9 Endotoxemia and Colitis

• Infectious colitis in adult horses involves endotoxemia and sepsis.
• The lecture will cover infectious colitis causes, clinical signs, diagnosis, endotoxin pathophysiology, specific treatments, and general colitis treatment.

Objectives - Colitis

• Concerns pathogens, diagnosis, time of year, specific treatment, and zoonotic diseases.
• Pathogens causing colitis include Salmonella, PHF, Coronavirus, and Clostridial which is more common in foals.

Objectives - Endotoxin

• Involves defining an endotoxin, its location in the body during disease, clinical signs, pathophysiology, and treatment mechanisms.

Diarrhea Causes

• Diarrhea causes include idiopathic factors, diet changes, stress, changes in flora, Salmonella, Clostridium, Coronavirus and PHF.
• Other causes include antibiotic use, sometimes related to infectious issues, parasites, NSAIDs, and blister beetles.

Salmonella Taxonomy

• Salmonella taxonomy can be confusing.
• Species include S. enterica and S. bongori.
• There are different subspecies of S. enterica; 60% belong to S. enterica subsp. Enterica.

S. Enterica subsp. Enterica

• Contains O-antigens A, B, C1, C2, D, and E.
• O-antigen B is the most common in horses, but others can be seen.
• Further classified on serotype like Salmonella enterica subsp. Enterica serotype Typhimurium and Salmonella Typhimurium.

Salmonella - Nosocomial Problem

• It has affected many Veterinary Medical Teaching Hospitals (VMTH) and private practices in the last 30 years.
• Strict biosecurity protocols are in place, including culture of all horses, isolation protocols for horses at "risk," and culture of environmental samples.

Percentage of Horses Shedding Salmonella

• The percentage of horses shedding Salmonella varies based on the study, geography, caseload/horse density, and if horses are at farm, hospitalized with/without diarrhea or have GI problems.
• Method of detection, PCR vs culture, affects results.

Fecal Shedding Normal Horses

• Less than 1% of normal horses on farms culture positive for Salmonella.
• Hospitalized horses culture positive at a rate of 4-8%.
• Higher rates of shedding are seen in horses in the ICU or with GIT disease, even if they do not have diarrhea.
• Colic and impactions can cause higher rates.
• Many VMTHs use barrier protocols for these cases.

Risk Factors for Salmonellosis

• The serotype involved determines risk.
• S. Typhimurium is considered highly pathogenic.
• The inoculation dose is also important.

Other Risk Factors

• Antibiotics are a risk factor associated with Clostridium difficile.
• Some places have a particular antibiotic they have a problem with.
• Concurrent illnesses, mainly GI illnesses like colics and impactions increases the risk.

Pathophysiology

• The most common route of transmission is fecal-oral.
• Salmonella invades GI epithelial cells
• Salmonella has been found intracellularly in macrophages.
• It can be found in the lymph nodes.
• Foals can develop septicemia and can be blood culture positive.
• Osteomyelitis has been reported.

Salmonella and Mucosal Injury

• Mucosal injury and absorption of toxins leads to endotoxemia.
• Translocation of bacteria causes septicemia but it may involve bacteria other than Salmonella.

LPS Structure

• LPS is a lipopolysaccharide found in gram-negative bacteria.
• LPS includes:
• O-region
• R-core
• Lipid A which is conserved, hydrophobic, and toxic.

Endotoxemia and Toxemia Defined

• Endotoxemia involves the presence of LPS in the bloodstream and its effects.
• Toxemia is the presence of bacterial toxins in the bloodstream and its effects, where Lipid A is a bacterial toxin.
• Systemic Inflammatory Response Syndrome (SIRS) has human and veterinary criteria.
• Sepsis is SIRS associated with infection; the infection doesn't have to be in the blood.
• Septicemia is the presence of an infection in the bloodstream that leads to sepsis.

Endotoxin Mechanism of Action

• LPS Binding Protein and acute phase proteins are produced by the liver, and increase product during inflammation.
• These bind endotoxin.
• The LPS-binding protein and endotoxin complex then is shuttled to mononuclear cells.
• LPS binding protein transfers endotoxin to CD14-MD2 receptor complex on monocytes.
• Soluble CD14 binds endotoxin, other cells like endothelial cells have a role.

TLR-4 Activation

• TLR/interleukin receptor associated protein (TIRAP) dependent recruitment of MyD88 adapter protein takes place.
• MyD88 activates NF-KB and causes a proinflammatory response.
• Gene transcription of inflammatory mediators are promoted.

Inflammatory Mediators

• Tumor Necrosis Factor (TNF).
• Interleukins that include IL-1β, IL-6, and IL-8.
• Prostaglandins & Leukotrienes.

Effects of Inflammatory Mediators

• Endothelial dysfunction.
• Failure to respond to vasoconstrictors.
• Vascular permeability.
• Neutrophil activation & margination.
• Sticky PMNs.
• Margination into tissues like the lung.
• Neutropenia.
• Coagulopathies.
• Shock & Organ Failure.

Endotoxemia Diagnosis

• Diagnosis involves using clinical signs, which can be seen on the horse
• There is no easy test for LPS.
• Additional signs include neutropenia, fever and toxic/injected mucous membranes.

Salmonella Clinical Syndromes

• Fever is a clinical sign.
• Leukopenia/Neutropenia.
• Diarrhea, which is not always present.
• Acute Diarrhea, Toxic mucous membranes and Colic/Diarrhea are clinical syndromes.
• Septicemia/Foals is a clinical syndrome where Salmonella can be cultured from bloodstream.
• Chronic diarrhea is a type of Salmonella Clinical Syndrome, and may intermittently cause illness

Clinical Pathology of Salmonella

• Often seen are diarrhea combined with endotoxemia leading to hemoconcentration.
• Total protein can be low due to GI loss.
• Blood work includes leukopenia, neutropenia, and left shift.
• Chemistry reveals electrolyte losses, decreased Na, Cl, total calcium & ionized, potassium is either low to increased as it is an intracellular ion affected by acid/base, azotemia that is pre-to-renal, and coagulopathies.

Diagnosing Salmonella

• Done with fecal cultures.
• Enrichment techniques is required to culture positive.
• PCR is a method to test but it will require 1 sample.
• The PCR method is more sensitive, but provides no data on serotype or sensitivity.
• Consider doing both culture & PCR.

Treating Salmonella

• Treat adult horses with supportive care.
• Use antibiotics in some cases, usually when they can alter the course of disease.
• Antibiotics should be used with immunocompromised cases such as, fever, neutropenia, and endotoxic.
• Antibiotics in foals can target Salmonella.

Potomac Horse Fever (PHF)

• Also known as Equine Monocytic Ehrlichiosis, Neorickettsia risticii, Ehrlichia risticii (old name), and Shasta River Crud.
• Causes anorexia, fever, diarrhea, laminitis (20-30% of cases), and abortion.
• Clinical signs are very similar to other infectious organisms.
• Diarrhea ranges from mild to severe.
• Can also have signs of endotoxemia.
• PHF is geographic such, found around water.
• Is more prevalent in certain states.
• Occurs in the Summer/Fall.
• The disease is seen with intracellular organisms, mostly monocytes, and macrophages but other intestinal cells might be affected too.
• Experimentally it can be spread via fecal oral transmission.
• Fresh water snails (Juga sp.) and second insects that are hosts include the Mayfly, Stoneflies & Caddis fly.

Blood Work: CBC

• Initially shows neutropenia/left shift.
• Later, leukocytosis is seen.
• In contrast, Salmonella presents with consistent neutropenia.

Chemistry

• Hemoconcentration is seen.
• Loss of electrolytes.
• Coagulation problems.
• The presentation is similar to other diarrhea cases.

Diagnostic Options

• Past diagnostics included serology.
• PCR on feces and blood are recomended.
• Endemic areas use response to treatment diagnostics often.

Treatment of PHF

• Oxytetracycline for 3-5 days causes a response in 24-48 hours.
• Earlier treatment results in better outcomes.
• Use of oxytetracycline can have problems and make Salmonella worse, be administered slowly for chelation of calcium and prevent cardiovascular collapse.
• High doses can cause nephrotoxicity and contracted tendons in foals.

Clostridial Diarrhea

• C. perfringens & difficile reported in adult horses.
• Presentation includes hemorrhagic feces.
• Should be considered if antibiotic use is associated.
• Antibiotic use related is often a C. difficile infection.
• Do not use macrolides in adult horses.
• This is due to mares of foals being treated with R. equi showing reports of ingestion of macrolides from faces of foals, which is fatal.
• The geographical location has a play in which antibiotics are used.
• Development of disease can occur without antibiotic use as well.

Equine Coronavirus

• Coronavirus is seen in disease outbreaks in adult horses worldwide.
• RNA virus with respiratory & GI disease in other species.
• Beta coronavirus that is seen in horses is a enteric disease.
• Originally reported in foals.
• Occurs in many contries and frequently reported in large number of states.
• Seen often at horse shows/large events.
• Causes fever(101-106), anorexia, lethargy, soft feces/diarrhea in 20% of horses, colic and low white cell count.
• Some horses develop neurological signs like- hyperammonemia.
• Outbreaks result in large percentage of horses affected, between 20-57% of horses.
• Most horses have clinical signs for 1-4 days, outbreaks last 3 weeks.
• Mortality is rare except those with hyperammonemia.
• Appears most frequently in winter months & Stress.

Diagnosing Equine Coronavirus

• Diagnosed with PCR on fresh feces.
• Virus being shed in feces has been reported in respiratory tract.
• Can be shed for as long as 21 days.
• Treat with supportive care.
• Isolation & biosecurity is recommended.

General Supportive Treatment

• The following concepts are used for diarrhea in general.

Oral Fluids

• To maintain hydration, assess frequency, volume of diarrhea, heart rate, PCV TP, creatinine concentration, and urine specific gravity.
• Make sure the horse has functioning kidneys before administering oral fluids.
• Give plain water and water with electrolytes.

Intravenous Crystalloids

• Intravenous crystalloids include, LRS for fluid therapy.
• Used to correct dehydration, provide maintenance, and replace continuing losses.
• Asses ongoing vitals and hydration via clinical signs, volume of diarrhea, heart rate, PCV, and TP.

Fluid Plans

• Dehydration is equal to 0.08 multiplied by the weight in kg, for example .08 x 450 kg = 36 L in volume loss.
• Maintenance is provided with 60ml per kg per day example- 60ml/kg/day x 450 kg = 27 L.
• Severe/moderate diarrhea ongoing assesment loss ranges from 20 -30 L/day.
• Total fluid to provided is within a range of 80-90 L.

Fluid Therapy-Electrolytes

• Electolyte abormalities are Hyponatremia, and hypochloremia.
• Hypokalemia is common.
• Acid/base imbalances interfere with cellular K regulation,.
• May need to provide more K 20 mEq/L for hypokalemia management.
• Hypocalcemia needs to be determined if it is total or ionized.
• Balance for acid base and adjust for albumin concentration.

Managing Acid/Base

• Treat Metabolic Acidosis that is common. – Due to Lactic Acid & Loss of HCO3.
• Rehydrate, reassess, and determine if to provide supplement.
• Baking Soda (NaHCO3) 1 gm = 12 mEq.
• Baking soda can supplement orally.

Fluid Therapy - Colloids

• Use when hypoproteinemia/hypoalbuminemia is present.
• TP , 3.0 gm/dl can use colloids.
• Albumin , 1.5 gm/dl can use colloids.
• Plasma and hetastarch can be used.
• Colloid products are generally expensive.

Treatment Protocols for Endotoxin

• Remove source of endotoxin.
• Neutralization/bind endotoxin.
• Inhibit inflammatory mediators.
• Supportive Care.

Neutralize Endotoxin with Polymyxin-B

• Polymyxin-B binds to Lipid A, but it is nephrotoxic.
• Plasma or Endoserum contains antibodies that bind Lipid A.
• Biosponge® will administer oral for binding endotoxins in the gut (and exotoxins for clostridial diseases).

Inhibit Inflammatory Mediators with NSAIDs

• NSAIDs inhibit COX and block prostaglandin production.
• It does not bind endotoxin.
• Banamine®is best as "anti-endotoxic".
• A 0.25 mg/kg tid dose is used
• A 1.1 mg/kg also has anti-endotoxic effects.
• Pentoxifylline acts as a phosphodiesterase inhibitor.
• Pentoxifylline inhibits various cytokines and neutrophils.
• Pentoxifylline has rheological effects on RBC.

Antibiotics and Use Cases

• PHF cases can be treated with oxytetracycline.
• Clostridial is treated with metronidazole.
• A broad spectrum may be used for immunosuppressed horses IV or IM.
• Likely use of broad spectrum will not alter disease in other causes (Salmonella)
• Antibiotics in foals manage diarrhea.

Managing Antibiotics in Foals

• Manage diarrhea in foals less than 2-3 months of age.
• Address concerns of sepsis and bacteremia.
• Salmonella is common in these infections.

Treatment: Nonspecific

• Oral protectants like bismuth subsalicylates and kaolin/pectin.
• There are questions about their efficacy.
• Administer in large Volumes.

Probiotics

• Some probiotics have no demonstrated efficacy and are problematic with the number of live organisms present.
• Other probiotics with yeast has efficacy in horses & humans
• These are known as Saccharomyces boulardii.
• The beneficial probiotics have been shown to have 10 x 109 CFU and have decreased duration of diarrhea in horses.
• Consider Fecal transfaunation.

Managing Laminitis

• Prevention is key.

General Prevention of Colitis

• Isolation protocols are crucial.
• Proper hygiene and disinfectants like Clorox.

Isolation

• All horses with diarrhea should be isolated.
• Diarrhea/Fever/Neutropenia are key signs where 2 of 3 indicate isolation.
• PHF control includes isolation. Salmonella is still a possibility so isolation is needed.

PHF-Prevention

• Reducing exposure is very difficult.
• Killed Vaccines will decreases clinical signs.
• There is still concern about wild vs. vaccine strain.