A canine vaccine against Leptospira serovars Icterohaemorrhagiae, Canicola and Grippotyphosa provides cross protection against Leptospira serovar Copenhageni

Efficacy of the Leptospira components of multivalent vaccine DAPPi-L was previously demonstrated against virulent challenge with three serovars of Leptospira interrogans (Canicola, Icterohaemorrhagiae and Grippotyphosa) carried out 14 days after primary vaccination. In this study we demonstrate that this vaccine provides, two weeks after vaccination, an additional protection (prevention of mortality, clinical signs, renal infection, bacterial excretion, renal carriage and renal lesions) against fatal leptospirosis due to Leptospira interrogans serovar Copenhageni (serovar of major medical importance).

Compatibility between a rabies vaccine and a combined vaccine against canine distemper, adenovirosis, parvovirosis, parainfluenza virus and leptospirosis

In many cicumstances, veterinarians are requiring to be able to administer rabies vaccine in dogs at the same time as vaccinating against canine distemper, adenovirus, parvovirus, parainfluenza virus and leptospirosis. The aim of this study was to assess the compatibility between a multivalent vaccine and a rabies vaccine when injected at two separate sites. Lack of interference was assessed by comparing serological response to viral components during one year following primary vaccination with vaccines administered alone or concomitantly. Antibody response to all tested components was comparable, irrespective of whether vaccines were administered individually or concurrently. Notably, the rabies vaccine induced very strong and protective seroconversion in dogs, whether it was administered concomitantly with the combo vaccine or not. This facilitates administration of rabies vaccine, which is a key factor for controlling the disease.

Onset and duration of protective immunity against clinical disease and renal carriage in dogs provided by a bi-valent inactivated leptospirosis vaccine

Protection against clinical disease and prevention of the renal carrier state remain the key objectives of vaccination against leptospirosis in the dog. In the present paper, groups of dogs were vaccinated twice with a commercial bacterin (EURICAN^® L) containing Leptospira interrogans serovars icterohaemorrhagiae and canicola and challenged with heterologous representatives of both serovars at 2 weeks (onset of immunity) or 14 months (duration of immunity) after the second vaccination. Control dogs were not vaccinated against leptospirosis and kept with the vaccinated dogs. The challenges, irrespective of the serovar, reliably produced clinical signs consistent with Leptospira infection in the control pups with up to 60% mortality. As expected clinical disease in the adult controls was less severe, but we were able to induce morbidity and mortality as well. Under these extreme challenge conditions, clinical signs in the vaccinated dogs were rare, and when observed, mild and transient in nature.

Following experimental infection, 100% of the control pups and 83% of the adult controls became renal carriers. Despite the heavy challenges, none of the 18 vaccinated puppies (onset of immunity studies) and only 2 out of the 16 vaccinated adult dogs (duration of immunity studies) developed a renal carrier state. These results show that a primary course of two doses of EURICAN^® L provided quick onset and long-term protection against both clinical leptospirosis and the renal carrier stage. This vaccine should provide veterinarians with a powerful tool to prevent clinical disease in dogs and zoonotic transmission of leptospirosis to humans.

Use of DNA and recombinant canarypox viral (ALVAC) vectors for equine herpes virus vaccination

In this study, experimental canarypox virus (ALVAC) and plasmid DNA recombinant vaccines expressing the gB, gC and gD glycoproteins of EHV-1 were assessed for their ability to protect conventional ponies against a respiratory challenge with EHV-1. In addition, potential means of enhancing serological responses in horses to ALVAC and DNA vaccination were explored. These included co-administration of the antigen with conventional adjuvants, complexation with DMRIE-DOPE and co-expression of the antigen along with equine GM-CSF. Groups of EHV primed ponies were vaccinated twice intra-muscularly with one dose of the appropriate test vaccine at an interval of 5 weeks. Two to 3 weeks after the second vaccination, ponies were infected intra-nasally with the virulent Ab4 strain of EHV-1 after which they were observed clinically and sampled for virological investigations. The results demonstrated that DNA and ALVAC vaccination markedly reduced virus excretion after challenge in terms of duration and magnitude, but failed to protect against cell-associated viremia. Noteworthy was the almost complete absence of virus excretion in the group of ponies vaccinated with ALVAC-EHV in the presence of Carbopol adjuvant or DNA plasmid formulated with aluminium phosphate. The administration of the DNA vaccine in the presence of GM-CSF and formulated in DMRIE-DOPE and of the ALVAC vaccine in the presence of Carbopol adjuvant significantly improved virus neutralising antibody responses to EHV-1. These findings indicate that DNA and ALVAC vaccination is a promising approach for the immunological control of EHV-1 infection, but that more research is needed to identify the immunodominant protective antigens of EHV-1 and their interaction with the equine immune system.

Efficacy of a recombinant equine influenza vaccine against challenge with an American lineage H3N8 influenza virus responsible for the 2003 outbreak in the United Kingdom

Fifteen influenza-naive Welsh mountain ponies were randomly assigned to three groups of five. A single dose of a recombinant ALVAC vaccine was administered intramuscularly to five of the ponies, two doses, administered five weeks apart, were administered to five, and the other five served as unvaccinated, challenge controls. Two weeks after the completion of the vaccination programme, the ponies were all challenged by exposure to an aerosol of influenza virus A/eq/Newmarket/5/03. Their clinical signs were scored daily for 14 days according to a standardised scoring protocol, and nasal swabs were taken daily for 10 days to monitor the excretion of virus. The challenge produced severe clinical signs of influenza (fever, coughing, nasal discharge and dyspnoea) in all five control ponies, but the vaccinated ponies developed only mild disease, consisting of a serous nasal discharge lasting for only one day. The excretion of virus was almost completely suppressed in the vaccinated ponies, but the control ponies shed the virus for up to seven days after the challenge.

Protection of puppies against canine herpesvirus by vaccination of the dams

Six bitches free of canine herpesvirus 1 (CHV-1) were vaccinated against the virus; a first injection was given 10 days after the presumed date of mating and a second six weeks later. Six similar bitches were left unvaccinated as controls, and all the pups were challenged oronasally with a virulent strain of CHV-1 at three days of age. All the vaccinated bitches seroconverted and had high antibody titres when the puppies were challenged, but the control bitches remained seronegative. In the control group, 62 per cent (18 of 29) of the pups died of CHV-1-induced disease; most of them showed typical clinical signs and macroscopic lesions, and CHV-1 infection was confirmed by the isolation of the virus or by PCR. None of the puppies in the vaccinated group died of CHV-1 infection. The efficacy of the vaccine was confirmed in CHV-1-positive breeding units. The rate of pregnancy tended to be higher in vaccinated bitches and the mortality of pups before weaning was significantly reduced in the litters born to vaccinated bitches.