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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Salmonellosis refers to clinical disease resulting from infection with various serovars (aka serotypes) of Salmonella enterica ssp. enterica.

Pathophysiology!!navigator!!

Considered an opportunistic pathogen, S. enterica colonizes the small intestine, cecum, and colon of warm- and cold-blooded vertebrates. Organisms can be shed intermittently in feces and may be carried latently in mesenteric lymph nodes. Transmission occurs by the fecal–oral route. Once in the GI tract, bacteria can invade the mucosa (typically through M cells) and spread to lymphoid tissue. Virulence factors promote host tissue invasion, damage mucosa and epithelial cells, promote the inflammatory response and neutrophil recruitment, stimulate fluid secretion into the GI tract, and can lead to severe cardiovascular impairment and toxemia.

Systems Affected!!navigator!!

Primarily affects the GI tract, causing enterocolitis.

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

  • Equine shedding prevalence varies markedly from an estimated 0.8% among the general population up to 13% among horses with GI illness
  • Outbreaks have been recognized on farms, at boarding and sales facilities, and veterinary hospitals; and are commonly associated with inadequate environmental hygiene

Signalment!!navigator!!

No breed or sex predilection has been reported.

Signs!!navigator!!

  • 4 clinical syndromes are classically reported in horses: (1) asymptomatic disease with intermittent shedding, (2) fever without diarrhea, (3) enterocolitis, and (4) sepsis
  • Salmonella is often carried asymptomatically with intermittent shedding occurring at times of stress
  • Signs are nonspecific and may include fever, diarrhea, colic, and leukopenia. In addition, cardiovascular function may be compromised owing to dehydration and systemic effects of endotoxemia. If infection results in severe intestinal inflammation, horses may have tachycardia, injected mucous membranes, delayed capillary refill time, hypoproteinemia, and peripheral edema
  • Adult horses may have fever and colic signs without diarrhea
  • Neonatal foals may develop septicemia and thus clinical signs may vary according to organ system(s) affected

Causes!!navigator!!

The most common serotypes reported in horses in 2014 by the USDA National Veterinary Services Laboratory were Salmonella Typhimurium, Salmonella Javiana, Salmonella Newport, Salmonella Anatum, and Salmonella Rubislaw/Thompson.

Risk Factors!!navigator!!

  • Factors that may disrupt natural barriers can predispose to development of clinical salmonellosis; including antimicrobial therapy, sudden feed change, systemic illness, surgical intervention, and transportation
  • Any horse with severe disease has an increased risk of shedding Salmonella in its feces

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Other causes of acute diarrhea in adult horses may include Potomac horse fever, intestinal clostridiosis, antibiotic-associated diarrhea, sand enteropathy, NSAID toxicity, cyathostomiasis, arsenic toxicity, cantharidin toxicity, and idiopathic colitis
  • Endotoxemia due to GI disorders and in mares with placental retention
  • Signs of colic may be associated with other disorders
  • Congestive heart failure and vasculitis

CBC/Biochemistry/Urinalysis!!navigator!!

CBC

  • Hemoconcentration
  • Decreased to normal total solids
  • Leukopenia due to neutropenia
  • Leukocytosis in colitis of several days’ duration
  • White blood cells can have a highly reactive appearance
  • ±Hyperfibrinogenemia

Serum Chemistries

  • Azotemia
  • Hypoalbuminemia
  • Hyponatremia, hypochloremia, hypokalemia, hypocalcemia
  • Metabolic acidosis
  • Hyperglycemia

Urine Analysis

Isosthenuria, proteinuria, hematuria, cylindruria, and glucosuria.

Other Laboratory Tests!!navigator!!

  • Fecal culture (3–5 enriched cultures) or PCR testing with subsequent antimicrobial susceptibility testing and serotyping of isolates
  • Abdominocentesis for animals with signs of colic

Imaging!!navigator!!

Transabdominal or transrectal ultrasonography may be used to detect bowel wall thickening or peritoneal fluid accumulation.

Other Diagnostic Procedures!!navigator!!

  • Rectal palpation
  • Exploratory laparotomy may be indicated to rule out other causes of colic; intestinal biopsy for culture of Salmonella may be done to confirm a suspected case. The risk vs. benefit of such a biopsy must be considered on a case-by-case basis

Pathologic Findings!!navigator!!

Lesions at necropsy include diffuse fibrinous or hemorrhagic inflammation of the cecum and colon. Mucosa may be thickened, have areas of necrosis, greyish pseudomembranes, and, in chronic cases, focal mucosal ulcers.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

N/A

Nursing Care!!navigator!!

  • Correction of electrolyte deficits and restoration and maintenance of fluid volume are critical for patients with severe diarrhea
  • If severe hypoproteinemia, colloidal fluids (e.g. plasma, hetastarch), with or without heparin, should be administered
  • Separation of suspect or confirmed cases from other patients and personnel via isolation and/or use of contact precautions is recommended. To minimize bacterial transmission, ensure compliance with all environmental and personal hygiene policies
  • Regular cleaning of soiled areas on the patient to reduce skin damage from fecal material

Activity!!navigator!!

Restricted proportionate to severity of illness.

Diet!!navigator!!

  • Feeding small amounts of palatable feed frequently may improve food consumption. Low-bulk, low-soluble-carbohydrate feeds (e.g. complete pelleted rations, good quality grass hay) are ideal
  • Fresh water should always be available. Some horses will consume electrolyte-containing fluids orally, which can reduce the need for IV electrolytes
  • Patients with prolonged anorexia may benefit from parenteral nutrition

Client Education!!navigator!!

  • In general, infected horses should be maintained separately from other horses including separate housing and cleaning utensils, and contact precautions should be used when managing these horses or their environments
  • Salmonella is a zoonotic pathogen that may cause GI illness in people, and, in particular, in immune-compromised individuals

Surgical Considerations!!navigator!!

If shedding or suspect horses are taken to surgery, optimal biosecurity procedures should be used.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antimicrobial Therapy

  • Antimicrobial treatment of horses with subclinical infections has not been shown to eliminate the carrier state
  • Opinions differ as to whether antimicrobial drugs should be given to adult horses with salmonellosis
  • Foals with salmonellosis, particularly with concurrent septicemia, are routinely treated with antimicrobial drugs
  • Use of an appropriate antimicrobial drug should be based on antimicrobial susceptibility testing or previous experience with Salmonella infections in a given geographic area. Antimicrobials used in salmonellosis include combinations of penicillin and gentamicin; ceftiofur and gentamicin; and fluoroquinolones such as enrofloxacin (contraindicated in foals owing to potential for cartilage damage)

Other Therapies

  • Flunixin meglumine and ketoprofen to ameliorate effects of endotoxemia
  • DMSO and products that contain antibody to LPS or that neutralize circulating LPS (e.g. polymyxin B) have been used with variable results
  • Use of products to absorb bacterial toxins in the digestive tract (e.g. di-tri-octahedral smectite and/or bismuth subsalicylate) and those that may benefit enterocyte recovery (e.g. psyllium) may be indicated

Contraindications!!navigator!!

Use of NSAIDs, aminoglycosides, and polymyxin B in azotemic or dehydrated patients without ensuring rehydration and adequate urine production.

Precautions!!navigator!!

If glomerular filtration is impaired, administering drugs that depend on renal clearance should be done judiciously.

Possible Interactions!!navigator!!

Concurrent use of NSAIDs along with aminoglycosides, particularly in dehydrated or azotemic patients, can potentiate nephrotoxicity of each drug.

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Clinical signs, CBC, and biochemistry abnormalities should resolve with appropriate therapy
  • Fecal culture can be performed to determine cessation of shedding. To overcome low test sensitivity of fecal culture for the detection of Salmonella, 3–5 enriched cultures should be performed at 12–24 h intervals

Prevention/Avoidance!!navigator!!

  • Practicing effective personal and environmental hygiene is critical for protecting patients and personnel
  • Thorough cleaning and disinfection of areas where fecal contamination is likely, of common use equipment such as stomach tubes and buckets, and use of rigorous hand hygiene are key to effective risk mitigation
  • Prompt detection of clinical and subclinical cases with subsequent contact precautions and separation or isolation from other horses and personnel is necessary to decrease the likelihood of transmission and environmental contamination

Possible Complications!!navigator!!

  • Laminitis
  • Thrombophlebitis
  • Colon infarction
  • Disseminated bacterial infection
  • Chronic diarrhea
  • Chronic or recurrent colic
  • Persistent poor body condition
  • Persistent, intermittent fecal shedding of Salmonella spp.

Expected Course and Prognosis!!navigator!!

  • Horses with fever and neutropenia without diarrhea have a good prognosis, often recovering within a few days
  • Horses with profuse diarrhea and toxemia require intensive care and have a poor prognosis for survival. Horses that survive typically show substantial improvement within 7 days

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Laminitis
  • Venous thrombophlebitis
  • Weight loss

Age-Related Factors!!navigator!!

Foals are predisposed to developing extraintestinal sites of infection such as joint and bone infections.

Zoonotic Potential!!navigator!!

S. enterica is a zoonotic pathogen. Immunocompromised individuals (e.g. due to illness, medical therapy, young/old, or pregnancy) should take appropriate precautions.

Pregnancy/Fertility/Breeding!!navigator!!

Abortion may occur with any serovar; however, Salmonella Abortusequi has been associated with abortion. S. Abortusequi has not been recognized in the USA in decades.

Abbreviations!!navigator!!

  • DMSO = dimethylsulfoxide
  • GI = gastrointestinal
  • LPS = lipopolysaccharide
  • NSAID = nonsteroidal anti-inflammatory drug
  • PCR = polymerase chain reaction
  • USDA = United States Department of Agriculture

Suggested Reading ⬆ ⬇

Burgess BA, Morley PS. Managing Salmonella in equine populations. Vet Clin North Am Equine Pract 2014;30:623–640.

Burgess BA, Traub-Dargatz JL. Biosecurity and control of infectious disease outbreaks. In: Sellon DC, Long MT, eds. Equine Infectious Diseases, 2e. St. Louis, MO: Elsevier, 2014:530–543.

Dallap Schaer BL, Aceto H, Rankin SC. Outbreak of salmonellosis caused by Salmonella enterica serovar Newport MDR-AmpC in a large animal veterinary teaching hospital. J Vet Intern Med 2010;24:1138–1146.

Hernandez JA, Long MT, Traub-Dargatz JL, Besser TE. Salmonellosis. In: Sellon DC, Long MT, eds. Equine Infectious Diseases, 2e. St. Louis, MO: Elsevier, 2014:321–333.

Author(s) ⬆

Author: Brandy A. Burgess

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa