ID - Equine Infectious Gastrointestinal Diseases Flashcards
Name 5 major causes of infectious equine gastrointestinal disease
Salmonella - acute fibrinonecrotic colitis
Clostridium perfringens & clostridium difficile
Acute necrotic colitis & dysentery (Colitis X)
Rotavirus - acute enterocolitis in foals
Ehrlichia risticii - Potomac Horse Fever (acute colitis)
What is the policy for a horse with suspected infectious colitis?
Policy is not to admit any horse with a high suspicion of having infectious colitis in a hospital without an appropriate isolation facility
What 3 clinical signs is a referring veterinarian looking for when deciding if a case needs full isolation (it needs 2 out of 3 symptoms for iso)?
Acute diarrhoea
Fever (temperature over 38.5 degrees C)
Low white blood cell count (less than 4.0 x10^9 cells/L)
How varied is the salmonella enterica species?
6 subspecies esp salmonella enterica subsp enterica
Over 2000 serovars esp. typhimurium
Others include Newport, Anatum, and Agona
What is the significant difference between host specific and non-host specific salmonella enterica?
Host specific causes more systemic disease
What disease could be described by the following?
- gram -ve motile bacillus
- modified flagellae & pilli used for plasmid exchange
- facultative anaerobe
- facultative intracellular - the most pathogenic strains are best at this
- wide range of antibiotic resistance
Salmonella enterocolitis
Name 4 different ways in which Salmonella interacts with the hosts
Adhesion molecules - 3 different types (species selectivity).
Invasion genes - encode proteins that cause ruffles in enterocyte membrane and Salmonellae become interiorised.
Salmonella Virulence Plasmids - allow for intracellular growth, serum resistance, and cellular invasion.
3 exotoxins that all result in diarrhoea - cAMP, Cytotoxin, Phospholipase A activity
Describe the host response to Salmonella
Without invasion there is no response (opportunistic)
Lipopolysaccharide (endotoxin) triggers massive neutrophil dominated inflammatory cascade
LPS > macrophage > IL-1 & TNF > Neutrophil activation
Persistance of facultative intracellular pathogen in macrophages maintains inflammatory response
Inflammation and tissue necrosis lead to leakage of protein and fluid > diarrhoea
What disease does the following symptoms describe?
Angry purple looking mucous membrane, saliva tacky due to dehydration, purple rings visible?
Salmonella
How can salmonella lead to severe disease or even death?
Diarrhoea dilutes salmonella and toxins and removes them from the body. Diarrhoea and endotoxaemia leads to severe shock and cardio-circulatory collapse. Variable mortality (related to virulence) - if hydration can be maintained diarrhoea and inflammatory response eliminates infection and mucosa heals - otherwise...
How long can salmonella survive in damp soil?
9 months
How is salmonella transmitted?
- Contagious spread by direct contact & fomites
- Water & feed contaminated with faecal material
- Recovered animals may shed for weeks or months
- Host stress increases susceptibility and lowers required spore dose
- most frequently reported outbreaks are amongst hospitalised patients
How can you personally help prevent and control the spread of salmonella?
- Washing hands after working with horse and before eating/drinking (pay particular attention to under the nails and use antibacterial soap)
- Gloves, shoe covers and outer protective clothing (disposable overalls) must be put on before entering the stable and removed upon leaving it. Boots must also be dipped before leaving the isolation area
- Hands should be washed immediately after leaving the stable with antibacterial soap
How can you prevent and control the spread of salmonella at the stable?
- Muck out horses in isolation last
- Bag and dispose of soiled bedding in feed as clinical waste. Don’t compost
- After the horse has been discharged empty stable and dispose of all bedding, waste feed and PPE as clinical waste
- Rinse equipment to remove visible contamination, then clean with bleach (hypochlorite) or Virkon and then dried completely
- Rinse stable with detergent to remove visible contamination, then clean with bleach (0.5%) and leave for 10, then rinse and clean with Virkon S (1%) and leave for 10 then rinse
- stable should be swabbed for bacterial culture then left to dry (if culture negative stable can be used again, if positive clean again)
How long does a horse with salmonella need to stay in isolation?
Once isolation protocol is in place it must remian until either all 5 faecal cultures for salmonella (q12 - 24 hours) are reported back as negative, or the horse goes home (culture not PCR as PCR often too sensitive - would isolate more cases than necessary)
List 7 other control and prevention methods that should be put into action to limit salmonella spread
- ensure safety of food and water sources
- quarantine newly admitted horses for 10 days
- quarantine affected and recently recovered animals
- avoid crowding - sales, transport
- avoid rapid changes in diet
- remove from pasture
- barrier nurse at risk horses
List differentials for acute colitis in horses
Clostridium perfringens & clostridium difficile
Acute necrotic colitis & dysentery (Colitis X)
Rotavirus - acute enterocolitis in foals
Ehrlichia risticii - Potomac horse fever (acute colitis)
Describe clostridium perfringens & clostridium difficile
- saprophytic and part of normal intestinal flora
- large gram positive endospore forming bacilli
- obligate anaerobes and haemolytic in culture
- C. perfringens - non-motile
- C. difficile - motile
What is the most common type of C. perfringens in horses?
Type A
What toxins do C. perfringens and C. difficile use in host interactions?
C. perfringens
- enterotoxin - cytotoxic
- alpha toxin - lecithinase (phospholipase activity)
- Beta 2 toxin - toxigenic strain
C. difficile - toxin A - proinflammatory (IL-1 & TNF)
- toxic to macrophages
If clostridium is part of the normal flora, how does it cause disease?
requires host stress or intestinal floral change
stress factors examples: high/low temp, thirst, overcrowding, sudden diet change, transport, antibiotics, anaesthesia
How does clostridium interact with the environment?
Spore forming (survive indefinitely)
Resistant to heat and cold
Resistant to many disinfectants
How can you diagnose clostridium infection?
Culture is not reliable (part of normal culture and not all isolates are toxogenic)
ID of C. perfringens enterotoxin by ELISA or Beta 2 toxin by ELISA or PCR
ID of C. difficile toxin A by ELISA or PCR
How do you prevent and control clostridium infections?
Avoid crowding and stress Avoid rapid diet change Quarantine infected animals - barrier nurse - dispose of soiled bedding carefully - change outer clothing - wash hands
What genus does the rotavirus belong to, and what other significant diseases belong to it?
Reoviridae, and AHS and Bluetongue
What protein dictates species susceptibility to rotavirus?
Coat protein VP4 is the haemagglutinin that dictates species susceptibility.
VP4 protein - target antigen of neutralising antibody response
Describe the pathogenesis of rotavirus
- Virus ingested and infects the absorptive epithelium of the apices of the villi
- mostly the small intestine is involved (and occasionally colon)
- Damage and loss of cells in villi leads to villous atrophy, resulting poor nutrient absorption and osmotic diarrhoea
- Virulent strains cause more necrosis and haemorrhage
- Humoral response by the host neutralises virus
What is the incubation period of rotavirus?
18-24 hours
How long is the course of the disease?
5-7 days (self limiting)
How long do recovered foals shed for?
2 weeks
What is the most common infectious diarrhoea of horses?
rotavirus
Rotavirus…
- Host stress increases susceptibility
- Low mortality but can be high morbidity
- Age less than 2 months i.e. naive immune status
- Stressed adult horses can intermittently shed
How is rotavirus spread?
- Contagious spread by direct contact and fomites
- Water and feed contaminated by faecal material
- Survive in environment for up to 9 months
- Resistant to bleach disinfectant (ethanols, phenols, and formalin can inactivate the virus)
How can you diagnose rotavirus?
- Clinical signs and identification of virus in faeces
- Electron microscopy (Gold Standard)
- latex agglutination or ELISA field tests
- Must rule out concurrent disease
How can you prevent and control rotavirus?
- Ensure clean food and water sources
- Avoid crowding foals together
- Clean foal bedding frequently
- Isolate severely affected foals
- barrier nurse, wash hands, change outer garments
- Vaccination Equine Rotavirus vaccine (Zoetis)
- Mare in 8th, 9th, and 10th months of each pregnancy
- relies on good passive transfer and protects for approximately 60 days
- Mare in 8th, 9th, and 10th months of each pregnancy
What should be done in the case of acute necrotic colitis & dysentery (Colitis X)?
Not contagious but isolation required until contagious causes can be ruled out
What disease is caused by Ehrlichia risticii?
Potomac Horse Fever
What disease is described by the following?
- USA and rarely reported in europe
- spread by ingestion of snails and other aquatic invertebrates (not contagious)
- diagnosis can be confirmed by paired serum samples demonstrating a rise in titre (4-fold) or PCR test is available
Ehrlichia risticii AKA Potomac Horse Fever
