Ground Avian Flu Fears

And although migratory birds are often the focus when it comes to the spread of H5N1, they are not solely responsible for spreading the virus, given the fact that infectious diseases travel from host to host in a chain. All too often, the infection occurs locally when H5N1 transmission is promoted among densely packed flocks of poultry. Sometimes there are 50,000 birds in two-story sheds; the consequent close contact offers opportunity for the virus to spread by way of secretions. Improved farming practices are needed to contain the spread of bird flu. These include improved biosecurity measures, quarantine for sick birds, disinfection of transport vehicles and cages, and protective clothing for farm workers.

Technology and Food Safety Testing

Outbreaks of bird flu have been occurring sporadically for the last 10 years, with no end in sight, imposing grave losses on the poultry industry. Vaccination, drug treatment, and other containment efforts cannot be maximized unless the infection is detected quickly enough. Diagnosing primary bird flu infection should be of the utmost concern; early diagnosis can allow swift implementation of biosecurity, quarantine, and culling, as well as other control measures to safeguard the poultry industry.

During the 2006 outbreak, the chicken industry in the United States sought to reassure the public by testing every flock for bird flu before the birds were slaughtered. Developed countries can afford to bear the financial costs of rapid and expensive tests for poultry diagnosis. But countries with limited resources need new, rapid, accurate, and cost-effective tests to diagnose bird flu, monitor contaminated food, and swiftly implement preventive measures. Current methods for diagnosing bird flu fall into three categories: virus culture, laboratory antigen detection tests, and tests using nucleic acid amplification techniques (NATs).

Virus culture is considered the gold standard for identifying viral infections. Virus isolation in embryonated eggs, along with subsequent H and N subtyping, can take up to 14 days. In an outbreak, time is the limiting factor; the sooner bird flu is diagnosed, the sooner control measures can be put into place.

The second type of test is the antigen detection test, which must be carried out in a laboratory. Antigen detection tests include the immunofluorescence assay and enzyme-linked immunosorbent assay (ELISA). Although these tests are inexpensive, easy to use, and fast, they are prone to coreactivity between proteins, which affects results. They are also less sensitive than virus isolation and other techniques such as NATs.

NATs provide results in a few hours. This type of testing also offers convenient and quick automated result analysis, achieves higher sensitivity compared with virus isolation, and is more specific than traditional immunological testing. NAT tests include polymerase chain reaction (PCR) and nucleic acid sequence-based amplification (NASBA). PCR amplifies millions of copies of DNA using a single polymerase in step-wise reactions and requires an expensive thermocycler and/or real-time PCR machine. NASBA amplifies RNA in a single reaction utilizing three enzymes. It is particularly good for RNA viruses such as bird flu. It also offers an exceptional advantage over other testing methods in that it requires no expensive machines.

NASBA-EOC assays utilize an ELISA plate reader, making them extremely cost-effective. Moreover, standardization among different laboratories is possible, because NASBA-EOC is an isothermal process. NASBA-EOC assay is in use in China and Japan to assist in the monitoring programs for H5N1 avian influenza diagnosis in poultry.

Early Diagnosis the Best Defense

In a crisis of global importance, standardized testing will play a key role in deterring a catastrophic outbreak of avian influenza. Early diagnosis is the best defense against avian influenza. Therefore, there is an obvious need for rapid testing to enhance food safety and to minimize economic losses to the poultry sector.