Field studies on infectious bronchitis virus variants in Argentina (VIBAR)

Infectious bronchitis, diagnosed for the first time in 1932, continues causing severe losses in poultry farming around the world, despite the existence of vaccines from the 1950s. Many of the problems of partial protection conferred by the vaccines in use have been attributed to the great variability of immune profiles of the bronchitis virus. (Niester et al., 1986)

In Argentina, field studies using one isolated area in a large operation, with birds of multiple ages showing recurrent, compatible infectious bronchitis clinical pictures allowed us to infer empirically that we were against a variant strain of the virus which was not fully covered by the Mass and Conn vaccines available in Argentina.

Subsequent studies using molecular techniques of genomic sequencing (Rimondi et al., 2009) confirmed in an absolute way that both this strain and almost all bronchitis viruses circulating in Argentina are closely grouped variants and that the one used by us in field tests could be considered a protectotype suitable for the development of a live an immune agent against all of them.

Field veterinarians face permanently cases of infectious bronchitis compatible with such a disease, since they fail to confirm the diagnosis.

Three field trials that would respond to how to proceed in situations in which a bronchitis outbreak is suspected.

During the year 2003 in a complex of more than half a million laying hens, in one smaller group of 6 sheds with 12,000 birds each, and decreasing age of 27 to 19 weeks, the position in the group of greater age, after reaching 90% fell to 83 per cent. There were no clinical respiratory symptoms of any kind, only a very slight increase in the humidity of the faeces. A thorough observation managed to separate 5 birds that, according to the expert eye of the man in charge of the farm, could be suspect of any condition. The birds were slaughtered and an in-situ autopsy was performed it was noted that all showed injured ovarian follicles and that both ovaries and oviducts were in a process of regression. Furthermore, cecal tonsils were enlarged from two to three times and hemorrhagic. Using maceration of these tonsils, 10-day chicken embryos were inoculated and the isolation of a bronchitis virus was achieved which, since the first transmission, produced a great atrophy and abundant allantoidal amniotic liquid with a title of approximately 10⁷ DIE 50% ml. (embryo infectious dose).

In the operation in question for more than 15 years it had not been possible to control the outbreaks of bronchitis which, inevitably, occurred around the peak of position and were recurring throughout the production cycle. Different experiences reinforcing the use of vaccines with Mass and Conn strains, adding imported inactivated vaccines or inactivated self-vaccines using viral isolations from the operation did not produce the expected results.

Decision was made to run the risk of vaccination of birds in the second shed depending on the age that had reached 50 per cent of posture, with the second passage in embryos of the isolated virus, applied in spray.  This was named BIP strain.

As, after one week, the batch had reached the posture expected by the table, decision was made to "inoculate" the four remaining sheds. All batches largely exceeded the 90% posture, did not have any break in their production cycle, the quality and quantity of eggs produced by hen lodged increased significantly and mortality caused by peritonitis and other unspecific causes was reduced to half of the historical values.

Since then, several million replacement hens have been vaccinated during the rebreeding with the BIP strain in drinking water and no new episode of the disease has been seen in this operation.

During the year 2008 in a heavy breeding complex, in several successive generations'''' clinical pictures compatible with infectious bronchitis were observed. At the beginning of 2009 the rebreed began to be vaccinated with the BIP strain in drinking water and never again has this disease been observed in this operation.

During 2009 we studied an unprecedented case. The possible reasons why a farm of broilers with 8 sheds and 5 different ages could operate with less than 4% loss were studied. For several years, the only vaccine applied was against Gumboro disease.

In the course of 2010, a variant strain of the bronchitis virus was introduced in the hatchery after a major biosafety failure. Respiratory, gastrointestinal, renal, locomotor and septicemic complications by germs multiresistant to antibiotics were getting worse with each new batch entered and made the operation unviable. A preventive plan to give a soft Mass vaccine via spray in cabinet in the incubation plant and a revaccination in drinking water 14 days later, with the BIP strain succeeded in reversing the picture, and without stopping the farm or taking any other additional measures the mortality returned to 3-4% at the 60-65 days of ageing common in this farm.

It was demonstrated in a previous study (Rimondi et al., 2009) that the majority of circulating bronchitis viruses in Argentina belong to variants that are not fully covered by the vaccine to Mass and Conn strains, i.e. that vaccination is taking place against strains that do not exist in the country.

The use of the BIP strain (henceforth named BIVAR: Bronquitis Infecciosa Variante Argentina)[Infectious Bronchitis, Argentine Variant] as a live-virus vaccine is safe for both broilers and laying hens and heavy breeders operations.

The BIVAR strain would constitute a new effective protectotype as a vaccine against infectious bronchitis caused by any of the variant strains circulating in Argentina.

The often mentioned characteristic of high and constant variability of the avian infectious bronchitis virus (Niester et al., 1986) would not apply in these cases. For more than eight years, in this operation, passed several million commercial laying hens, with high immunity to the MASS - CONN and BIVAR strains, no new variant strain has been isolated or has emerged.

On the other hand, in a longitudinal study from the year 2000 to date, except for isolation of MASS and CONN strains, possibly of vaccination origin, all other isolations of bronchitis virus carried out in the very different and distant regions producing poultry in Argentina are grouped into three clusters: A, B and C, closely linked between them (98-99% of kinship) and with only 70% of kinship to the pattern strain pattern, 41 M (manuscript in preparation). A plausible explanation for such dissemination of the virus and with so much uniformity would be rooted in the possibility of transovaric transmission of the virus, demonstrated by Mc Ferran et al. (1971).

Mc Ferran JB et al. 1971. Isolation of infectious bronchitis virus from new born chicks. Dead-in shell embryos. Veterinary Record 89(21):560-561.

Niester HGM et al.1986. The peplomer proteín sequence of the M41 strain of coronavirus IBV and its comparison with Beaudette strain. Virus Res. 5:253-263.

Rimondi A, Craig MI, Vagnozzi A, Konig G, Delamer M, Pereda A. 2009. Molecular characterization of avian infectious bronchitis virus strains from outbreaks in Argentina (2001-2008). Avian Pathology 30(2):149-153.