zoster)

What viruses are cultivated by human diploid cell? (4)

Chick embryo cells or in human diploid cells

In the cultivation for vaccine production, rabies virus is cultivated with what? (2)

yeast ; mammalian cells

viral DNA encoding for a vaccine surface antigen is expressed in ____ (S. cerevisiae) or _____ (Chinese hamster cells or other suitable lines

aluminum salts

Antigens are absorbed to the _____

monophosphoryl lipid A

What is used to increase or modulate the host immune response to the antigens?

immunoglobulin

What plays a role in the protection of patients with a compromised immunity against viral infections?

Human Normal Immunoglobulin

What is prepared from a pool of donated human plasma that has been checked to be non-reactive for hepatitis B surface antigen, Hepa C virus and HIV (types 1 and 2)?

Hepa A Ig

For immunocompromised patients visiting highly endemic areas

Measles Ig

To protect against or attenuate infection in immunocompromised patients

Rubella Ig

For pregnant women where the risk of termination of pregnancy is unacceptable

Disease-specific immunoglobulin

What is prepared from a pool of plasma obtained from specific human donors who have high-specific levels of the specific antibody required?

Hepa B Ig

used following accidental inoculation by a risk material (needlestick injury), or for infants born from mothers infected with the virus

Rabies Ig

used following the bite of an animal suspected of carrying the disease or originating from an area where the disease is endemic

Varicella zoster Ig

for individuals at high risk as neonates whose mothers develop chicken pox or for those exposed to the virus while requiring intensive care or prolonged special care for immunocompromised individuals

prevention ; exposed

Vaccines are used for _____, while Ig are used if they are ____ already

via surfaces

Where are viruses generally transmitted hence the need for use of viricidal disinfectants?

lipid-rich envelope

What is damaged easily by chemical or physical agents?

____ viruses are more resistant to disinfectants

Smaller

biocides

The viricidal activity of ____ varies

envelope, glycoproteins, capsid, viral nucleic acid

What sites are targeted by chemical agents? (4)

cationic biocides

What biocide interacts with the envelope and glycoproteins, inhibiting viral infectivity, without altering the capsid and genome?

polyhexamethylene biguanide

Example of cationic biocides

capsid (severely damaged)

For highly reactive biocides, what is the target site?

helical

What type of capsid structure are more susceptible since the destruction/alteration of the capsid is more likely to cause damage to the viral nucleic acid?

peracetic acid, hydrogen peroxide, chlorine dioxide

Oxidizing agents (3)

Oxidizing agents

_____ penetrate the capsid and destruct/alter the viral genome which is the infective part or damage viral nucleic acid released from a damaged capsid (viral inactivation)

Quaternary ammonium compounds (QACs) and biguanides (chlorhexidine)

What are less reactive biocides?

less reactive biocides

What damage viral capsid to a LESSER extent and has limited activity to non-enveloped viruses?

heat and radiation - pasteurization

physical agents

physical agents

These are important in control of viral contaminants in pharmaceutical products

physical agents

use temperatures above 60C for 30 minutes

viral nucleic acid

UV and ionizing radiation (x-ray and accelerated electron) can destroy ______

germicidal lamps

What are used to decontaminate both water (used for medicines' manufacture) and air (as in biological containment cabinets)?

UV and ionizing radiation

What is used for terminal sterilization processes to medical and pharmaceutical products?

bacteriophages (phages)

What are viruses that only infect bacteria?

Bacteriophages

20-200nm; highly diverse in structure and host range

typing

Bacteriophages are extremely specific and some will only infect a specific bacterial strain - can be used in bacterial _____