8.2.2: Equine infectious respiratory disease

Question 1

What type of virus is Equine Influenza A and how is it transmitted?

Answer 1

• Negative sense ssRNA virus with segmented genome
• Transmission is via aerosol and fomites -> highly infectious including 1 mile downwind

Question 2

Pathogenesis of Equine Influenza A

Answer 2

• Infectious of respiratory epithelial cells of the upper respiratory tract
• Destroys cilia
• Virus is shed from nasopharynx

Question 3

Clinical signs of Equine Influenza A infection

Answer 3

• Fever
• Cough
• Nasal discharge: initially serous (viral), may become mucopurulent with secondary bacterial infection

Question 4

Treatment of Equine Influenza A virus

Answer 4

• Nursing care
• NSAIDs
• Antibiotics for secondary infection

Question 5

Prevention of Equine Influenza A virus

Answer 5

• Vaccines available

Question 6

Diagnosis of Equine Influenza A virus

Answer 6

Nasal swab - hit the back of the nose with a flexible swab
* Virus is only there for a short period of time -> swab in-contact animals
* Detection of viral antigen (ELISA)
* Detection of RNA (RT-PCR)

Serum samples
* Detection of antibodies (serology)
* ELISA
* Haemagglutination inhibition (HI) - 4 fold increase in titre indicates seroconversion

Question 7

What type of virus is Equine herpesvirus 1 and 4 and how is it transmitted?

Answer 7

• Linear, double-stranded DNA genome
• Transmitted via aerosol, contact with infected fomites, reactivation from latency

Question 8

Pathogenesis of Equine herpesvirus 1 and 4

Answer 8

• Infection of respiratory epithelial cells
• Shed from nasopharynx
• Multiple cell types affected inc WBCs (cell-associated viraemia) -> this leads to dissemination to sites of secondary replication. Can cause neuro disease in spinal cord or abortion in pregnant uterus.
• Causes inflammation and thrombi in endothelial cells
• Latency is established and there is reactivation during times of stress e.g. pregnancy

Question 9

Clinical signs of Equine herpesvirus 1 and 4

Answer 9

• Commonly: fever
• Occasional mild cough, slight nasal discharge (less likely to cause cough and secondary bacterial infection that equine influenza)
• Poor performance (age/ immunity dependent)
• Occasionally: abortion/ sick neonatal foal
• Occasionally: neurological disease (equine herpesvirus myeloencephalopathy, EHM)

Question 10

Treatment of Equine herpesvirus 1 and 4

Answer 10

• Rest in athletic animals
• EHM: nursing care and NSAIDs

Question 11

Prevention of Equine herpesvirus 1 and 4

Answer 11

• Vaccines available
• Hard to vaccinate against because of its ability to be latent
• Need to develop a cell-mediated response to identify and kill off infected cells where it is hiding as well as just produce antibodies when it invades

Question 12

Diagnosis of Equine herpesvirus 1 and 4

Answer 12

• Nasal swab / placenta / foetus -> PCR for viral DNA
• Blood samples: virus isolation in tissue culture (anti-coagulated blood; acute) or detection of antibodies by complement fixation test (serum)

Question 13

What type of virus is Equine viral arteritis (EVA) and how is it transmitted?

Answer 13

• Positive-sense ssRNA virus
• Transmission is via respiratory, venereal and congenital routes, or by indirect means (fomites)

Question 14

Pathogenesis of EVA

Answer 14

• Invades upper and lower respiratory tract
• Infected monocytes and T lymphocytes transport EVA to the regional LNs e.g. bronchial LNs
• Here it undergoes a further cycle of replication before being released into the blood-stream (=cell-associated viraemia)
• 10-70% of stallions may become persistentl infected; carrier stallions may shed the virus into their semen
• Can cause abortion in mares (this may be due to high fever)

Question 15

Clinical signs

Answer 15

• Often asymptomatic
• Fever
• Nasal discharge
• Loss of appetite
• Respiratory distress
• Skin rash
• Muscle soreness
• Conjunctivitis (common)
• Depression

Question 16

Is EVA circulating in the UK?

Answer 16

• No but we do see occasional cases
• ⚠️EVA is notifiable⚠️
• It is notifiable in all stallions, and in mares that have been mated or inseminated within 14 days

Question 17

Diagnosis of EVA

Answer 17

• Virus detection in body secretions, whole blood, tissues -> by virus isolation, RT-PCR, and in situ hybridisation
• Identification of viral antigen in tissues
• ELISA for viral-specific antibodies on serology; routine pre-breeding/ pre-sales

Question 18

Treatment and prevention of EVA

Answer 18

• General supportive care during the acute phase of infection
• No treatment to eliminate persistent infection in stallions
• Inactivated virus is available but not widely used
• Routinely test for this virus before breeding because we don’t want it circulating

Question 19

Life cycle of which parasite?

Answer 19

Dictyocaulus arnfieldi
= equine lungworm

Question 20

How do horses become infected with lungworm

Answer 20

• Ingestion of Dictyocaulus arnfieldi larvae L3 from faeces/ pasture
• Donkeys are the main source of pasture contamination - tend to be the main source of lungworm
• Pilobolus fungi is involved in dissemination

Question 21

Clinical signs of lungworm infection

Answer 21

• Mucopurulent discharge
• Moderate to severe coughing (worse with exercise)

Question 22

Diagnosis of lungworm

Answer 22

• L1 in faeces (infrequent and few)
• Tracheal wash for eggs, larvae, WBCs
• Consider: previous failure of antibiotic therapy, season, history

Question 23

Pathogenesis of lungworm

Answer 23

• There is mucopurulent exudate and hyperplastic epithelium
• There is lymphocytic infiltrate in the lamina propria (-> alveolitis, bronchiolitis, bronchitis)
• Raised areas of over-inflated pulmonary tissue

Question 24

Treatment of lungworm

Answer 24

• Anthelmintics: moxidectin, ivermectin
• Bring indoors to treat

Question 25

Answer 25

Lungworm larvae

Question 26

What is a good protocol to follow for control of respiratory disease outbreaks?

Answer 26