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Submitted to: Biologicals
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/18/2005 Publication Date: 10/15/2005 Citation: Suarez, D.L. 2005. Overview of avian influenza DIVA test strategies. Biologicals. 33:221-226. Interpretive Summary: Avian influenza can cause a serious disease in chickens and turkeys. The losses from a disease outbreak can be both from the sickness and death in the birds, but also the loss of trade to other countries. The U.S. poultry industry exports large amounts of poultry to other countries. One way to reduce the losses associated with an avian influenza outbreak is to vaccinate the flocks at risk of being infected. One disadvantage of vaccination is the difficulty in differentiating infected from vaccinated animals (DIVA). Since it has been difficult to assure that vaccinated birds had not been naturally infected, most countries will not accept vaccinated birds for import. The review describes four different potential methods of DIVA vaccination, that could differentiate infected from vaccinated birds and may allow the export of vaccinated birds. This includes the use of unvaccinated “sentinel” birds in the flock that can be monitored. Three other methods, including the subunit approach, the heterologous neuraminidase approach, and the NS1 approach, all rely upon detecting antibodies that are only found in infected animals and not vaccinated animals. Only the use of sentinel birds has been widely used, but the other three methods maybe simpler to use. Further work needs to be done to see which method will work the best. Technical Abstract: The use of vaccination in poultry to control avian influenza has been increasing in recent years. Vaccination has been primarily with killed whole virus-adjuvanted vaccines. Proper vaccination can reduce or prevent clinical signs, reduce virus shedding in infected birds, and increase the resistance to infection. Historically, one limitation of the killed vaccines is that vaccinated birds cannot be differentiated serologically from naturally infected birds using the commonly available diagnostic tests. Therefore surveillance for avian influenza becomes much more difficult and often results in trade restrictions because of the inability to differentiate infected from vaccinated animals (DIVA). Several different DIVA strategies have been proposed for avian influenza to overcome this limitation. The most common is the use of unvaccinated sentinels. A second approach is the use of subunit vaccines targeted to the hemagglutinin protein that allows serologic surveillance to the internal proteins. A third strategy is to vaccinate with a homologous hemagglutinin to the circulating field strain, but a heterologous neuraminidase subtype. Serologic surveillance can then be performed for the homologous NA subtype as evidence of natural infection. The fourth strategy is to measure the serologic response to the non-structural protein 1 (NS1). The NS1 protein is produced in large quantities in infected cells, but it is not packaged in the virion. Since killed vaccines for influenza are primarily made with whole virions, a differential antibody response can be seen between naturally infected and vaccinated animal. However, poultry vaccines are not highly purified, and they contain small amounts of the NS1 protein. Although vaccinated chickens will produce low levels of antibody to the NS1 protein, virus infected chickens will produce higher levels of NS1 antibody, and the two groups can be differentiated. All four DIVA strategies have advantages and disadvantages, and further testing is needed to identify the best strategy to make vaccination a more viable option for avian influenza. |
