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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Internal abdominal abscesses are commonly associated with weight loss, chronic or recurrent colic signs, or fever, or any combination of these signs.

Pathophysiology!!navigator!!

  • Internal abdominal abscesses are classified as primary or secondary depending on anatomic origin. Primary abscesses originate from systemic infection and secondary abscesses may occur due to abdominal trauma, ulceration, perforation, or surgery
  • The pathogenesis of mesenteric abscesses has not been elucidated; however, it has been proposed that the development of the internal infection is associated with the inability of the animal to develop adequate immune response to the microorganisms involved, thereby allowing systemic spread of infection
  • Given that abdominal abscesses are often caused by Streptococcus equi ssp. equi, it has been suggested that treatment with penicillin prior to abscess maturation and drainage may favor the hematogenous spread of the bacteria
  • Once the internal abdominal abscess has developed, it can remain dormant or flare up and peritonitis may develop. This seems to be responsible for the different clinical presentations. Colic events may be due to tension on the mesentery or from acute or chronic obstruction secondary to intestinal adhesions

Systems Affected!!navigator!!

Gastrointestinal

Incidence/Prevalence!!navigator!!

There is no information regarding incidence or prevalence.

Signalment!!navigator!!

All horses are at risk.

Signs!!navigator!!

  • Usually, horses with internal abdominal abscesses present with 1 of 2 chief complaints—a history of intermittent or prolonged colic. However, there are cases with a history of acute colic. These animals show depression, congested mucous membranes, increased rectal temperature (>38.6°C), increased and shallow respiratory rate, groaning on expiration, partial or complete anorexia, constipation, decreased peristaltic sounds, and dehydration. Dysuria can be noticed in some cases
  • In the second form, the chief complaint is chronic ongoing weight loss. The body condition in these animals ranges from the cachectic horse to the thin horse that is unable to gain weight. Some animals are depressed, inconsistently anorexic, and have poor shaggy haircoats. The rectal temperature and heart and respiratory rates may be elevated. Abdominal peristaltic sounds are usually normal. Combinations of the 2 forms can occur
  • In some cases there is evidence of diarrhea, and this seems to be more commonly associated with abscesses caused by Rhodococcus equi infection in foals and in growing horses

Causes!!navigator!!

  • The infectious agents implicated are variable but most commonly involved are S. equi ssp. equi, S. equi ssp. zooepidemicus, Corynebacterium pseudotuberculosis, Salmonella spp., Escherichia coli
  • Rarely Serratia marcescens and R. equi in foals, and obligate anaerobes (Bacteroides spp., Clostridium novyi type A, and Fusobacterium necrophorum)
  • There has been a report of internal abdominal abscess in association with Parascaris equorum in a foal

Risk Factors!!navigator!!

  • Heavy parasitism, or a previous history of respiratory disease or lymphadenitis are believed to predispose to internal abdominal abscessation
  • More common on farms where infections with S. equi ssp. equi and R. equi are present
  • Abdominocentesis should be considered a risk factor when enterocentesis has occurred

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Other causes of chronic weight loss, such as pleuropneumonia, neoplasia, chronic hepatic disease, chronic intestinal malabsorption, chronic renal failure, severe parasitism, and dental problems
  • Other causes of colic and peritonitis

CBC/Biochemistry/Urinalysis!!navigator!!

  • The CBC may indicate anemia of chronic inflammation
  • The WBC count is variable and >40% of the affected horses may present a neutrophilic leukocytosis and a left shift
  • Plasma fibrinogen concentration is frequently increased, with values >1000 mg/dL (10 g/L) in some cases
  • Hyperproteinemia due to increased globulin fractions and hypoalbuminemia are common. The albumin to globulin ratio may be decreased, ranging from 0.17 to 0.63 (normal 0.65–1.46)

Other Laboratory Tests!!navigator!!

Peritoneal fluid is usually determined to be an exudate based on specific gravity (>1.017), protein level (>2.5 g/dL (>25 g/L)), and WBC count (>10 000 cells/μL (>109 cells/L)). The protein levels, WBC count, and fibrinogen can be as high as 8.5 g/dL (85 g/L), 400 000 cells/μL (365 × 109 cells/L), and 500 mg/dL (5 g/L), respectively. Intracellular bacteria (both cocci and bacilli) can be observed, but only on rare occasions are free bacteria observed.

Imaging!!navigator!!

Transrectal or percutaneous US can be useful in diagnosing these abscesses, especially when they can be located during rectal examination. Nuclear scintigraphy using technetium-99 m or indium-111-labeled WBCs can be potentially used to diagnose abscesses that are difficult to localize.

Other Diagnostic Procedures!!navigator!!

  • Rectal palpation may be limited by the fact that some animals often show severe abdominal straining and rectal expulsive efforts during the colic episodes. In both clinical presentations, detailed rectal examination may allow the detection of an abdominal mass
  • A Gram stain and anaerobic and aerobic bacterial culture of the peritoneal fluid should be carried out
  • Abdominal laparoscopy/laparotomy may allow visualization of masses. Fine needle aspiration of the abscess could be done percutaneously with US guidance or by laparoscopy

Pathologic Findings!!navigator!!

Abdominal abscessation can involve the mesentery or intraabdominal organs, such as lymph nodes, intestines, spleen, liver, and kidneys. Rare cases involve umbilical remnants. When localized in the mesentery, adhesions to various organs might be present.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

Most cases can be managed in a farm setting. However, hospitalization may be warranted in some cases.

Activity!!navigator!!

Stall or pasture rest until the problem has resolved.

Diet!!navigator!!

Normal diet when colic has been resolved.

Client Education!!navigator!!

Long-term antibiotic therapy may be required once discharged from hospital. Compliance can be a problem, particularly with parenteral therapy, as many horses rapidly become intolerant to IM injections.

Surgical Considerations!!navigator!!

  • The severity of the colic signs may warrant intensive care management and even surgical management in some cases
  • Surgical treatment can be attempted in cases with a grave prognosis, but it is complicated by the need to drain the abscess without contaminating the abdominal cavity
  • Abdominal lavage is indicated in cases where rupture of the abscess occurs. This procedure is not without constraints and difficulties. There have been reports of successful outcomes following marsupialization of the abscesses when they are located close to the abdominal wall

Medications ⬆ ⬇

MEDICATIONS

Drug(s) of Choice

  • Medical treatment of abdominal internal abscesses is usually preferred. For the most part it is empirical, as the causative organism(s) is not usually positively identified. Farm history and clinical findings are the basis for antibiotic selection. Antimicrobials are usually administered for a minimum of 30 days and may extend up to 90 days in some cases, depending on the response to therapy
  • Sodium or potassium penicillin have been used in a dose range of 20 000–40 000 IU/kg IV every 6 h. Procaine penicillin at 20 000–50 000 IU/kg every 12 h has been also recommended
  • In the author's experience, the combination of rifampin (rifampicin) 10 mg/kg BID PO and trimethoprim–sulfamethoxazole 30 mg/kg BID PO has been successful
  • Rifampin may alternatively be combined with erythromycin estolate 15 mg/kg BID to TID, or clarithromycin 7.5 mg/kg BID in foals
  • Metronidazole 20–25 mg/kg TID could be added in the case of a suspected or isolated anaerobic pathogen

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

In order to follow up the patient, repeated rectal examinations, CBC, abdominocentesis, and US examinations are necessary.

Prevention/Avoidance!!navigator!!

On problem farms, careful monitoring of all horses may lead to early detection of the problem. If S. equi ssp. equi is the etiologic agent, then consideration should be given for a vaccination program.

Possible Complications!!navigator!!

  • Peritonitis
  • Purpura haemorrhagica
  • Intestinal adhesions

Expected Course and Prognosis!!navigator!!

The prognosis is usually good to guarded when there is a favorable response within 2 weeks of treatment. The prognosis becomes grave if there is either intestinal involvement and obstruction or internal rupture of the abscess and evidence of intestinal adhesions. In a review of 61 cases only 24.6% survivability was reported.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Abbreviations!!navigator!!

  • US = ultrasonography, ultrasound
  • WBC = white blood cell

Suggested Reading ⬆ ⬇

Arnold CE, Chaffin MK. Abdominal abscesses in adult horses: 61 cases (1993–2008). J Am Vet Med Assoc 2012;241:1659–1665.

Berlin D, Kelmer G, Steinman A, Sutton GA. Successful medical management of intra-abdominal abscesses in 4 adult horses. Can Vet J 2013;154:157–161.

Mair TS, Sherlock CE. Surgical drainage and postoperative lavage of large abdominal abscesses in six mature horses. Equine Vet J 2011;43(Suppl. 39):123–127.

Mogg TD, Rutherford DJ. Intra-abdominal abscess and peritonitis in an Appaloosa gelding. Vet Clin North Am Equine Pract 2006;22:e17–e25.

Pusterla N, Whitcomb MB, Wilson WD. Internal abdominal abscesses caused by Streptococcus equi subspecies equi in 10 horses in California between 1989 and 2004. Vet Rec 2007;160:589–592.

Author(s) ⬆

Author: Olimpo Oliver-Espinosa

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa