Study on the Canine Adenovirus Type 1 (CAdV-1) Infection in Domestic Dogs in Southern Italy

Canine Adenoviruses in Wildlife: Role in At-Risk Species Conservation and Interface with Domestic Animals

Canine adenovirus type 1 (CAdV-1) and type 2 (CAdV-2) are well known pathogens of domestic dogs but are little investigated in wild animals. The few available studies about CAdV-1 in wild animals show that it circulates in various species and that transmission of the virus in the interface between wildlife and domestic animals is a frequent event. Furthermore, wild animals are usually subject to asymptomatic infections, but cases of serious and fatal diseases have been documented, with possible effects on the conservation of the species. In contrast, CAdV-2 infection was reported only recently and sporadically in some wild animals, with few data regarding its pathogenic role in these species. However, the real prevalence of these viruses in wildlife is still uncertain due to the use of serological tests that are largely unable to distinguish antibodies against CAdV-1 and CAdV-2. This review, reporting all the data currently available on CAdV-1 and CAdV-2 infection in wild animals, highlights the importance of these pathogens for wildlife conservation and their role in the potential transmission of the infection to domestic dogs.

Establishment of ELISA method for canine adenovirus type 1

Canine adenovirus (CAdV) had a high prevalence in fox populations and induced fox encephalitis. No ELISA kits specifically for CAdV-1 antigen had been commercialized for foxes in China. It is crucial to develop a rapid and accurate ELISA method for detecting of CAdV-1. The monoclonal antibodies (mAbs, IgG1A) and HRP-labeled polyclonal antibodies (pAbs) were used to establish the ELISA method in this experiment. The results showed that the optimal concentration and coating time for the mAbs (IgG1A) were 2.15 μg/mL and overnight at 4°C, respectively. The dilution ratio of the HRP-labeled pAbs was 1:2000. Five percent skimmed milk was selected as the blocking agent. The optimal incubation times for blocking, CAdV-1, and HRP-labeled pAbs were all 1 h. The cut-off value for negative rectal swab was determined to be 0.366 ± 0.032. The maximum dilution ratio was 100 TCID50/mL. The ELISA method was positive to CAdV-1, and that was negative to CAdV-2, Canine Parvovirus (CPV) and Canine Distempervirus (CDV). The ELISA method showed good repeatability, sensitivity, and specificity. Compared with RT-PCR, the sensitivity, specificity, and coincidence rates of the ELISA method were 93.75, 90.9, and 92.86%, respectively. These results indicate that the established ELISA method can be used for the large-scale screening and epidemiology surveillance of CAdV-1 in foxes.

Construction and application of adenoviral vectors

Adenoviral vectors have been widely used as vaccine candidates or potential vaccine candidates against infectious diseases due to the convenience of genome manipulation, their ability to accommodate large exogenous gene fragments, easy access of obtaining high-titer of virus, and high efficiency of transduction. At the same time, adenoviral vectors have also been used extensively in clinical research for cancer gene therapy and treatment of diseases caused by a single gene defect. However, application of adenovirus also faces a series of challenges such as poor targeting, strong immune response against the vector itself, and they cannot be used repeatedly. It is believed that these problems will be solved gradually with further research and technological development in related fields. Here, we review the construction methods of adenoviral vectors, including "gutless" adenovirus and discuss application of adenoviral vectors as prophylactic vaccines for infectious pathogens and their application prospects as therapeutic vaccines for cancer and other kinds of chronic infectious disease such as human papillomavirus, hepatitis B virus, and hepatitis C virus.

Multiplex One-Step RT-qPCR Assays for Simultaneous Detection of SARS-CoV-2 and Other Enteric Viruses of Dogs and Cats

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was transmitted from humans to dogs and cats (reverse zoonosis) during the COVID-19 pandemic. SARS-CoV-2 has been detected in fecal samples of infected dogs and cats, indicating potential fecal-oral transmission, environmental contamination, and zoonotic transmission (i.e., spillback). Additionally, gastrointestinal viral infections are prevalent in dogs and cats. In this study, we developed and validated a panel of multiplex one-step reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assays for the simultaneous detection of SARS-CoV-2 and common canine enteric viruses: Canine Enteric Assay_1 (CEA_1) for the detection of canine adenovirus-1, canine enteric coronavirus, canine distemper virus, and canine parvovirus, and CEA_2 for the detection of rotavirus A (RVA), and SARS-CoV-2); or common feline enteric viruses (Feline Enteric Assay_1 (FEA_1) for the detection of feline enteric coronavirus, feline panleukopenia virus, RVA, and SARS-CoV-2). All assays demonstrated high analytical sensitivity, detecting as few as 5-35 genome copies/µL in multiplex format. The repeatability and reproducibility of the multiplex assays were excellent, with coefficient of variation <4%. Among the 58 clinical samples tested, 34.5% were positive for at least one of these viruses, and SARS-CoV-2 was detected in two samples collected from one dog and one cat, respectively. In conclusion, these newly developed one-step multiplex RT-qPCR assays allow for rapid diagnosis of enteric viral infections, including SARS-CoV-2, in dogs and cats.

Effect of Aging on the Immune Response to Core Vaccines in Senior and Geriatric Dogs

Elderly dogs are steadily increasing worldwide as well as veterinarians' and owners' interest in their health and wellness. Aging is not a disease, but a combination of changes negatively affecting the organism in general and the immune system in particular, resulting in a decline in protection over time. The aim of this study was to measure the specific serum antibody titers against the main dangerous and widespread viral diseases preventable by core vaccinations in senior and geriatric dogs using the in-practice test VacciCheck. A cohort of three hundred fifty elderly dogs was analyzed for Protective Antibody Titers (PATs) against CPV-2, CDV and CAdV-1. The age ranged from 5 to 19 years, with two hundred fifty-eight seniors (73.7%) and ninety-two geriatrics (26.3%), and 97.4% of them were vaccinated at least once in their lives. More than half of the entire study population (52.9%) had PATs simultaneously for all three diseases, with 80.5% seniors and 19.5% geriatrics. Specific PATs were found in 88.6% of aging dogs for CPV-2, 82.3% for CadV-1 and 66.0% for CDV, demonstrating that unprotected aging dogs represent a minority. Unexpectedly, the larger elderly dogs resulted as more protected than smaller ones for CPV-2. Protection then decreases over time, with geriatric dogs less protected than senior ones. Veterinary practitioners should therefore always consider whether to maintain core vaccinations in aging dogs as in adults on a three-year basis or opt instead for closer boosters (every 1 or 2 years). PATs for core vaccines could then represent a good biomarker of protection and their titration could become a standard of care, especially in such a sensitive period of the dogs' life.

Can Chemotherapy Negatively Affect the Specific Antibody Response toward Core Vaccines in Canine Cancer Patients?

The life expectancy of our pets has been getting longer in recent years due to new therapeutic opportunities, better nutrition, and better diagnostic approaches. This positive effect, however, has been accompanied by a concomitant increase in neoplasms, particularly in canine patients. Therefore, veterinarians inevitably face new issues related to these diseases, poorly or never investigated in the past, such as the possible side effects resulting from chemotherapy. The aim of this study was to investigate whether and how chemotherapy influences the antibody response against CPV-2, CDV, and CAdV-1 in dogs vaccinated before starting chemotherapy. Twenty-one canine patients with different types of malignancies were sampled before, during, and after different chemotherapy protocols to determine their actual levels of seroprotection against CPV-2, CDV, and CadV-1 by using the in-practice test VacciCheck. Differences related to sex, breed size, type of tumor, and chemotherapy protocol were evaluated. No statistically significant changes in antibody protection emerged for any of the chemotherapy protocol used, suggesting that, contrary to expectation, chemotherapy does not have a marked immunosuppressive effect on the post-vaccine antibody response. These results, although preliminary, may be useful in improving the clinical approach to the canine cancer patient, helping veterinarians fully manage their patients, and enabling owners to feel more confident about their pets' quality of life.

Prevalence of Serum Antibody Titers against Core Vaccine Antigens in Italian Dogs

Canine vaccination is the main tool for preventing dangerous and widespread diseases. The strongly recommended (core) dog vaccines are against Canine Parvovirus type 2 (CPV-2), Canine Distemper Virus (CDV), and Canine Adenovirus (CAdV-1), but vaccination protocols should be tailored to dog lifestyles. Vaccination guidelines suggest vaccinating adult dogs no more frequently than every 3 years using modified live (attenuated) vaccines (MLV), thus obtaining a long-lasting (sometimes throughout life) specific protection in many but not all animals. The aim of this study was to determine the actual levels of seroprotection against CPV-2, CDV and CAdV-1 in a cohort of Italian dogs by using the in-practice test VacciCheck. A total of 1,027 dogs (951 vaccinated and 76 unvaccinated) were analyzed for Protective Antibody Titers (PATs) against CPV-2, CDV, and CAdV-1. Differences related to sex, age, breed size, health status, and time elapsed since last vaccination were evaluated. Half of the entire canine cohort (50.6%) had PATs for all three viruses (68.5% considering only vaccinated dogs). In particular, 90.8% of dogs were protected against CPV-2, 68.6% against CDV, and 79.8% against CAdV-1. Most dogs remained protected for 3 years after vaccination or longer. Revaccination on a 3-year basis can then be recommended for core MLV vaccines without altering individual's seroprotection or even herd immunity.