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 (10^7.5EID50/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

Vaccination and testing scheme for the different groups
Age in days	Groups and treatments
0	Ma5	Ma5+4/91	Ma5	-	-
14	4/91 serology^a	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	serology virology

a = data not shown
* Protected < 50%
Unprotected > 50%

Results of the ciliostasis test: Protection Index (%)
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

Results of the virus detection
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, K. J., Currie, R. J. W. & Jones, R.C. (2008).
A reverse transcriptase-polymerase chain reaction survey of infectious bronchitis virus genotypes in Western Europe from 2002 to 2006.
Avian Pathology, 37, 247-257.
Read abstract and full article
Proceedings of the IV.International Symposium on Avian Corona- and Pneumovirus Infections
Rauischolzhausen, Germany, 20-23 June, 2004

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Protectotypes

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