Location: Exotic & Emerging Avian Viral Diseases Research
Project Number: 6040-32000-072-006-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2014
End Date: Jul 30, 2019
Objective:
We propose to develop reliable and affordable assays for testing the viability of Newcastle Disease Virus (NDV) vaccines in Africa to provide assurance to the consumer of a quality product. The assays developed will be used to test commercial vaccines purchased from retail shops in Tanzania to provide a proof of concept of the approach and provide useful surveillance data of the vaccine quality and availability in that country.
Approach:
The effectiveness of live NDV vaccine requires that a certain amount of viable virus is properly administered to the poultry species. Although the amount of virus can vary, a typical target is to have 10^5 Egg infectious dose 50 (EID50) viral particles administered to the bird. The administration can be by eye drop, aerosol, or water administration; however, the eye drop administration typically provides the most consistent vaccine response.
The project has two major objectives: (1) Evaluate affordable methods to test vaccine viability and titer that is transmissible to African veterinary laboratories. (2) Do a survey in Tanzania of NDV vaccine purchased from retail stores for product assessment.
Four approaches for vaccine evaluation will be initially considered:
(1) NDV, both field and vaccine strains, have the ability to hemagglutinate chicken red blood cells, because the virus attaches to the receptors on host cells. The hemagglutination test allows a simple and reproducible way to measure the virus from a vaccine sample. By using different dilutions of the virus, a semi-quantitative system can be developed to estimate viral titer in the sample.
(2) The hemagglutination procedure can determine if NDV is present in the sample, but it doesn’t differentiate live from inactivated virus. Titering of samples to detect live virus is routinely performed in embryonating chicken eggs. Vaccine samples will be titered to assure that the virus detected by hemagglutination is a viable virus.
(3) Two different strains of Newcastle disease are commonly used for vaccines, LaSota and I2. Specific RT-PCR tests will be developed to confirm the identity of the vaccines as being what is claimed on the vaccine packaging. Systems for traditional and real-time RT-PCR will be developed.
(4) Differential and quantitative RT-PCR. Quantitative RT-PCR is a well documented technique to estimate viral load based on the amount of PCR product produced with a standard curve. Real-time RT-PCR tests can be used to titer viral RNA which provides the best correlate of virus levels. However, this technique cannot distinguish between live and dead virus.
