Equine Viral Respiratory Disease Flashcards
Risk factors for strangles?
- 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
How is the influenza virus transmitted?
- aerosol (& fomites)
- highly infectious, downwind 1 mile
- Young / unvaccinated animals susceptible
How does the influenza virus cause disease?
- 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
Why is secondary infection common with the influenza virus?
The damage to the cilia means they cannot clear bacteria from the respiratory tract
Why is it so easy for the influenza virus to mutate?
- 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
Clinical signs of influenza virus?
- 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
Treatment of influenza virus?
Nursing care and anti-inflammatory medication (antibiotics for secondary infection)
Diagnosis of influenza virus?
- Nasal swab
- Detection of viral antigen (ELISA)
- Detection of virus genetic material = RNA (RT-PCR)
- Virus isolation (usually in eggs
- Serum samples for serology
How are Equine herpesvirus-1 and -4 transmitted?
- 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
What does Equine herpesvirus-1 and -4 infect?
- 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)
Clinical signs of equine herpesvirus 1/4
- Fever
- Occasional mild cough
- Slight nasal discharge
- Poor performance (age/immunity dependent)
- Occassional signs:
- Abortion/sick neonatal foal
- neurological disease (equine herpes virus myeloencephalopathy)
Treatment of equine herpes virus?
- Rest in athletic animals
- if neurological disease then nursing care and anti-inflammatories
How is equine herpes virus diagnosed?
- 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
- Virus isolation in tissue culture
How is Rhodococcus equi spread?
- Inhalation of air, faeces, water, soil laden with bacterium
- Zoonotic potential
Clinical signs of Rhodococcus equi?
- Cough
- mild increase resp rate
- increased resp effort
- mild tracheal rattling
- pulmonary crackling
- fever
- (bronchopneumonia)
- +/- polysynovitis
- +/- diarrhoea
Rhodococcus equi diagnosis?
- 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
Rhodococcus equi treatment?
- Antibiotics - macrolide and rifampin
- monitored via ultrasound and CBC
- passive transfer of hyperimmune plasma
What age do we tend to see Rhodococcus equi?
Foals 6m and under
Prevention of Rhodococcus equi?
- Identify high risk farms
- Improve pasture management/rotation
- low stocking density
- surveillance/early detection
What is the lungworm parasite?
Roundworm Dictyocaulus arnfieldi
Lungworm life-cycle?
- 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
Transmission of lungworm?
- Donkeys are main source of pasture contamination.
- ?Pilobolus fungi involved in dissemination
Clinical signs of lungworm?
moderate–severe coughing (exercise)
Diagnosis of lungworm?
- (1) first-stage larvae L1 in faeces (infrequent & few);
- (2) tracheal wash for eggs, larvae & WBCs;
Treatment of lungworm?
antiparasitic drugs (esp. moxidectin and ivermectin) – bring indoors to treat
Prevention of lungworm?
Management e.g. not grazing donkeys with horses, anthelmintics. No vaccine
What vaccines are available for equine influenza?
-
Antibody and cellular immunity
- Rely mainly on stimulating antibody to find the virus before it can infect cells
- Live attenuated (USA), live vectored, killed
What vaccines are available for equine herpes virus?
-
Antibody and cellular immunity
- Want cellular as well as antibody immunity as the virus can get into cells and travel around the body
What are the regulatory requirements for influenza vaccination?
- 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.
What are the regulatory requirements for vaccinating for equine herpes virus?
- 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
What management factors can be used to minimise the transmission of infectious disease on yards?
- 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
What vaccines would you recommend for a 4-year-old Warmblood gelding purchased for eventing?
- 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)
What vaccines would you recommend for a 6-month-old Thoroughbred filly intended for racing?
- 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).
What vaccines would you recommend for a 12-year-old breeding stallion?
- Herpes virus in case of passing it to a brood mare
- Influenza
- Tetanus
- Equine viral arteritis because it is venerially transmitted
What vaccinations would your recommend for a 12-year-old Shetland pony (pasture pet)?
- 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
