Gastrointestinal disease

What are the infectious causes of equine gastrointestinal disease

• Salmonella spp.

• Clostridium perfrongens and clostridium difficile

• Equine coronavirus

• Rotavirus

• Potomac horse fever

What is the admission policy

Not to admit any horse with a high suspicion of having infectious colitis in a hospital without an appropriate isolation facility

What 2 of the 3 signs would a horse have to not be admitted

• Acute diarrhoea

• Fever

• Low white blood cell count

What should be done when entering an equine isolation facility

1. Green zone - get changed into scrubs, remove shoes, put disposable covers on feet, put on rectal sleeves then blue gloves

2. Amber zone - place treatments, handle green rubber suit only by inside and put on

3. Red zone - put on rubber boots over the line and grab treatments and enter stable

How many serovars of salmonella is there

Over 2000

Is salmonella host specific

• Host specific and non-host specific

• Host specific cause more systemic disease

What are the key features of salmonella as a pathogen

• Gram negative motile bacillus

• Modified flagellae and pili used for plasmid exchange

• Facultative anaerobe

• Facultatively intracellular

• Shows a wide range on antibiotic resistance

How does Salmonella interact with hosts and the environment

• Motility and modified structures aid the survival and gene exchange

• Ability to live both anaerobically and inside host cells supports persistence

• Antibiotic resistance enhances survival in diverse environments

How many adhesion molecules does Salmonella have

3 different types

What do invasion genes of salmonella do

Encode proteins that cause ruffles in enterocyte membrane and salmonellae become interiorized

What do salmonella virulence plasmids do

They allow for intracellular growth, serum resistance and cellular invasion

What exotoxins do salmonella have

• cAMP

• Cytotoxin

• Phospholipase A activity

What are the host risk factors caused by salmonella

• Antibiotic treatment

• General anaesthesia

• Transport

• Competition

• Hospitilisation

• Surgery

• Feed withdrawal

• Anthelmintic treatment

• Stress

What is required for a host response to Salmonella, and what initiates inflammation

• No response occurs without invasion - opportunistic

• Lipopolysaccharide triggers a massive neutrophil dominated inflammatory cascade

• LPS → macrophage → IL-1 and TNF → neutrophil activation

How does Salmonella cause tissue damage

Persistence of the facultative intracellular pathogen in macrophages maintains inflation

How does Salmonella cause diarrhoea

• Inflammation and tissue necrosis cause leakage of protein and fluid causing diarrhoea

• Exotoxins worsen inflammation and necrosis promoting more diarrhoea

Why does Systemic Inflammatory response syndrome cause low arterial blood pressure

• Fluid loss - diarrhoea and oedema

• Wide spread vasodilation - reduced venous return to heart

• Multiorgan failure - including heart

What does diarrhoea cause

• It dilutes salmonella and toxins and removes them from the body

• Leads to severe shock and cardio-circulatory collapse

How does salmonella interact with the environment

• Survive in damp soil up to 9 months

• Contagious spread by direct contact and fomites

• Water and feed contaminated with faecal material

• Recovered animals may shed for weeks or months

• Host stress increases susceptibility

• Most frequent reported outbreaks are amongst hospitalised patients

How can you personally control and prevent salmonella

• Gloves, shoe covers and outer protective clothing put on before entering stable

• Must be removed upon leaving stable and boots dipped

• Wash hands

How can you control and prevent salmonella in the stable

• Horses in isolation mucked out last to avoid spreading faecal contamination

• Soiled bedding and feed bagged and disposed as clincial waste

• After discharge fully empty and dispose as clinical waste

• Rinse equipment with bleach or virkon and dired

• Steam clean or scrub with detergent then spray with bleach and virkon

• Swab for bacterial culture

• Clean again if bacteria present

How should a stable be cleaned after discharge of a patient with salmonella

• Steam clean or scrubbed with detergent

• Walls sprayed with 0.5% bleach for 10 minutes

• Walls and floor sprayed with 1% Virkon for 10 minutes

How long does a horse with salmonella need to stay in isolation

Until 5 consecutive faecal cultures are negative

What are key characteristics of Clostridium perfringens and Clostridium difficile

• Saprophytic and part of normal intestinal flora

• Large gram positive endospore forming bacilli

• Obligate anaerobes and haemolytic in culture

How do Clostridium perfringens and Clostridium difficile differ

• C. perfringens is non motile

• C. difficile is motile

What toxins are produced by Clostridium perfringens type A

• Enterotoxin - cytotoxic

• Alpha toxin - lecithinase

• Beta toxin - present in toxigenic strains

What toxins are produced by Clostridium difficile and what do they do

• Toxin A and Toxin B

• Proinflammatory

• Toxic to macrophages

What host factors influence Clostridium difficile disease

• Normally part of the intestinal flora

• Disease requires host stress of flora disruption

• High mortality rates

How is Clostridium difficile controlled and why is it important

• Good management and hygiene usually provide effective control

• Is a significant cause of diarrhoea in people

What stress factors effect Clostridium difficle

• Intercurrent infections

• Extreme temperature

• Water deprivation

• Overcrowding

• Sudden change in diet

• Transportation

• Antibiotic therapy

• General anaesthesia

How does Clostridium difficile interact with the environement

• Spore forming

• Resistant to heat and cold

• Resistant to many disinfectants

How is Clostridium perfringens diagnosed

• Culture is not reliable

• Identification of enterotoxin or beta toxin by ELISA or toxogenic genes by PCR

How is Clostridium difficile diagnosed

• Culture not reliable

• Identification of toxin A or B by ELISA or toxogenic genes by PCR

How do you prevent and manage C. perfringens

• Avoid stress and crowding

• Avoid rapid changes in diet

• Quarantine affected animals

What are the symptoms of equine coronavirus

• ANorexia

• Fever

• Lethargy

• Colitis

What are key characteristics of rotavirus in young foals

• Genus in the Reoviridae family

• Multiple strains and serotypes with varying virulence

• Strains are mostly host species specific

What roles does the VP4 coat protein play in rotavirus infection

• VP4 is the haemagglutinin determining species susceptiblity

• VP4 is the target antigen for the neutralising antibody response

How does rotavirus infect and damage the intestine

1. Virus is ingested and infects absorptive epithelial cells at villus tips

2. Mainly affects the small intestine

3. Loss of villus cells causes villus atrophy and nutrient absorption

4. Osmotic diarrhoea results

5. Virulent strains cause more necrosis and haemorrhage

What are the key features of the host response and disease course in rotavirus infection

• Host humoral response neutralises the virus

• Incubation period of 18-24 hours

• Disease course of 5-7 days

• Recovered foals shed virus for 2 weeks

How does rotavirus interact with the host

• Recovered animals may shed for weeks

• Host stress increases susceptibility

• Low mortality but can be high morbidity

What host factors increase susceptibility to rotavirus

• Age less than 2 months

• Intercurrent infections

• Extreme temperature

• Poor food and water sanitation

What management and environmental factors increase rotavirus spread

• Overcrowding

• Transpiration

• High infection levels on the property the previous years

• Stressed adult horses may intermittently shed the virus

How is rotavirus transmitted and how long can it survive in the environment

• Spreads via direct contact and fomites

• Water and feed can be contaminated with faeces

• Can survive in the environment for 9 months

How can rotavirus be inactivated and controlled in the environment

• Resistant to bleach

• Inactivated by ethanol, phenols and formalin

• Good management and hygiene usually provide effective control

How is rotavirus diagnosed 

• Clinical signs and identification of virus in faeces

• PCR of rotavirus type A and B

• Electronmicroscopy

• Must rule out concurrent disease

How is rotavirus controlled and prevented

• Ensure clean food and water sources

• Avoid crowding foals together

• Clean foal bedding frequently

• Isolate severly affected foals

• Vaccination equine rotavirus vaccine