Viruses and Vaccinations

Question 1

Define a VIRUS

Answer 1

A virus is an infective agent that typically consists of a nucleic acid molecule in a protein coat. It is too small to be seen by light microscopy and can only multiply within the living cells of a host.

Question 2

What are characteristics of viruses?

Answer 2

They are made up of DNA or RNA, a protein coat (a capsid), some have an envelope around the capsid.

They do not respire, move or grow but they do reproduce.

Question 3

What is the pathogenesis of viruses?

Answer 3

1. Replication happens at the primary site. This localised infection causes high concentrations of the virus.
2. Virus moves to other cells and tissues
3. There is no initial replication - the virus invades macrophages and is carried to susceptible cells elsewhere.

Question 4

What is the effect of a virus on cells?

Answer 4

• vacuolation (formation of fluid fill gaps in the cytoplasm)
• ballooning degeneration
• hypertrophy (enlargement of organs or tissue due to enlargement of cells within).
• margination of nuclear chromatin
• chromosomal damage/rearrangement

Question 5

What is the effect of a virus on the animal?

Answer 5

• pyrexia (increased temp)
• myalgia (muscle pain)
• anorexia (loss of appetite)
• malaise (tiredness)
• headache

Question 6

What are the stages of infection and invasion for a virus?

Answer 6

The initiation phase, the replication phase, the maturation/release phase

Question 7

Describe the initiation phase

Answer 7

The virus attaches to specific receptors (glycoproteins) on the cell wall and the cell is tricked into thinking it should be there. The virus penetrates the cell and any envelope on the virus is broken down.

Question 8

Describe the replication phase

Answer 8

The virus makes use of the cell’s ability to replicate to reproduce.

Question 9

Describe the maturation and release phase

Answer 9

Cell components unite and are pushed through the plasma membrane. Nucleoplasmid is formed and cell lysis occurs which releases the virions (the complete, infectious form of a virus).

Question 10

What are some common equine viruses?

Answer 10

Equine influenza, herpes, cold, rotavirus

Question 11

Describe equine influenza

Answer 11

Symptoms include a harsh, dry cough, pyrexia and laboured breathing. Prevention is maintained through vaccinations and hygiene procedures.
Vaccinated horses may have become infected due to different strains of the virus that are not covered by the vaccine (e.g. 2019 cases).

Question 12

Describe the herpes virus

Answer 12

Herpes in horses is associated with a lot of different diseases. 5 different strains of herpes:
EHV1 and EHV4 are primarily respiratory pathogens, are surprisingly common and can cause widespread outbreaks. These respiratory diseases commonly affect younger horses (between weaning and 2-3 years).

Herpes may lie latent - can stay with a carrier horse for its entire lifetime.

Question 13

Describe the ‘cold’ virus

Answer 13

A common cause of acute respiratory disease.
Symptoms include snotty nose, weepy eyes, coughing.
Full recovery usually made but secondary bacterial infection is possible.

Question 14

Describe the rotavirus

Answer 14

High morbidity and low mortality. Foals less than 4 months are the most susceptible. Caused by poor hygiene and dense stocking of horses.
Symptoms: pyrexia, diarrhoea, dehydration, depression, inappetance, mild colic.
Mares vaccinated during pregnancy pass on the immunity to foals.

Question 15

How are viruses identified?

Answer 15

• tests in the lab
• virus isolation - slow to yield results and expensive but allows further study of the virus.
• detection of viral nucleic acid - o=polymerase chain reaction replicates DNA to identify virus against the standard
• ELISA - enzyme linked immunosorbent assay. Detects and measures the antibodies in blood and looks for particular ones for different diseases.

Question 16

Define VACCINATION

Answer 16

Vaccination is an artificial way of achieving protection from diseases. A harmless microbe is injected in order to confer resistance to a dangerous microbe. This results in the body producing memory cells that have been triggered by the immune response.

Question 17

What are the different types of immunity?

Answer 17

Innate - inborn, depends on genetic factors

Acquired; either active (which may be natural or artificial) or passive (natural or artificial)

Question 18

What is the composition of a vaccine?

Answer 18

Made up of inactive toxins (toxoids). Ensures that the memory response is triggered but the disease is not contracted.

Question 19

What is the difference between a live/dead vaccine?

Answer 19

Live:

• capable of replicating within the horse
• attenuated pathogenicity
• stimulate a broad range of immune responses
• generally long lasting immunity
• risk if the immune status of the horse is compromised

Dead:

• lack pathogenicity
• cant replicate or spread between hosts
• typically require multiple doses in the primary sries and regular boosters
• efficiency often reliant on use of potent adjuvants (substance that enhances the body’s immune response).

Question 20

What is the aim of a vaccine?

Answer 20

The aim of vaccination programmes is to stimulate and maintain adequate levels of memory cells. With each vaccine the antibody/antigen binding is better and the antibody numbers are greater.