Protection against feline leukemia virus challenge for at least 2 years after vaccination with an inactivated feline leukemia virus vaccine.

Twelve cats were vaccinated at 8 and 11 weeks of age with a commercially available inactivated FeLV vaccine (Nobivac FeLV, Intervet/Schering-Plough Animal Health). Eleven cats served as age-matched, placebo-vaccinated controls. All cats were kept in isolation for 2 years after vaccination and were then challenged with virulent FeLV to evaluate vaccine efficacy and duration of immunity. Cats were monitored for 12 weeks after challenge for development of persistent viremia using a commercial FeLV p27 ELISA. Persistent viremia developed in all 11 (100%) of the control cats, whereas 10 of 12 (83%) vaccinated cats were fully protected from persistent viremia following challenge. The results demonstrate that the vaccine used in this study protects cats from persistent FeLV viremia for at least 2 years after vaccination.

Transmission of canine influenza virus (H3N8) among susceptible dogs.

Canine influenza virus (CIV) is an emerging pathogen that causes acute respiratory disease in dogs. As with any communicable disease, dog-to-dog transmission of CIV occurs when infected dogs come in contact with other susceptible dogs. We demonstrate that CIV transmission occurs readily from CIV-infected dogs to susceptible dogs following co-mingling. Four experimentally infected dogs were co-mingled with a group of eight CIV-negative dogs at 1 day post-infection and both groups were observed for CIV-associated respiratory disease. The onset of clinical signs, virus shedding, seroconversion, and appearance of lung lesions were observed earlier in experimentally infected dogs; however, the severity of the clinical signs and lung lesions were very similar in both groups. One hundred percent of the experimentally infected dogs and 75% of the contact-exposed dogs excreted virus in their nasal secretions. Additionally, 100% of experimentally infected dogs and 75% of the contact-exposed dogs exhibited varying degrees of pneumonia. Our study results demonstrate that CIV spreads readily from infected dogs to other susceptible dogs through direct contact.

Evaluation of the efficacy of a canine influenza virus (H3N8) vaccine in dogs following experimental challenge.

Canine influenza virus (CIV) subtype H3N8 is an emerging pathogen with sustained horizontal transmission in the dog population in the United States. This study evaluated the efficacy of an inactivated CIV vaccine in 6- to 8-week-old beagle pups challenged with virulent CIV. One group of CIV-seronegative pups was vaccinated with two doses of a CIV vaccine 3 weeks apart; a second group of pups received adjuvanted placebo as a control. Blood samples were collected at various times to determine antibody titers. All pups were challenged with a virulent CIV isolate 13 days after the second vaccination and monitored for clinical signs of respiratory disease, virus shedding, and lung consolidation. Vaccinated pups developed hemagglutination inhibition antibody titers after vaccination. The severity of clinical signs (P < .001) and the magnitude and duration of virus shedding (P < .0001) were significantly lower in vaccinated pups compared with control pups. These results demonstrate that the CIV vaccine used in this study provides protection against virulent CIV challenge in dogs.

Three-year duration of immunity in cats following vaccination against feline rhinotracheitis virus, feline calicivirus, and feline panleukopenia virus.

Forty-two seronegative cats received an initial vaccination at 8 weeks of age and a booster vaccination at 12 weeks. All cats were kept in strict isolation for 3 years after the second vaccination and then were challenged with feline calicivirus (FCV) or sequentially challenged with feline rhinotracheitis virus (FRV) followed by feline panleukopenia virus (FPV). For each viral challenge, a separate group of 10 age-matched, nonvaccinated control cats was also challenged. Vaccinated cats showed a statistically significant reduction in virulent FRV-associated clinical signs (P = .015), 100% protection against oral ulcerations associated with FCV infection (P < .001), and 100% protection against disease associated with virulent FPV challenge (P < .005). These results demonstrated that the vaccine provided protection against virulent FRV, FCV, and FPV challenge in cats 8 weeks of age or older for a minimum of 3 years following second vaccination.

Effects of bacterial coinfection on the pathogenesis of avian pneumovirus infection in turkeys.

Four- and nine-week-old poults were inoculated with cell culture propagated avian pneumovirus (APV) into each conjunctival space and nostril, followed by inoculation 3 days later with Escherichia coli, Bordetella avium (BA), or Ornithobacterium rhinotracheale or a mixture of all three (EBO). Clinical signs were evaluated on days 3, 5, 7, 9, 11, and 14 postinoculation (PI) of APV. The poults were euthanatized on days 2, 4, 6, 10, and 14 PI, and blood and tissues were collected. The poults that received APV followed by EBO or BA alone developed more severe clinical signs related to nasal discharge and swelling of intraorbital sinuses than did poults inoculated with APV alone or bacteria alone. More severe pathologic changes were found in poults inoculated with APV+BA that extended to the air sacs and lungs, particularly in 9-wk-old poults. Bordetella avium was recovered from tracheas and lungs of birds that were inoculated with APV followed by EBO or BA alone. APV was detected by immunohistochemical staining in the upper respiratory tract longer in the groups of poults inoculated with APV and pathogenic bacteria than in those that received only APV, particularly when BA was involved. Viral antigen was also detected in the lungs of poults that were inoculated with APV followed by administration of EBO or BA alone. Loss of cilia on the epithelial surface of the upper respiratory tract was associated with BA infection and may enhance infection with APV, allowing deeper penetration of the virus into the respiratory tract.

Rapid detection of avian pneumovirus in tissue culture by microindirect immunofluorescence test.

An indirect immunofluorescence (IFA) test with a 96-well, flat-bottomed microplate was developed to detect avian pneumovirus (APV) antigen in Vero cell cultures. Samples of nasal turbinates and swabs from infraorbital sinuses and trachea were collected from 4-week-old poults experimentally inoculated with APV. The APV titers by tissue culture IFA staining were compared with that of visual reading of cytopathic effect (CPE). The ability of IFA staining to detect APV antigen correlated well with visualizing CPE. The use of IFA staining of Vero cell cultures allowed detection of APV in substantially less time than the use of visualizing CPE. In addition, the use of IFA allowed specific identification of the virus in cell culture.

Isolation of avian pneumovirus from mallard ducks that is genetically similar to viruses isolated from neighboring commercial turkeys.

Our earlier studies demonstrating avian pneumovirus (APV) RNA in wild geese, sparrows, swallows, starlings and mallard ducks suggested that wild birds might be involved in the circulation of APV in the United States. To determine whether turkey virus can be transmitted to the free flying birds, we placed APV-negative mallard ducks next to a turkey farm experiencing a severe APV outbreak and in an area with a large population of waterfowls. The sentinel ducks did not develop clinical APV disease but infectious APV (APV/MN-12) was recovered from choanal swabs after 2 weeks, and anti-APV antibodies detected after 4 weeks. Four APV isolates recovered from the neighboring turkeys that were experiencing an APV outbreak at the same time shared 95-99% nucleotide identity and 97-99% predicted amino acid identity with the duck isolate. In addition experimental infection of turkey poults with APV/MN-12 resulted in detection of viral RNA in nasal turbinates and APV-specific IgG in serum. These results indicate that the APV isolates from turkeys and ducks shared a common source, and the viruses from different avian species can cross-infect.