Bird flu – the pandemic clock is ticking

Box 5 | Antivirals bring hope

The influenza virus has found an ideal strategy – one that makes it difficult for the body's immune system to deal with. The surface of the virus is constantly changing, making it difficult for the immune system to 'recognise' the virus and fight off the infection. But the flu virus does have a 'weak spot'. The enzyme neuraminidase is needed for the virus to get to the site of infection and to release new viruses from infected cells. Both of these activities are associated with a pocket-shaped structure on neuraminidase that does not change shape. A group of Australian researchers thought that if the unchanging pocket was blocked by a dummy molecule, then the virus would be unable to increase in number and spread to other cells. The compound they found is called zanamivir, and is now marketed by the name Relenza. Three researchers – Peter Colman, Graeme Laver and Mark von Itzstein – shared the 1996 Australia Prize for excellence in the field of pharmaceutical design for their work on Relenza.

Based on the Australian research, another compound that worked in a similar way was found by overseas researchers, and that compound is now marketed as Tamiflu.

Relenza is used as a nasal spray, whereas Tamiflu is taken orally as a tablet. They are both very effective at preventing the flu in human volunteers. If taken within 48 hours of the first signs of the flu, they decrease the number of people who get the flu, the severity of the symptoms and the duration of the infection. Importantly, they also work against H5N1 viruses in laboratory tests.

Although vaccination is the preferred option to prevent the flu, Tamiflu and Relenza also have the ability to prevent the flu when taken as a prophylactic, before exposure to the virus. The combination of vaccination and prevention with Tamiflu or Relenza can also be used.

One question still remains. Will pressure on the virus, arising from widespread use of Relenza or Tamiflu select virus resistant to the drugs? Work to date indicates that the virus is having a difficult time changing the pocket structure and still being able to multiply in cells. But that may be a matter of time and opportunity. New forms of drugs similar to Relenza and Tamiflu are being made and tested, to add to the number of drugs available to prevent and treat the flu.

Boxes
Box 1. An ever-changing virus
Box 2. Past flu pandemics
Box 3. Controlling an outbreak
Box 4. Vaccines for pandemics

Related sites
Flu cure (Australia Advances, CSIRO)(Requires QuickTime to view the associated video.)
Do cough, cold and flu remedies work? (Choice Magazine, Australia)
Relenza – medicine guide (Medicines Information Project, UK)
Tamiflu – medicine guide (Medicines Information Project, UK)
Tamiflu (oseltamivir phosphate) (US Food and Drug Administration)
Relenza (zanamivir) (US Food and Drug Administration)

External sites are not endorsed by the Australian Academy of Science.
Posted July 2005.