4 Equine Viral Respiratory Diseases

• A variety of pathogens can lead to viral respiratory illnesses in horses.
• Clinical signs are typically nonspecific across different forms of the disease.
• Supportive care is generally recommended for most cases.
• The prognosis for many endemic viruses in the US is usually favorable.
• Prevention should include appropriate vaccine protocols and biosecurity to induce herd immunity.
• Serious and sometimes life-threatening viral pathogens are found worldwide.

Objectives In Summary

• Identification of common viral pathogens that induce disease in horses is key.
• Recognition of differing clinical signs and disease manifestation among pathogens is also essential.
• Understanding preventative strategies aimed at reducing disease frequency is needed.
• Knowing the international/travel implications of pathogens in the equine industry is also required.

Equine Viral Respiratory Diseases

• Equine Influenza (EIV) is a significant viral disease to consider.
• Equine Herpesvirus (EHV) is a further viral disease to consider.
• Adenovirus is another viral cause of respiratory illness.
• Equine Viral Arteritis (EVA) may also lead to respiratory disease.
• African Horse Sickness can be a cause of respiratory distress
• Hendra/Nipah viruses are additional viral concerns.

Clinical Signs

• Common symptoms include fever, depression, anorexia, and lymphadenopathy.
• Serous nasal discharge may be present.
• Concern for secondary bacterial infection is important.

Treatment

• Treatment consists of rest.
• Non-steroidal anti-inflammatory drugs (NSAIDs).
• Tender loving care (TLC).
• Antibiotics (+/-) may be indicated based on the disease.

Influenza A

• The virus is an Orthomyxovirus.
• Neuroaminidase (NA) and Hemagglutinin (HA) are proteins found on the virus.

Antigenic Shift

• Involves a sudden change in hemagglutinin (HA).
• Can involve recombination with another influenza virus.
• May occur via human and avian influenza viruses.

Antigenic Drift

• Random mutation in HA and NA is involved.
• This limits vaccine efficacy

EIV: Epidemiology

• Young horses, specifically those over 6 months to 5 years, are most often affected.
• A brief incubation period occurs.
• Transmission occurs directly from horse-to-horse, with the virus able to cough 50 yards.
• Paroxysmal coughing is a sign
• Little subclinical/convalescent shedding happens.
• Latency does not occur with EIV.
• EIV is characterized by high morbidity and low mortality.

Equine Influenza Pathogenesis

• The virus attaches to the respiratory epithelium via hemagglutinin (HA) spikes.
• Severe destruction of the respiratory epithelium results.
• An explosive, dry, paroxysmal cough is a common sign.
• Secondary bacterial infection is not uncommon due to failure of normal mucociliary clearance.
• Streptococcus equi subsp. zooepidemicus is the most common pathogen of the equine lung.
• Colonization of respiratory tract will occur if damage is present.

Equine Influenza in Australia

• Australia was EIV-free on August 7.
• Four Thoroughbred stallions arrived from Japan on August 8.
• Fever was recorded at a quarantine station on August 17.
• EIV was confirmed on August 24.
• By August 27, 400 horses across 50 premises were infected
• A/equine/Wisconsin/1/03 (H3N8) is a specific isolate of the equine virus.

EIV in Australia Response

• New South Wales took the lead.
• The response involved containment and eradication efforts.
• 11,000 horses were vaccinated in buffer zones.
• An additional 26,000 high-risk, high-performance horses were involved in the response.
• The vaccine used was DIVA (Differentiate Infected from Vaccinated Animals).
• Equine veterinarian income was reduced 90% in some areas.
• Many veterinarians worked without payment.
• The Australian government provided $110 million in assistance.

Clinical Management of EIV

• Rest from exercise helps with the restitution of the respiratory epithelium.
• Regeneration of the epithelium requires 3 weeks.
• NSAIDs are employed to encourage eating and drinking, as high fevers may result in poor conditions.
• Good supportive care includes protection from harsh weather.
• Antibiotics are indicated if bacterial colonization is present.

Diagnosing Influenza

• Quantitative Polymerase Chain Reaction (qPCR) is an option for diagnosis.
• Virus isolation from a chick embryo is an option.
• ELISA (Influenza A), a human assay, is also a possibility with 68% sensitivity in horses.

Prevention: Influenza Vaccine

• The vaccine is administered intramuscularly.
• It helps to control viral shedding and clinical signs like fever, weight loss, and nasal discharge.
• Efficacy is good.
• It induces circulating Immunoglobulin G (IgG).
• Performance horses require vaccination every six months.
• A foal series of 3 is recommended in the first year of life.
• Light use/pasture horses need annual administration.
• Pregnant mares must receive it to provide colostral IgG.

Modified Live Vaccine

• Given intra-nasally and is temperature sensitive.
• Local mucosal immune response is developed
• Provides 12 months of protection (though the label says 6 months).
• Provides rapid immune response (7 days).
• Effective in the face of an outbreak.
• More closely represents natural disease, as well as mucosal immunity.
• Safe for at-risk foals (younger than 6 months).

Canarypox Vectored Vaccine

• This yields adequate titers with an accelerated (2-week) schedule.
• A 2-dose priming schedule is utilized.
• Exhibits DIVA capability.
• Safe for at-risk foals younger than 6 months.
• Pregnant mares can be vaccinated 4-6 weeks prior to foaling.

Influenza Vaccines for Foals

• The AAEP recommends initiating vaccination at 6 months of age.
• Clinical disease is less common in very young foals.
• The early vaccination may induce "tolerance".
• Circulating maternal antibody (Ab) provides protection.

Influenza Vaccination for Performance Horses

• AAEP Recommendation/USEF requirement may mandate vaccination under certain jurisdictions.
• Vaccination should occur against EIV (+EHV-1/4) every 6 months (minimum).

Equine Herpesviruses

• EHV-1 is an alpha-herpesvirus.
• EHV-2 is a gamma-herpesvirus.
• EHV-3 is an alpha-herpesvirus.
• EHV-4 is an alpha-herpesvirus.
• EHV-5 is a gamma-herpesvirus.

Equine Herpes Virus 1/4

• These are alpha herpesviruses and ubiquitous equine viral pathogens.
• These viruses are large (150 kb) and have double-stranded DNA.
• DNA viruses are responsible.
• They are nucleocapsids with envelope proteins.
• Both viruses are related, but separate.
• Can result in respiratory problems.

Equine Herpesvirus EHV-1 and EHV-4

• Both are alpha herpesviruses.
• EHV-1/4 can cause respiratory disease.
  • Rhinopneumonitis
• Abortion can result.
  • EHV-1/4 abortion
• Neonatal illness can also result.
  • EHV-1/4
• Neurologic disease can present
  • EHV-1 neurologic disease = equine herpes myelitis = EHM

Difficult Control - EHV

• Control is difficult due to latency, subclinical carriers, convalescent shedding, fomite transmission, as well as foals and weanlings.

Clinical Signs in Horses with EHV

• Fever, depression, anorexia, and lymphadenopathy are common signs.
• Nasal discharge, which can be serous to mucoid, is another sign.
• Coughing is less likely to be observed.
• The disease tends to progress more slowly through the herd.

EHV and Disease Pathogenesis

• The respiratory epithelium is primarily targetted.
• The Lymph nodes are affected
• Lymphocytes and monocytes become infected -Infected leukocytes circulate -CD8+ leukocyte associated viremia

Pathogenesis of Respiratory Disease

• Virus transmitted through exposure of contaminated fluids such as nasopharynx secretions, fluids from the reproductive tract or fluids from infected fetus.
• Exposure to Aerosolized particles that transfer over short distances allows the spread of infection.
• Exposure to items contaminated with the virus such as handler's hands, feeds, water and tack facilitate spread.

Viral Reactivation

• Stress, weaning, long-distance transport, and concurrent illness are commonly associated with viral reactivation.
• Iatrogenic factors, including the use of corticosteroids and cyclophosphamide, can contribute to reactivation.

Treatment of EHV infections

• NSAIDs, CCS, Rest, Tender Loving Care (TLC), antibiotics (+/-) and immunostimulants are treatment considerations. They are determined based on individual circumstances.

Diagnosis of EHV

• PCR of tissues or blood is utilized.
  • Outbreak = nasal swab and blood -Nylon / Dacron swab for nasal secretion collection
  • Virus Isolation or Serology -Nasal swab -Buffy coat -Tissue samples (abortus).

Vaccine Options for EHV 1/4:

• Inactivated (killed) vaccines are safe in pregnant mares but Modified live vaccines are not indicated for pregnant mares
• Modified live has mucosal protection and CTL activation important

Vaccine protocol for respiratory rhinopneumonitis (EHV-1/4) respiratory disease

• Inactivated vaccine administered via intramuscular injection.
• Six-month intervals for active horses.
• Series of 3 injections for foals/weanlings that begin at 3-4-month age
• Young horses have no cross protection for EHV-1 and EHV-4 and vaccine must be multivalent and contain both strains to have adequate response.

Modified vaccine

• Utilizes MLV with EHV-1 strain
• Safe for pregnant mares. However, MLV are not ideae
• Does not offer protection against neurologic herpes

EHV-1 Abortion

• Typically occurs Late in the gestation period
• Weeks/months after viremic episode
• Mares appear healthy with a sporadic abortion storm.
• Fetal destruction may present
• Gross and histological fetal lesions
• Testing via polymerase chain reaction can definitively diagnose.

Equine Neonatal Disease EHV-1:

• Destruction of lymphoid tissue, lungs, bone marrow, adrenal glands
• Causes Icterus

Neurologic Disease from EHV:

• May present with ataxia, paresis, and urinary incontinence -Xanthochromia and Decreased tail tone

EHV-2

• Results in Cytomegalovirus

EHV-3

• Results in Coital exanthema:
• Presents as a self-limiting and vesicular pregenital lesion;
• This condition does not impact the capacity to reproduce
• In aetiology.

EHV-5

• Causes Equine multinodular pulmonary fibrosis (EMPF)
• AssociatedwithInterstitial pneumonia

Equine Rhinoviruses

• Equine rhinitis virus A (ERAV) can act similar to a pathogen.
• Equine rhinitis virus B (ERBV) can act similar to a pathogen. -Easily isolated from young horses with respiratory disease. -Vaccine investigation underway and application is questioned. -Single stranded RNA viruses, including Picornavirus Be aware of confusion between the terms "rhinopneumonitis" and "EHV-1/4"

Equine Viral Arteritis

• Etiology:* Equine Arteritis Virus
• Clinical Signs:* Respiratory disease, abortion, and limb edema
• Characteristics:* Togavirus, infects standardbreds, and high percentage of seropositive-EAV horses.

EVA Route of Propagation

• Aerosol and fomite transmission
• Venereal transmission: carrier Stallions (standardbreds) have infectious semen -Venereal transmission causes disease in the mare.

Transmission by Carrier Stallions

• Infection spreads solely by venereal route concentrated with high doses of viral materials in semen. -Transmission rate 85-100% where susceptible mares bred naturally or artificially inseminated with infected semen. -Frozen semen retains its infectivity for extended periods of time.

EVA Pathogenesis

• Involves viral replication in bronchial macrophages.
• Causes Viremia low mortality.

EVA: Clinical signs

• Present with Fever that induces anorexia and depression
• Serous nasal discharge and cough.
• Conjunctivitis causes lacrimation and palpebral edema.
• Limb swelling due to vasculitis causes asymmetric, painful swelling.
• Preputial and scrotal areas swell into ventral edemas.
• Abortion occurs during the convalescent and fetal destruction phases.

Equine Arteritis Diagnosis

• Signs include Marked lymphopenia or 4-fold rise in an SN-Ab titer
• Diagnostics also include Virus isolation/RT-PCR of the semen, fetal tissues, blood, and respiratory secretions.

Equine Arteritis Treatment

• Requires NSAIDs that cause general comfort and supportive care.
  • May require the use of Limb bandages.
• Rest must stop breeding.
• Antibiotics treat apparent cases of secondary infections.

Persistently Infected Stallions

• Appear normally
• Seropositivity for EVA
• Virus isolated form semen -Semen affected during the persistent phase

EVA Vaccine

• Contains contains highly attenuated Bucyrus strains of attenuated virus is
• Developed through 1985, through it is safe effective.
• Vaccine protects carrier stallions state cannot be be distinguished.

EVA Vaccination Strategy

• Test seronegative stallions 30 days before breeding before isolates from non-vaccinated for 21
• Test seropositive stallions for viability of semen to avoid contamination

Recommendations for EVA Vaccination of Mares

• Vaccination with labeled (or recommended) for pregnant mares.
• When mare breading, isolate (semen virus testing with
• Mare Vaccinated /Isolate prior to starting cycle.
• Mares will not require testing until full grown and vaccinated.

Importation of EVA

• EVA outbreaks associated with with carriers
• Can come with no symptoms so the USA is at risk.

Adenovirus

• Ubiquitous (Everywhere)
• Causes Immune deficiency(Severe combined) -Testing includes(DNA analysis which test and genetic code) -Testing SCID( Arabians) , check check for Lymphopenia -Antibody production -Lack of lymphoid tissue
  • IgM deficiency -Emerging to become a pathogen

African Horse Sickness.

• Characterized by Non-contagious, insect borne disease of equids -AHS virus is classified as AHSV
• Characterized by family and genius Bluetongue Mortality of is high >95% (Naïve) -Transmission is vector based

African Horse Sickness.

• Vector born disease that requires an insect vector called a fly (Culicoides spp.).

African Horse Sickness presents with the following clinical signs:

Acute respiratory distress in conjunction Cardiac issues

Control

• Requires Vaccination to provide for proper level of protection

• Must utilize a polyvalent to provide necessary immune attenuation

• Must utilize the initial 3 dose regiment The vector is based

Hendra Virus

• Morbillivirus. Currently defined. Classify the disease.
• Affects
• Causes potential exposure to bats/ the ingestion of animal matter.
• Hendra Virus Symptoms*
• Fever.
• Respiratory Distress.
• Neurologic Signs.
• Vaccination.*