Unit 1 - Viral Respiratory Disease Flashcards
Severity of viral disease depends upon what factors?
agent, virulence of circulating virus, infectious dose, management/environmentla conditions, degree of immunity in an individual animal
What clinical signs are often used to make a presumptive diagnosis of viral respiratory disease?
acute and rapidly spread, fever, cough, and serous nasal discharge
Identify three ways in which you can make a definitive diagnosis of viral respiratory disease.
isolation of the etiologic agent, demonstration of virion, the firus genome or viral particles, and electron microscopy
How do you detect viral antigens?
immuofluorescence, ELISA, immunoperoxidase
How do you detect the viral genome?
PCR
How do you detect virus-specific antibodies?
serology
True or false: viral shedding is required for successful virus isolation and shedding is greatest after several days of infection.
false - it is greatest within the first few days after infection - its best to take a swab within the first 24-48 hours
Why do false negative results often occur when performing antibody detection tests?
They’re usually associated with insufficient time between infection and measurement of an antibody response. Additionally, immunocompromised horses may fail to produce a detectable antibody response despite infection.
In general, how do you treat viral respiratory infections?
mostly symptomatic and supportive care - keep sick animals in a well-ventilated, clean, and stress-free environment, NSAIDs in hydrated animals, monitor for secondary complications, antiviral therapy
Identify the two M2 ion channel blockers used in equine medicine.
Amantadine and Rimantadine (Flumadine)
What drug is a neuraminidase inhibitor used in horses?
Oseltamivir (Tamiflu)
What drugs are chain-terminating nucleoside analogs?
Acyclovir, Valacyclovir, Ganciclovir
_____ _____ _____ is the most frequently diagnosed cause of viral respiratory disease in the horse.
Equine Influenza Virus
What influenza group are equine influenza viruses members of?
Influenza A
What are the two subtypes of EIV? Which is currently still seen?
Type 1: H7N7 (extinct) Type 2: H3N8 (current cases)
What age of animal is typically susceptible to EIV?
animals older than 6 months of age - after recovering there is protection for 8 months and then partially protected for over a year
What is the most common risk factor in EIV outbreaks? List the three modes of transmission.
Most comon - close contact
Direct contact with infected animals or fomites
Droplet transmission (droplets >10 micrometers) projected over moderate distances by coughing
Aerosol transmission (droplets of less than 5 micrometers) capable of wide dissemination and reaching the lower respiratory tract
What is the incubation period of EIV in naive horses?
Around two days. Disease spreads between naive horses within hours to days. Horses may shed in nasal secretions for 6-7 days.
Where does EIV replicate?
throughout the respiratory tract with the most significant lesions in the lower airways
Describe the pathogenesis of EIV.
- EIV is inhaled and directly attaches to sialic acid receptors on the surface of the respiratory epithelial cells enters the cell via endocytosis
- the virus replicates within the cell
- infective virus released from the cell (cell death by apoptosis)
- spreads throughout the respiratory tract.
What are the clinical signs of EIV?
fever (48-96 hours post infection), anorexia, nasal discharge (72-96 hours), cough (up to 3 weeks), and secondary complications
What secondary complications are associated with EIV infection?
Secondary complications include bacterial pneumonia, myositis, myocarditis, and limb edema.
How do you control EIV?
Biosecurity: isolate new horses for 4 weeks or 2 weeks with a vaccine booster.
Vaccinate with Florida clade 1 and 2 strains. The MLV intranasal has the longest protection of up to 12 months.
Vaccination of foals after 6 months of age.
Vaccination of high risk horses at least every 6 months.
Which alphaherpesviruses has respiratory tract implications in horses?
EHV-1 and EHV-4
How can you inactivate EHV?
General cleaning and disinfection.
True or false: the EHV-1 N752 genotype is less virulent than the D752 genotype.
TRUE
Which form of EHV is the primary cause of concern due to its cause of respiratory disease, abortion, neonatal foal death, EHM, and chorioretinopathy?
EHV-1
Describe the pathogenesis of EHV-1 infections.
- Infection of EHV-1
- respiratory epithelium of the upper respiratory
- erosion of the respiratory mucosal lining
- cell to cell spread
- viral presence in respiratory LN (24-48 hours post infection)
- +/- establishment of lymphocyte-associated viremia
- viral transfer from lymphocytes to secondary site endothelial cells
- vasculitis, hemorrhage, thrombosis, and schema tissue necrosis
______ is a prerequisite to EHM or abortion caused by EHV-1. Abortion most commonly occurs I the ____ trimester.
viremia, third
True or false: EHV-4 is confined to the respiratory tract.
true
Where does EHV latency occur in the horse?
In the lymphoreticular system and in the trigeminal ganglion.
True or false: high levels of virus neutralizing antibody can prevent EHM and abortion.
false - it can reduce the amount and duration of viral nasopharyngeal shedding however
What is the most important component of EHV protective immunity?
Intracellular virus is susceptible to CMI responses, specifically cytotoxic T lymphocytes (CTLs) [CD8+] which can lyse virus laden cells.
Describe the 5 ways EHV evades the immune system.
cytokine modulation, modification of CTL responses, down regulation of MHC class I expression, alteration of NK cell lysis, and loss of efficient chemoattraction
Describe the clinical signs of respiratory form EHV.
fever (often biphasic, 24-48 hour post infection, 4-8 day second wave viremia), lethargy, anorexia, nasal discharge
What happens to neonatal foals infected in utero that survive to birth?
They are born or become weak, lethargic, and in profound respiratory distress.
______ is likely the etiologic agent for Equine Multinodular Pulmonary Fibrosis (EMPF).
EHV-5
How frequently should you vaccinate against EHV?
Every 6 months
True or false: Equine Arteritis Virus infections are usually subclinical with only occasional outbreaks resulting in respiratory disease in adult horses, abortion, and fatal pneumonia in foals.
true
How can you inactivate EAV?
By using lipid solvents and disinfectants, however it is:
Infectious for 75 days at 4 degrees C.
Infectious for years in tissue samples stored at -20 degrees C.
Infectious for decades in semen, embryos, and tissues stored at -70 degrees
How is EAV transmitted?
Through respiratory and venereal routes.
Where does EAV reside in the male anatomy?
In the ampulla. It is testosterone dependent and castration will resolve the infection. Spontaneous reinfection can occur in some stallions.
True or false: EAV immune response is robust and leads to years long protective immunity.
true
Describe the pathogenesis of EAV infection.
- Respiratory transmission
- respiratory epithelium viral invasion
- infects bronchial / alveolar macrophages
- reaching the bronchial / regional LNs (within 48 hours)
- viremia
- additional replication in adrenals, liver, thyroid, and testes
- virus infects endothelial cells resulting in vasculitis (fibrinoid necrosis of small muscular arteries)
- virus is cleared and the presence of neutralizing antibody occurs by 28 days post infection (EXCEPT IN STALLIONS THAT BECOME CARRIERS).
What are the general clinical signs of EAV?
General CS: fever, anorexia, lethargy, serous nasal / ocular discharge, mandibular LN enlargement, and cough.
What are the ocular clinical signs of EAV?
Ocular CS: Conjunctivitis (“pinkeye”), periorbital edema, and photophobia.
What are the vascular clinical signs of EAV?
Vasculitis CS: dependent edema, urticaria, petechiae (nasal, conj, oral mm).
What are the reproductive clinical signs of EAV?
Abortion, neonatal foals show severe respiratory signs and a high mortality. Few survive more than 24 hours.
How can you prevent the transmission of EAV most effectively?
Vaccinate all colts with breeding potential in the first year of life and annual revaccination thereafter.
What are the two general serotypes of Equine Rhinitis Virus?
Equine rhinitis A virus (ERAV) and Equine rhinitis B virus (ERBV)
When are most horses infected by ERAV?
At two years of age - when most young horses commingle with large groups.
What clinical signs may be associated with ERAV?
fever, anorexia, nasal discharge, pharyngitis, lymphadenitis, laryngitis, mild bronchitis
Which form of Equine Adenovirus is associated with respiratory disease, conjunctivitis, and Arabian SCIDs?
EAdV1
How is Equine Adenovirus believed to be spread?
Via direct and indirect contact with respiratory secretions.
Describe the clinical presentation of Equine Adenovirus in a normal foal and a SCID foal.
Signs within 3-5 days - fever, nasal and ocular discharge, tachypnea, and cough, diarrhea, initial lymphopenia transitioned to lymphocytosis - recovery is 10 days post inoculation
