Efficacy of an inactivated and a fowlpox-vectored vaccine in Muscovy ducks against an Asian H5N1 highly pathogenic avian influenza viral challenge.

The efficacy of an inactivated vaccine containing the Eurasian isolate A/chicken/Italy/22A/98 H5N9 (H5N9-It) was compared with that of the fowlpox-vectored TROVACTM-AIV H5 (rFP-AIV-H5) vaccine against an H5N1 highly pathogenic avian influenza challenge. Five-week-old Muscovy ducks were vaccinated with either H5N9-It (0.5 ml) or rFP-AIV-H5 (5 log10 50% tissue culture infectious dose (TCID50)/dose), followed by a boost at 7 wk of age with the same vaccine (1.0 ml of H5N9-It or 5 log10 TCID50/dose rFP-AIV-H5), and a challenge at 9 wk of age with 10(7) egg infectious dose (lethality 50%) of A/crested eagle/ Belgium/01/2004 (H5N1). All unvaccinated challenged birds showed severe nervous signs (loss of balance, torticollis) starting 7 days postinfection (dpi). None of the vaccinated ducks showed these nervous signs. Shedding was measured in oropharyngeal and cloacal swabs, sampled from 3 to 19 dpi by titration in chicken embryo fibroblasts and by real-time reverse transcription-polymerase chain reaction. Virus shedding was significantly higher in oropharyngeal compared to cloacal swabs. Both vaccines reduced the percentage of positive swabs and the viral load in the swabs, but the reduction was higher with the H5N9-It vaccine. The inactivated vaccine induced hemagglutination inhibition (HI) titers (5.4 log2) that were boosted after the second administration (7.5 log2). rFP-AIV-H5-induced HI titers were lower (3 log2 only after the second administration), most probably because the fowlpox vector does not replicate in ducks. Altogether, these results indicate that significant protection from clinical signs and reduction in virus shedding may be achieved in ducks with conventional inactivated or fowlpox-vectored vaccine as compared with nonvaccinated challenged control birds.

Use of a vectored vaccine against infectious bursal disease of chickens in the face of high-titred maternally derived antibody.

Interference by maternally derived antibody (MDA) is a major problem for the vaccination of young chickens against infectious bursal disease (IBD). The choice of the timing of vaccination and of the type (degree of attenuation) of modified-live vaccine (MLV) to use is often difficult. An IBD vectored vaccine (vHVT13), in which turkey herpesvirus (HVT) is used as the vector, was recently developed. This vaccine is administered once at the hatchery, either in ovo or by the subcutaneous route, to 1-day-old chicks at a time when MDA is maximal. In terms of safety, the vHVT13 vaccine had negligible impact on the bursa of Fabricius when compared with classical IBD MLV. Vaccination and challenge studies demonstrated that this vaccine is able to protect chickens against various IBD virus (IBDV) challenge strains including very virulent, classical, and USA variant IBDV, despite the presence of high-titred IBD MDA at the time of vaccination. These data show that the vector vaccine combines a safety and efficacy profile that cannot be achieved with classical IBD vaccines.

Efficacy of a new attenuated duck parvovirosis vaccine in Muscovy ducks.

The efficacy of a new live attenuated parvovirosis vaccine was tested in conventional ducklings against Derzsy's disease by comparing two vaccination regimens. Ducklings were vaccinated with either one injection at 17 days of age or two injections at 1 and 17 days of age. Controls and vaccinated ducklings were challenged with a virulent Derzsy strain at 21 days of age (day 20). Weight was measured on days 20, 34 and 42/43. Surviving birds were necropsied on day 42/43. Protection rates were significantly higher in the groups vaccinated once (90 per cent, P=0.003) and twice (95 per cent, P<0.001) than in the control group (59 per cent). The bodyweight was significantly higher in both vaccinated groups than in the control group on day 34 (P=0.008 and P<0.001, respectively) and day 42/43 (P<0.001 for both groups). The growth was significantly higher in the group vaccinated twice than the group vaccinated once on day 34 (P=0.047) and day 42/43 (P=0.017). Both vaccination regimens provided a quick onset of immunity. The higher weight gain in the group vaccinated twice suggests that an early vaccination at hatchery followed by a second injection at 17 days of age is an optimal and practical schedule to prevent parvovirosis.

Field efficacy trial of a novel HVT-IBD vector vaccine for 1-day-old broilers.

Two vaccination programmes for infectious bursal disease (IBD) were compared in broiler chickens with maternal immunity, placed on two farms. A turkey herpes virus (HVT)-IBD vector vaccine was administered by the subcutaneous route, at the hatchery, into the chicks of farm A at the age of 1 day. On farm B, an attenuated intermediate live IBD vaccine was given orally at the ages of 17 and 24 days. The vaccine uptake was monitored via serology and bursa/body weight ratio evolution, as well as PCR-based viral IBDV detection in the bursa of Fabricius at various time points. It was also verified by an experimental very virulent IBDV challenge performed at the age of 30 days in birds transferred from the farms with appropriate control groups in a laboratory. An immunity gap was observed in birds from farm B between the decay of the passive and the rise of the active immunity based upon serological data. The level of protection against challenge is not possible to establish in this farm as the reduction of the bursa/body weight ratio observed could be due to the residual pathogenicity of the vaccine strain or the challenge as well. This immunity gap was not present on farm A showing higher serological titres at the ages of 26 and 45 days via a suitable ELISA test and 93% protection against the very virulent challenge at the age of 30 days was observed. The maternal immunity interfering with the live IBDV vaccine replication had no detectable effect on the vector vaccine take.

Prime-boost vaccination with a fowlpox vector and an inactivated avian influenza vaccine is highly immunogenic in Pekin ducks challenged with Asian H5N1 HPAI.

The efficacy of different vaccination schedules was evaluated in 17-day-old Pekin ducks using an experimental inactivated whole virus vaccine based on the H5N9 A/chicken/Italy/22A/98 isolate (H5N9-It) and/or a fowlpox recombinant (vFP-H5) expressing a synthetic HA gene from an Asian H5N1 isolate (A/chicken/Indonesia/7/2003). Full protection against clinical signs and shedding was induced by the different vaccination schemes. However, the broadest antibody response and the lowest antibody increase after challenge were observed in the group of ducks whose immune system was primed with the fowlpox vectored vaccine and boosted with the inactivated vaccine, suggesting that this prime-boost strategy induced optimal immunity against H5N1 and minimal viral replication after challenge in ducks. In addition, this prime-boost vaccination scheme was shown to be immunogenic in 1-day-old ducklings.

[Comparison of sensitivity of four turkey genetic types infected with virulent or attenuated strains of haemorrhagic enteritis virus]. / Sensibilite comparee de quatre varietes genetiques de dinde a des souches virulentes ou attenuees du virus de l'enterite hemorragique.

Four turkey genetic strains reacted differently to an experimental infection with different strains, virulent or attenuated, of haemorrhagic enteritis virus. Criteria used were: clinical signs (diarrhoea, mortality), daily weight gain, histopathology and virus recovery in the spleen. Turkeys of one genetic type developed more quickly the disease; the serological response to vaccine using ELISA and agar gel precipitation techniques was also faster. Turkeys of two other genetic types responded later both to the virus and the vaccine. Turkeys of the fourth genetic type responded last. The origin of this discrepancy is discussed.

A recombinant canarypox virus protects rabbits against a lethal rabbit hemorrhagic disease virus (RHDV) challenge.

An ALVAC (canarypox)-based recombinant virus ALVAC-RHDV (vCP309) expressing a native rabbit hemorrhagic disease virus (RHDV) capsid protein was derived and assessed for its protective efficacy in rabbits. Protection against a lethal RHDV challenge was demonstrated in rabbits inoculated twice with either high (10(7) p.f.u.) or low (10(5) p.f.u.) doses of vCP309. However, animals in the high dose group developed significantly higher antibody response. These results have implications that are relevant to the development of a safe rabbit hemorrhagic disease (RHD) vaccine and further illustrate the utility of the ALVAC vector system to elicit protective immune responses in nonavian species.

Mycoplasma iowae: field and laboratory studies to evaluate egg transmission in turkeys.

In order to study the egg transmission of Mycoplasma iowae in turkeys, two experiments are undertaken. Experiment 1 was a field trial designed to investigate egg transmission in naturally infected turkeys: commercial hens were inseminated with semen from naturally infected toms. Mycoplasma iowae was regularly cultured from dead-in-shell embryos, pips and culls but not from healthy poults. Egg transmission occurred from the second up to the tenth week of production. Experiment 2 was a laboratory study conducted to observe persistence and egg transmission of M. iowae in experimentally infected turkeys. Specific pathogen free (SPF) hens were inoculated either intracheally or intravaginally. They were then artificially inseminated with semen from SPF toms. Very little egg transmission was observed. The cultures from tracheal or vaginal swabs of the inoculated hens showed a limited invasive ability of M. iowae in the adult bird. The humoral immune response as detected by the metabolism inhibition test, was very poor. The observations made in these two experiments show the importance of venereal spread of M. iowae, especially under artificial insemination. Consequently, the need for monitoring toms is obvious.

[Study on the immunosuppressive effect of virulent and vaccine strains of hemorrhagic enteritis of turkey]. / Etude de l'effet immunodépresseur de souches virulente ou vaccinale de l'entérite hémorragiquede la dinde.

The immunosuppression caused by virulent and vaccine strains of haemorrhagic enteritis administered in turkey, is assessed, by their influence on the serological response to Newcastle disease vaccination. The histological modifications of lymphoid organs after haemorrhagic enteritis vaccination are also studied. It is concluded that the vaccine virus has an immunosuppressive effect comparable to those of the virulent virus, but the duration of this effect is very short with some variations depending on genetic breed of turkey.

[Comparison of three techniques for the enumeration of Aspergillus fumigatus spores in the hatcher as part of an epidemiologic survey of Aspergillosis risks in hatchery houses]. / Comparaison de trois techniques de numeration des spores d'Aspergillus fumigatus en eclosoir, dans le cadre de la surveillance epidemiologique au couvoir des risques d'aspergillose.

Methods of enumerating Aspergillus fumigatus spores on the down of hatching chicks in swabs of hatcher walls and in lungs of hatching chicks were compared under field conditions as part of an official survey of hatchery houses. Correlations and agreements between the results were studied. Their lack of accuracy is stressed, especially with the swab technique. This impels the aspergillosis risk to be evaluated from the average of the enumerations obtained simultaneously in a set of 10 hatchers.