Urban domestic dog populations as a source of canine distemper virus for wild carnivores in the Coquimbo region of Chile.

Urban areas can support dog populations dense enough to maintain canine distemper virus (CDV) and can be a source of infection for rural dogs and free-ranging carnivores. The aim of this study was to investigate the relationships between urban and rural domestic dog and wild carnivore populations and their effects on the epidemiology of CDV to explain retrospectively a CD outbreak in wild foxes in 2003. From 2005 to 2007 a cross-sectional household questionnaire survey was conducted in Coquimbo and Ovalle cities, in three towns and in rural sites along two transects from these cities to the Fray Jorge National Park (FJNP) in the Coquimbo region, Chile. Blood samples were collected from unvaccinated dogs at surveyed households and from free-ranging foxes in rural areas along the transects. The seroprevalence of CDV in domestic dogs was higher in urban than in rural areas and in the later was highest in dogs born before 2001-2002. The seroprevalence of CDV in foxes was higher in areas closer to human settlements. A high seroprevalence in dogs born before 2001-2002 further supports a link between CDV patterns in rural dog and fox populations. In our study area, urban dogs are proposed to be the source of CDV infection to wild carnivores. The large dog population size and density detected in Coquimbo and Ovalle provides optimal conditions for maintaining a large and dense susceptible population of dogs, which can act as a reservoir for highly infectious diseases and could have been the source of infection in the CD outbreak in wild foxes.

Canine parvovirus type 2 vaccine protects against virulent challenge with type 2c virus.

The ability of dogs vaccinated with a live attenuated CPV type 2 (Nobivac Intervet) vaccine to resist challenge with a current CPV2c isolate was investigated. Six SPF beagle dogs were given the minimum recommended course of vaccination, comprising a single inoculation of vaccine (Nobivac Lepto+Nobivac Pi) at 8-10 weeks of age followed 3 weeks later with a parvovirus vaccine in combination with distemper, adenovirus and parainfluenza virus (Nobivac DHPPi) and a repeat leptospirosis vaccine. Six control dogs were kept unvaccinated. All animals were challenged orally with a type 2c isolate of CPV and monitored for clinical signs, virus shedding, white blood cell fluctuations and serological responses. All vaccinated dogs were fully protected; showing no clinical signs nor shedding challenge virus in the faeces, in contrast to control animals, which displayed all the typical signs of infection with pathogenic CPV and shed challenge virus in the faeces.

Greyhound meningoencephalitis: PCR-based detection methods highlight an absence of the most likely primary inducing agents.

Greyhound meningoencephalitis is currently classified as a breed-associated idiopathic central nervous system inflammatory disorder. The non-suppurative inflammatory response can be distinguished from the other breed-associated disorders based on histopathology and lesion topography, however the nature of the response primarily suggests a viral infection. In the present study PCR and RT-PCR technologies were employed on frozen cerebral tissue from confirmed cases of meningoencephalitis to target specific viruses and protozoa likely to be implicated and to exclude the presence of bacterial 16SrRNA. Secondly, degenerate primers were used to detect viruses of the herpesvirus and flavivirus families. In addition cerebral tissues were probed for West Nile Virus. Viral nucleic acid sequences to Borna disease virus, to louping ill, tick borne encephalitis, West Nile and other flaviviruses were not detected. Canine distemper virus was detected in one animal with 97% homology to strain A75/15. Degenerate PCR for herpesviruses detected viral amplification products in one animal with 90% homology to canine herpesvirus DNA polymerase gene. Protozoal amplification products were only detected in a single dog with pathological confirmation of a combination of lesions of greyhound meningoencephalitis and a protozoal encephalomyelitis. Neospora was confirmed with sequence homology to Austrian strain 1. Bacterial 16SrRNA was not detected. The present study supports previous observations that many of the known microbial causes of canine meningoencephalitis are not involved. Findings could reflect that the causal agent was not specifically targeted for detection, or that the agent is at undetectable levels or has been eliminated from brain tissue. The potential roles of genetics and of molecular mimicry also cannot be discounted.

Overview of new vaccines and technologies.

Molecular technology has given us a greater insight into the aetiology of disease, the functioning of the immune system and the mode of action of veterinary pathogens. The knowledge gained has been used to develop new vaccines with specific, reactive antigens which elicit protective immune mediated responses (humoral and/or cell mediated) in the host. These vaccines should not burden the immune system by initiating responses against non-essential antigens. However, the efficacy of these vaccines is only as good as the delivery technology or route used to present them to the immune system. Some vaccines, traditionally given by the parenteral route, are now given by the natural route; either orally or intranasally. Two major advantages, often interrelated, are the rapid onset of immunity and stimulation of the local, mucosal immunity. These new technologies are now making an impact on current vaccine development. The balance has to be found between what is technologically feasible and what will provide at least as good a protective immunity as current, conventional vaccines. As new and emerging diseases appear globally, new opportunities arise for molecular and conventional technologies to be applied to both the development and delivery of novel vaccines, as well as the improvement of vaccines in current use.

A field trial to assess the effect of vaccination against feline herpesvirus, feline calicivirus and feline panleucopenia virus in 6-week-old kittens.

A trivalent (feline panleucopenia, feline herpesvirus, feline calicivirus), modified live, commercially available cat vaccine was used at either 6, 9 and 12 weeks of age (early schedule) or 9 and 12 weeks of age (conventional schedule), and the serological response to vaccination was assessed. The level of maternally derived antibody present at 6 weeks of age was also established. The use of early vaccination at 6 weeks of age induced an antibody response to each virus by 9 weeks of age in a significant proportion of kittens compared with unvaccinated littermates. There was no difference between the conventionally and early-vaccinated groups in terms of antibody response to any antigen by 12 and 15 weeks of age.

Contact rates between wild and domestic canids: no evidence of parvovirus or canine distemper virus in crab-eating foxes.

Evaluating the risk of disease spill-over from domestic dogs to wildlife depends on knowledge of inter-specific contact rates and/or exposure to aetiological agents in dog environments. Here, contact rates of crab-eating foxes (Cerdocyon thous) with sympatric domestic dog populations were measured over 25months in Amazon Brazil. Foxes and dogs were serologically and clinically monitored for exposure to canine parvovirus (CPV-2) and canine distemper virus (CDV), pathogens known to have caused wildlife population declines elsewhere. Twenty-two of 24 (92%) tagged foxes visited one or more houses in a median 2 (range 1-3) villages per night where dog densities ranged from 7.2 to 15.4 per km(2) (mean 9.5 per km(2)). Foxes spent an average 6.4% (0-40.3%) of their 10h nocturnal activity period in villages, the equivalent of 38m (range 0-242) per night. The rate of potential exposure to disease agents was thus high, though varied by 3 orders of magnitude for individual foxes. Overall, 46% of the fox population was responsible for 80% of all contacts. None of the 37 monitored foxes however showed serological or clinical evidence of infection with CPV-2 or CDV. Seroprevalences for CPV-2 and CDV antibodies in the local domestic dog population were 13% (3/23) and 9% (2/23), respectively, and 89% of 97 monitored pups born during the study presented clinical signs consistent with active CPV-2 infection (haemorrhagic diarrhoea, vomiting, rapid morbidity and emaciation). Although there was no evidence for infection with either virus in foxes, the high level of contact of foxes with peridomestic habitats suggests that the probability of potential spill-over infections from dogs to foxes is high.

Serological and demographic evidence for domestic dogs as a source of canine distemper virus infection for Serengeti wildlife.

Following an epidemic of canine distemper virus (CDV) in Serengeti lions in 1994, the role of domestic dogs in the epidemiology of the disease was investigated by serological and demographic analyses. From 1992 to 1994, data were collected from two domestic dog populations bordering the Serengeti National Park. Several lines of evidence indicated that patterns of CDV infection differed significantly between higher-density dog populations of Serengeti District to the west of the park and lower-density populations of Ngorongoro District to the south-east: (a) CDV age-seroprevalence patterns differed significantly between years in Ngorongoro District populations but not in Serengeti District populations; (b) CDV seropositive pups (<12 months of age) were detected in Ngorongoro District only in 1994, whereas a proportion of pups in Serengeti District were seropositive in each year of the study; (c) in Ngorongoro District, the proportion of deaths attributed to disease was significantly higher in 1994 than in 1993, whereas in Serengeti District, there was no significant difference in disease-related mortality between years; (d) in Ngorongoro District, significantly more CDV seronegative dogs than seropositive dogs died in 1994, whereas there was no difference in survival of CDV seropositives and seronegatives between years in Serengeti District. We concluded that, between 1992 and 1994, CDV persisted in higher-density dog populations of Serengeti District, but occurred only sporadically in lower-density Ngorongoro District populations. Data from Ngorongoro District are consistent with exposure of dogs to CDV in 1991 and 1994, but not in 1992 and 1993. These findings suggest that higher-density domestic dog populations to the west of the Serengeti National Park were a more likely source of CDV infection for wildlife during 1994 than lower-density pastoralist dogs to the south and east of the park.

Efficacy of feline panleucopenia vaccine to prevent infection with an isolate of CPV2b obtained from a cat.

Cats vaccinated against FPLV were protected against infection with a feline isolate of CPV2b. Nonvaccinated cats developed a lymphopenia and excreted virus which infected susceptible in-contact cats.

Canine distemper antibodies in lions of the Masai Mara.

Canine distemper virus (CDV) has been implicated in some recent deaths of lions, which showed clinical signs of distemper, in the the Serengeti plain. Similar clinical findings have since been reported in lions of the Masai Mara. Fifty-five per cent of serum samples obtained from wild lions of the Masai Mara have been found to contain neutralising antibody to CDV, indicating that they had been exposed to the virus. Adult orphan lions kept in captivity, were vaccinated with the live attenuated Onderstepoort strain of CDV. The results indicated that the vaccine is both safe and immunogenic, and may be potentially useful for the prophylactic vaccination of lions at high risk.

Use of a live chlamydial vaccine to prevent ovine enzootic abortion.

A lyophilised chlamydial vaccine was prepared from the 1B temperature-sensitive strain of ovine Chlamydia psittaci. Ewes inoculated with a low titre of the live vaccine four weeks before artificial insemination were challenged on day 70 of gestation with five UK field isolates of C psittaci, including strains A22 and S26/3 previously incorporated into a commercial inactivated vaccine. There was a significantly lower chlamydial abortion rate after challenge in the vaccinated group (7.1 per cent) than in the unvaccinated group (80 per cent). All the lambs born to the vaccinated ewes were viable and of good quality. The vaccine also reduced the number of infected ewes in the group and the severity of the infection. The compatibility of the chlamydial vaccine and a toxoplasma vaccine was also tested. The abortion rate of ewes vaccinated with the two vaccines at separate injection sites (16 per cent) was less than that of ewes vaccinated with both vaccines at one site (32 per cent).

Vaccination against feline leukaemia using a new feline herpesvirus type 1 vector.

A recombinant feline herpesvirus type 1 (FHV-1) was constructed expressing the envelope glycoprotein gene from feline leukaemia virus (FeLV). The expression cassette containing the long terminal repeat promoter from Rous sarcoma virus was stably integrated at the locus downstream of the gC homologue in FHV-1. Oronasal vaccination with recombinant FHV-1 engendered significant protection against challenge with the homologous FelV-A/Glasgow-1 isolate. Three of four vaccinated cats did not become viraemic for FeLV and developed serum neutralizing antibodies while five of six controls became persistently infected after challenge. However, latent FeLV was detected at 12 weeks after challenge in bone marrow cultures of all animals except one. The potential of this new vector to protect against FeLV was compared with previous reports using live recombinant vaccines.

In vivo properties of a feline herpesvirus type 1 mutant carrying a lacZ insertion at the gI locus of the unique short segment.

The major cause of upper respiratory tract disease in cats in the feline herpesvirus type 1 (FHV-1). FHV-1 replicates predominantly in the mucosal epithelium of the oral and nasal cavities, local immunity should therefore be the key target for vaccine development. Recombinant DNA technology enables accurate manipulation of the genetic content of the FHV-1 genome, hopefully resulting in a next generation of safe vaccine strains that can be used intranasally in cats. Integration of a reporter gene into the glycoprotein I (gI) homologous gene of FHV-1, resulted in strain C4-1-4-1 which displayed reduced replication not only in cell culture but also in the respiratory tract of infected cats. Oronasal application of strain C4-1-4-1 caused less severe clinical signs than local administration of the parent virus. In addition, oronasally vaccinated cats were better protected against the clinical signs of a challenge infection than cats vaccinated subcutaneously.

Comparison of isolates of canine parvovirus by restriction enzyme analysis, and vaccine efficacy against field strains.

Canine parvovirus isolates from clinical cases of enteritis were obtained from the United Kingdom, Germany and the USA and differentiated by restriction enzyme analysis into three groups, namely CPV2, CPV2a and CPV2b. The three groups were readily identified by their HphI restriction profile. CPV2 was not prevalent in cases of canine parvovirus disease after 1986. Only two CPV2 strains (original type) were found among 110 strains isolated after 1980. In Europe the frequency of isolation of the CPV2a and CPV2b field strains was similar whereas in the USA the CPV2b strain predominated. Dogs inoculated with a vaccine strain were resistant to infection after challenge with UK isolates of CPV2a and CPV2b.

The gene downstream of the gC homologue in feline herpes virus type 1 is involved in the expression of virulence.

Feline herpesvirus type 1 (FHV-1) mutants were constructed, carrying a beta-galactosidase marker gene integrated into the region downstream of the gene encoding the homologue of glycoprotein C (gC) of herpes simplex virus type 1. In cell culture, no differences in replication were observed between mutants and the parent FHV-1 strain. However, in experimentally infected cats, mutants caused fewer clinical signs after oronasal administration although they replicated to the same extent as the parental strain. Sequence analysis in the region of the UL segment surrounding the insertion site revealed an open reading frame (ORF 2) encoding a putative polypeptide of 21K. RNA analysis indicated a corresponding transcript of 0.8 kb that was detected late after infection of cells in culture. This particular UL locus downstream of the gC gene has not been thoroughly investigated in any of the herpesviruses. The putative gene product showed only limited evolutionary conservation since similarity could be found only with the assumed homologue of equine herpesvirus type 1. Further characterization of this newly identified FHV-1 gene involved in virulence may provide insight into the development of disease owing to herpesvirus infection.

A comparison of canine distemper vaccine and measles vaccine for the prevention of canine distemper in young puppies.

Two groups of six-week-old beagle puppies were vaccinated with either high titre canine distemper virus or human measles virus, a third group remaining unvaccinated. All the puppies were subsequently challenged by the nasopharyngeal route at 10 weeks old with the virulent Snyder-Hill strain of canine distemper. Severe clinical signs were observed in 90 per cent of the unvaccinated dogs but both groups of vaccinated dogs survived the challenge. High temperatures were recorded in 20 per cent of the measles vaccinates and abdominal petechial rashes were observed in 60 per cent of them. The only clinical signs observed in the puppies vaccinated with distemper virus were transient rashes in 20 per cent of the group. The high titre canine distemper vaccine stimulated a humoral response quickly in 78 per cent of the puppies in the presence of maternally derived antibody and protected them against challenge with the virulent Snyder-Hill strain of distemper virus. The remaining dogs responded sluggishly but were still protected against challenge. The results of field surveys showed that 95 per cent of young puppies with different levels of maternally derived antibodies responded to the distemper component in a vaccine also containing canine parvovirus. No incompatibility was observed between the two components.

Feline bordetellosis: challenge and vaccine studies.

Four eight-week-old cats, shown to be free from feline calicivirus, feline herpesvirus and Chlamydia psittaci were challenged with an aerosol of Bordetella bronchiseptica. Within five days the cats developed signs of respiratory disease, characterised by nasal discharge, sneezing, spontaneous or induced coughing and dry or wet rales at auscultation. These signs were present for about 10 days, after which they began to resolve. To test the protective capacity of an experimental fimbrial antigen-based subunit vaccine, 10 kittens were vaccinated twice, with two weeks between the vaccinations, and five kittens were left unvaccinated. Two weeks after the booster the 15 kittens were challenged with an aerosol of B bronchiseptica as the sole pathogen. On the day of challenge the vaccinated kittens had a mean bordetella antibody titre of 2(9.5) whereas the control cats remained seronegative (titre < 2(2)). The control cats developed signs of respiratory disease after challenge, whereas the vaccinated cats were almost completely protected. The degrees of protection against rhinitis, sneezing, spontaneous or induced coughing, and dry or wet rales at auscultation were 100 per cent, 95 per cent, 95 per cent and 100 per cent, respectively. Furthermore, the vaccinated kittens cleared the challenge bacteria more quickly than the controls, resulting in a reduction of 80 per cent on days 15 and 18 after challenge and a reduction of 99 per cent on days 22 and 29 after challenge. The results show that B bronchiseptica can act as a primary pathogen in cats and that a vaccine containing the fimbrial antigen induces a protective immune response.

Detection of Chlamydia psittaci from various animal species by reverse passive haemagglutination.

A reverse passive haemagglutination test (RPH) has previously been developed to detect the genus-specific antigen of Chlamydia. Clinical samples were obtained from various sites of different animal species. The RPH test detected chlamydial antigen from clinical cases of conjunctivitis in cats, abortion in sheep and psittacosis in birds. Although not as sensitive as cell culture isolation, this test has the advantages of rapidity and of detecting antigen from dead chlamydiae.