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Flashcards in Equine - Gastrointestinal Dz Deck (6)
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Describe the aetiologic agent of Potomac Horse Fever (PHF).

- Neorickestia risticii.
- Obligate intracellular gram negative bacteria.


Describe the proposed pathophysiology of PHF.

- Intracellular parasite; infects peripheral monocytes and macrophages, SI epithelial cells and large colon mast cells.
- Incompletely understood; horses appear to develop CSx and complications similar to Salmonellosis.
- Experimental infection --> fever in 2-4d and GI signs in 10-14d.
- CSx of sepsis incl fever, leukopaenia, MM congestion, hypercoagulability.
- Magnitude of intestinal inflammation less than Salmonella, but hypoproteinaemia can be severe through GI loss.


Described the epidemiology of PHF.

- Association between affected horse and proximity within 5 miles of a river is strong.
- Trematode stages have been found in aquatic snails (Pleurocerdia, Juga spp, Acanthatrium spp, Lecithodendrium spp) and aquatic insects (cadis flies).
- Suggested route of transmission is ingestion of aquatic insects or trematode stages release by snails into water.


List clinical signs of PHF.

- Anorexia, lethargy, fever, depression, inappetence.
- GI signs from mild colic and soft faeces to severe dxa.
- Congested MMs.
- Laminitis in up to 30% horses w PHF (w or w/out dxa).


Outline diagnosis of PHF.

- Serum IFA or ELISA: 4 fold inc b/w acute and convalescent samples confirms infection, but negative does not rule it out b/c CSx can be delayed up to 14d post-infection.
- qPCR of N. risticcii in leukocytes (whole blood) appears to be sensitive and specific in horses w supportive CSx.


Describe treatment and prevention of PHF.

- Oxytet IV for 4d, can use doxy but absorption may be poor with GI dz; some horses replase 2-3 wks after initial resolution but ABs should eliminate infection.
- +/- plasma.
- Endemic areas vacc horses early Spring and early to mid-Summer --> dec severity of dz.