Disseminated Mycobacterium avium infection in a cat on long-term ciclosporin therapy and potential latent infection of an in-contact cat.

Case summary: An 8-year-old domestic shorthair cat receiving long-term ciclosporin treatment was evaluated for a history of weight loss and hyporexia. The main clinical finding was a cluster of enlarged mesenteric lymph nodes. Cytological examination of fine-needle aspirates showed granulomatous inflammation with abundant acid-fast bacilli. A diagnosis of Mycobacterium avium complex (MAC) infection was confirmed by PCR. The cat's clinical condition deteriorated rapidly despite appropriate antibiotic treatment and it was euthanased 2 weeks after initial presentation due to development of severe paraparesis and ataxia. Post-mortem examination revealed granulomatous inflammation affecting multiple lymph nodes and other organs with intrahistiocytic acid-fast bacilli consistent with mycobacteria when stained using Ziehl-Neelsen stain. Another cat in the same household was screened for infection using the interferon gamma release assay (IGRA), with the result being consistent with infection by non-tuberculous mycobacteria (NTM), which includes MAC; however, it had no grossly detectable disease. Relevance and novel information: This case report is an unusual presentation of disseminated MAC infection in a cat, which remains a rare diagnosis. Clinicians should be aware of unusual and rare presentations of this infection. The clinical findings, progression of disease and histopathology results add to the current clinical database for feline disseminated MAC infections. Another cat in the same household tested positive for NTM by IGRA without any gross disease. This was suggestive of latent MAC infection which, to our knowledge, has not been previously reported in an in-contact cat.

Primary multifocal muscular T-cell lymphoma with cutaneous involvement in a dog: A case report and review of the literature.

Canine lymphoma represents a heterogeneous group of lymphoid neoplasms, with multicentric nodal lymphoma being the most common presentation. Musculoskeletal involvement is uncommon, and primary muscular lymphoma is a very rare presentation. Only a few cases have been described in dogs, which were of variable classification and immunophenotype. Here, we report the case of a 5-year-old female neutered Beagle that presented with an intramuscular mass on the right shoulder and associated lameness and lethargy. One month after initial presentation, multiple cutaneous nodules appeared on the head, and staging with advanced imaging revealed additional masses affecting other muscles. Cytology, histopathology, immunohistochemistry, and PCR for antigen receptor rearrangements of one of the muscle masses and skin lesions supported a diagnosis of peripheral T-cell lymphoma with large granular lymphocytes at both sites. The dog was euthanized after diagnosis due to the poor prognosis. This is the first report of primary muscular peripheral T-cell lymphoma with large granular lymphocytes and cutaneous involvement in the dog. Despite being a rare presentation, lymphoma must be considered a differential in dogs presenting with a discrete, intramuscular, soft tissue mass.

Optimisation and validation of a PCR for antigen receptor rearrangement (PARR) assay to detect clonality in canine lymphoid malignancies.

PCR for antigen receptor gene rearrangements (PARR) analysis is being increasingly used to assist diagnosis of canine lymphoma. In this study, PARR was carried out on consecutive samples received as part of routine diagnostic practice from 271 patients: 195 with lymphoid malignancies, 53 with reactive conditions and 23 with other neoplasms. Initially, published primer sets were used but later minor primer modifications were introduced and primers were rationalised to give a PARR panel that provides a good compromise between sensitivity and cost. Results were compared to diagnoses made by histology or cytology, coupled with immunophenotyping by flow cytometry or immunohistochemistry where possible. After exclusion of 11 poor quality samples, 230/260 (88%) gave a clear result with 162/163 (99%) of samples classified as clonal and 56/67 (84%) classified as polyclonal giving results concordant with the cytological/histological diagnosis. Among 30 samples with equivocal results, 21 had clonal peaks in a polyclonal background and nine showed little amplification. These were from patients with a range of neoplastic and non-neoplastic conditions emphasising the need to interpret such results carefully in concert with other diagnostic tests. The combination of primer sets used in this study resulted in a robust, highly specific and sensitive assay for detecting clonality.

Use of CD134 as a primary receptor by the feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) induces a disease similar to acquired immunodeficiency syndrome (AIDS) in cats, yet in contrast to human immunodeficiency virus (HIV), CD4 is not the viral receptor. We identified a primary receptor for FIV as CD134 (OX40), a T cell activation antigen and costimulatory molecule. CD134 expression promotes viral binding and renders cells permissive for viral entry, productive infection, and syncytium formation. Infection is CXCR4-dependent, analogous to infection with X4 strains of HIV. Thus, despite the evolutionary divergence of the feline and human lentiviruses, both viruses use receptors that target the virus to a subset of cells that are pivotal to the acquired immune response.