Test 2- Prevention and control of Viruses

Question 1

Antiviral Drugs

Answer 1

Interfere with the ability of a virus to infiltrate a target cell or target different stages of replication/Synthesis of components required for replication of the Virus.

Question 2

Immune system stimulation

Answer 2

Interferons, class of proteins that has antiviral effects and modulate functions of the immune system.

Question 3

Antimicrobial chemotherapy

Answer 3

Antimicrobial chemotherapy is defined as the treatment of infectious diseases by drugs

(chemical compounds) that are inhibitory or lethal to the pathogenic microbe.

Question 4

Antibiotics

Answer 4

Antibiotics, also known as antibacterials, are types of medications that destroy or slow down the growth of bacteria.

Question 5

Antimycotics

Answer 5

Antimycotics are medications used to treat fungal diseases.

Question 6

Antiparasitics

Answer 6

Antiparasitics are a class of medications which are indicated for the treatment of parasitic diseases

Question 7

Antiviral drugs

Answer 7

Antiviral drugs are a class of medication used specifically for treating viral infections

Question 8

Compared to antibiotics, there are only few effective antivirals available so far.

Have you wondered why?

Answer 8

Viruses are intimately dependent on the metabolic pathways of their host cell for their replication, hence most agents that interfere with virus replication are toxic to the cell.

Question 9

A logical approach to the development of new antiviral drugs is

Answer 9

A logical approach to the development of new antiviral drugs is to devise strategies that will interfere with virus replication without harming or causing minimal harm to the infected host cell.

Question 10

Antiviral chemotherapeutic agents are not in common use in veterinary practice because

Answer 10

 The high cost of development of new chemical compounds, particularly for use in food species.

 Often use restricted to a single virus and a specific animal species .
 Difficulties encountered in development of broad-spectrum antivirals with low

cytotoxicity

 Absence of rapid diagnostic techniques allowing prompt use of a specific antiviral agent in the course of an acute infection

Question 11

In the future how will this change?

Answer 11

 The successful use of antiviral chemotherapy in some human viral diseases has increased confidence and awareness of the existence of efficient antiviral drugs that can also be used in veterinary medicine.

 In addition, veterinary internal medicine has undergone refinement and progress with diagnostics and treatment, allowing the use of sophisticated and expensive protocols.

 Vaccination has limitations, attributed to the antigenic diversity of viruses, stressing on development of new antivirals.

Question 12

Acyclovir

Answer 12

 Antiviral activity primarily restricted to herpesviruses.
 Administered as a prodrug, inactive form.
 Requires virus enzymes in infected host cell to convert itself into active form, which then interferes with virus replication.

 Treatment of:
 Herpesvirus infections in humans
 Feline herpesvirus 1 induced corneal ulcers
 Equine herpesvirus-1 induced encephalomyelitis

Question 13

Mechanism of Antiviral effect of Acyclovir

Answer 13

 Acyclovir molecules entering the cell are converted to acyclovir monophosphate by virus induced thymidine kinase enzyme.

 Host-cell enzymes add two more phosphates to form acyclovir triphosphate, which is transported to the nucleus.

 Cleavage of 2 phosphates from the acyclovir triphosphate by the herpes simplex’s own enzymes to form acyclovir monophosphate.

 The herpes simplex’s DNA polymerase enzyme incorporates the acyclovir monophosphate into the growing DNA strand as if it were 2-deoxyguanosine monophosphate (a “G” base).

 Stop the growing viral DNA chain: Further elongation of the growing viral DNA chain is impossible because acyclovir monophosphate lacks the attachment point necessary for the insertion of any additional nucleotides.

Question 14

Acyclovir is________ to the uninfected host cell

Answer 14

Acyclovir is Non-toxic to the uninfected host cell

 Since the enzymes herpesvirus thymidine kinase and herpes virus DNA polymerase are viral enzymes and not found in uninfected host cells, acyclovir cannot be phosphorylated and incorporated into the host DNA.

 Thus, acyclovir is non-toxic to uninfected host cells.

Question 15

Acyclovir: Mechanisms for Resistance

Answer 15

 Some herpesviruses are resistant to acyclovir because of following:

 Absent production of viral thymidine kinase due to mutations in virus genome(TK-

negative mutants)

 Partial decrease in the production of viral thymidine kinase (TK-partial mutants)

 Altered viral thymidine kinase substrate specificity that results in phosphorylation of thymidine but not acyclovir (TK-altered mutants)

 Mutations in viral DNA polymerase that causes a decreased binding of acyclovir- triphosphate to viral DNA polymerase.

Question 16

Amantadine

Answer 16

 Amantadine is a synthetic tricyclic amine of the adamantane family.
 Amantadine acts as both antiviral and anti-Parkinson drug.
 Amantadine inhibits replication of most strains of influenza A viruses by blocking and uncoating the virus

Question 17

Uncoating of Influenza viruses in host cell cytoplasm

Answer 17

 As the endosomal vesicles that contain the virus particles move towards the cell nucleus, their pH drops.

 When the endosomal pH reaches 5.0, the viral HA protein undergoes a conformational rearrangement.

 When this occurs, the viral RNAs are released into the cytoplasm. They are then transported into the cell nucleus where viral RNA replication occurs.

 In the influenza virion, the viral RNAs are bound to a number of viral proteins, including the M1 protein.

 This M1 protein forms the shell that underlies the lipid membrane of the virion.

 Unfortunately, if the viral RNAs are bound to M1 protein when they are released from the virion, the viral RNA cannot enter the nucleus.

 The viral M2 protein forms a channel in the membrane that actively pumps protons from the endosome into the interior of the virion.

 These protons lower the pH in the interior of the virion, releasing the viral RNAs from M1 protein.

Question 18

Mechanism of Antiviral effect of Amantadine

Answer 18

 The M2 ion channel is the target of the antiviral Amantadine.- THE M2 channel is very important for virus replication

 These compounds clog the channel and prevent it from pumping protons into the virion.
 In the presence of amantadine, viral RNAs remain bound to M1 and cannot enter the nucleus. Virus replication is inhibited.

 Resistance to amantadine occurs by changes in amino acids that line the M2 channel. These changes prevent the drug from plugging the channel.

Question 19

In certain strains of influenza A virus, the pH changes that result from M2 inhibition alter t

Answer 19

In certain strains of influenza A virus, the pH changes that result from M2 inhibition alter the conformation of hemagglutinin during its intracellular transport later in replication and thus block the viral assembly also.

Question 20

Neuraminidase Inhibitors

Answer 20

Inhibitor of neuraminidase [NA] enzyme synthesized by Influenza A and B viruses.

 Oseltamivir (Tamiflu)

 Laninamivir
 Zanamivir
 Peramivir

Question 21

Oseltamivir phosphate (Tamiflu) is a

Answer 21

Oseltamivir phosphate (Tamiflu) is a prodrug that, after its metabolism in the liver, releases an activate metabolite that inhibits neuraminidase.

Question 22

What are the major glycoproteins found on the surface of the Influenza virus?

Answer 22

Neuramindase (NA) and hemagglutinin (HA) are major membrane glycoproteins found on the surface of influenza virus.

Question 23

Neuramindiase activity

Answer 23

HA of influenza virus binds to receptors containing sialic acid on host cell membrane.- where the hemmaglutin spikes attach!

 After budding, HA of progeny influenza virions are still bound to sialic acid containing receptors on infected host cell surface. NA present on virus will cleave the sialic acid containing cell surface receptors and release HA. The virus is freed from the infected cell.

 NA is thus critical in cell to cell spread of influenza viruses

Question 24

Neuramindiase Inhibitors

Answer 24

 Blocking the function of neuraminidase with NA inhibitors is an effective way to treat influenza.

 This prevents release of virus and spread of infection, as the HA of virus is still bound/attached to the sialic acid containing receptors on surface of already infected host cell.- they do not prevent replication

 Inhibition of neuraminidase, therefore, slows virus spread, giving the immune system the opportunity to “catch up” and mediate virus clearance.

Question 25

Nucleoside Analog Reverse Transcriptase Inhibitors (NRTIs)

Answer 25

Zidovudine (ZDV) or AZT [Azidothymidine]

ddI [Didanosine]

Question 26

ZDV/AZT

Answer 26

 ZDV/AZT belongs to the family of nucleoside analog reverse transcriptase inhibitors (NRTIs)

 Nucleoside analog of thymine, i.e. resembles the deoxyribonucleotide containing the base thymine.

Question 27

 AZT/ZDV is phosphorylated by

Answer 27

 AZT/ZDV is phosphorylated by kinases present in host cell to AZT-triphosphate (AZT-TP).

Question 28

Since ZDV/ AZT resembles thymine deoxyribonucleotide-triphosphate

Answer 28

Since it resembles thymine deoxyribonucleotide-triphosphate, the reverse transcriptase cleaves two phosphates and inserts AZT monophosphate into the cDNA that is being synethized from viral RNA

STOPS CHAIN ELONGATION

Question 29

Synthesis of cDNA from Viral RNA by Reverse Transcriptase

Answer 29

In order for a cDNA strand to elongate, the phosphate group of a free deoxyribonucleotide bonds to the hydroxyl (OH) on the 3 prime carbon of the deoxyribose of the last deoxyribonucleotide in the growing cDNA strand.

Question 30

What happens then?

Answer 30

 Competitive inhibition of Reverse Transcriptase activity: AZT-triphosphate competes with thymine deoxyribonucleotide triphosphate for reverse transcriptase.

 Insertion of AZT-monophosphate into cDNA blocks the growth of the cDNA being transcribed from the viral RNA by reverse transcriptase.

Question 31

Zidovudine (ZDV, AZT) has an

Answer 31

Zidovudine (ZDV, AZT) has an azide (N3) group instead of a hydroxyl (OH) group on its pentose sugar. Once the phosphate group of the zidovudine bonds to OH of the last deoxyribonucleotide in the strand, no further free deoxyribonucleotides can attach. (The phosphate groups of free deoxyribonucleotides can only bond to OH groups, they are unable to bond to N3groups.). This results in an incomplete cDNA/provirus.

Question 32

Since reverse transcription of virus genome takes place

Answer 32

Since reverse transcription of virus genome takes place in the cytoplasm where the drug appears first and is in highest concentration, the RNA-dependent DNA polymerase (Reverse Transcriptase) of the virus is 100 times more sensitive to AZT/ZDV than the cellular DNA polymerase (in host cell nucleus), resulting in selective activity and low mammalian toxicity.

Question 33

Major toxicities of AZT/ZDV include

Answer 33

Major toxicities of AZT/ZDV include anemia and granulocytopenia, which can occur in up to 45% of treated patients.

LESS TOXIC TO HOST AND MORE TOXIC TO THE VIRUS

Question 34

AZT/ZDV is considered as a

Answer 34

AZT/ZDV is considered as a maintenance drug, because, at best, it slows down the progression of HIV infection, but does not eradicate or eliminate the virus.

Question 35

AZT has been shown to reduce

Answer 35

AZT has been shown to reduce clinical signs in FIV-positive cats when administered at a dose of 10mg/kg twice a day, subcutaneously, for a period of 3 weeks.

Question 36

Proteases are required to cleave the

Answer 36

Proteases are required to cleave the HIV polyproteins into functional proteins

Question 37

HIV must use a

Answer 37

HIV must use a HIV encoded enzyme called protease in order to cleave a large Gag- Pol polyprotein (p120), a Gag polyprotein (p55), and an Env polyprotein (gp160) into functional proteins essential to the structure of HIV and to its RNA packaging. The active site of the HIV protease binds to the polyproteins and cleaves them into functional proteins

Question 38

Proteases inhibitors inhibit the proteases. HIV polyproteins cannot be cleaved

Answer 38

Proteases inhibitors inhibit the proteases. HIV polyproteins cannot be cleaved into functional proteins.- REPLICATION CAN GO FORWARD

Protease inhibitors bind to the active site of the HIV protease and prevent the enzyme from cleaving HIV polyproteins into functional proteins. As a result, HIV can not mature and noninfectious viruses are produced.

Question 39

The four ‘W’s of immunization:

Answer 39

A. Where?

 Primarily populations in endemic areas.

B. When?

 If the disease has a distinct “season,” such as seen with Vector-borne agents, immunization just before the season will provide the maximum efficiency.

 Outbreak of a nonendemic disease occurs

C. Who?

 Population at Risk.

D. Why?

 For a program of vaccination to be justifiable, the loss caused by the disease must be greater than the cost of immunization.

Question 40

 Features of a Good Vaccine:

Answer 40

Safe to use

Effective against diverse strains of the same Pathogen

Few side effects

Give long lasting, appropriate protection

Low in cost

Stable with long shelf life (no special storage requirements)

Easy to administer

Inexpensive

Benefit outweighs the risk

Question 41

Prevention and Control of Viruses

A.1. Live-Attenuated Virus Vaccines:

Answer 41

A.1. Live-Attenuated Virus Vaccines:

A. Vaccination:
 Vaccines Produced from Naturally Occurring Attenuated Viruses

The original vaccine, introduced by Jenner in 1798 for the control of human smallpox, utilized cowpox virus. Cowpox virus produced only a mild infection in humans, but offered immunity against the deadly small poxvirus. This is because cowpox is antigenically related to smallpox virus.

Other examples:

 Protection of chickens against Marek’s disease using a vaccine derived from a related herpesvirus of turkeys.

 Protection of piglets against porcine rotavirus infection using a vaccine derived from a bovine rotavirus.

Question 42

A. Vaccination:
 Life attenuated Vaccines Produced by ______________

Answer 42

A. Vaccination:
 Vaccines Produced by Attenuation of Viruses by Serial Passage in Cultured Cells

 Most of the live-attenuated(virus looses it’s virulence but keeps it antegenesity— THEREFORE IT HELPS WITH IMMUNITY) virus vaccines in common use today were derived empirically by serial passage of virulent viruses (wild-type or field strains) in cultured cells. The cells may be of homologous or, more commonly, heterologous host origin.

 During repeated passage in cultured cells, viruses typically accumulate nucleotide substitutions in their genome, which in turn lead to attenuation.

Question 43

A. Vaccination:
A.1. Live-Attenuated Virus Vaccines:
 Vaccines Produced by Attenuation of Viruses by Serial Passage in Heterologous Hosts

Answer 43

Rinderpest (deadly disease of cattle) and classical swine fever (deadly disease of pigs) viruses were each adapted to grow in rabbits and, after serial passage, became sufficiently attenuated to be used as vaccines.

• in hosts that it doesn’t induce disease- it just looses it virulence

Question 44

A. Vaccination:
A.1. Live-Attenuated Virus Vaccines:
 Vaccines Produced by Attenuation of Viruses by Selection of Cold-Adapted Mutants and Reassortants

Answer 44

 Cold-adapted mutant viruses would be safer vaccines for intranasal administration, in that they would replicate well at the lower temperature of the nasal cavity (about 33°C in most mammalian species), but not at the higher temperature (37°C) of the more vulnerable lower respiratory tract and pulmonary airspaces.

 Cold-adapted influenza vaccines that contain mutations in most viral genes do not revert to virulence, and vaccines against equine influenza have been developed utilizing the same principle.

Question 45

A. Vaccination:

A.2. Non-Replicating Virus Vaccines
 Vaccines Produced from Inactivated Whole Virions

Answer 45

 Inactivated (syn. killed) virus vaccines are usually made from virulent virus

 Chemical or physical agents are used to destroy infectivity while maintaining immunogenicity.

 Need to contain relatively large amounts of antigen to elicit an antibody response commensurate with that induced by a much smaller dose of live- attenuated virus vaccine.

 Killed vaccines usually must be formulated with chemical adjuvants to enhance the immune response

Question 46

 Vaccines Produced from Purified Native Viral Proteins

Answer 46

 The virion is solubilized and its components released, including the glycoprotein

spikes of the viral envelope.

 Differential centrifugation is used to semi-purify these glycoproteins, which are then formulated for use as so-called split vaccines

Question 47

A. Vaccination:
A.3. Vaccines Produced by Recombinant DNA and Related Technologies

Answer 47

 Vaccines Produced by Attenuation of Viruses by Gene Deletion or Site-Directed Mutagenesis

 Subunit Vaccines Produced by Expression of Viral Proteins in Eukaryotic (Yeast, Mammalian, Insect), Bacterial, or Plant Cells

 Vaccines Utilizing harmless Viruses as Vectors for Expression of Other (Heterologous) Viral Antigens

 Vaccines Utilizing Viral DNA (“DNA Vaccines”)

Question 48

DIVA (Differentiating Infected from Vaccinated Animals)

Answer 48

 Vaccination with the only live attenuated vaccines (LAV) leads to production of an antibody response that does not differ from the antibody response developed after natural infection.

 Thus, it is impossible to differentiate animals vaccinated with LAV vaccines from animals infected with the field strain using serology.

Question 49

How does DIVA work?

Answer 49

DIVA (Differentiating Infected from Vaccinated Animals):

 Subunit ‘marker vaccines’ DIVA vaccines have only a portion (subunit) of the pathogen in the vaccine, i.e. has less antigens than natural strains.- ONLY TEST POSTIVE FOR THE MARKER

 If antibodies to other parts/antigens of the pathogen not included in the vaccine are detected the animal has been infected with the pathogen.

 If only antibodies to the vaccine subunit/antigens are detected, the animal has not been infected. An accompanying diagnostic test allows us to actually make that differentiation.

Question 50

Vector Control

Answer 50

1. source reduction- espesically controlling where they bred
2. Biological control- Use of natural enemies to manage mosquito populations., such as predatory fish that feed on mosquito larvae (Gambusia affinis, carps and minnows).
3. . Chemical control: Insecticides-

 Larvicides: Insecticides that specifically targets the larval life stage of mosquitoes.

 Adulticide: Insecticides against adult mosquitoes.

Question 51

Prevention and Control of Viruses C. Reducing Contact Potential:

Answer 51

 Isolation: Applies to animals/persons who are known to be ill with a contagious disease.

 Reduces the probability of contact with a susceptible host

 Facilitates treatment

 Not effective, if detectable pathogen shedding does not occur, as in carriers or

during incubation period.

 Relies on Sensitivity of Diagnostic tool.

 Quarantine: Applies to those who have been exposed to a contagious disease.

 Enforced for the longest incubation period of the disease
 Not effective with diseases involving chronically infected healthy shedders.

 Population control programs:

 Population reduction may be used to control spread of a zoonosis within a

reservoir population.

 Biological control of wildlife reservoirs.

Question 52

Prevention and Control of Viruses

 Quarantine & Culling:

Answer 52

 To separate and restrict the movement of animals.

 Culling (killing) of Animals
 Proper Disposition of Culled Animals

Question 53

D. Protection of Portals of Entry:

Answer 53

Personal protection:

 Protective clothing
 Repellents
 Nets on doors and windows

 Mosquito nets

Question 54

Decontamination

Answer 54

Decontamination is a term used to describe a process or treatment that renders a medical device, instrument, or environmental surface safe to handle.

 A decontamination procedure can range from sterilization to simple cleaning with soap and water.

 Sterilization, disinfection and antisepsis are all forms of decontamination.

Question 55

Sterilization

Answer 55

Sterilization describes a process that destroys or eliminates all forms of microbial life/

Pathogens, including highly resistant pathogens, such as Bacteria with Spores.

 No degrees of sterilization: an all-or-nothing process

Question 56

Disinfection

Answer 56

Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects.

 Less effective than sterilization, does not necessarily kill all microorganisms.

Question 57

Antisepsis

Answer 57

Antisepsis is the application of a liquid antimicrobial chemical to skin or living tissue to inhibit or destroy microorganisms.

Question 58

Sterilization Methods:

Answer 58

 Moist Heat:
- Use of steam. Autoclave (Use of steam heated

to 121°C (250 °F) for at least 15 min in 15 psi pressure).

 Dry Heat:
- Hot air oven, at least two hours at 160 °C (320 °F).

 Chemical Methods:
- Gases like Ethylene oxide, Ozone. - Chemicals like Hydrogen peroxide

at high concentrations.

 Radiation:
- Non-ionizing: Ultraviolet Radiation. - Ionizing: Gamma rays, X-Rays

 Sterile Filtration:
- Microfiltration using membrane filters

(pore size <0.2 μm remove most microbes)

Question 59

Distribution of Transmissible GastroEnteritis (TGE) in Pigs

Answer 59

TGE has been reported in USA, the Americas, Europe and many parts of Asia, primarily in the northern hemisphere. In densely pig farming areas, such as Midwestern USA, TGE is one of major causes of mortality and morbidity in piglets.

Question 60

Sentinel Surveillance in forecasting Equine encephalitis, a vector-borne disease of horses and humans transmitted by mosquitoes.

Answer 60

1. Trapping and testing mosquitoes for viruses
2. Use of sentinel animals/birds to monitor presence of viruses, such as chicken.
3. Sentinel chicken serology
4. Dead bird reporting and testing

5.

Question 61

Farm Biosecurity:

Answer 61

Farm Biosecurity: Biosecurity on a farm comprises all measures taken to minimize the risk of the introduction and the spread of infectious agents.

2 components:

External biosecurity- Measures taken to prevent an infectious disease from entering or leaving the farm

Internal Biosecurity-Measures taken to combat spread of an infectious disease within the farm

Question 62

Biosecurity Measures:
A. Housing and Management:

Answer 62

 Minimize contact between young and older animals or consecutive production batches.

 Maintain optimal Stocking density. High stocking density facilitates disease spread, and

also increases stress, lowering immunity and predisposing animals to infectious disease.

 Adoption of the All-in and All-out housing system- when a new batch of animals comes and you isolate them for the period of the incubation period of the diseases that they can have

Question 63

Biosecurity Measures:
B. Vermin and bird control:

Answer 63

 Prevent contact with free roaming animals (e.g. wildlife, cats, dogs, etc.).
 Minimize bird contact
 Maintain a rodent and insect control program.
 Secure all feed storage areas and clean up spilled feed to minimize access by pests.  Pasture management, for Microbes and Parasitic Diseases.

Question 64

Biosecurity Measures:

C. Purchasing policy:

Answer 64

 Adopt a Closed Herd System, avoid buying animals from outside. Difficult to follow.

 Reduce the number of new animals brought to the farm. More animals-More Risk.

 Limit the number of farms or sources from where you are buying the animals.

 Determine the vaccination & health status of newly purchased animals and of the herd of origin.

 Farms from which you buy animals or semen should have a higher sanitary status

 Quarantine or keep newly arrived animals in isolation, away from the main herd.

 The quarantine period should be long enough and depend upon the incubation period of important infectious diseases.

 Use the quarantine period to test the animals for possible and important infectious diseases.

 Vaccinate, if necessary.

Question 65

Biosecurity Measures:
E. People (Visitors and Farm Workers):

Answer 65

 Keep Visitors to the minimum.
 Current Health record/history of Visitor and Workers.
 Maintain a log book of all entering and leaving the Farm.
 Make Visitors aware of farm protection methods. Train and Educate Farm workers.
 Discourage visitors from entering the housing and feeding areas, and touching animals.

 Ensure supply of clean rubber boots or plastic disposable boots and clean coveralls.

 Provide a footbath containing disinfectant before entering Stables.

 Insist workers wash their hands before and after handling animals.

 Insist workers wear protective plastic or rubber gloves when required, such as for calving cows

 Establish a working line. Attend animals in order of increasing age groups, and at the last, visit sick animals.

Question 66

incubation period

Answer 66

is the time elapsed between infection and when clinical symptoms are first apparent.

Question 67

What are the 3 ways that you can treat viral diseases?

Answer 67

1. Antivirals
2. Immune system stimulation:
3. Synthesize antibodies or administration of natural antiserum (antibodies)

Question 68

Antivirals can target which parts of the virus replication cycle?

Answer 68

receptor binding, uncoating, nucleic acid and protein synthesis, assembly, release, or modulating the immune system

Question 69

Acyclovir is a synthetic nucleoside of….

Answer 69

synthetic nucleoside analog of deoxyguanosine.

It stops elongation of DNA chains

Also, competitive inhibition of Viral DNA polymerase, as acyclovir- triphosphate compete with dGTP for viral DNA polymerase

Question 70

Targets for Anti-retroviral Therapy

Answer 70

• inhibit protease
• inhibit reserve transcriptase
• inhibit integrase
• inhibit fusion

Question 71

survillence

Answer 71

tracking a virus through different method of infection

i.e. reservoirs, route/ portal of entry, mode of transmission etc