Fatal multidrug-resistant Bordetella bronchiseptica and CAdV-2 coinfection in an 8-month-old boxer puppy, Southern Italy

Canine adenovirus type 2 (CAdV-2) is a widespread virus and one of the etiological agents of “kennel cough”, a mul tifactorial disease involving both viral and bacterial pathogens, including Bordetella bronchiseptica (B. bronchiseptica). Clinical manifestation is characterized by tracheobronchitis, which is generally associated with mild, self-limiting respira tory signs. In this study, we describe a respiratory outbreak associated with CAdV-2 and B. bronchiseptica infection in a Boxer breeding kennel in Southern Italy during the winter of 2023/2024. Several dogs showed fever and respiratory signs, characterized by a typical hacking cough. One adult dog exhibited more severe clinical signs and was urgently referred to a private veterinary hospital. Bordetella bronchiseptica was isolated from a bronchoalveolar lavage (BAL) sample; subsequent antimicrobial susceptibility testing guided the antimicrobial treatment, leading to clinical improvement. A few weeks later, a six-month-old puppy from the same kennel showed similar respiratory signs. Thoracic radiological exami nation revealed signs of bronchopneumonia, and bacteriological examination of a BAL sample resulted in the isolation of B. bronchiseptica. This puppy had not completed the immunization plan due to recurrent respiratory disease and died in February 2024 when was eight-month-old. Necropsy evidenced acute bronchopneumonia with lung hepatization. CAdV-2 DNA was detected by PCR in multiple organs. Other respiratory viruses were excluded using real-time or end-point PCR protocols. Sequencing of E3, Hexon and Fiber was performed to compare them with related sequences in international databases. A high degree of nucleotide identity with CAdV-2 strains detected in dogs and wild animals in northern Italy, as well as in raccoon dogs in South Korea has been reported. This case report demonstrates that CAdV-2, although gener ally considered a secondary respiratory pathogen, can be a cause of severe and fatal disease, particularly under epidemic conditions and in association with multidrug-resistant bacterial co-infections with B. bronchiseptica.