Equine Viral Respiratory Disease

Question 1

Risk factors for strangles?

Answer 1

• Contact with other horses / health status
• New arrivals
• Previous strangles / carrier status (10%)
• Health plans: quarantine and/or testing
• Water troughs: separate vs communal
• Personnel traffic between horses

Question 2

How is the influenza virus transmitted?

Answer 2

• aerosol (& fomites)
• highly infectious, downwind 1 mile
• Young / unvaccinated animals susceptible

Question 3

How does the influenza virus cause disease?

Answer 3

• Infection of respiratory epithelial cells (URT) - destroys cilia
• Prone to secondary bacterial infection following infection with influenza
• Virus usually limited to URT
  
  • Usually a couple of weeks to recover

Question 4

Why is secondary infection common with the influenza virus?

Answer 4

The damage to the cilia means they cannot clear bacteria from the respiratory tract

Question 5

Why is it so easy for the influenza virus to mutate?

Answer 5

• Negative-sense ssRNA virus with segmented genome
• RNA replication is very error prone, so accumulates mutations
• The segmented genome means that if two different viruses infect the same cell, these can be swapped and you get a completely different subtype
• Equine virus not as quick at evolving as the human virus

Question 6

Clinical signs of influenza virus?

Answer 6

• Fever, cough and nasal discharge (serous, may become mucopurulent – secondary bacterial infection) (harsh, dry cough is supposed to be really distinctive)
• Once horses are vaccinated the first thing to be suppressed is the clinical signs
• So the animal may not have clinical signs but could still be shedding virus

Question 7

Treatment of influenza virus?

Answer 7

Nursing care and anti-inflammatory medication (antibiotics for secondary infection)

Question 8

Diagnosis of influenza virus?

Answer 8

• Nasal swab
  
  • Detection of viral antigen (ELISA)
  • Detection of virus genetic material = RNA (RT-PCR)
  • Virus isolation (usually in eggs
• Serum samples for serology

Question 9

How are Equine herpesvirus-1 and -4 transmitted?

Answer 9

• inhalation of aerosol / contact with infected fomites / reactivation from latency
• Virus can go latent, and hide away in the body, can be reactivated under stress, e.g. pregnancy

Question 10

What does Equine herpesvirus-1 and -4 infect?

Answer 10

• respiratory epithelial cells (NASOPHARYNGEAL VIRUS SHEDDING)
• multiple cell types including white blood cells (DISSEMINATION)
• endothelial cells (INFLAMMATION & THROMBI)
• pregnant uterus (ABORTION - rare)
• spinal cord (NEUROLOGICAL DISEASE - rare)

Question 11

Clinical signs of equine herpesvirus 1/4

Answer 11

• Fever
• Occasional mild cough
• Slight nasal discharge
• Poor performance (age/immunity dependent)
• Occassional signs:
  
  • Abortion/sick neonatal foal
  • neurological disease (equine herpes virus myeloencephalopathy)

Question 12

Treatment of equine herpes virus?

Answer 12

• Rest in athletic animals
• if neurological disease then nursing care and anti-inflammatories

Question 13

How is equine herpes virus diagnosed?

Answer 13

• Nasal swab (and placenta / fetus)
  
  • Viral DNA - PCR
• Blood samples
  
  • Virus isolation in tissue culture
    (anti-coagulated blood - acute)
  • Detection of antibodies (serum)
    
    • Complement fixation test

Question 14

How is Rhodococcus equi spread?

Answer 14

• Inhalation of air, faeces, water, soil laden with bacterium
• Zoonotic potential

Question 15

Clinical signs of Rhodococcus equi?

Answer 15

• Cough
• mild increase resp rate
• increased resp effort
• mild tracheal rattling
• pulmonary crackling
• fever
• (bronchopneumonia)
• +/- polysynovitis
• +/- diarrhoea

Question 16

Rhodococcus equi diagnosis?

Answer 16

• Tracheobronchial wash / aspirate
  
  • Bacteriology
  • Cytology
  • PCR (vapA gene)
• Blood sample?
  
  • CBC, plasma protein, hyperfibrinogenaemia?, neutrophilic leukocytotis
• Ultrasonography, low specificity
  
  • Peripheral pulmonary abscesses & “comet tails”
• Thoracic radiography, unusual
  
  • Prominent alveolar pattern

Question 17

Rhodococcus equi treatment?

Answer 17

• Antibiotics - macrolide and rifampin
• monitored via ultrasound and CBC
• passive transfer of hyperimmune plasma

Question 18

What age do we tend to see Rhodococcus equi?

Answer 18

Foals 6m and under

Question 19

Prevention of Rhodococcus equi?

Answer 19

• Identify high risk farms
• Improve pasture management/rotation
• low stocking density
• surveillance/early detection

Question 20

What is the lungworm parasite?

Answer 20

Roundworm Dictyocaulus arnfieldi

Question 21

Lungworm life-cycle?

Answer 21

• Ingestion of L3 larvae from faeces / pasture, invasion of intestinal mucosa, migration to mesenteric LNs, moult
• L4 migrate via blood and lymph to lung capillaries > alveoli
• Adults hatch, migrate to small bronchi,
• Adults lay eggs with L1 larvae which hatch & migrate up trachea
• Eggs / L1 coughed up & swallowed, pass through intestine then hatch in faeces

Question 22

Transmission of lungworm?

Answer 22

• Donkeys are main source of pasture contamination.
• ?Pilobolus fungi involved in dissemination

Question 23

Clinical signs of lungworm?

Answer 23

moderate–severe coughing (exercise)

Question 24

Diagnosis of lungworm?

Answer 24

• (1) first-stage larvae L1 in faeces (infrequent & few);
• (2) tracheal wash for eggs, larvae & WBCs;

Question 25

Treatment of lungworm?

Answer 25

antiparasitic drugs (esp. moxidectin and ivermectin) – bring indoors to treat

Question 26

Prevention of lungworm?

Answer 26

Management e.g. not grazing donkeys with horses, anthelmintics. No vaccine

Question 27

What vaccines are available for equine influenza?

Answer 27

• Antibody and cellular immunity
  
  • Rely mainly on stimulating antibody to find the virus before it can infect cells
  • Live attenuated (USA), live vectored, killed

Question 28

What vaccines are available for equine herpes virus?

Answer 28

• Antibody and cellular immunity
  
  • Want cellular as well as antibody immunity as the virus can get into cells and travel around the body

Question 29

What are the regulatory requirements for influenza vaccination?

Answer 29

• Vaccination mandatory for racehorses in France, Ireland, UK since 1981. Also many other disciplines including show jumping
• For more recent vaccination than the norm, 6 monthly for competition animals
• To achieve herd immunity we need to vaccinate at least 75%, on a national scale this is not achieved.

Question 30

What are the regulatory requirements for vaccinating for equine herpes virus?

Answer 30

• Vaccination mandatory for racehorses in France
• Vaccine not the best at protecting as difficult to achieve the required immunity
• Thoroughbred bloodstock industry - Required due to its impact with abortion

Question 31

What management factors can be used to minimise the transmission of infectious disease on yards?

Answer 31

• Maintain horses in small, consistent groups
• Use separate tack (bridles / head-collars) and equipment (forks, barrows etc)
• Avoid shared water sources / contact across stable or field boundaries
• Handle new or young horses last
  
  • Until you know they are not infected
• Monitor at risk animals (observation, temperature etc.)
• Clean boxes, trailers / lorries between each occupant

Question 32

What vaccines would you recommend for a 4-year-old Warmblood gelding purchased for eventing?

Answer 32

• Influenza compulsory
• Tetanus (but don’t need to give this everytime as the antibodies last a lot longer, influenza vaccines come with or without it so give appropriately)

Question 33

What vaccines would you recommend for a 6-month-old Thoroughbred filly intended for racing?

Answer 33

• Influenza compulsory
• Tetanus
• Schedule: as she is 6 months old it may be the first time she has been vaccinated, so may give primary, secondary (6 weeks later) and then a booster (6-12months).

Question 34

What vaccines would you recommend for a 12-year-old breeding stallion?

Answer 34

• Herpes virus in case of passing it to a brood mare
• Influenza
• Tetanus
• Equine viral arteritis because it is venerially transmitted

Question 35

What vaccinations would your recommend for a 12-year-old Shetland pony (pasture pet)?

Answer 35

• Tetanus
• Depends on his lifestyle
• If he is on his own he is not much at risk of anything
• But if he has companions/even if they come and go then vaccinate