History
A 24-hour-old filly was evaluated at the Kansas State University Veterinary Health Center because of diarrhea and inability to stand of approximately 6 hours’ duration. History included complete failure of passive transfer, which was treated with a plasma transfusion approximately 12 hours prior to evaluation.
Clinical and Gross Findings
Immediate physical examination abnormalities included fever (rectal temperature, 39.2°C [102.5°F]), tachycardia, slightly prolonged capillary refill time (2 seconds), hyperemic mucous membranes, and diarrhea. Clinicopathologic abnormalities included profound panleukopenia and hypoglycemia, high serum creatinine concentration, hypoproteinemia, slight hypoalbuminemia, and high serum sorbitol dehydrogenase activity; metabolic acidosis was detected by venous blood gas analysis. Fecal and blood samples were collected for aerobic and anaerobic microbial culture. After a few hours of hospitalization, owing to poor prognosis, the foal was euthanized by IV administration of an overdose of pentobarbital solution.
On necropsy, remarkable gross lesions included thick yellow gelatinous and edematous capsules of both kidneys. Multifocally, the renal cortices had pinpoint to 1-mm-diameter white foci that resembled microabscesses (Figure 1). Diffusely, the small intestine and large colon mucosae were mildly edematous. The small colon contained yellow liquid feces.
Photograph of the cut surface of the right kidney from a 24-hour-old filly that was evaluated because of diarrhea and inability to stand of approximately 6 hours’ duration. The foal had complete failure of passive transfer and received a plasma transfusion at approximately 12 hours after birth. The foal was euthanized owing to a poor prognosis.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photograph of the cut surface of the right kidney from a 24-hour-old filly that was evaluated because of diarrhea and inability to stand of approximately 6 hours’ duration. The foal had complete failure of passive transfer and received a plasma transfusion at approximately 12 hours after birth. The foal was euthanized owing to a poor prognosis.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photograph of the cut surface of the right kidney from a 24-hour-old filly that was evaluated because of diarrhea and inability to stand of approximately 6 hours’ duration. The foal had complete failure of passive transfer and received a plasma transfusion at approximately 12 hours after birth. The foal was euthanized owing to a poor prognosis.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Histopathologic and Microbiological Findings
Histologic examination of sections of kidney tissues revealed cortices that contained multiple embolic multifocal to coalescing 0.25-mm-diameter abscesses that regularly centered on glomeruli and occasionally extended into adjacent interstitium and tubules (Figure 2). Abscesses were composed of abundant necrotic debris with sheets of degenerate and intact neutrophils, and fewer lymphocytes and macrophages. Multifocally within abscesses, interstitium, and tubules, there were large colonies of approximately 1 × 2-μm gram-negative bacterial rods (Figure 3). Sections of small intestine had evidence of mild submucosal edema.
Photomicrograph of a section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. Throughout the cortex, there are multiple abscesses containing abundant colonies of bacteria that often involve glomeruli (arrow). H&E stain; bar = 100 μm. Inset—Photomicrograph of an abscess within the kidney tissue from the foal in Figure 1. A glomerulus is filled with bacteria (asterisk) and surrounded by sheets of neutrophils. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photomicrograph of a section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. Throughout the cortex, there are multiple abscesses containing abundant colonies of bacteria that often involve glomeruli (arrow). H&E stain; bar = 100 μm. Inset—Photomicrograph of an abscess within the kidney tissue from the foal in Figure 1. A glomerulus is filled with bacteria (asterisk) and surrounded by sheets of neutrophils. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photomicrograph of a section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. Throughout the cortex, there are multiple abscesses containing abundant colonies of bacteria that often involve glomeruli (arrow). H&E stain; bar = 100 μm. Inset—Photomicrograph of an abscess within the kidney tissue from the foal in Figure 1. A glomerulus is filled with bacteria (asterisk) and surrounded by sheets of neutrophils. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photomicrograph of another section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. The bacterial colonies are composed of small Gram negative rods. Bacteria often extend into the interstitium (arrow). Twort's Gram stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photomicrograph of another section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. The bacterial colonies are composed of small Gram negative rods. Bacteria often extend into the interstitium (arrow). Twort's Gram stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Photomicrograph of another section of renal cortex from the right kidney of the 24-hour-old filly in Figure 1. The bacterial colonies are composed of small Gram negative rods. Bacteria often extend into the interstitium (arrow). Twort's Gram stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 246, 4; 10.2460/javma.246.4.415
Antemortem blood and postmortem kidney tissue samples were placed on 5% sheep blood agar in trypticase soy agar base and MacConkey agar, respectively, and incubated at 37°C with 5% CO2 overnight (approx 15 hours). Both samples yielded abundant growth of small gray nonhemolytic colonies on sheep blood agar, consistent with Actinobacillus equuli. Aerobic culture of fecal samples yielded Escherichia coli (hemolytic) and was negative for Salmonella spp. Anaerobic culture of fecal samples yielded Clostridium perfringens; in-house PCR genotyping of C perfringens revealed that it was type A.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: severe, acute, embolic suppurative nephritis with numerous colonies of gram-negative bacterial rods (A equuli).
Case summary: A equuli embolic nephritis in a neonatal filly.
Comments
In neonatal foals, bacteremia resulting in embolic suppurative nephritis is most commonly caused by A equuli infection.1 Neonatal bacteremia caused by A equuli is known as sleepy foal disease1; infection results in acute fatal septicemia and has a worldwide distribution.1–3 Actinobacillus equuli is a natural commensal bacteria on mucosal membranes of adult horses; therefore, it is thought that foals are directly infected by their dams through the oral cavity, respiratory tract, or umbilicus during parturition, shortly after birth, or up to several days of age.2–4 As with any case of neonatal septicemia, prematurity, failure of passive transfer, dam malnutrition, and environmental factors are known predisposing factors. Infection with A equuli among foals is considered sporadic. However, an outbreak of the disease was reported at 1 horse premises in Great Britain5; 4 neonatal foals were found dead, of which 2 submitted for postmortem examination were positive for A equuli infection via histologic evaluation and tissue culture. It has been suggested that foals with actinobacillosis can be distinguished clinically from other bacteremic foals on the basis of the facts that they are more likely to be recumbent, have diarrhea, be sick from birth, and have lower neutrophil counts with higher band neutrophil counts.2 Additional clinicopathologic findings among infected foals include metabolic acidosis, fibrinogenemia, leukopenia, hypocalcemia, and hypoglycemia; many of these abnormalities were present in the foal of this report. Treatment is dependent on antimicrobials, which should be promptly administered to affected foals. Among neonatal foals with bacterial infections, survivability is variable. However, a retrospective study2 of 101 bacteremic foals found an overall survival rate of 54%. Those foals with actinobacillosis appeared sicker and had a slightly lower survival rate, compared with foals infected with other bacteria, but the type of bacteria isolated had no significant influence on survivability.
Actinobacillus spp cause various diseases in domestic animals other than horses (often associated with septicemia, abscesses, arthritis, or pneumonia); Actinobacillus bovis is the cause of wooden tongue disease in cattle. Rarely, A equuli had been reported to cause abortion, septicemia, and polyarthritis in swine.3 Currently, 2 subspecies of A equuli have been identified: Actinobacillus equuli subsp haemolyticus and Actinobacillus equuli subsp equuli. The latter is associated with foal and piglet septicemia.3,6,7 These as well as additional species and subspecies of Actinobacillus have been implicated in mare reproductive loss syndrome.8
In infected foals that survive 2 to 3 days, characteristic gross lesions in the kidneys appear as multifocal pinpoint abscesses in the cortex.1 Additional gross lesions, although not observed in the case described in the present report, may include fibrinosuppurative polyarthritis, polysynovitis, and abscesses in other viscera. Histopathologic findings coincide with gross lesions and are described as embolic nephritis (or acute suppurative glomerulitis) that is composed of sheets of degenerate and intact neutrophils admixed with abundant colonies of gram-negative rods centered on glomeruli. The inflammatory changes may extend into adjacent tubules and interstitium. The embolic pattern in a bacteremic animal is the result of thromboemboli that become lodged into small glomerular capillaries. Other bacteria that are a common cause of embolic nephritis include Erysipelothrix rhusiopathiae (in pigs), Truperella (Arcanobacterium) pyogenes (in cattle), and Corynebacterium pseudotuberculosis (in goats).
In the foal of the present report, an unequivocal etiologic diagnosis of A equuli was made via results of antemortem bacteriologic culture of blood and postmortem bacteriologic culture of the kidney tissues in conjunction with gross and microscopic findings. Micro-abscesses in the kidneys are an unusual finding in infected foals < 2 days old.1
References
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3. Thompson AB, Postey RC, Snider T, et al. Actinobacillus equuli as a primary pathogen in breeding sows and piglets. Can Vet J 2010; 51: 1223–1225.
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5. Baker JR. An outbreak of neonatal deaths in foals due to Actinobacillus equuli. Vet Rec 1972; 90: 630–632.
6. Christensen H, Bisgaard M, Olsen JE. Reclassification of equine isolates previously reported as Actinobacillus equuli, variants of A. equuli, Actinobacillus suis or Bisgaard taxon 11 and proposal of A. equuli subsp. equuli subsp. nov. and A. equuli subsp. haemolyticus subsp. nov. Int J Syst Evol Microbiol 2002; 52: 1569–1576.
7. Holyoak GR, Smith CM, Boyette R, et al. Serum antibodies in mares and foals to Actinobacillus equuli whole cells, outer membrane proteins, and Aqx toxin. Vet Immunol Immunopathol 2007; 118: 310–316.
8. Donahue JM, Sells SF, Bolin DC. Classification of Actinobacillus spp isolates from horses involved in mare reproductive loss syndrome. Am J Vet Res 2006; 67: 1426–1432.
