EVALUATION OF THE EFFICIENCY OF THE SEROLOGICAL HAI METHOD FOR THE DETECTION OF ANTIBODIES TO THE EGG DROP SYNDROME VIRUS

Abstract

The article describes the features of the course of the disease of laying hens with Egg drop syndrome (EDS). This is a contagious viral disease of commercial and breeding laying hens, which is characterized by damage to the reproductive organs, a sharp decrease in laying capacity, changes in the pigmentation and shape of laid eggs, the appearance of effusions, thinning, deformations, and in some places the complete absence of a shell, a decrease in the percentage of hatching of chickens from hatching eggs and a deterioration in their viability. Morbidity is 10–70 %, mortality is 1–10 %. The disease in chickens occurs during the egg-laying period, until then no clinical signs of infection are observed. Three forms of EDS have been described: classic, endemic, and sporadic. The diagnosis of EDS is established on the basis of the results of laboratory tests, taking into account epizootological data, clinical signs and pathological anatomical changes. At the same time, special attention is paid to the decrease in egg production and the appearance of deformed and shelles eggs in clinically healthy chickens, the death of embryos and day-old chicks. Laboratory diagnostics is based on express, virological and retrospective methods. One of the most common methods of diagnosing EDS is retrospective diagnosis, which consists in detecting a diagnostic (minimum 4-fold) increase in the antibody titer in paired blood sera of chickens by the methods of HAI, IHA or ELISA. HAI is recommended for mass serological examinations of poultry farms. The detection of Anti-Hemagglutinin Antibody (Anti-HA) in the studied blood sera at a titer of 1:16 (4 log2) and higher in farms where specific prevention of EDS is not carried out indicates the circulation of the field strain of EDS virus among poultry. It should be noted that chickens that do not yet lay deformed eggs can be infected with the virus, but do not give a humoral immune response to latent infection. Thus, in flocks of chickens that were infected transovarially, antibodies are not synthesized during the breeding period. A negative serological test in chickens under the age of 20 weeks does not guarantee the absence of EDS infection. Differential diagnosis requires the exclusion of infectious bronchitis, infectious laryngotracheitis, Newcastle disease and respiratory mycoplasmosis. An analysis of 20 inactivated vaccines from various manufacturing companies registered in Ukraine for the specific prevention of EDS was carried out, including monovalent – 3 and associated, namely 3-component – 10 and 4-component – 7. During serological monitoring, it was established, that the average titers in the sera of laying hens to the EDS virus from batches of different ages due to different terms after vaccination with inactivated vaccines ranged from 7.0 log2 to 13.2 log2. The average titers to the EDS virus above the basic norm were 16 % among birds of 4-8 batches (280, 310 and 460 days). It was established that the percentage of protective antibodies to the EDS virus in 25 batches of laying hens ranged from 78 to 100. The use of inactivated vaccines against EDS stimulates the formation of an active immune response in laying hens in 84 % of the studied batches. Carrying out constant monitoring of the effectiveness of inactivated vaccines against by means of serological monitoring of blood sera from birds in the HAI will allow, depending on the epizootic situation, to timely adjust the vaccination scheme and ensure stable economic indicators in commercial and breeding flocks of laying hens.