Diseases of the Upper Respiratory Tract, Pt. 3 Flashcards
What is the guttural pouch?
bilateral outpouching of the Eustachian tube that connects the throat to the middle ear with medial and lateral segments containing sensitive vascular and nervous structures
What are 4 presumed functions of the guttural pouch?
- pressure equalization
- warming of air
- resonating chamber during vocalization
- cooling of blood directed to the brain during exercise
What causes Strangles?
Streptococcus equi subsp. equi
What are 3 factors that affect Streptococcus equi subsp equi infection? What is its incubation and shedding cycle like?
- horse age and immune status
- virulence
- management - number of horses in barn/pasture and their proximity
10-14 days (longer than viruses)
sheds 1-4 days after fever (still isolate!!) and lasts 2-6 weeks after purulent discharge —> carrier for years
What are the 5 steps to the pathogenesis of strangles? What is bastard strangles?
- entry of pathogen (inhaled) and attachment to cells of crypts of lingual and palatine tonsils
- spread to mandibular and suprapharyngeal LN with influx of neutrophils
- failure of neutrophils to kill bacteria due to hyaluronic acid capsule and SeM/Mac proteins
- bacterial streptolysin causes abscess formation by damaging cell membranes and activating plasminogen
- spread to other organs
abscesses in LN, thoracic, and abdominal organs
What are 6 common clinical signs associated with strangles?
- fever
- lethargy, decreased appetite
- lymph node abscess formation and rupture
- purulent nasal discharge
- cough
- respiratory distress
What are the 3 main complications associated with strangles?
- bastard strangles - metastasis
- purpura hemorrhagica and myositis - immune-mediated swelling of the liegs and tissue necrosis
- carriers - GP, sinus, decreased clearance (no clinical signs, acts as a source of infection to a herd)
What is commonly seen in the guttural pouch in strangles?
- irritation
- empyema: accumulation of pus
- chondroids: “pus stones”
What general techniques are used to diagnose strangles?
- hematology and biochemistry
- imaging: endoscope (upper airways, GP) and radiograph/ultrasound (metastasis)
What is the preferred specific technique used to diagnose strangles?
qPCR of nasopharyngeal wash (recover more fluid)
- swab
- aspirate of abscess
- guttural pouch lavage of possible carriers
Why is it uncommon to diagnose strangles with a culture?
- takes about a week
- typically overgrown by other bacteria
(can be done in parallel of other tests)
How is strangles infection prevented?
- quarantine new and returning horses
- screen temperatures and serology
(reportability depends on state)
What should be done during an outbreak of strangles? When are horses able to be released?
- isolate and stop movement of horses
- biosecurity using a traffic light system
- screen for carrier status with qPCR and serology
if they test negative on 3 qPCR tests in 3 weeks
What 2 vaccines are available for strangles? What do they do?
- INTRANASAL - MLV, given last due to possible transient clinical signs, like abscess formation
- INTRAMUSCULAR - killed, given in hindquarters due to possible local reaction
decrease the likelihood of spread and severity of clinical signs
Are horses vaccinated during an outbreak of strangles? Why or why not?
NO
can lead to immune reactions, like purpura hemorrhagica