Some physical and growth characteristics of a canine adenovirus isolated from dogs with laryngotracheitis

A survey of diseases of working farm dogs in New Zealand

AIMS

To record the incidence of specific diseases affecting working farm dogs; identify any apparent breed predispositions; determine the most important causes of loss from death, euthanasia, or retirement of the dog; and identify potential interventions that could reduce the incidence of disease.

METHODS

A national questionnaire-based cross-sectional study was conducted to identify the incidence of specific diseases, and circumstances of trauma affecting working farm dogs that presented to rural veterinary practices over a 12-month period, between April 2008 and April 2009. The practices were convenience-sampled on the basis of geography and size.

RESULTS

Sixty-six practices were approached, and veterinarians from 30 practices agreed to participate, with representation from all major rural regions of New Zealand. Data were provided on 2,214 presentations, excluding revisits, of which 51% were for Huntaways and 39% Heading dogs. Trauma was identified as a cause of injury in 848 (38%) visits. Huntaways were apparently over-represented in cases of constipation, gastric dilatation-volvulus (GDV), theriogenological problems, laryngitis, hip dysplasia, and degenerative lumbosacral disease. In contrast, Heading dogs were over-represented among cases of multiple ligamentous injury of the stifle, disruption of the gastrocnemius or Achilles tendon, tarsal injuries, and hip luxation. Traumatic injury involved injury by stock (20%), automotive incidents (19%), transit across fence lines (16%), and dog bites (12%). Loss occurred following 10% of visits, of which trauma was known to be involved in 32%. The most important non-traumatic causes of loss were GDV, degenerative joint disease, mammary neoplasia and diseases involving the female reproductive tract, cardiac disease, and poisoning.

CLINICAL RELEVANCE

Several important diseases appear amenable to intervention through nutrition, neutering, or behavioural modification, including constipation, GDV, theriogenological problems, dog-bite injuries, and laryngitis. Altering modes of transit across fence lines has the potential to reduce large numbers of serious orthopaedic injuries to working farm dogs.

Generation of E3-deleted canine adenovirus type 2 expressing the Gc glycoprotein of Seoul virus by gene insertion or deletion of related terminal region sequences

Seoul virus (SEOV) is one of the four hantaviruses known to cause haemorrhagic fever with renal syndrome. The medium genome segment encodes the Gn/Gc glycoproteins of SEOV, which form the major structural part of the virus envelope. Gc and/or Gn are the candidate antigens of hantavirus for induction of a highly immunogenic response for hantavirus vaccine. In this study, the immune response induced by a replication-competent recombinant canine adenovirus type 2 expressing the Gc protein of SEOV was evaluated in BALB/c mice. Sera from immunized mice contained neutralizing antibodies that could specifically recognize SEOV and neutralize its infectivity in vitro. Moreover, the recombinant virus induced complete protection against an intensive infectious challenge with approximately 1000 50 % infective doses for SEOV strain CC-2. Protective-level neutralizing antibodies were maintained for at least 20 weeks. This recombinant virus is therefore a potential alternative to the inactivated vaccine.

Oral vaccination of dogs (Canis familiaris) with baits containing the recombinant rabies-canine adenovirus type-2 vaccine confers long-lasting immunity against rabies

Rabies is a reemerging and fatal infectious disease in Asia mainly caused by exposure to rabid dogs. Prevention of dog rabies would be the most effective way to stop rabies transmission to humans. However, vaccinating stray dogs in urban and rural areas using conventional vaccines is always difficult and is not cost-effective for use in most areas including China. Further to previous studies from our laboratory, we developed a bait containing the recombinant rabies vaccine and performed a non-parenteral trial in dogs. This vaccine was intranasally administrated once to 46 dogs in solution form with 1 x 10(8.5) PFU and orally to 90 dogs in specially designed baits with 3 x 10(8.5) PFU of the recombinant canine adenovirus. Results showed that about 87.5% (119/136) of the immunized dogs developed virus neutralizing antibodies (VNA). The immune response against rabies in dogs was detectable at 2-3 weeks after administration, reaching a peak by 5-6 weeks. Among the seroconverted animals, 90.8% (108/119) elicited a VNA response for over 24 months. The antibody titer during the 2 years was above 0.5IU /ml while showing a gradual but slow decline from the 6th week after vaccination. In a challenge experiment of 10 dogs with 60,000 mouse LD(50) of CVS-24 2 years after the vaccination, all the dogs survived. This demonstrated that the recombinant vaccine could be orally administrated and the bait was effective for the oral vaccination of dogs.

Canine respiratory viruses

Acute contagious respiratory disease (kennel cough) is commonly described in dogs worldwide. The disease appears to be multifactorial and a number of viral and bacterial pathogens have been reported as potential aetiological agents, including canine parainfluenza virus, canine adenovirus and Bordetella bronchiseptica, as well as mycoplasmas, Streptococcus equi subsp. zooepidemicus, canine herpesvirus and reovirus-1,-2 and -3. Enhancement of pathogenicity by multiple infections can result in more severe clinical forms. In addition, acute respiratory diseases associated with infection by influenza A virus, and group I and II coronaviruses, have been described recently in dogs. Host species shifts and tropism changes are likely responsible for the onset of these new pathogens. The importance of the viral agents in the kennel cough complex is discussed.

Macromolecular content of inclusions produced by a canine adenovirus

Early inclusions induced by a canine adenovirus in a canine cell line, appearing before the formation of infectious virus particles, were purified by differential centrifugation in sucrose followed by CsCl density gradient centrifugation. Chemical analysis of these inclusions revealed that they contained deoxyribonucleic acid (DNA), ribonucleic acid, and protein. On the basis of density gradient centrifugation, the DNA extracted from the inclusions was found to be viral DNA. Electron microscope autoradiography showed that these inclusions were the sites of DNA synthesis. In addition, association of DNA polymerase activity with the inclusions was detected by incorporation of radioactivity from (3)H-thymidine triphosphate into a DNA product. The in vitro product of the enzyme had a density equal to that of viral DNA rather than host DNA. The level of DNA polymerase activity in exponentially growing infected and uninfected whole cells was similar, but in cells in stationary phase the enzyme activity of infected cells was twice that in noninfected cells. Furthermore, nuclei isolated from infected cells showed a fourfold increase in DNA polymerase activity over the noninfected cells.

Biophysical comparison of two canine adenoviruses

The two canine adenoviruses, infectious canine hepatitis (ICH) virus and infectious canine laryngotracheitis (ICL) virus (also designated as Toronto A26/61 virus), were studied with respect to their morphology and the biological properties of their soluble components. The two viruses were found to be composed of soluble components similar to, and carrying biological activities corresponding to, those of the human adenoviruses after fractionation by rate zonal centrifugation and anion-exchange chromatography. The following soluble components were identified: hexons (carrying a common group-specific complement-fixing antigen), penton oligomers (complete soluble hemagglutinin), and penton and fiber monomers (incomplete soluble hemagglutinins). The latter were indicated by hemagglutination enhancement with selected antisera directed against human adenovirus soluble components. Elution characteristics of corresponding components of the two viruses in anion-exchange chromatography experiments were distinctly different. Electron microscopic examination of purified virions and soluble components revealed the fiber component of ICL virus to be 35 to 37 nm in length, and that of ICH virus to be 25 to 27 nm long.

T antigens of bovine and canine adenoviruses demonstrated by immunofluorescence

The intracellular development in acutely infected cells of bovine and canine adenovirus T antigens was followed by immunofluorescent staining. With both species of adenovirus, antigen was first detected as intranuclear pin-points at 18 hr postinfection and coalescence into large lobular masses was noticed by 24 hr. Cross-reactions between bovine 1 (nononcogenic) and bovine 3 (oncogenic) T antigens were not observed by the direct technique although the more sensitive indirect procedure did reveal cross-reactivity. Extensive cross-reactions were observed between the T antigens of the oncogenic canine hepatitis virus and the "nononcogenic" Toronto strain of canine adenovirus. The magnitude of these reactions places the two canine strains in the same T antigen subgroup. The canine and bovine T antigens were not stained by tumor antisera against any of the known human or simian T antigen subgroups. Antigen synthesis was not prevented by inhibitors of deoxyribonucleic acid synthesis although the appearance was altered markedly.