• Open Access

Ralstonia pickettii Septicemia in a Dog with Immune-Mediated Thrombocytopenia

Authors


Corresponding author: Melissa A. Herrera, DVM, DACVIM, Department of Medicine and Epidemiology, University of California, Davis, Davis, CA; e-mail: mherrera@vmth.ucdavis.edu

A4-year-old, female spayed, Rottweiler weighing 53.3 kg presented to the William R. Pritchard Veterinary Medical Teaching Hospital (VMTH) at the University of California, Davis for the primary complaint of epistaxis of 3 days' duration. Initial physical examination revealed severe bilateral epistaxis as well as petechiation and ecchymoses along the ventrum, inner pinnae, conjunctiva, and buccal mucosa. Melena was noted on rectal examination. A CBC revealed severe thrombocytopenia (14,000/μL; reference range, 150,000–400,000/μL); mild normocytic, normochromic nonregenerative anemia (PCV, 36%; reference range, 40–55%); and a normal leukogram (9,600 WBC/μL; reference range, 6,000–13,000 WBC/μL). Serum biochemistry results included mildly increased BUN concentration (23 mg/dL; reference range, 5–21 mg/dL), increased activities of alkaline phosphatase (ALP) (835 IU/L; reference range, 21–170 IU/L) and GGT (7 IU/L; reference range, 0–6 IU/L), and mild hypercholesterolemia (406 mg/dL; reference range, 135–361 mg/dL). Urinalysis (obtained by voiding) revealed a specific gravity of 1.030 with proteinuria (30 mg/dL). A bone marrow aspirate revealed mild megakaryocytic hyperplasia consistent with immune-mediated thrombocytopenia (IMTP). Thoracic radiographs and an abdominal ultrasound were normal. Serologic titers for Ehrlichia canis, Anaplasma phagocytophilum, Rickettsia rickettsii, and Babesia canis were negative.

Treatment with prednisone (1 mg/kg PO q12h) and azathioprine (1.4 mg/kg PO q24h) was initiated. The platelet count remained below 14,000/μL for 8 consecutive days and epistaxis, petechiation, and melena persisted. Because of progressive anemia (PCV, 20%) as well as clinical signs of weakness and tachycardia, a cross-matched packed red blood cell (pRBC) transfusion was administered. The dog received 300 mL of pRBCs at an initial rate of 2 mL/kg/h, which then was increased to 4 mL/kg/h. The posttransfusion PCV was 28%. Two hours after the transfusion, the dog's rectal temperature increased from 101 to 104°F. A transfusion reaction was suspected and the dog was treated with dexamethasone (0.15 mg/kg IV, once) and diphenhydramine (2.0 mg/kg SC, once). Rectal temperature decreased to 101.5°F over the next 4 hours and no other adverse effects were noted. Cyclosporine (3.8 mg/kg PO q12h) was added to the treatment regimen on day 8, and the dose of azathioprine was decreased (1.4 mg/kg PO q48h). On day 10, the platelet count increased to 48,000/μL and the dog was discharged from the hospital. Treatment at discharge included prednisone (1 mg/kg PO q12h), azathioprine (1.4 mg/kg PO q48h), cyclosporine (3.8 mg/kg PO q12h), and famotidine (0.5 mg/kg PO q12h).

The dog was reevaluated on day 12 after initial presentation. Physical examination was unremarkable with resolution of petechiation and melena. A CBC revealed regenerative anemia (PCV, 22.8%; reticulocyte count, 210,900/μL; reference range 7,000–65,000/μL), mature neutrophilia (12,737/μL; reference range, 3,000–10,500 cells/μL), and a platelet count of 79,000/μL. A trough whole blood cyclosporine concentration was 410 ng/mL. The immunosuppressive medications were continued at the same dosages. The dog returned to the VMTH for reevaluation on day 17. At that time, the owner reported polyphagia, polyuria, and polydipsia. A CBC at that time revealed anemia (PCV, 30%), leukocytosis (WBC, 15,870/μL), and a platelet count of 118,000/μL. No changes were made to the treatment regimen.

On Day 24, the dog presented to the VMTH for decreased activity, inappetence, weakness, and mucoid nasal discharge of 24 hours duration. Physical examination revealed quiet mentation, bilateral mucoid nasal discharge, temporal muscle atrophy, and hepatomegaly. A CBC revealed regenerative anemia (PCV, 29%; reticulocytes, 110,600/μL), mature neutrophilia (16,131/μL), and a platelet count of 155,000/μL. Serum biochemistry revealed high liver enzyme activities (ALP, 5,190 IU/L; ALT, 513 IU/L: reference range, 19–67 IU/L; AST, 151 IU/L: reference range, 19–42 IU/L; GGT, 167 IU/L) and hyperbilirubinemia (1.2 mg/dL; reference range, 0–0.2 mg/dL). Pancreatic lipase immunoreactivity was 518 μg/L (reference range, 0–200 μg/L). Based on these results, pancreatitis was suspected. Abdominal ultrasound examination was not performed. Amoxicillin-clavulanic acid (14 mg/kg PO q12h) was prescribed for the mucoid nasal discharge and azathioprine was discontinued. The prednisone dosage was decreased (0.64 mg/kg PO q12h) and treatment with cyclosporine (3.8 mg/kg PO q12h) was continued. The dog's clinical condition improved over the next 4 days.

Six days later (day 30), the dog presented for anorexia and profound weakness of 24 hours' duration. On physical examination, the dog was obtunded, laterally recumbent, febrile (103.7°F), and had pale mucous membranes, tachycardia (pulse rate, 140 beats/min), and weak pulse quality. The dog's sclera, pinnae, and mucous membranes were mildly icteric. Increased breath sounds were auscultated over all lung fields and the dog had increased respiratory effort. Oxygen support and fluid therapy (lactated Ringer's solution, 2 L over 1 hour then 150 mL/h, IV) were initiated. A CBC revealed a normocytic, hypochromic, regenerative anemia (PCV, 22%; reticulocytes, 160,100/μL; mean corpuscular volume, 65 fL, reference range 65–75 fL), a left shift (neutrophils, 7,918/μL; band neutrophils, 2,247/μL) with moderate toxic neutrophil changes, and thrombocytopenia (83,000/μL). Serum biochemistry revealed hypoalbuminemia (2.4 g/dL), high liver enzyme activities (ALP, 4,575 IU/L; ALT, 598 IU/L; AST, 180 IU/L; GGT, 121 IU/L) and hyperbilirubinemia (3.0 mg/dL). Thoracic radiographs showed focal alveolar infiltrates in the left cranial lung lobe and normal cardiovascular structures. Abdominal ultrasound examination identified hepatomegaly with diffusely hyperechoic hepatic parenchyma and multiple, triangular hyperechoic lesions in both kidneys. Cytologic evaluation of a fine needle aspirate of the liver indicated suppurative inflammation and mild hepatocellular dysplasia. Two blood samples collected aseptically approximately 1 hour apart were submitted for aerobic and anaerobic bacterial culture and susceptibility. Both samples yielded Ralstonia pickettii from the enrichment broth. The isolate was susceptible to all antimicrobials tested except for ampicillin, cefazolin, and cefpodoxime, with intermediate sensitivity to tetracycline and ticarcillin. Because of the patient's guarded prognosis, the owner elected euthanasia and authorized a necropsy.

On gross necropsy examination, the peritoneal cavity contained approximately 100 mL of pink, cloudy fluid, and all serosal surfaces were dull and slightly roughened. Two 2.0 cm × 1.0 cm ulcers were present in the pylorus. The liver was diffusely pale and friable, with rounded lobe margins and an enhanced reticular pattern. Multifocal petechiation of the parietal pleura, mediastinum, and pericardium was present, and each kidney contained a 1.0-cm diameter, acute cortical infarct. The lungs were heavy and edematous. Histopathologic examination of the liver showed scattered, acute necrosis and marked, diffuse, midzonal hepatocellular vacuolation (Fig 1). Small mats of fibrin were present on the hepatic capsule and multiple serosal surfaces. Histopathologic examination of the lung confirmed moderate diffuse edema with alveolar histiocytosis, and revealed multifocal pulmonary interstitial mineralization (Fig 2). Moderate, multifocal mineralization of the splenic trabecular arteries was also present. Samples of liver, spleen, and lung were submitted for aerobic and anaerobic bacterial culture, and all samples yielded R. pickettii.

Figure 1.

 Photomicrograph of a focus of scattered hepatic necrosis in a septicemic dog. Necrotic hepatocytes are shrunken and hypereosinophilic (arrowheads), and admixed with small numbers of neutrophils. Many hepatocytes in the surrounding parenchyma contain markedly vacuolated cytoplasm, consistent with glycogen accumulation. Hematoxylin and eosin stain; scale bar=100 μm. 239 × 180 mm (432 × 432 DPI).

Figure 2.

 Photomicrograph of lung with multifocal mineralization in a septicemic dog. Alveolar septa are disrupted and expanded by granular, basophilic material deposited in the interstitium (arrowheads). Hematoxylin and eosin stain; scale bar=100 μm. 239 × 180 mm (432 × 432 DPI).

To the authors' knowledge, this is the first reported case of R. pickettii septicemia in a dog. R. pickettii is an aerobic, oxidase-positive, nonfermenting, Gram-negative bacillus found in water and soil.1R. pickettii formerly was known as Pseudomonas (Burkholderia) pickettii and was first described in 1973.2 In human patients, infections with R. pickettii generally are associated with impaired immunocompetence.3 In a recent report, 64% of human infections with R. pickettii were nosocomial and 36% of these nosocomial infections included bacteremia or sepsis.1 Nosocomial outbreaks due to contamination of chlorhexidine, various irrigating solutions and drugs for injection or inhalation, and indwelling IV devices have been reported in human medicine. Nosocomial outbreaks also have been reported in pediatric and oncology wards, and in human intensive care units.4–9R. pickettii has been identified in humans with pre-existing immunosuppressive or myelosuppressive disease, including cystic fibrosis, Crohn's disease, and chemotherapy administration.10–12

A variety of opportunistic bacterial, viral, fungal, and protozoal infections have been documented in immunosuppressed veterinary patients.13,14 With increasing use of potent, immunosuppressive agents for treatment of dogs with immune-mediated disease, such infections are likely to be recognized more frequently. In human patients, infection is related to the magnitude of immunosuppression, which increases with the use of multiple immunosuppressive agents and prolonged duration of treatment.15

Treatment with glucocorticoids is the mainstay of management of immune-mediated diseases. Modification with other immunosuppressive agents, however, may improve acute and long-term control of disease.16 The dog of this report was treated with azathioprine and cyclosporine to control severe IMTP and resultant anemia. Azathioprine was combined with prednisone from the outset to permit more rapid tapering of the prednisone dosage so that anticipated adverse effects of prednisone therapy could be minimized.17 Cyclosporine, a calcineurin inhibitor, inhibits T-cell activation and prevents synthesis of several cytokines, especially IL-2.18 Cyclosporine has been used to treat several immune-mediated conditions in dogs, such as myasthenia gravis,19 perianal fistulas,20,21 atopic dermatitis,22 immune-mediated hemolytic anemia,23 and for prevention of allograft rejection after renal transplantation.24,25 In canine renal transplant recipients, trough whole blood cyclosporine concentrations have been recommended to be maintained between 250 and 500 ng/mL.24,26 However, at this time, there is no evidence-based recommendation for therapeutic concentrations of cyclosporine in veterinary medicine nor is it known whether trough or peak concentrations provide the best measure of the extent of immunosuppression. Similarly, the timing and target concentrations of cyclosporine are not standardized in human medicine.27–29 In this case, the trough cyclosporine concentration was measured at 410 ng/mL, which is in with the recommended concentration range.24,26 Given the scarcity of data on appropriate cyclosporine concentrations in the dog, no conclusion can be made as to whether this cyclosporine concentration predisposed this dog to infection. Multimodal immunosuppressive therapy may have contributed to opportunistic infection.

After the diagnosis of R. pickettii sepsis, the owner was asked additional questions. The dog was housed primarily indoors with a healthy adult Rottweiler and did not go on walks after immunosuppressive therapy was instituted. The dog drank tap water and occasionally water from a swimming pool. It is also possible that infection may have developed during hospitalization. The dog was hospitalized for 10 days (days 0–9). Three different IV catheters were placed during hospitalization (days 0, 1, and 4) and no catheter was in place for more than 72 hours. The catheters were used for fluid therapy and famotidine administration. At the VMTH, standard catheter care consists of unwrapping, cleaning with chlorhexidine solution, and rewrapping the catheter once daily. Although possible, it was felt to be unlikely that R. pickettii infection was acquired during hospitalization because the dog remained clinically healthy for 14 days after discharge in the absence of antimicrobial therapy. This possibility does however emphasize the importance of minimizing hospital stays in immunosuppressed patients, frequent hand washing and wearing gloves while handling such patients, as well as use of an isolation ward for immunosuppressed patients to help prevent nosocomial infections.

At necropsy, metastatic mineralization was noted in the lungs and splenic trabecular arteries. These changes were similar to those seen with severe uremia, which was not present in this case. The cause of the mineralization in this patient was unknown. Interestingly, several Ralstonia species, including R. pickettii, are capable of mineral precipitation in vitro.30,31R. pickettii has been investigated as a soil bioremediation agent because of its ability to degrade and mineralize environmental pollutants such as polychlorinated biphenyls.31 The scattered hepatic necrosis was consistent with embolic showering of the liver, and was supportive of septicemia. The marked hepatocellular vacuolation was consistent with glycogen accumulation associated with steroid hepatopathy.

Although rare, R. pickettii should be considered as a cause of bloodstream infections in immunosuppressed veterinary patients. Care should be taken to minimize the length of immunosuppression and minimize the potential of opportunistic infections by controlling the environment along with appropriate client education. Future studies regarding timing and target concentrations of cyclosporine in veterinary patients are warranted to help guide immunosuppressive therapy.

Ancillary