Lecture 35- Upper respiratory tract dz 2

Importance of URT disease

Affects performance; economic impact; secondary infection/disease risk

Primary barriers to respiratory infection

Mucus gel/sol layer, cilia, goblet cells, mucous glands, intact bronchial epithelium

Common equine respiratory pathogens

EIV, EHV‑1, EHV‑4, ERAV, ERBV, EAV, EHV‑2, EHV‑5, Strep. equi subsp. equi

RealPCR program pathogens

EHV‑1, EHV‑4, EIV, Strep. equi, ERAV, ERBV (results within 24 hrs)

Comprehensive RealPCR panel contents

Adenovirus, EIV, EHV‑1/2/4/5, ERAV/ERBV, Strep. equi + culture; optional EAV

Best sample for EIV PCR

Nasopharyngeal swab superior to nasal swab; cannot differentiate Florida clade 1 vs 2

Best sample for EHV‑1

Respiratory secretions + whole blood; PCR can differentiate lytic vs non‑replicating virus via mRNA activity

Strep. equi PCR considerations

Sensitivity varies by sample; cannot distinguish viable vs non‑viable or vaccine vs wild‑type strains

ERAV detection window

Very short nasal detection; urine may be positive; serology recommended concurrently

ERBV sampling

Must collect nasal secretions during acute phase; sample multiple affected animals

EHV‑2/5 testing

Not recommended for URTD due to high prevalence; EHV‑5 detection in BAL/lung biopsy relevant for EMPF

Most common URTD pathogen (2008–2020)

EHV‑4 (32% of positives), followed by EIV (29%) and Strep. equi (22%)

Seasonal pattern of EHV‑4

More prevalent in fall; EIV more prevalent in winter/spring

Outbreak investigation steps

History, vaccination status, clinical signs, measures taken, plan, PPE order, dedicated staff/equipment, foot baths, sample collection, monitoring

Shared URTD clinical signs

Fever, cough, nasal discharge, exercise intolerance

Shared URTD treatment

Rest, low dust, supportive care

Shared URTD diagnostics

Nasopharyngeal swab, nasal swab

Rest recommendation for EIV

1 week of rest per day of fever; 2 weeks after cough resolution to prevent cardiovascular damage

EIV management

Clean ventilated stall, hay/water, NSAIDs (Banamine), strict rest schedule

Biosecurity measures

28‑day isolation, personal equipment only, disinfect tack, wash exposed skin/clothing, call vet if signs appear, ensure all caretakers follow hygiene

USEF vaccination rule

EIV & EHV vaccination required every 6 months for competition horses

EIV etiology

Orthomyxoviridae; RNA virus; antigenic drift; subtypes H7N7, H3N8 (Eurasian, American, South American, Kentucky, Florida clade 1 & 2)

EIV incubation

1–3 days

EIV risk factors

Young/old horses, naïve/unvaccinated, stress, shipping, mingling

EIV transmission

Direct aerosol/breathing space; indirect fomites

EIV explosive outbreak pattern

Rapid spread days 1–6 in naïve populations

EIV clinical signs

Fever, deep dry cough, serous→mucopurulent nasal discharge, inappetence, enlarged LN, myalgia, edema, secondary infections/myositis possible

EIV diagnosis

ELISA (NP swab), PCR (NP swab), virus isolation, serology (2–3 weeks)

EIV prevention

Biosecurity + risk‑based vaccination (IM or intranasal)

EHV etiology

Ubiquitous; 80–90% infected before age 2; 80% latent; dsDNA virus; Alphaherpesvirinae

EHV epidemiology

Respiratory disease, abortion, neonatal death, myeloencephalopathy, pulmonary vasculotropic disease; aerosol/fomite/vertical transmission; 2–10 day incubation; latency in trigeminal ganglia & T‑lymphocytes

EHV pathogenesis

Focal epithelial erosion, inflammation, vasculitis; infection → latency → reactivation → transmission

EHV‑1 vs EHV‑4 syndromes

EHV‑1: respiratory, abortion, neurologic; EHV‑4: respiratory (abortion rare)

EHV‑1 viremia

Cell‑associated; EHV‑4 viremia rare

EHV URTD signs

Mild MP nasal discharge, transient biphasic fever, submandibular LN adenopathy, inappetence, lethargy, edema, epiphora

EHV abortion signs

Last trimester abortion without warning; fetus not autolyzed; EHV‑1 causes storms; EHV‑4 sporadic; weak foals unable to nurse → death

EHV‑2/5 notes

Mild signs; “doorman” function; exercise intolerance?; ubiquitous; EHV‑5 associated with EMPF

EHV diagnostics

Fluorescent Ab (NP swab, fetal tissue), PCR (NP swab, blood, fetal tissue), virus isolation, serology

EHV prevention

Supportive care, biosecurity, vaccination every 6 months for adults; increased frequency for at‑risk horses (breeding farms, pregnant mares, high movement)

EAV etiology

Reportable; Arteriviridae; ssRNA; Bucyrus strain

EAV epidemiology

Worldwide except Japan/Iceland; aerosol, fomites, vertical, venereal; incubation 3–14 days; persistence in male accessory sex glands; respiratory + reproductive disease

EAV pathogenesis

Focal epithelial erosion, inflammation, viremia, pan‑vasculitis, persistent infection

EAV clinical signs

Mostly subclinical; fever, depression, anorexia; conjunctivitis, edema, stiffness, rash; foals: interstitial pneumonia/pneumoenteritis; abortion (3–10 months) with partially autolyzed fetus

EAV diagnostics

PCR (semen, fetal tissue, swabs), virus isolation (swabs, blood, semen, placenta/fetal tissue), serology

EAV prevention

Supportive care, biosecurity, vaccination (AAEP guidelines)

Competition vaccination frequency

Every 6 months for EIV & EHV1 (USEF rule)

EHV‑1 vaccine limitation

Questionable efficacy against neurologic form (EHM)

Comparative etiology

EIV: Orthomyxoviridae; EHV: Alphaherpesvirinae/Gammaherpesvirinae; EAV: Arteriviridae

Comparative transmission

EIV: aerosol/fomites; EHV: aerosol/fomites/vertical; EAV: aerosol/fomites/vertical/venereal

Comparative incubation

EIV 1–3d; EHV 2–10d; EAV 3–14d

Comparative pathogenesis

EIV: mucociliary damage; EHV: inflammation + vasculitis; EAV: pan‑vasculitis + persistent infection

Comparative persistence

EIV: acute self‑limiting; EHV: latency/reactivation; EAV: persistent infection in stallions