Pathogens involved in reproductive failure and disease 2

Question 1

What is the most common viral cause of abortion in mares?

Answer 1

EHV1

Question 2

What are the possible outcomes of infection with EHV-1?

Touch on both a young horse thats exposed, and recrudecence of infection

Answer 2

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

Question 3

How do mares become infected with EHV-1?

Answer 3

• Mares become infected through inhalation or “re-activation” from latent virus in their sensory nerves

Question 4

Why does EHV1 cause abortion?

Answer 4

• 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

Question 5

Do we usually see clinical signs associated with EHV1?

Answer 5

• 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

Question 6

What body systems can be involved in EHV1?

Answer 6

• Reproductive system
• Respiratory disease
• neurological disease (very rare in Aus)

Question 7

How is EHV1 maintained?

Answer 7

• 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.

Question 8

What is the diagnostic approach for EHV1?

Answer 8

• 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.

Question 9

Does a negative EHV1 PCR result in the mare mean that it isnt EHV1?

Answer 9

• 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

Question 10

What does a positive EHV1 PCR result tell us in the mare?

Answer 10

Either:
- EHV-1 is causing disease
- EHV-1 coincidentally present
- EHV-1 was reactivated by another disease

Question 11

Is it better to take samples for PCR from the mares or foals?

Answer 11

sampling of mare is of limited value

Question 12

Where does EHV1 come from?

4 possibilities

Answer 12

• reactivation of her own latent herpesvirus
• from another horse shedding the virus
• aborted foetus from another mare
• fomite transfer from humans, feed, equipment etc

Question 13

What are some management strategies for EHV1?

Answer 13

• Vaccination
• Separation of pregnant mares
• minimise the stress of mares to decrease recrudescence

Question 14

Is there always a risk of recrudescence for hepesviruses?

Answer 14

Yes

Question 15

Does vaccination against herpesviruses stop infection?

Answer 15

No it just reduces clinical signs

Question 16

What features of alpha-herpesviruses assist their “global survival strategy”?

Answer 16

• 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

Question 17

What features of alpha-herpesviruses assist us in our attempts to contain infection/disease?

Answer 17

• Enveloped = fragile in environemnt
• require close contact for transmission
• Not zoonotic

Question 18

What is the significance of seeing brucella spp. in a joint?

Answer 18

Can cause back pain and lameness

Question 19

Which brucella spp. are present in Aus? Are they zoonotic

Answer 19

• B. suis - this is zoonitic
• B. ovis

Question 20

What are some characteristics of brucella spp.

Answer 20

• intracellular
• obligate parasite
• requires an animal resovoir for maintenance
• repro system secretions are a huge source of brucella

Question 21

What does B. canis cause in dogs?

This is exotic in Aus

Answer 21

• Abortion (~50 days gestation)
• Epididymitis and orchitis in dogs
• Systemic dissemination in dogs (meningoencephalitis, osteomyelitis, discospondylitis and anterior uvelitis)

Question 22

What does B. suis cause in sows and boards?

Answer 22

• Abortion in sows
• orchitis and epididymitis in boars

Question 23

Is B. suis in domestic populations in Aus?

Answer 23

• 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

Question 24

What 3 syndromes are associated with B. suis in dogs?

Answer 24

1. Repro tract: aboriton, stillbirth, orchitis/epididymitis
2. Axial skeleton: disconspondylitis and back pain
3. Appendicular skeleton: lameness

Question 25

What are the diagnostic methods for Brucella spp.?

Answer 25

• 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

Question 26

How might a dog get B. suis?

Answer 26

• A pig hunting dog
• A dog that has been around feral pigs

Question 27

How is brucellois in dogs treated?

Answer 27

• 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