Retroviruses Flashcards
What is the classification of retroviruses?
- RNA genome
- Icosahedral capsids
- Enveloped (inactivated by solvents, detergents and heat)
- More resistant to UV
Name 4 common characteristics of retroviruses
- Infect wide range of mammals
- Host adapted and rarely cross host barriers
- Diseases induced by retroviruses are diverse and have distinct pathogenic mechanisms
- They integrate into the host cell genome (activate specific genes)
Name 4 characteristics of Alpharetroviruses
- Tumour forming
- Very well studied
- Need to have an understanding of tumour cell biology
- Oncogene discovery
What is Jaagskiekte sheep retrovirus responsible for in sheep?
It is responsible for contagious lung tumours
(ovine pulmonary adenocarcinoma)
How is Jaagskiekte transmissed?
Via aerosol spread
What are the main symptoms of Jaagsiekte sheep retrovirus?
The symptoms are similiar to pneumonia
General loss of condition and breathing difficulties
* watery discharge from the nose
What clinical sign is unique to OPA?
over-production of fluid in the lungs
What are sheep affected by OPA invariably more susceptible to?
other types of pneumonia, particularly pasteurelliosis
What cells does EBL target?
Targets B cells
* the clonal expansion and accumulation of B cells creates tumours
How is EBL mainly transmissed?
Give 3 ways
- mainly via milk to calves from dams
- Can be iatrogenic
- Mechanical transfer from biting insects
What are the usual post mortem findings for EBL?
- Abomsal tumours that may result in diffuse thickening of the mucosa and sub-mucosa with associated ulceration and haemorrhage
What may you see in the EBL serology?
- AGIDT on single sera.
- ELISA on serum on single and pooled sera.
- ELISA on single and bulk milk.
What is equine infectious anaemia also known as
Swamp Fever
Where does equine infectious anaemia have increased prevalence?
Warm humid environments
How is EIA transmissed iatrogenically?
- Re-using needles
- Blood/ Plasma donation to young foals
How is EIA transmissed mechanically?
- Via biting insects, such as horseflies and deerflies
What does it mean when we say that retroviruses rarely cross host barriers?
Typically only affects one species or closely related species
Retroviruses typically affect mammals
What is the capsid shape of retroviruses?
Icosahedral
What sense is the RNA?
- Positive sense
- BUT contains reverse transcriptase
- this means it can convert into DNA to integrate into the host cell
How many copies of the RNA genome are there?
two copies
What is the meaning of the retrovirus being enveloped?
- Inactivated by solvents, detergents and heat
- More resistant to UV
When provirus DNA enters the cell where is it integrated into the host genome?
In areas of active transcription
What is the function of Gag and Gag-Pol Polyproteins?
Polyproteins that are responsible for synthesising a new virus
What do sheep with OPA not respond to?
Antibiotics
How many sheep are invariably lost to OPA?
- Affected flocks may lose 1-5% sheep per annum
- More than 20% in some cases
What should you do if you have a sheep flock with recurring pneumonia?
They should be investigated so you can determine if OPA is an underlying factor
What are the three main clinical signs of EBL?
- Neurological manifestations
- weakness/ general debility
- inappetence/ weight loss
How much may the milk production reduce in a cow with EBL?
2.5%
What may you see in the serology of EBL?
- AGIDT in single sera
- ELISA on serum in single and pooled sera
- ELISA on single and bulk milk
What are lentiviruses characterised by?
Retroviruses that are characterised by their ability to evade the immune system and have long incubation periods
What are the clinical signs of acute EIA?
- lethargy, anaemia, pyrexia, thrombocytopenia, emaciation
What are the clinical signs of EIA when they are in the ‘inapparanet carrier state’
- Asymptomatic due to strong immune control
How quickly may horses with acute EIA die?
may die within 2-3 weeks
What are the main clinical signs of chronic/ recurring EIA?
- Fever- generally around 40.5
- Depression- generally listless
- Wasting away
- Blood shows a marked drop in RBC count
- Oedema- horses may show swelling under the skin in legs and chest
What do over 90% of EIA infected horses look like?
- No overt clinical abnormalities
- they survive as reservoirs of infection
- have dramatically lower concentrations of EIAV
What is considered to be the ‘gold-standard’ test for EIA?
the AGID test
uses serum to detect antibodies
Where do retroviruses replicate within the cell?
They begin replication in the cytoplasm,- then pro-virus integrates into the host genome and replication continues within the nucleus
How do the retroviruses replicate (simply)
- Single stranded RNA enters the cytoplasm
- Converted into DNA
- DNA integrates into the host genome in the areas of active transcription
- Provirus DNA is used to produce mRNA
- mRNA enters the cytoplasm and is used as a template to produce proteins and virions
What are the four main methods of EIA transmission?
- Iatrogenic (needles)
- Mechanical (flies)
- Aersols
- Vertical (in-utero/ milk)
