Lecture 33 4/14/25 Flashcards
What are the possible clinical syndromes of Salmonellosis?
-asymptomatic carriers +/- active shedding
-mild clinical disease
-acute colitis
-chronic diarrhea
-proximal enteritis
-small colon impaction
What are the key points regarding Salmonellosis clinical presentation?
-highly variable clinical presentation
-can be subclinical, acute and possibly fatal, or chronic
-signs often shared by other causes of diarrhea
What are the mechanisms via which Salmonella causes dz?
-invasive organism that denudes mucosa and invades submucosal vessels in cecum and colon
-enterotoxin that promotes secretion
-endotoxin that damages gut wall
What are the diagnostic options for Salmonellosis?
*culture
-typically at least 5 fecal cultures
-can culture rectal mucosal biopsy
*PCR
-want at least 3 samples
*necropsy and culture
What are the characteristics of Salmonellosis treatment/management?
-virulence varies by serotype
-want to isolate affected horses for 30 to 60 days
-zoonotic potential
-treatment includes supportive care and potentially antibiotics
What are the risk factors for Salmonellosis?
-nasogastric intubation
-antibiotic use; esp. increased if given orally
-admitted for colic
What are the criteria for isolation?
one or multiple of the following:
-diarrhea
-fever
-neutropenia
What are the characteristics of Neorickettsia risticii?
-causes potomac horse fever
-obligate intracellular parasite
-multiple strains
-affinity for monocytes and macrophages, colonic epithelium, and mast cells
What is the typical seasonality of potomac horse fever?
most cases occur between May and November
How do horses develop potomac horse fever?
-ingestion of infested water, snails/insects or bird/bat feces
-parasite is absorbed in intestine
-parasite replicates in and is transported by monocytes
-infected monocytes infiltrate lamina propria in GI tract
What are the clinical signs of potomac horse fever?
-diarrhea
-biphasic fever
-anorexia
-lethargy
-laminitis
-abortion
How is potomac horse fever diagnosed?
*identification in monocytes
*serology
-paired samples
-IFA or ELISA
*PCR
-blood or feces
What is the treatment and prognosis for potomac horse fever?
-oxytetracycline and supportive care
-decent prognosis (60-76% recover); better prognosis with early treatment
How is potomac horse fever prevented?
-vaccination available but not super effective
-minimize insects in feeding and watering areas
Which Clostridium species can cause diarrhea in horses?
-C. perfringens**
-C. difficile**
-C. sordelli
What are the possible co-infections that occur with Clostridium?
-mixed clostridial infections
-Salmonella
-N. risticii
-rotavirus
-coronavirus
What are the characteristics of Clostridium prevalence?
-variable, but increasingly recognized
-can occur as a farm outbreak
-wide range of morbidity and mortality
What are the characteristics of Clostridium bacteria?
-anaerobic
-spore-forming
-rods
-some inhabit soil
-some are commensal intestinal organisms
What are the characteristics of C. perfringens?
-5 types (A through E) with subtypes
-classified based on pattern of toxin production
-cause necrotizing enterocolitis
What are the characteristics of C. perfringens enterotoxin?
-found in less than 15% of bacterial isolates
-most commonly associated with C. perfringens type A
-binds to surface receptors on intestinal epithelial cells
-leads to loss of intracellular fluid and cell death
Which other toxins are produced by C. perfringens besides enterotoxin?
-alpha
-beta (poor prognosis)
-beta-2
-NetF
-iota
-epsilon
-theta
What are the characteristics of C. difficile?
-causes pseudomembranous colitis
-about 25% of strains are non-toxigenic and do not cause dz
-toxin strains work synergistically to cause dz
What are the toxigenic strains of C. difficile?
-toxin A: enterotoxin
-toxin B: cytotoxin
-binary toxin (CDT)
What are the effects of the C. difficile toxins working synergistically?
-disruption of actin cytoskeleton
-cytotoxic to mucosal epithelium/increased permeability
-exacerbates inflammatory response
