Raw Diet Link? 3 Cats with Listerial Mesenteric Lymphadenitis—Diagnosis & Long-Term Outcomes

Listerial mesenteric lymphadenitis in 3 cats

Thomas W. Fluen; Michael Hardcastle; Matti Kiupel; Randolph M. Baral

Background

Listeriosis is uncommon in cats and typically described as isolated cases. Mesenteric lymphadenitis caused by Listeria monocytogenes had not been previously characterized in this species. The authors aimed to describe clinical presentation, diagnostic confirmation, management, and outcomes for feline listerial mesenteric lymphadenitis, and to note potential risk factors such as raw meat–based diets.

Methods

This case report details three client-owned cats evaluated at referral centers in Australia and New Zealand. Diagnostic workups included physical examination, abdominal ultrasound, exploratory laparotomy with lymph node biopsy/debridement, histopathology, Gram stains, immunohistochemistry targeting L. monocytogenes, and aerobic/anaerobic culture with speciation by 16S rRNA or MALDI-TOF MS when growth occurred. Retroviral testing (FIV/FeLV) and routine laboratory testing were performed. Treatments included surgery (node debridement/omentalization) and prolonged antimicrobial therapy (primarily amoxicillin ± clavulanate; other agents as indicated).

Results

All three cats had marked mesenteric lymphadenomegaly on palpation and ultrasound; two had concomitant enteritis/hepatitis on histology. L. monocytogenes was confirmed in mesenteric nodes by immunohistochemistry in all cases, with culture-positive confirmation in two. Two cats had a history of raw meat–based diets before illness. All cats survived long term with medical and/or surgical management: one cat remained clinically well 27 months after diagnosis, another was well at 20 months with a regressing palpable mass, and one survived >5 years before euthanasia for an unrelated hepatic mass.

Limitations

As a small case series, generalizability is limited. Cultures were sometimes negative despite histologic/IHC confirmation, and no necropsy was performed in the cat euthanized for presumed hepatic neoplasia. Fecal shedding was not assessed; thus zoonotic risk from affected cats could not be determined. The contribution of raw diets is suggestive but unproven.

Conclusions

Listerial mesenteric lymphadenitis should be included among differentials for abdominal lymphadenopathy in young to middle-aged cats, even without overt systemic signs. Diagnosis relies on histopathology with immunohistochemistry and, when possible, culture. Prolonged survival is possible with surgical extirpation/omentalization and extended amoxicillin-based therapy. Raw meat–based diets may represent a risk factor and warrant counseling.

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