A new modified live equine influenza virus vaccine: phenotypic stability, restricted spread and efficacy against heterologous virus challenge.

Flu Avert IN vaccine is a new, live attenuated virus vaccine for equine influenza. We tested this vaccine in vivo to ascertain 1) its safety and stability when subjected to serial horse to horse passage, 2) whether it spread spontaneously from horse to horse and 3) its ability to protect against heterologous equine influenza challenge viruses of epidemiological relevance. For the stability study, the vaccine was administered to 5 ponies. Nasal swabs were collected and pooled fluids administered directly to 4 successive groups of naïve ponies by intranasal inoculation. Viruses isolated from the last group retained the vaccine's full attenuation phenotype, with no reversion to the wild-type virus phenotype or production of clinical influenza disease. The vaccine virus spread spontaneously to only 1 of 13 nonvaccinated horses/ponies when these were comingled with 39 vaccinates in the same field. For the heterologous protection study, a challenge model system was utilised in which vaccinated or naïve control horses and ponies were exposed to the challenge virus by inhalation of virus-containing aerosols. Challenge viruses included influenza A/equine-2/Kentucky/98, a recent representative of the 'American' lineage of equine-2 influenza viruses; and A/equine-2/Saskatoon/90, representative of the 'Eurasian' lineage. Clinical signs among challenged animals were recorded daily using a standardised scoring protocol. With both challenge viruses, control animals reliably contracted clinical signs of influenza, whereas vaccinated animals were reliably protected from clinical disease. These results demonstrate that Flu Avert IN vaccine is safe and phenotypically stable, has low spontaneous transmissibility and is effective in protecting horses against challenge viruses representative of those in circulation worldwide.

Efficacy of a cold-adapted, intranasal, equine influenza vaccine: challenge trials.

A randomised, controlled, double-blind, influenza virus, aerosol challenge of horses was undertaken to determine the efficacy of a cold-adapted, temperature sensitive, modified-live virus, intranasal, equine influenza vaccine. Ninety 11-month-old influenza-naïve foals were assigned randomly to 3 groups (20 vaccinates and 10 controls per group) and challenged 5 weeks, 6 and 12 months after a single vaccination. Challenges were performed on Day 0 in a plastic-lined chamber. Between Days 1 and 10, animals were examined daily for evidence of clinical signs of influenza. Nasal swabs for virus isolation were obtained on Day 1 and Days 1 to 8 and blood samples for serology were collected on Days 1, 7 and 14. There was no adverse response to vaccination in any animal. Following challenge at 5 weeks and 6 months, vaccinates had significantly lower clinical scores (P = 0.0001 and 0.005, respectively), experienced smaller increases in rectal temperature (P = 0.0008 and 0.0007, respectively) and shed less virus (P<0.0001 and P = 0.03, respectively) over fewer days (P<0.0001 and P = 0.002, respectively) than did the controls. After the 12 month challenge, rectal temperatures (P = 0.006) as well as the duration (P = 0.03) and concentration of virus shed (P = 0.04) were significantly reduced among vaccinated animals. The results of this study showed that 6 months after a single dose of vaccine the duration and severity of clinical signs were markedly reduced amongst vaccinated animals exposed to a severe live-virus challenge. Appropriate use of this vaccine should lead to a marked reduction in the frequency, severity and duration of outbreaks of equine influenza in North America.

Examination of Koch's postulates for Borrelia burgdorferi as the causative agent of limb/joint dysfunction in dogs with borreliosis.

Borrelia burgdorferi has been implicated as the causative agent of borreliosis in dogs, which is characteristically a limb/joint disorder, but can be associated with multiple-organ dysfunction. Attempts to reproduce this disease by inoculating dogs with B burgdorferi have not been successful. In the study of this report, B burgdorferi from Ixodes dammini ticks was used to induce signs of limb/joint dysfunction, fever, anorexia, depression, and systemic infection in dogs. A pure culture of this bacterium from the blood of an infected dog has been used to fulfill Koch's postulates for B burgdorferi as the causative agent of limb/joint dysfunction associated with borreliosis in dogs.

Immunogenicity and efficacy study of a commercial Borrelia burgdorferi bacterin.

The immunogenicity and efficacy of a commercial Borrelia burgdorferi bacterin was evaluated for stimulation of the host immune response and protection against clinical disease associated with experimentally induced borreliosis in dogs. A total of 30 vaccinated and 24 control dogs were used in 3 separate studies. The vaccine was given IM as two 1-ml doses separated by a 3-week interval. Two weeks or 5 months following the last vaccination, the dogs were challenge inoculated with 7 daily doses of a virulent preparation of a B burgdorferi field isolate through intraperitoneal, subcutaneous, and intradermal routes with or without glucocorticoid administration at the same time. The development of B burgdorferi spirochetemia and clinical disease in the dogs after challenge exposure was studied. Serum samples were obtained from the dogs at various times during the study for serum neutralizing antibody determination and protein immunoblot antibody assay against various geographic isolates of B burgdorferi. Challenge exposure induced limb/joint disorder, fever, anorexia, signs of depression, and B burgdorferi spirochetemia in the nonvaccinated control dogs. The vaccine was found to elicit cross-reactive serum neutralizing and protein immunoblot antibody responses in dogs to various isolates of B burgdorferi and to protect the vaccinated dogs against experimentally induced borreliosis.

The enumeration of Leptospira interrogans serovar pomona by a bioluminescence ATP assay.

A rapid method for enumerating viable Leptospira interrogans serovar pomona cells was investigated using a bacterial adenosine triphosphate (ATP) assay. The ATP was assayed by the luciferin-luciferase bioluminescence reaction. Samples of serovar pomona grown in liquid polysorbate 80-bovine albumin (P80-BA) medium for 1-3 days were analysed for ATP content, culture density (nephelometry), direct cell count and most probable number of viable cells (MPNVC) as determined by the dilution tube technique. A linear relationship was found between ATP content and the number of viable cells over the range of 4 X 10(8) to 8 X 10(9) leptospires/ml. Over this range the correlation coefficient for ATP content versus viable cells (0.96) was similar to the coefficient for culture density versus the number of viable cells. The coefficient for direct counts versus the number of viable cells was smaller. The bioluminescence assay of bacterial ATP is a promising method for enumerating viable leptospires in pure culture.