Duodenal perforation caused by Rhizomucor species in a cat

Abstract

Clinical summary A 7-month-old female Persian cat presented with gastrointestinal (GI) necrosis and perforation caused by Rhizomucor species. Unfortunately, the cat died of bacterial peritonitis and sepsis before a definitive diagnosis, based on histopathology and fungal culture, was achieved.

Practical relevance This appears to be the first reported case of GI disease caused by Rhizomucor species in a cat. Mucorales infections typically cause acute and rapidly progressive disease. As illustrated by this case, clinicians should be alert to the potentially fatal consequences of an opportunistic Rhizomucor species infection in their feline patients.

Clinical report

A 7-month-old female Persian cat presented with a 10-day history of signs of inappetence, fever, weight loss and abdominal distension. The cat was one of a litter of kittens born in the owner's house, and had free access to the backyard (which had fertilized soil and plants). The owners also reported the recent death (of unknown cause) of another cat of the same litter. Clinical examination revealed pale mucous membranes, mild dehydration, a body temperature of 39.8°C, and evidence of abdominal effusion and mesenteric lymph-adenomegaly on abdominal palpation. The initial presumptive diagnosis was feline infectious peritonitis.

A hematologic profile (including complete blood count, blood urea nitrogen [BUN], creatinine, total protein and fractions, alanine aminotransferase and alkaline phosphatase), feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) enzyme-linked immunosorbent assay, abdominal fluid analysis and abdominal ultrasound were undertaken.

Blood results revealed a packed cell volume of 19% (reference interval [RI] 24–45%), leukocytes 10,200/mm ³ (RI 5500–19,500/mm ³ ), bands 1122/mm ³ (RI 0–300/mm ³ ), neutrophils 8772/mm ³ (RI 2500–12,500/mm ³ ), lymphocytes 306/mm ³ (RI 1000–9000/mm ³ ), plasma protein 5.6 g/dl (RI 5.5–8.0 g/dl) and severe hypoalbuminemia (1.3 g/dl, RI 2.1–3.3 g/dl). Globulin, BUN and creatinine were unremarkable, and serology for FIV and FeLV disease was negative. Abdominal ultrasound revealed effusion, mesenteric lymphadenomegaly and severe thickening of the stomach and duodenal wall (0.8–1.5 cm in thickness), which was hypoechoic and showed loss of layering. Abdominal fluid analysis revealed a septic exudate, with protein measuring 2.6 g/dl, globulin 2.0 g/dl, albumin 0.6 g/dl, specific gravity >1018, erythrocytes 500,000/mm ³ and nucleated cells 39,600/mm ³ . Effusion cytology revealed high cellularity, comprising inflammatory cells — mostly intact and degenerate neutrophils, but also macrophages, plasma cells, lymphocytes and rare eosinophils. Many neutrophils were phagocytosing (rod) bacteria. Additionally, there was basophilic amorphous material and free bacteria.

On immediate exploratory laparotomy, the predominant findings were necrosis and perforation of the duodenum, enlarged mesenteric lymph nodes (measuring about 2.0 cm in diameter) and bacterial peritonitis (Fig 1a). The necrotic area was resected, the duodenum was sutured and an abdominal drain placed. The entire surgical specimen was sent for histopathology. The cat was then put on ceftriaxone (Rocephin; Roche, 50 mg/kg IV q24h), metronidazole (Flagyl; Sanofi Aventis, 10 mg/kg IV q12h), meloxicam (Maxicam; Ourofino, 0.1 mg/kg SC q24h), tramadol (Tramal; Pharmacia, 2 mg/kg IM q12 h), ranitidine (Antak; GlaxoSmithKline, 2 mg/kg SC q12h) and sucralfate (Sucrafilm; Ems, 0.5 g PO q12h), and a cross-matched blood transfusion (50 ml whole fresh blood) was performed. The abdominal cavity was washed with saline (10 ml/kg) three times a day. A soft food (Hill's prescription diet a/d) was gradually introduced.

FIG 1.

Zygomycosis in a cat. (a) Duodenal necrosis and perforation (arrow). (b) Short and broad hyphae (arrow-heads) revealed by histopathology; Grocott's stain × 400. (c) Macroscopic appearance of a culture of Rhizomucor species; colonies resemble cotton-candy with a white to gray surface. (d) Microscopy of Rhizomucor species, showing poorly septate, broad hyphae (black arrows) with only a few small rhizoids (∗) between sporangia (white arrow)

Within 3 days, the cat showed some improvement; it was more responsive, and there was no fever and no bacteria in the abdominal fluid. However, on the fourth postoperative day, the patient became extremely prostrate again, with a new episode of fever and septic abdominal effusion. Systolic blood pressure (<50 mmHg) and blood glucose (2.05 mmol/l) were extremely low. Blood work revealed severe anemia and leukopenia with a left shift, indicating sepsis. A second exploratory laparotomy was performed, which revealed another duodenal perforation, enlargement of mesenteric lymph nodes and peritonitis of bacterial origin. The perforation was in an area distinct from the previous surgery, and the first suture remained intact. The duodenum was again resected and sutured, and the abdominal cavity was washed with sterile saline. A second blood transfusion (50 ml whole fresh blood) was undertaken, and a colloid infusion (Voluven; Fresenius Kabi, 20 ml/kg/day) was administered. However, the cat died after surgery.

On histopathology of the resected area of duodenum, a mixed inflammatory infiltrate in the enteric wall, with extensive areas of necrosis, was seen. Grocott's staining revealed short, broad and poorly septate pseudo-hyphae permeating the necrotic tissue and vessel walls (Fig 1b). These structures were not stained by periodic acid-Schiff. The regional lymph node had an activated germinal center, but there was no evidence of fungal structures in its parenchyma.

A necropsy was performed, and tissue specimens from the stomach, intestines, liver, spleen, peritoneum, lungs, heart, kidney and pancreas were sent for histopathology. A small specimen of duodenal tissue was sent for fungal culture.

Mucor species have been isolated from the fur of cats, so it is possible that this cat had been infected by ingestion of the organism.

There was evidence of fungus in the stomach, small intestine and peripancreatic fat, but not in any other organs. Culture of the organism at 37°C revealed cotton-candy-like colonies with a white surface, which became gray as the colonies aged (Fig 1c); the reverse of the colonies had no color. On microscopic examination of the culture, poorly septate broad hyphae, with only a few small rhizoids between sporangia, were observed (Fig 1d). The sporangia were round with irregularly branched sporangiophores. As Rhizomucor species and Rhizopus species are very similar morphologically, the suspect colonies were cultivated again on Sabouraud's medium incubated at 50°C for 15 days. Resistance to this high temperature identified the fungus as being Rhizomucor species.

Much of the information available on zygomycosis in cats has been extrapolated from the disease in dogs and humans.

Discussion

Zygomycetes are opportunistic organisms present in the soil, water, decaying matter and feces. ^1–4 Infection is believed to be acquired by inhalation, ingestion or contamination of wounds. ^2,5,6 The cat of the present report had an outdoor lifestyle and contact with fertilized soil. Mucor species have been isolated from the fur of cats, ⁷ so it is possible that this patient had been infected by ingestion of the organism.

In humans, zygomycosis generally manifests in two forms — pulmonary/systemic and rhinocerebral. ^4,6,8,9 There are rare reports of Mucor species infections in animals, including disseminated infection in cattle and horses, ^10,11 systemic disease in animal models, ¹² cutaneous mycosis in the platypus, ¹³ a case of cerebral mycosis in a cat ¹⁴ and infection of the subcutis of a cat. ¹⁵ To our knowledge, this is the first case of gastrointestinal (GI) disease caused by Rhizomucor species in a cat.

Infection with organisms belonging to the Mucorales usually causes acute, rapidly progressive disease. A granulomatous reaction to the fungus occurs in the skin, with nodules, ulceration, purulent discharge and fistulous tract formation. Zygomycosis may also involve the lungs and the GI tract, causing granuloma formation and lymphadenopathy of adjacent lymph nodes. ³ In this cat, the disease was acute in nature, with intestinal necrosis and perforation leading to bacterial peritonitis and death.

Postoperative medications included antibiotics, opioids, non-steroidal anti-inflammatory drugs, an H₂ receptor antagonist and a GI (antiulcer) protectant. Meloxicam was given for postoperative pain control, along with ranitidine to minimize possible GI adverse effects. Meloxicam might have contributed to the GI ulceration observed at the second surgery, and should have been avoided.

A definitive diagnosis of zygomycosis is made by cytology or histopathology and a positive culture. ² Often, in cats, the diagnosis is only made post mortem. ² Broad (>8 μm), poorly septate hyphae are typically found on cytology of impression smears if they are treated with 10% potassium hydroxide and then stained. ² Hyphae are usually readily seen on histopathological specimens that are stained with Gomori methenamine and hematoxylin and eosin stains. ² A distinguishing feature of zygomycosis is the presence of a wide (2.5–25 μm) eosinophilic sleeve around the hyphae; this differentiates zygomycetes from phycomycetes, in which the sleeve is either thin or absent. ¹⁶ The fungal elements are typically found in eosinophilic granulomas. ¹⁷ The organisms are readily cultured from biopsy specimens or deep swabs of lesions. ¹⁷ In this case, histopathology and tissue culture were effective in establishing the definitive diagnosis of zygomycosis.

Little information exists on the treatment of mucormycosis in cats and much of the information available on zygomycosis in cats has been extrapolated from the disease in dogs and humans. ^2,4,15,17 In the reported case, the diagnosis was unfortunately made only after the animal's death, and systemic antifungal treatment was not administered. Possibly, if cytology had been performed at the time of the first surgery, or the histopathology result had been obtained sooner, the diagnosis would have been made earlier.