Surveillance Of Avian Leucosis,Reticuloendotheliosis,Pullorum Disease In Grandparent Breeding Farms Of China

Avian leucosis (AL), Reticuloendotheliosis (RE) and Pullorum disease (PD) are three vertically transmitted infectious diseases through egg, which could cause significant economic losses to the poultry industry. Therefore, eradication is the key measure to control these three diseases. The"National Medium- and Long-Term Plan for Animal Diseases Prevention and Control (2012-2020)"was launched and included the eradication programs for AL and PD in breeding chicken farms. It is important to clarify the prevalence of these three diseases in breeding farms in China. In this study,44476 and 46502 samples of albumen and serum were collected in 60 breeding farms from 29 provinces from 2011 to 2016. Albumens were tested for ALV-p27 antigen, while serums were tested for ALV-J, ALV-AB, REV and PD antibody through ELISA, which acquired 229639 results in all. Our results of systemic epidemiological surveillance described here helps to trace the group, space and time distribution and provides the basis for implementation of eradication program of vertically-transmitted diseases in breeding chicken farms in China.The results showed that, during six years, the positive farm rate of ALV p27 antigen was 18.75%?66.67% and the positive individual rate was 0.07%?4.64%. The positive farm rate of ALV-J antibody was 26.32%?64.71% and the positive individual rate was 0.35%?5.57%, while the positive farm rate of ALV?A/B antibody was detected to be 36.84?88.24% and the positive individual rate 1.58?9.23%. The farm proportion of the mixed ALV-J and A/B infection fluctuated from 15.79% to 58.82%. It is indicated that the infection of ALV widely existed with the positive farm rate above 35%in six years and the positive individual rate increased by years. The infection of different ALV subpopulations also increases the difficulty of detection and prevention. Therefore, it is important to adopt some ALV universal detection technology, and the positive flocks should be monitored in a timely and careful manner to stop their transmission in the future.The positive farm and individual rates of the REV antibody were 63.16%?88.24% and 2.71%?13.22% from 2011 to 2016. It is indicated that the highest rate of antibody was REV among three years, and the general direction of the trend was rising at first and then falling. REV infection is very common in China breeding chicken farms,which might affect the immune of the flocks and the prevention of other diseases.The positive rates of PD antibody were quite high in grandparent breeding farms (the farm and individual rates 17.65%?78.95% and 0.34%-6.73%, respectively). The results showed that the rate of PD antibody of breeding farms changed a lot in six years, and the positive rate of PD was consistent with the fluctuation trend of REV and ALV. The prevention and control of PD needs to be focused on in breeding flocks for a long-term, and it might be connected with other immunosuppressive diseases such as REV and ALV when the infection rate has significant difference.In the epidemiological investigation, we found that the positive farm rate with two or three co-infection of ALV,REV and PDwas 23.53%?68.42%,with co-infection of ALV, REV and PD being the most common and serious, followed by ALV-REV and REV-PD co-infection, and ALV-PD at the least. It is indicated that the co-infection of ALV, REV and PD is highly significant in grandparent breeding farms. The co-infection in great grandparent and grandparent breeding flocks might increase the risk for transmission to the next generation. It is also suggested that great challenge and a variety of weaknesses exist in the import of poultry, the pollution of vaccine, disease prevention and control measures.Finally, we performed a questionnaire survey in order to compare the differences among generation, variety and source of flocks. The results indicated that the positive rate of ALV-p27 antigen and ALV-J, REV and PD antibody was significant higher in grandparent breeding flocks than in great grandparent ones; it was significant higher in broiler flocks than in laying ones; it was also significant higher in local breeding flocks than in imported and domestic breeding flocks. But the positive rate of ALV-A/B antibody was significant higher in great grandparent than in grandparent flocks; it was higher in broiler flocks than in laying ones; it was also significant higher in domestic breeding farms than in imported and local breeding ones. These data suggested that grandparent,broiler and local breeding flocks were likely the risky factors of infection of ALV-J, REV and PD,while great grandparent, broiler and domestic breeding flocks was ALV-A/B. We suggested, therefore,that surveillance should be focused on poultry populations with high risk based on the epidemiological characteristics of different diseases.