Pathology and Microbiology of Respiratory Infections - Horses

Question 1

bacteria

Answer 1

β-haemolytic streptococci
Rhodococcus
Actinobacillus
Mycoplasmas

Question 2

viruses

Answer 2

Equine influenza virus
Equine herpesvirus types 1 and 4
Equine arteritis virus (EVA) - notifiable

Question 3

strep. equi

Answer 3

Gram-positive; obligate parasite of horses
Carried without disease in nasopharynx
Strongly β-haemolytic with mucoid colonies
Hyaluronic acid capsule which become matt (hyaluronidase)
Causes strangles in horses & ponies.
Circulating antibody raised by infection or vaccination - mucosal immunity probably essential for protection

Question 4

strep. equi infection pathology

Answer 4

Suppurative lymphadenitis and guttural pouch empyaema (site of long-term carriage)

Question 5

strep. zooepidemicus

Answer 5

Affects many animal species - primarily the horse & dog
Inhabits skin, N/P, respiratory mucosa
2° invader post viral disease in horses, wound infections

Question 6

strep. pneumoniae

Answer 6

Some evidence this is an occasional cause of respiratory disease in the training horse
a-haemolytic

Question 7

rhodococcus equi

Answer 7

Gram-positive rod, variably acid fast, Actinomycete group
Naturally present in soil & intestine of horses
Persistent in manure for long periods

Question 8

rhodococcus equi - pathology in foals

Answer 8

chronic suppurative bronchopneumonia in foals between 2-6months
complex lipid cell wall - resists host digestion
foci of caseous necrosis in lungs
lesions often extensive before clinical signs become apparent
high mortality rate of 40-80%
bronchial lymph nodes may also contain caseating foci
dissemination to other viscera can occur esp abd organs e.g. liver and intestine
Adult horses are immune

Question 9

actinobacillus sp.

Answer 9

Adult horses - thoroughbreds

Tracheal washes taken during infection

Question 10

mycoplasmas

Answer 10

Recent efforts to find mycoplasma involvement in low-grade resp. disease
M. felis considered relevant in pleuritis and predisposition to 2° infect.
Other mycoplasmas may emerge as primary agents

Question 11

equine influenza virus (EIV)

Answer 11

Infection of URT that may spread to LRT and cause bronchitis and bronchiolitis
Cough, pyrexia, depression
Secondary infections: Strep., Staph., Klebsiella
vaccine needed for racing

Question 12

equine herpesvirus (EHV)

Answer 12

Infection of URT
Nasal discharge, coughing, pyrexia
Inactivated vaccines containing EHV-1 and EHV-4 available

Question 13

equine herpesvirus (EHV) - EHV-1

Answer 13

resp disease

abortion + paresis(weakness)

Question 14

equine herpesvirus (EHV) - EHV-4

Answer 14

mainly resp disease

rarely abortion

Question 15

equine herpesvirus (EHV) - EHV-5

Answer 15

equine multinodular pulmonary fibrosis

Question 16

equine arteritis virus (EAV)

Answer 16

Arteriviridae
Infection of URT, systemic spread + infection of endothelial cells + macrophages (arteritis)
May spread to lung in macrophages + cause interstitial pneumonia
Nasal discharge, conjunctivitis, oedema
Arteritis causes oedema and abortions
Frequently subclinical if less virulent strains

Question 17

Mycoses: equine guttural pouch mycosis

Answer 17

Aetiology - Aspergillus nidulans

Severe bleeding from the nose/dysphagia

Question 18

Mycoses: equine guttural pouch mycosis - diagnosis

Answer 18

Endoscopy
radiology 
serology 
Culture 
Microscopy

Question 19

Mycoses: equine guttural pouch mycosis - treatment

Answer 19

Local delivery of antifungal
Ligation of carotid artery
?systemic azole antifungal