Antivirals

Question 1

List viral bovine respiratory diseases

Answer 1

• RSV (respiratory synctial virus)
• BHV-1 (bovine herpesvirus-1)
• PI-3 (Parainfluenza- 3)
• BVDV (bovine viral diarrhoea virus)
• Bovine adenovirus
• Bovine coronavirus

Question 2

What is the main method of viral disease control?

Answer 2

• Vaccinations (very few antiviral drugs licensed for veterinary use)
• Biosecurity is very important for production animals

Question 3

How are virally infected animals treated?

Answer 3

Mainly with supportive therapy

Some drugs can be used under cascade

Question 4

Name some drug targets during the virus replication cycle

Answer 4

• Target viral proteins (inhibition of virus replicative enzymes)
• Drugs which target host proteins (block receptors)
• Drugs which enhance host defences (interferons)

Question 5

What is drug selectivity?

Answer 5

difference between the dose of drug which inhibits the viral protein versus any similar cellular protein (less selective= more side effects)

Question 6

How may drugs inhibit virus attachment/ entry to host cell?

Answer 6

• They can target the viral proteins (e.g. bind to the envelope) or target host cell receptors and block them

Question 7

Give an example of a drug inhibiting viral uncoating

Answer 7

• Influenza A
• Hydrogen ions enter the virion via M2 which allows the virus proteins to exit and enter the cell.
• However AMANTADINE blocks M2 so the ions can’t enter and hence the virion is not uncoated

Question 8

How do antiretroviral drugs work? eg. Nevirapine (non nucleotide reverse transcriptase inhibitors)

Answer 8

They bind near the catalytic site of reverse transcriptase but don’t bind to or inhibit host enzymes= VERY SPECIFIC
However resistance develops rapidly and only a single Aa substitution is needed

Question 9

How do integrase inhibitors for HIV work?

Answer 9

• Bind to viral integrase which prevents viral cDNA being inserted into host genome

Question 10

Describe how antivirals can inhibit virus assembly

Answer 10

• Protease inhibitors, where viral proteins are produced as polyproteins and require cleavage by a protease this is a good drug target
• Used for HIV, Hep C in man

Question 11

In which class of viruses is drug resistance a particular problem?

Answer 11

RNA viruses- very high mutation rate

Question 12

How do some drugs help enhance patient immune system?

Answer 12

• Cans timulate TLRs e.g Imiquimod stimulates TLR-7 and 8 (used to treat equine sarcoids)

Question 13

Name a retrovirus, coronavirus and herpresvirus that affects cats

Answer 13

Retro= FeLV or FIV
Corona= FIP
Herpes= FHV

Question 14

Briefly list what supportive therapy includes

Answer 14

• Nursing
• Antibiotics if secondary bacterial infections likely
• Fluid therapy
• Nutrition
• Vitamin supplements
• Appetite stimulants

Question 15

What is Virbagen Omega?

Answer 15

• It is an antiviral drug licensed for use in cats
• Used to treat retroviruses

(Notes: virbac can also be used but isn’t llicensed and nucleotide analogue drug, zidovudine has been used but causes renal toxicity)

Question 16

What is the treatment regime of Virbagen Omega? (drug has a mechanism of action of type 1 IFN)

Answer 16

In cats:
Given subcut at 1 MU/kg 1x daily for 5 consecutive days
-Repeat as required 2 weeks later and 2 months later
In dogs:
Used for parvo infections
recommended at 2.5 MU/Kg/d for 3 consecutive days

Question 17

What is LTCI and how does it work?

Answer 17

-Lymphocyte T cell immunomodulator
- has been shown to increase CD-4 lymphocyte function/ number
0increase IL-2 production
-Increase RBC count in severely anaemic cats
- Licensed in America BUT not in the UK

Question 18

Are the any licensed drugs for the treatment of FHV in cats?

Answer 18

No.
But therapy is needed in acute cases or where corneal ulceration is developing
-TFT drops can be used but are expensive
-Acyclovir ointment has low efficacy
-Feline interferon omega

Question 19

Treatment of herpes viruses in other species

Answer 19

• In horses can use Valacyclovir to treat/ prevent neurological disease
• In elephants Famicylcovir has been used