equine pathogens Flashcards
What pathogen causes strangles?
Streptococcus equi equi
What type of bacteria is Streptococcus equi equi?
Gram-positive cocci
What are the clinical signs of strangles?
- Mucopurulent nasal discharge
- Enlarged submandibular lymph nodes
- Fever
- Anorexia
How can you confirm a diagnosis of strangles?
- Culture and sensitivity
- qPCR
- ELISA to test for Strep M protein-specific antibody (mostly just if you are suspicious of bastard strangles or purpura hemorrhagica)
What are the four clinical presentations of strangles?
- Classic strangles (upper airway infection with submandibular and/or retropharyngeal abscesses)
- Bastard strangles (internal abscesses)
- Purpura hemorrhagica (vasculitis)
- Immune-mediated myositis (cachexia)
What are the two most common pathogens causing pneumonia in horses?
- Rhodococcus equi
- Streptococcus equi zooepidemicus
How would you determine the causative agent of pneumonia in a horse?
Do a transtracheal wash to determine the agent via Gram-stain, culture and sensitivity, and/or PCR
What is the pathogenesis of Rhodococcus equi?
- Inhalation of pathogen
- R. equi infects macrophages
- Replicates inside macrophages (must have this virulence factor called VapA to do this)
- Destroyed macrophages become pyogranulomas in the lung tissue
True or False: Both foals and adult horses can get sick from Rhodococcus equi
False. Adults are essentially immune and only some foals exposed will get sick (we don’t really know why) but most infected foals are < 4 months old
What type of pneumonia does Rhodococcus equi cause?
Pyogranulomatous
What are the four clinical presentations of Rhodococcus equi?
- Chronic pyogranulomatous pneumonia (fever, tachypnea, increased effort)
- Abdominal disease (enterocolitis, typhlitis, pot-bellied appearance)
- Non-septic uveitis
- Bone and joint disease (septic arthritis)
What pathogen causes proliferative enteritis in horses?
Lawsonia intracellularis
What are the clinical signs of proliferative enteritis in horses?
- Mild colic
- Hypoproteinemia
- Pot-bellied appearance
- Depression
- Weight loss
What is the most common lesion of equine proliferative enteritis?
Thickened small intestine
What pathogen causes potomac horse fever?
Neorickettsia risticii
What are the symptoms of potomac horse fever?
- Liquid diarrhea
- Acute enterocolitis
- Fever
- Laminitis (rare)
Describe how horses become infected with potomac horse fever
- Neorickettsia risticii infects flukes
- Flukes multiply inside snails
- Horses drinking fresh water accidentally ingest snails or other infected aquatic insects
Neorickettsia risticii has a preference for which anatomical site in the horse?
The intestinal wall, especially the large colon
What is the best treatment for potomac fever?
Oxytetracycline
What pathogen is most commonly associated with injection site abscesses/myositis?
Clostridium perfringens
Which veterinary products have been associated with causing clostridium myositis when injected IM?
Flunixin meglumine and dexamethasone. This reaction causes a fever, local tissue necrosis, sloughing of skin, and eventually sepsis.
What are the clinical signs of botulism in a horse?
- Weak tongue tone
- Generalized muscle weakness
- Inability to rise
How does Clostridium botulinum cause paralysis?
The neurotoxin produced by clostridium botulinum binds at the neuromuscular junction where it prevents the release of acetylcholine
What are the three ways horses can get infected with botulism?
- Ingestion of preformed toxin in feed (most common)
- Toxicoinfectious botulism (called shaker foals and occurs when spores are ingested and toxin is released in digestive tract)
- Wound botulism (rare - wound becomes contaminated and toxin is released in vivo)
