The avian influenza virus is a global pathogen with significant health and economic implications. While primarily a pathogen of wild and domestic birds, recent outbreaks of the H5N1 highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4b have caused mortality in a wide variety of mammals, including members of the Canidae family, on multiple continents. Despite sporadic mortality events globally, the epidemiology and pathobiology of H5N1 HPAIV in wild canids remains poorly defined. During 2022–2024, 41 wild canid carcasses (diagnostic cases), including 23 red foxes and 18 gray foxes, were tested for the influenza A virus (IAV) via PCR, with five red fox kits testing positive (12%). Infected animals had variably severe encephalitis, pneumonia, and occasionally myocarditis associated with strong immunolabeling for IAV. Serum from 269 wild canids in Pennsylvania was tested for antibodies to IAV, including 133 samples collected prior to 2021 (pre-H5N1 HPAIV 2.3.4.4b introduction) and 136 collected after 2022 (post-H5N1 HPAIV 2.3.4.4b introduction). All samples collected prior to 2021 were seronegative for IAV. Two coyotes from 2024 were seropositive for IAV but were negative for antibodies to the H5 and N1 subtypes. Collectively, these data suggest that while sporadic H5N1 HPAIV infection and mortality can occur in wild canids, particularly juvenile red foxes, infection was limited in these outwardly healthy and opportunistically sampled animals. Future studies should utilize a risk-based approach to target sampling of wild canids at increased risk for H5N1 HPAIV infection, such as those around waterfowl habitats or spatially around wild bird or domestic animal outbreaks.

Intracranial abscesses are a common cause of morbidity and mortality in neurologic free-ranging white-tailed deer (Odocoileus virginianus). These infections are typically attributed to Trueperella pyogenes and occur most often in adult males with concurrent antler and skull infections. A subset of intracranial abscesses in white-tailed deer are localized to the pituitary gland, with previously described reports in five white-tailed deer. In this case series, five additional free-ranging white-tailed deer in Pennsylvania were diagnosed with pituitary abscesses at necropsy. Two cases were female deer, and four cases were yearling or juvenile deer. Two cases presented with conjunctivitis and keratitis due to extension of pituitary abscesses into the retrobulbar and peri-orbital spaces. One case had a concurrent liver abscess. This case series demonstrates a unique clinical presentation of keratitis and conjunctivitis and emphasizes the potentially unique pathogenesis for pituitary abscesses compared to other intracranial abscesses described in white-tailed deer.

Rabies is a universally fatal viral disease that affects a wide variety of mammalian species, including carnivores and herbivores. While testing and confirmed reports in wild carnivores are common, comparatively less is known about this disease in wild herbivores. Between 2022 and 2024, nine white-tailed deer (Odocoileus virginianus) in Pennsylvania, USA were diagnosed with rabies. Eight (89%) presented with erratic neurologic signs and one was found dead. Evidence of chronic self-mutilation characterized by hair loss and thickened, hardened, and hyperpigmented skin was present on the head in seven cases (78%) and/or body or legs in two cases (22%), while two (22%) did not have any evidence of external lesions. Microscopically, lesions were like those in other mammalian species, with variably severe inflammation and abundant cytoplasmic inclusion bodies with associated antigen immunoreactivity. This case series highlights a common and characteristic gross lesion that can prompt caution and testing for rabies in deer and further expands understanding of this disease in an uncommonly diagnosed species.