Pathogens involved in reproductive failure and disease 2 Flashcards
What is the most common viral cause of abortion in mares?
EHV1
What are the possible outcomes of infection with EHV-1?
Touch on both a young horse thats exposed, and recrudecence of infection
Young horses that are exposed
- self limiting disease
- Local resp infection or subclinical infection (‘the snots’)
Recrudescence of EHV1 or first infection as an adult:
- No signs
- Abortion and perinatal deaths
- Myeloencephaltits
How do mares become infected with EHV-1?
- Mares become infected through inhalation or “re-activation” from latent virus in their sensory nerves
Why does EHV1 cause abortion?
- Systemic spread of virus leads to leucocyte associated viraemia causing infection of foetus in utero – abortion 2 to 12 weeks (i.e. weeks to months) after infection
Do we usually see clinical signs associated with EHV1?
- Late pregnancy abortion (last trimester)
- Foals may also be born weak and die in few days
- Usually sporadic but may result in an outbreak or ‘abortion storm’ where as many as 80% mortality
What body systems can be involved in EHV1?
- Reproductive system
- Respiratory disease
- neurological disease (very rare in Aus)
How is EHV1 maintained?
- Mare to foal spread (pre-weaning)
- Foal to foal spread (pre-weaning)
- Foal to foal spread (post-weaning)
These pathways are what lets the virus maintain itself in the herd.
What is the diagnostic approach for EHV1?
- PM of foal: Jaundice, fluid accumulation in SC tissue, pleura and peritoneum, oedematous lungs, splenic enlargement, liver necrosis
- PCR: swabs or tissue taken from foals liver, lung, spleen and thymus.
Does a negative EHV1 PCR result in the mare mean that it isnt EHV1?
- It can but not always.
- May not have taken the sample from the infected area
- EHV1 may not have been shedding at the time the sample was taken
What does a positive EHV1 PCR result tell us in the mare?
Either:
- EHV-1 is causing disease
- EHV-1 coincidentally present
- EHV-1 was reactivated by another disease
Is it better to take samples for PCR from the mares or foals?
sampling of mare is of limited value
Where does EHV1 come from?
4 possibilities
- reactivation of her own latent herpesvirus
- from another horse shedding the virus
- aborted foetus from another mare
- fomite transfer from humans, feed, equipment etc
What are some management strategies for EHV1?
- Vaccination
- Separation of pregnant mares
- minimise the stress of mares to decrease recrudescence
Is there always a risk of recrudescence for hepesviruses?
Yes
Does vaccination against herpesviruses stop infection?
No it just reduces clinical signs
What features of alpha-herpesviruses assist their “global survival strategy”?
- Mucosal disease that facilitates transmission
- Latency in sensory nerve ganglia -> avoids host immune response
- Virus has several mechanisms of exiting a cell including syncytia formation
- High number of virions produced at replication
- Persistent infection
- High morbidity, Low mortality
- Periodic recrudescence of infection which may be clinical or subclinical
- Vaccination does not stop animal getting infected
What features of alpha-herpesviruses assist us in our attempts to contain infection/disease?
- Enveloped = fragile in environemnt
- require close contact for transmission
- Not zoonotic
What is the significance of seeing brucella spp. in a joint?
Can cause back pain and lameness
Which brucella spp. are present in Aus? Are they zoonotic
- B. suis - this is zoonitic
- B. ovis
What are some characteristics of brucella spp.
- intracellular
- obligate parasite
- requires an animal resovoir for maintenance
- repro system secretions are a huge source of brucella
What does B. canis cause in dogs?
This is exotic in Aus
- Abortion (~50 days gestation)
- Epididymitis and orchitis in dogs
- Systemic dissemination in dogs (meningoencephalitis, osteomyelitis, discospondylitis and anterior uvelitis)
What does B. suis cause in sows and boards?
- Abortion in sows
- orchitis and epididymitis in boars
Is B. suis in domestic populations in Aus?
- It is a notifiable disease due to zoonotic potential
- It is maintained in the feral pig population in Aus, it has not made its way into the domestic pig population
What 3 syndromes are associated with B. suis in dogs?
- Repro tract: aboriton, stillbirth, orchitis/epididymitis
- Axial skeleton: disconspondylitis and back pain
- Appendicular skeleton: lameness
What are the diagnostic methods for Brucella spp.?
- Culture from infected site (ring to warn diagnostic lab)
- Rose Bengal test (RBT) screening test all species: Highly sensitive (less false negatives)
- Complement fixation test (CFT) confirmatory test all species: highly specific
How might a dog get B. suis?
- A pig hunting dog
- A dog that has been around feral pigs
How is brucellois in dogs treated?
- Euthanasia is unnecessary
- Treat with a combination of Doxy and Rifampicin
- Castration
- surgical debridement of infected tissue
- keep dog isoloated from at risk humans and dogs
