Equine Respiratory Diseases Flashcards
what are some viruses associated with equine upper respiratory tract disease?
herpesvirus
influenza virus
rhinoviruses
equine arteritis virus
what viruses are most clinically significant of those that cause equine upper respiratory tract disease?
equine herpes types 1 and 4 (EHV-1, EHV-4)
equine influenza virus
who does respiratory infection by equine herpes virus types 1 and 4 primarily affect?
young horses: less than 2 years old
what do equine herpes virus types 1 and 4 cause?
typically mild, transient, or subclinical
spreads rapidly in susceptible populations
what do more severe forms of equine herpes virus type 1 and 4 cause?
EHV-4: respiratory infections
EHV-1: severe sequelae (abortion, neonatal death, myeloencephalopathy)
what percent of horses have latent herpes viruses?
up to 60% of infected horses
how can you confirm infection by herpes viruses?
virus isolation
polymerase chain reaction
immunofluorescent detection of viral antigen
serology
what does herpes virus infection in equine/rhinopneumonitis do?
cytolytic destruction and cell loss
vigorous inflammatory response with infiltration of mononuclear cells follows
viremic viral spread
infection of vascular endothelial cells may occur
how do horses with equine herpes virus infection/rhinopneumonitis present?
rhinitis
pyrexia
submandibular lympathadenopathy
conjunctivitis
what are the complications of equine herpes virus infection/rhinopneumonitis?
late term abortion
EHV-1: mortality in infected foals almost 100%
EHV-1: myeloencephalopathy potentially (vasculitis within small vessels of central nervous system): poor prognosis
what is the goal of vaccination for equine herpes viruses?
herd preventative
lessen respiratory disease severity and reduce spread
prevent late term abortions and provide suckling foals with passive antibody during first months of life
what causes equine influenza?
type A influenza virus: surface hemagglutinin antigens (HA) and neuraminidase (NA) as either H7N7 or H3N3
what does aerosol infection of equine influenza involve?
ciliated respiratory epithelium: upper respiratory infection
who do type A influenza viruses infect?
birds
swine
horses
humans
other mammals
what viruses serve as the reservoir for all type A influenza virus subtypes?
avian viruses in aquatic birds
how do influenza viruses infect?
aerosol route
infects ciliated epithelial cells: deciliation and loss of mucociliary protection
what is the incubation period of influenza viruses?
1-2 days
what bacteria commonly causes pneumonia in adult equines?
Streptococcus equi subspecies zooepidemicus
beta-hemolytic strep that is a normal part of equine pharyngeal flora
what are some other bacteria that may be involved in adult equine pneumonia (not Streptococcus equi subspecies zooepidemicus)?
Pasteurella spp
Escherichia coli
Klebsiella spp
Enterobacter spp
Pseudomonas spp
how do Streptococcus zooepidemicus organisms reach the lower respiratory tract?
inhalation
aspiration
hematogenous spread
when normal defense mechanisms are compromised
are mycoplasma known to be primary pathogens in equine respiratory disease?
no
what is pleuropneumonia associated with in equines?
stressful event: viral disease or extended transportation (elevated environmental temperature and increased aerosolized bacteria)
what organisms are often included in equine pleuropneumonia?
Streptococcus zooepidemicus
Pasteurella spp
Actinobacillus spp
E. coli
Klebsiella pneumoniae
mixed: anaerobic Bacteroides spp and Clostridium spp
is pleural effusion often associated with equine pneumonia?
yes: increased permeability of capillaries in visceral pleura
what do horses with equine pleuropneumonia present with?
fever
anorexia
weight loss
depression
cough
respiratory distress
possibly limb edema
what is the pathogenesis of equine pleuropneumonia?
pleural effusion, starts sterile, then bacterial invasion
fibrin deposits
how can progression of sterile pleural effusion to a septic pleuritis be prevented?
diligent assessment of pleural effusion via ultrasound and percussion
antimicrobial therapy to prevent bacterial colonization
at what age is foal pneumonia common?
1-6 months
what are the most common bacterial agents in foal pneumonia, and the less common ones?
most common: Streptococcus zooepidemicus and Rhodococcus equi
Actinobacillus spp, Bordatella bronchiseptica, Escherichia coli, Klebsiella pneumoniae, Pasteurella spp, Pseudomonas spp
anaerobic agents are uncommonly involved
what is Rhodococcus equi?
gram positive pleomorphic coccobacillus that is facultative intracellular pathogen of equine macrophages
how does Rhodococcus equi survive?
inhibits phagosome-lysosome fusion of alveolar macrophages: survives and replicates inside
what signs do foals develop with Rhodococcus equi?
fever
elevated respiratory rate
hyperfibrinogenemia
cough
other body systems may be infected: abscesses, enteritis, septic arthritis, polysynovitis
what is Strangles?
acute contagious disease of horses characterized by inflammation of the upper respiratory tract with abscessation of submandibular lymph nodes
how does Streptococcus equi work?
enters via mouth or nose and attaches to tonsillar epithelial cells, to subepithelial follicles and then to mandibular and pharyngeal lymph nodes
can spread further
how does Streptococcus equi evade killing?
antiphagocytic surface factors prevent neutrophil phagocytosis and killing
what is purpura hemorrhagica?
immune mediated necrotizing vasculitis resulting in subcutaneous edema after streptococcal infection (rare but very serious)
what does disease of the paranasal sinuses in horses occur from?
extension of rhinitis into the sinuses, by extension of tooth abscesses, and due to neoplasia
what is equine progressive ethmoid hematoma?
benign slowly enlarging encapsulated hemorrhagic mass in mucosa of equine ethmoid turbinates
what are guttural pouches in horses?
diverticulum of the auditory canal that communicates with the pharynx via a slit-like opening
what causes equine parasitic airway disease?
Dictyocaulus arnfieldi
who does Dictyocaulus arnfieldi infect?
horses
donkeys
mules
zebras
who is airway inflammation common in?
young equine athletes
what is recurrent airway obstruction caused by?
prolonged and debilitating inflammatory response to inhaled organic dusts
what are the clinical signs of recurrent airway infection?
elevated respiratory rate and accentuated expiration
what viruses may cause pneumonia in foals?
adenoviruses
what percent of adult horses have been exposed to equine herpes virus 1 or 4?
90%
fetuses infected with EHV-1 during late gestation _____________________________________
may be born alive, but mortality of congenitally infected foals is nearly 100%
what are some sequelae of equine influenza?
chronic pharyngitis
sinusitis
chronic bronchiolotis
airway hyperreactivity
what is pleuropneumonia associated with?
stressful event
viral disease
extended transportation
what do the organisms involved in equine pleuropneumonia suggest?
that aspiration of pharyngeal secretions likely occurs
what happens with fibroblasts in pleuropneumonia?
invade during organization phase and produce restrictive membrane
what is thought to predispose foals to pneumonia?
not respiratory viruses
overcrowding
parasitism
poor nutrition
heat stress
congenital immunodeficiency
what does Rhodococcus equi cause in foals?
chronic pyogranulomatous pneumonia
what conditions favor multiplication of Rhodococcus equi?
dry, dusty
what does survival and replication of Rhodococcus equi in macrophages result in?
abscess formation
what does Actinobacillus equuli do?
septicemia and septic arthritis in foals
what does localized inflammation from Streptococcus equi cause?
pharyngitis
difficulty swallowing
anorexia
depression
what can inspisated pus from strangles cause?
chondroids in guttural pouches with bacteria
what can result in serious disease with strangles?
metastatic absessation in abdominal or thoracic lymph nodes
what does immune-mediated necrotizing vasculitis occasionally follow?
streptococcal infections
immune complexes involving IgA and IgM and streptococcal antigens implicated
why does disease of the paranasal sinuses in horses occur?
extension of rhinitis into sinuses
extension of tooth abscesses
neoplasia
what is guttural pouch mycosis?
mycotic plaques on pouch wall
what is the most important respiratory tract evaluation in uncomplicated inflammatory airway disease?
transtracheal aspirate or bronchoalveolar lavage
what suggests an allergic response to mold species in the stable environment in recurrent airway obstruction?
elevated levels of IgE in bronchoalveolar lavage fluid
