Viral Diseases of the Lymphoid System

Question 1

Define immunocompromise

Answer 1

any aspect of host defences is deficient - impaired or weakened immune system

Question 2

Define immunosuppression

Answer 2

immune defences are specifically impaired - reduction in immune function

Question 3

Define immunodeficience

Answer 3

body’s immune response is compromised or absent - deficient immune response; if external agent related =secondary immunodeficiency; primary immunodeficiency is either due to inherited or acquired gene defect (e.g B cell problem related to antibody production)

Question 4

What defences against viruses does the host have?

Answer 4

• Specific (immune):
  ◦ PMNs (polymorphonuclear leukocytes) – phagocytosis
  ◦ Cell-medicated immunity (monocytes/macrophages, T-lymphocytes)
  ◦ Humoral immunity (B-lymphocytes)
  ◦ Complement cascade
• Non-specific (non-immune) – e.g. integument

Question 5

What are the different virus cell interactions?

Answer 5

Productive - bad outcome
* persistent infection - virus is persistently infecting the cells
* lytic infection - damaging the cells
‣ subacute infection - kills host quickly before spreading
‣ unless there is very close contact you may not be able to survive as a virus

Non productive
* latent infection - virus incorporates itself somewhere and sits
* viral destruction - host cells are able to kill virus
* oncogenic transformation - virus incorporates itself and causes changes that cause cancer

Question 6

What are the different ways for a virus to enter a cell?

Answer 6

• Utilisation of naturally occurring and useful receptors on the cell surface.
• Direct injection (bacteriophages)
• Fusion of the envelope (some enveloped viruses)
• Endocytosis: both enveloped and non-enveloped viruses.

Question 7

What kind of virus is canine distemper virus -1? What cells are targeted? How does the infection spread in the body? What are the main signs?

Answer 7

• RNA enveloped virus - poor survival in the environment
• Infects a number of cells but has particular ‘tropism’ for lymphocytes (causes their destruction).
• Oro-nasal infection (inhalation of aerosol) – replication in local lymphoid tissue-macrophages-dissemination to local lymph nodes – spread to other haemopoietic organs (spleen, bone marrow etc.)
• The main signs: respiratory (severe pneumonia), cutaneous, neurological (seizures in chronic infections.

Question 8

What kind of viruses are canine parvovirus 2 and feline panleukopenia virus? How are they linked? What cells do they target? What clinical signs are seen? What is the pathogenesis?

Answer 8

• Non-enveloped DNA virus - very difficult to destroy through disinfection
• Tropism for fast dividing cells (gastrointestinal tract-crypts, bone marrow, lymphoid tissue)
  ◦ vomiting and diarrhoea
  ◦ low white blood cell count
• Destruction of white blood cells precursors within bone marrow, sequestration of neutrophils within GI tract, damage to the barrier leading to bacterial translocation.

Canine virus that suddenly was able to infect cats - CPV 2a and 2b

Question 9

What type of virus is feline leukaemia virus? How is it transmitted? What are risk factors for infection? Why has it decreased in prevalence in many areas?

Answer 9

• Retrovirus, RNA virus
• Transmission through mutual grooming (‘love virus’) and rarely through bites.
• Risk factors: young age, increased population density, poor hygiene.
  ◦ dirty feeding bowls will help the virus survive
  ◦ feeding multiple cats in the same bowl is wrong because of hygiene but multiple bowls also enables behavioural issues
• In many areas low prevalence due to testing and vaccination

Question 10

What are the stages of FeLV?

Answer 10

Can go back and forth between both stages

Progressive infection
* has lots of antigen
* test positive on PCR
* doesn’t necessarily have clinical signs
* prognosis is a little bit worse

Regressive infection
* no antigen
* but when test PCR it will still be positive
* carrier
* won’t show up on snap test

Question 11

What kind of virus is feline immunodeficiency virus? How is it transmitted? Which cats are at risk? How does the infection spread in the body? What is a common presentation?

Answer 11

• Retrovirus, RNA virus, Lentivirus genus, closely related to HIV
• Transmission via deep wounds inoculation with saliva & Transmission in stable households – uncommon!
• promiscuous, old, male and stray cats at risk
• Infection
  
  • Infects CD4+ T lymphocytes ( T helper cells) which are crucial for humoral and cell-medicated immunity.
  • Invades dendritic cells, macrophages and CD4+ T-cells – can be detected in circulation, slow increase in viral particles and proviral DNA up to 12 weeks (clinical signs related to initial infection).
  • Seroconversion within 2-4 weeks
  • Decrease in viral load – entering asymptomatic phase.
  • Latency – protection from immune system.
  • Functional immunodeficiency through decline of CD4+ cells leading to AIDS-like deterioration.
  • Late in the disease, antibodies level may decline, and animal may test negative.
• common oral presentation - stomatitis