Chronic hepatitis and hepatocellular carcinoma (HCC) caused by the hepadnavirus hepatitis B virus (HBV) are significant causes of human mortality. A hepatitis-B-like virus infecting cats, domestic cat hepadnavirus (DCH), was reported in 2018. DCH DNA is hepatotropic and detectable in feline blood or serum (3.2 to 12.3%). Detection of HBV DNA has been reported in sera from 10% of free-roaming dogs in Brazil, whereas 6.3% of sera from dogs in Italy tested positive for DCH DNA by real-time quantitative PCR (qPCR). If DCH, HBV, or another hepadnavirus is hepatotropic in dogs, a role for such a virus in the etiology of canine idiopathic chronic hepatitis (CH) or HCC warrants investigation. This study investigated whether DCH DNA could be detected via qPCR in blood from dogs in Hong Kong and also whether liver biopsies from dogs with confirmed idiopathic CH or HCC contained hepadnaviral DNA using two panhepadnavirus conventional PCRs (cPCR) and a DCH-specific cPCR. DCH DNA was amplified from 2 of 501 (0.4%) canine whole-blood DNA samples. A second sample taken 6 or 7 months later from each dog tested negative in DCH qPCR. DNA extracted from 101 liver biopsies from dogs in Hong Kong or the USA, diagnosed by board-certified pathologists as idiopathic CH (n = 47) or HCC (n = 54), tested negative for DCH DNA and also tested negative using panhepadnavirus cPCRs. This study confirms that DCH DNA can be detected in canine blood by qPCR, although at a much lower prevalence than that reported previously. We identified no evidence to support a pathogenic role for a hepadnavirus in canine idiopathic CH or HCC.

Dermatophytic pseudomycetoma (DPM) is a rarely reported invasive fungal infection of humans and animals, especially cats. This study aimed to identify dermatophytes, breed associations, and the frequency of extracutaneous (EC) involvement in feline DPM. Electronic records and formalin-fixed paraffin-embedded tissue (FFPET) from 32 suspected DPM cases in 30 cats were retrieved from a diagnostic laboratory between 2018 and 2024. To confirm DPM and molecular identity, DNA was extracted from FFPET for ITS2 sequencing, and immunohistochemistry was performed on PCR-negative cases. All cases were confirmed as DPM. Microsporum canis was the only dermatophyte identified. The sensitivity and specificity of ITS2 sequencing for M. canis identification in FFPET were 22/32 (68.8%) and 21/22 (95.5%), respectively. Exotic (36.7%) and Persian (23.3%) but not British breeds (26.3%) were over-represented compared to feline admissions at an affiliated veterinary hospital (8.5%, p < 0.001; 3%, p < 0.001; 21.6%, p = 0.817, respectively). Five cases (16.7%) had EC lesions; two had intra-abdominal masses; two had oral cavity masses, including one which extended into the cranial vault; and one had superficial cervical lymph node invasion. Exotic and Persian breeds are over-represented for DPM and M. canis is the primary cause. EC lesions of DPM may occur more commonly than previously thought.

Lymphoma is the most common tumor of the nasal cavity in cats. Commonly used treatment modalities are radiotherapy and chemotherapy, or both. Typical chemotherapy protocols used in cats with nasal lymphoma are COP (cyclophosphamide, vincristine prednisolone) and CHOP (cyclophosphamide, doxorubicin, vincristine and prednisolone). Thus far, the use of single-agent chlorambucil in nasal lymphoma has been evaluated in a single case report. We report a case series of three cats with B cell nasal lymphoma, two cats with intermediate cell, and one large cell, all with a low mitotic index (MI) of less than 5 mitotic figures per ×400 field, treated with chlorambucil and prednisolone. Two of the cases achieved a long disease-free interval, while the one with the highest MI did not. Protocols using chlorambucil and prednisolone may have potential as a first-line therapy for feline nasal lymphoma cases with a very low mitotic index.