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Avian Infectious Bronchitis virus (IBV) is a highly contagious coronavirus that affects the upper respiratory tract of birds.
It is an RNA virus that, by nature, can change rapidly when it replicates within the host.
There are many types of IBV (and variants of those types) with little or no ability to cross-react. Therefore, developing a vaccine against only one type of virus is unlikely to provide adequate protection against another type.
Initially, tests based on neutralizing antibodies were used for IBV typing, but currently the IBV type is genetically identified from the sequence of the viral spike (glycoprotein).
The genetic type of the virus circulating in the field can provide information to select one or more commercial vaccines available for its prevention and control.
This implies that using a vaccine homologous to the circulating virus is the best strategy to guarantee success.
Numerous studies have been conducted to examine different combinations of IBV vaccine types against virus variants and this information can be extremely valuable in developing a vaccine strategy. However, it is currently impossible to predict which combination of vaccine types will provide an acceptable level of protection against new circulating variants of the virus in the field.
The only way to know for sure whether a combination of vaccines will provide adequate protection is to conduct challenge studies in chickens.
INTRODUCTION
Avian Infectious Bronchitis is a worldwide infectious disease of the upper respiratory system that affects chickens.
It is a very important disease from an economic point of view, causing millions of dollars in annual losses to the poultry industry due to production reductions, seizures during processing and mortality.
It also causes losses in breeders and layers due to infections with strains of the virus that cause kidney damage, diarrhea and dehydration.
The pathogen causing the disease is Avian Infectious Bronchitis Virus (IBV), an enveloped RNA virus. Currently, the best and only strategy to control this virus is the use of live attenuated and inactivated vaccines.
Typically, live vaccines are administered to day-old chicks in the hatchery and sometimes in the field at 14-18 days of age.
Inactivated vaccines, which must be injected, are used after primo-vaccination (with live virus) in breeders and layers to prolong immunity during the life of the flocks.
Regardless of the type of vaccine used, it is difficult to achieve complete protection since the different types of IBV do not generate cross protection.
In addition, it is difficult to apply live and inactivated vaccines correctly. Equipment failure, improper vaccine handling, poor administration technique, and dose reduction all lead to poorly protected flocks.
We vaccinate against IBV to prevent clinical signs of the disease, but vaccines can also reduce the replication and transmission of pathogenic field viruses.
Surveillance (or monitoring) of the types of IBV circulating in the field is critical and an essential component of a successful control strategy. The diagnosis of IBV is made almost exclusively by molecular biology techniques. Viral RNA can be detected by RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) and real-time RT-PCR. The tests are designed to detect all types of IBV and this is followed by sequencing the S1 gene to determine the genetic type or by a type-specific real-time RT-PCR test.
Determining the type(s) of IBV circulating in the field is necessary to select effective vaccines and design appropriate vaccine strategies for virus control.
IBV VARIANTS
The high rate of genetic modifications that this virus undergoes contributes to the circulation of many different types (variants) in the field.
The type of virus is determined by the spike protein located on the surface of the virus. This means that different types of viruses have different spike proteins on their surfaces.
Antigenic diversity (virus variants) arises when mutations, insertions, deletions and recombinations occur in the gene that encodes the spike protein. This can result in the presence of a significantly different spike protein on the surface of the virus and, consequently, a genetically and antigenically new IBV.
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