Natalia Shevchenko, Acting Director of the Production Department, BIOTESTLAB Ltd.
Valeriya Kilimenko, Head of Veterinary Drugs Implementation Department, BIOTESTLAB Ltd.
Avian infectious bronchitis virus (IBV) is the cause of serious pathologies of the respiratory and genitourinary systems in broilers, reduced egg production, and egg quality in commercial layers and breeding stock. The disease results in significant economic losses.
Recently, in the countries of Eastern Europe, the causative agent of IBV is increasingly the variant strain 2 (VAR2/V2). It was first isolated in Israel in the 1990s. The severe form of the virus appeared in 2006, when the second epidemic wave of the VAR2 spread throughout the Middle East region.
In 2010, the virus was identified in Egypt. A field species of the virus was soon found in Turkey. From there, the infection migrated to the countries of Central and Eastern Europe. In August 2015, the strain was isolated in Lithuania and later in Ukraine and Poland. In the last-mentioned country, infections, caused by the variant strain VAR2, account today for more than 30% of all clinical cases of infectious bronchitis, according to local reports.
This disease affected not only broilers, but also laying hens in commercial and breeding herds. When broilers are affected, two types of the disease are distinguished. The first (early infection) is diagnosed in the first week of a bird's life. The main manifestation of the disease: very rapid differentiation of the herd, diarrhea, lameness, and high mortality (1-2% per day). The disease is complicated by secondary bacterial infections caused by Ornithobacterium rhinotracheale, Escherichia coli, Mycoplasma spp. The peak of mortality falls on days 10-16, after which the mortality decreases, stabilizes, and remains at this level until slaughter.
The second type of disease is characterized by late infection with the VAR2 virus. In the absence of other clinical signs, mortality increases to 2-4% per day for 3-4 days. Birds die at the age of 29-32 days. Despite the fact that in some cases the symptoms of respiratory pathology are mild, broilers quickly develop secondary bacterial infections. After a few days, the mortality decreases, but the herd does not reach the desired productivity indicators.
In commercial laying hens and breeding broilers, the dominant clinical symptoms are reduced egg production, deterioration of egg shell quality, and respiratory symptoms. In such herds, infectious bronchitis is recurrent: after a decrease in egg production by 10-30% and other clinical signs, the situation returns to normal, but 6-12 weeks after the first infection, re-infection with the same symptoms is recorded.
Global manufacturers have already developed and are producing live vaccines from the VAR2 strain to prevent the disease. Ukrainian scientists are working in this direction as well. So, at the end of 2021, the BIOTETSLAB Company completed the development of the POLIMUN IB VAR2 vaccine. Registration certificate received in 2022.
Test for safety
The new vaccine meets the requirements of the European Pharmacopoeia for the safety and immunogenicity of biological products. The evaluation was carried out on chickens with SPF status (free from specific pathogens, and not having antibodies), which were divided into 4 groups of 20 heads. Each group was placed in separate isolation rooms. The design of the isolators ensured the maintenance of the chickens’ SPF status throughout the study (supply of sterile air, clean feed, drinking water).
Safety assessment was carried out by vaccinating birds in 10- and 100-fold doses per head, using different methods, followed by monitoring the clinical condition of the birds and studying pathomorphological changes.
Observation of chickens for 14 days after vaccination did not reveal clinical signs of respiratory tract damage in the experimental and control groups, respectively. Pathological-anatomical and pathomorphological examinations of internal organs of chickens (organs of the respiratory tract, abdominal cavity, kidneys) did not reveal any deviations in the structure and development of the studied samples, which indicates the safety of the vaccine.
Long term protection
The second, most important criterion for evaluating any vaccine is immunogenicity, the ability of the drug to induce the production of specific antibodies and form stable immunity.
For this purpose, SPF day-old chicks were vaccinated against IBV by several methods. The observation period was 50 days (vaccination scheme – Table 1).
Table 1. Scheme of vaccination of chicks against infectious bronchitis of chickens
Group | Age, days | Vaccine | Administration method |
1, 2, 3 | 1 | POLIMUN IB Н120 | Coarse drop spray |
1 | 14 | POLIMUN IB VAR2 | Drinking water |
2 | 14 | POLIMUN IB VAR2 | Intraocular |
3 | 14 | POLIMUN IB VAR2 | Coarse drop spray |
4 (control) | Unvaccinated | ||
The first three groups of chickens were primed against the avian IB virus with the Massachusetts serotype vaccine (POLIMUN IB H120) at one day of age using the coarse spray method. Then, on the 14th day, the chickens of the first three groups were vaccinated with the vaccine from the VAR2 strain (POLIMUN IB VAR2): the first group – by drinking water, the second – intraocularly, and the third – by spraying. The fourth control group was not vaccinated.
After the second vaccination, the blood serum of chickens of all experimental and control groups was examined every 7 days for the presence of antibodies to the IB virus by ELISA (IDEXX test system).
The formation of antibodies was observed already on the 7th day after vaccination in 80% of the birds, and after 14 days already in 100% of the population.
Formation of antibodies to the IB virus
(Titer <397 – no antibodies detected, negative. Titer ≥397 – antibodies detected, positive)
Humoral immunity remained at approximately the same level in 100% of chickens until the 49th day of the post-vaccination period (observation period). The use of different vaccination methods stimulated the formation of approximately the same level of antibodies.
Therefore, it can be concluded that the use of the POLIMUN IB VAR2 vaccine in chickens at fourteen days of age (by drinking, spraying, or intraocularly), after the primary vaccination with the POLIMUN IB H120 vaccine, causes the formation of humoral immunity in the birds for a period of more than 49 days.
Considering that 10- and 100-fold doses of the drug are absolutely harmless to chickens, starting from the day-old, this makes the use of POLIMUN IB VAP2 promising for reliable protection of poultry from infectious bronchitis.
