Nosocomial outbreak of serious canine infectious tracheobronchitis (kennel cough) caused by canine herpesvirus infection.

Canine herpesvirus (CHV; Canid herpesvirus 1) is principally a perinatal pathogen of pregnant bitches and newborn pups and secondarily a respiratory tract pathogen of older pups and dogs. Infectious disease of the canine respiratory tract frequently occurs among dogs in groups, in which it is called " infectious tracheobronchitis" (ITB). Mortality from ITB is generally negligible, and the clinical importance of CHV as an ITB pathogen is considered to be low. The present report describes a novel ITB outbreak accompanied by death among aged dogs in an animal medical center. Most inpatient dogs had received medications that could induce immunosuppression. CHV was the only pathogen identified, and several CHV isolates were recovered in cell culture. No other viral pathogens or significant bacterial pathogens were found. Molecular and serological analyses revealed that the causative CHV isolates were from a single source but that none was a peculiar strain when the strains were compared with previous CHV strains. The virus had presumably spread among the dogs predisposed to infection in the center. The present results serve as a warning to canine clinics that, under the specific set of circumstances described, such serious CHV outbreaks may be expected wherever canine ITB occurs.

Evidence for recombination between feline panleukopenia virus and canine parvovirus type 2.

Canine parvovirus type 2 (CPV) is a virulent pathogen that emerged in the late 1970s, probably originating from feline panleukopenia virus (FPLV) or a closely related carnivore parvovirus belonging to the feline parvovirus (FPV) subspecies. In contrast to FPLV, CPV has evolved rapidly since its emergence. The original antigenic type of CPV disappeared more than two decades ago and several new antigenic as well as genetic CPV variants have appeared and spread in the field. Both high mutation rate and positive selection of mutations in the capsid gene appear to be the driving force for such rapid evolution. In addition, genetic recombination has been assessed as a factor in parvovirus evolution. Recently, we provided the first evidence of inter-antigenic type recombination of CPV in nature. Here, an inter-FPV subspecies recombinant was revealed by analyzing the genetic data deposited in databases with several recombination detection programs, and by phylogeny. FPLV strain XJ-1, submitted by Su et al., Harbin, China in 2007 (GenBank accession no. EF988660), was most likely generated by recombination between CPV and FPLV. Its genome was generally composed of the NS1 gene of CPV origin and the VP1 gene of FPLV origin. This is the first demonstration of recombination between different FPV subspecies in nature. Consequently, recombination should be considered as an element in the generation and evolution of parvoviruses of the FPV subspecies.

Chronological analysis of canine parvovirus type 2 isolates in Japan.

Fifty-five canine parvovirus type 2 (CPV) samples, 12 fecal specimens and 43 cell culture isolates, were examined for their genetic characteristics of VP2 gene. They were collected from the diseased dogs at various districts of Japan during 27 years from 1980 to 2006. A fragment of VP2 gene was analyzed by restriction fragment length polymorphism assay and DNA sequencing. The original antigenic type 2 of CPV (CPV-2) was no longer found in the samples since 1984, and two antigenic variants CPV-2a and CPV-2b replaced CPV-2 as predominant types for about 5 years from 1982. A new genetic variant of prototype CPV-2a with non-synonymous substitution at the VP2 amino acid residue 297 from Ser to Ala was first detected in 1987. New CPV-2b with the same amino acid substitution at position 297 as new CPV-2a was also detected from the samples collected in 1997. Since then new CPV-2b has been the predominant CPV over the field of Japan. Several additional amino acid substitutions were detected in the VP2 gene of some recent CPV strains. Neither CPV-2c(a), CPV-2c(b), nor "Glu-426" of the antigenic variants previously found outside the country was detected in any samples tested. Reactivity of new CPV-2a and 2b variants against antibodies produced by the current vaccine products was determined by a cross hemagglutination-inhibition test. The recent field CPV isolates reacted more efficiently to the antibodies produced in dogs vaccinated with the new CPV-2b vaccine strain than the conventional CPV-2 vaccine strain.

Etiologic study of upper respiratory infections of household dogs.

Infectious tracheobronchitis (ITB), also known as the kennel cough, is a respiratory syndrome of dogs and usually appears to be contagious among dogs housed in groups. Etiologic agent of ITB is multiple and sometimes complex. In the present study, 68 household dogs showing clinical signs of respiratory infection were examined, and 20 dogs (29.4%) were found to be positive for either of following agents. Bordetella bronchiseptica (B.b.) was most frequently detected from nasal and oropharynx sites of 7 dogs (10.3%). Among the viruses examined, canine parainfluenza virus (CPIV) was detected with the highest frequency (7.4%). Other pathogens included in the order of frequency group 1 canine coronavirus (4.4%), canine adenovirus type 2 (2.9%), group 2 canine respiratory coronavirus (1.5%), and canine distemper virus (1.5%). Only 2 cases showed mixed infections. Neither influenza A virus nor canine bocavirus (minute virus of canines) was found in any dogs examined. These results indicate that both B.b. and CPIV are likely to be the principal etiologic agents of canine ITB in Japan, and they may be considered as the target for prophylaxis by vaccination.

Recombination between vaccine and field strains of canine parvovirus is revealed by isolation of virus in canine and feline cell cultures.

Canine parvovirus type 2 (CPV) is a pathogen that causes severe hemorrhagic gastroenteritis with a high fatality rate in pups worldwide. Since CPV emerged in the late 1970s, its origin has been explored with the conclusion that CPV originated from feline panleukopenia virus or a closely related virus. Both high mutation rate and recombination are assumed to be key factors in the evolution of parvoviruses. Here we provide evidence for natural recombination in CPV isolated from dogs in cell culture. Antigenic and genetic properties of isolates from 10 diseased pups were elucidated. Six pups had been vaccinated beforehand with live combined vaccine containing original antigenic type CPV (CPV-2). Six isolates recovered from 4 vaccinated pups in cell cultures were found to contain either CPV-2 or CPV-2-like viruses. The other isolates, including all those from non-vaccinated pups, were CPV-2b viruses. Antigenic typing of two CPV-2-like isolates, 03-029/M and 1887/f, with a monoclonal antibody panel suggested they were a mixture of CPV-2 and CPV-2a (03-029/M) and a recombinant of CPV-2 and CPV-2b (1887/f). Genetic analysis of the VP1 gene indicated that isolate 03-029/M was a mixture of CPV-2, CPV-2a and a recombinant of CPV-2 and CPV-2a viruses, while isolate 1887/f was composed of a recombinant of CPV-2 and CPV-2b viruses. This is the first demonstration of natural CPV recombination in the field and suggests that recombination in the evolution of CPV is a more frequent and important process than previously believed.

Sequence analysis of an Asian isolate of minute virus of canines (canine parvovirus type 1).

Minute virus of canines (MVC), also known as canine parvovirus (CPV) type 1, is an autonomous parvovirus that infects domestic dogs worldwide and responsible for clinical problems of neonates and pregnant bitches. It was preliminary described that MVC is antigenically as well as genetically different from CPV type 2 that emerged later. However, much of MVC is still obscure since only a limited number of MVC isolates have been available for the study. MVC infections of Japanese and Korean dogs were epidemiologically studied in the previous study, and several MVC isolates could be cultivated in vitro. In the present study an almost full-length nucleotide sequence of a Korean MVC strain HM-6 genome was obtained and comparatively analyzed with those of the American MVC strain GA3 characterized recently. Genome structure of the HM-6 strain was similar to the GA3 strain showing 96.4% identity at the nucleotide sequence. Each of the deduced amino acid sequences of NS1, NP-1, and VP1/2 showed homology of 96.5%, 92.5%, and 97.5% between the HM-6 and GA3 strains. When compared with other parvovirus species, the HM-6 strain was most closely related to bovine parvovirus (BPV) as described for the GA3 strain. These results suggest that MVC together with BPV can possibly be classified into a new clade in the Parvovirinae subfamily.

Virologic and serologic identification of minute virus of canines (canine parvovirus type 1) from dogs in Japan.

Minute virus of canines (MVC), also known as canine parvovirus type 1, was initially believed to be a nonpathogenic agent, since it was first isolated from canine fecal specimens in the late 1960s. However, subsequent pathological as well as epidemiological studies suggested that MVC is a pathogen of neonatal puppies and is widely distributed among domestic dogs in the United States. The virus also has been shown to cause fetal deaths. Nevertheless, the virus was not detected in dogs outside the United States until recently, presumably because of a lack of widespread availability of the only susceptible canine cell line, WRCC/3873D, used for MVC isolation. We examined 470 clinical specimens from 346 dogs by PCR and detected MVC-specific gene fragments from four diseased puppies (positive rate, 1.2%). Viruses were recovered from three PCR-positive rectal specimens by using WRCC/3873D and MDCK cells. The isolates possessed antigenic and genomic properties similar to those of the U.S. reference strain GA3 and were identified as MVC. In addition, seroepidemiological evidence that 5.0% of dogs possessed anti-MVC antibodies also indicated the presence of MVC infection among dogs in Japan. From this study and several recent European reports describing MVC field cases, it is evident that MVC is distributed among domestic dogs worldwide.