Avian Influenza (1): Introduction

With most of the UK enjoying the hot summer weather, being ill with the flu is the last thought on our minds. However, the threat of 'bird flu' still exists - it maybe out of sight but it's not out of mind to those who has to treat suspected incidences of bird flu in this country. During the last winter, avian flu hit the headlines, and will probably do so again once the cold weather approaches. For the paranoid or hypochondriacs among us, let me give you some facts about the infection. I have divided the information into parts and will post them up separately to make it easier to digest.

“Spanish flu” (H1N1) occurred between 1918 and 1919 and caused the highest number of known deaths, more than 500,000 in the United States and possibly as many as 50 million worldwide. Most of the deaths occurred within a few days of the person being infected, and nearly half of those who died were young, healthy adults.The second pandemic, called “Asian flu” (H2N2) occurred 40 years later (1957-1958) and caused approximately70,000 deaths in the United States. It was identified first in China in February 1957 and reached the United States by June of that year. The third and most recent pandemic occurred a decade later, in 1968 to1969. Known as the “Hong Kong flu” (H3N2), it was detected first in Hong Kong in early 1968 and later that year reached the United States, where it took 34,000 lives. The origin of the first pandemic virus remains unknown; the latter two pandemics were caused by viruses containing combinations of genes from both a human influenza virus and an avian influenza virus.

The H5N1 influenza virus, aka "avian flu" or "bird flu", was the first documented instance of human respiratory disease and death associated with a purely avian influenza virus in Hong Kong in 1997. This was thought to be the start of a potentially worldwide pandemic. The human disease was unusually severe, with an overall case-fatality rate of 33%. Except for one patient who was substantially immunocompromised, underlying disorders did not explain the severity of the course of the disease.

Human cases of avian influenza A(H5N1) infection have remained rare and sporadic, but the disease is very severe and the case fatality is high. With the H5N1 virus now confirmed in birds in more than 50 countries, additional sporadic human cases should be anticipated. Using innovative guideline development methods based on the best available evidence, the WHO assembled an international panel of experts in March 2006 to develop rapid advice for the pharmacological management of patients with H5N1 infection. The recommendations are classified as strong or weak. It also cover several specific patient and exposure groups for the treatment and chemoprophylaxis of H5N1 virus infection. All recommendations are specific to the current pre-pandemic situation and are based on careful consideration of the current evidence about benefits, harms, burdens and cost of interventions. As there are currently no clinical trials in patients with avian influenza H5N1 disease, the overall quality of evidence on which to base judgments is very low.

In part 2, I will go into basic virology of the H5N1 virus.

AMH