8.2.2: Equine infectious respiratory disease Flashcards
What type of virus is Equine Influenza A and how is it transmitted?
- Negative sense ssRNA virus with segmented genome
- Transmission is via aerosol and fomites -> highly infectious including 1 mile downwind
Pathogenesis of Equine Influenza A
- Infectious of respiratory epithelial cells of the upper respiratory tract
- Destroys cilia
- Virus is shed from nasopharynx
Clinical signs of Equine Influenza A infection
- Fever
- Cough
- Nasal discharge: initially serous (viral), may become mucopurulent with secondary bacterial infection
Treatment of Equine Influenza A virus
- Nursing care
- NSAIDs
- Antibiotics for secondary infection
Prevention of Equine Influenza A virus
- Vaccines available
Diagnosis of Equine Influenza A virus
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
What type of virus is Equine herpesvirus 1 and 4 and how is it transmitted?
- Linear, double-stranded DNA genome
- Transmitted via aerosol, contact with infected fomites, reactivation from latency
Pathogenesis of Equine herpesvirus 1 and 4
- 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
Clinical signs of Equine herpesvirus 1 and 4
- 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)
Treatment of Equine herpesvirus 1 and 4
- Rest in athletic animals
- EHM: nursing care and NSAIDs
Prevention of Equine herpesvirus 1 and 4
- 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
Diagnosis of Equine herpesvirus 1 and 4
- 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)
What type of virus is Equine viral arteritis (EVA) and how is it transmitted?
- Positive-sense ssRNA virus
- Transmission is via respiratory, venereal and congenital routes, or by indirect means (fomites)
Pathogenesis of EVA
- 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)
Clinical signs
- Often asymptomatic
- Fever
- Nasal discharge
- Loss of appetite
- Respiratory distress
- Skin rash
- Muscle soreness
- Conjunctivitis (common)
- Depression
Is EVA circulating in the UK?
- 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
Diagnosis of EVA
- 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
Treatment and prevention of EVA
- 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
Life cycle of which parasite?
Dictyocaulus arnfieldi
= equine lungworm
How do horses become infected with lungworm
- 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
Clinical signs of lungworm infection
- Mucopurulent discharge
- Moderate to severe coughing (worse with exercise)
Diagnosis of lungworm
- L1 in faeces (infrequent and few)
- Tracheal wash for eggs, larvae, WBCs
- Consider: previous failure of antibiotic therapy, season, history
Pathogenesis of lungworm
- 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
Treatment of lungworm
- Anthelmintics: moxidectin, ivermectin
- Bring indoors to treat
Lungworm larvae
What is a good protocol to follow for control of respiratory disease outbreaks?
