Infectious Bronchitis Virus variants
Available vaccines are able to cross-protect against IBV variant Italian-02 that was isolated in Italy in the 1990's.
IBV variant Italian-02
In the late 1990's a series of IBV strains isolated in Italy were studied closely. The sequence analysis of one of these, designated “Italian-02”, was published in 2002 (NCBI-BLAST, number AJ457137). Then, in a study carried out in 2004 using the RT-PCR technique, (Worthington KC et al, 2004) it was found that this Italian-02 strain, is widespread in Europe and that, apart from IBV variant strain 4/91 it has become one of the most predominant genotypes in the UK, Spain, France and The Netherlands. Nevertheless, the importance of “Italian-02” as a major pathogen for poultry is still questionable. This is because the studies so far performed have simply detected the virus genome, very few virus isolates have been obtained and so it has not been proved that this IBV strain is pathogenic in chickens in the field.
Protection against Italian-02
Several experiments were carried out in order to investigate the efficacy of different vaccination programs against a challenge with Italian-02. The following experiment was carried out by Dr. Giovanni Tosi, from the “Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia Romagna” in Forlí, Italy.
Design
- 150 SPF chickens of 1 day of age, divided in 5 groups (30 birds/group) in isolators.
- Vaccination with Nobilis Ma5 and Nobilis 4/91 by the oculo-nasal route (see table below for vaccination scheme).
- Challenge with Italian-02 by the oculo-nasal route (107.5EID50/ml) at 36 or 56 days of age.
- Protection was assessed by means of the ciliostasis test and virus detection by PCR and reisolation.
Results
| Age in days | Groups and treatments | ||||
|---|---|---|---|---|---|
| 0 | Ma5 | Ma5+4/91 | Ma5 | - | - |
| 14 | 4/91 serologya | serology | 4/91 serology | serology | serology |
| 28 | serology | serology | serology | serology | serology |
| 36 | IT-02 challenge | IT-02 challenge | - | IT-02 challenge | - |
| 40 | ciliostasis test* | ciliostasis test | - | ciliostasis test | - |
| 43 | ciliostasis test | ciliostasis test | - | ciliostasis test | - |
| 56 | - | - | IT-02 challenge | - | - |
| 60 | - | - | ciliostasis test | - | - |
| 62 | serology virology | serology virology | ciliostasis test | serology virology | serology virology |
a = data not shown
* Protected < 50%
Unprotected > 50%
| Group | Vaccination schedule | IT-02 challenge | Protection index (40 days) | Protection index (43 days) |
|---|---|---|---|---|
| A | Ma5 at 1 day 4/91 at 14 days | 36 days | 92.35 | 90.82 |
| B | Ma5+4/91 at 1 day | 36 days | 90.82 | 87.76 |
| C | Ma5 at 1 day 4/91 at 14 days | 56 days | 95.41 (60 days) | 91.74 (62 days) |
| Protection Index = | Average score of the vaccinated group | x 100 |
| Average score of the infected group |
| Group | Vaccination schedule | IT-02 challenge | 43 days | 62 days |
|---|---|---|---|---|
| A | Ma5 at 1 day 4/91 at 14 days | 36 days | Reisolation+ PCR = IT-02 | Reisolation |
| B | Ma5+4/91 at 1 day | 36 days | Reisolation+ PCR = IT-02 | Reisolation |
| C | Ma5 at 1 day 4/91 at 14 days | 56 days | Not done | Reisolation+ PCR= IT-02 |
| D | None | 36 days | Reisolation+ PCR= IT-02 | Reisolation |
Conclusion:
- All vaccination programs induced a good level of protection against challenge with Italian-02 as shown by the ciliostasis test results and the absence of clinical signs in the vaccinated birds in spite of the virus reisolation (or recognition by PCR) in all groups after challenge.
- This experiment reinforces the importance of the concept of protectotypes.
References
Worthington KJ, Savage C, Naylor CJ, Wijmenga W and Jones R. (2004).
An RT-PCR survey of infectious bronchitis virus genotypes in the UK and selected European countries between 2002 and 2004 and the results from a vaccine trial.
Proceedings of the IV.International Symposium on Avian Corona- and Pneumovirus Infections
Rauischolzhausen, Germany, 20-23 June, 2004
