Written By: Hanan Khalaf. RPH.

AVIAN = BIRD FLU = INFLUENZA

WHAT IS AN AVIAN FLU?

Avian flu is an infection that occurs in birds and is caused by an influenza virus. This virus is usually found in the stomach of wild birds particularly wild ducks without causing a problem for them. Virus is shed through feces leading to contaminated water and air. When poultry is affected, they tend to develop a more severe disease.

HOW DIFFERENT IS BIRD FLU FROM HUMAN FLU?

Both originate from influenza virus type A. This virus is considered one of the viruses that cause human influenza. Influenza A virus is classified into 16 HA subtypes and 9 NA subtypes. Only 3 out of these subtypes cause human influenza namely H1N1, H1N2, H3N2, while most other subtypes infect mainly birds. The subtype that is implicated in the current epidemics is H5N1.

HOW VIRULENT IS BIRD FLU VIRUS?

Of all the subtypes that cause bird flu, only viruses of the H5 & H7 subtypes are known to cause highly pathogenic form of the disease. The current understanding is that whenever H5 or H7 viruses are introduced into domestic birds, they are usually in their low pathogenic form. Then after circulating for few months, they will develop the ability to mutate to highly pathogenic form of the disease.

Low pathogenic avian influenza (LPAI) can lead to mild form of the disease, while high pathogenic avian influenza (HPAI) can lead to high mortality rate (reaching 100%) within almost 48 hours of acquiring the disease. H5N1 is considered HPAI.

HOW DOES BIRD FLU SPREAD TO HUMANS?

Although the spread doesn’t occur easily, it is believed that direct contact with infected poultry, or surfaces and objects contaminated by their feces is the main route of human infection. There is no evidence that properly cooked poultry or eggs can be a source of infection.

IS THERE ANY EVIDENCE OF HUMAN-TO-HUMAN TRANSMISSION CURRENTLY?

According to WHO, human-to-human transmission of H5N1 and other avian influenza have occurred in very limited occasions and is considered rare. This has been noticed with outbreaks in poultry and only within the first generation of close contacts. This issue, according to WHO, should not be a cause of alarm.

WHAT ARE THE SYMPTOMS OF AVIAN FLU WHEN IT OCCURS IN HUMANS?

According to the cases reported, symptoms ranged from typical flu-like namely fever, cough, sore throat, muscle aches, to more severe like pneumonia, severe respiratory disease.

DOES AVIAN FLU TEND TO OCCUR IN A SPECIFIC AGE GROUP THAN THE OTHER?

No, over 100 human cases have occurred with the current outbreak and included different age groups.

WHAT IS THE TREATMENT SUGGESTED FOR AVIAN FLU IN HUMANS?

Oseltamivir (Tamiflu®) and Zanamivir (Relenza®) are two neuraminidase inhibitors Known for their ability to reduce the severity and duration of illness caused by seasonal influenza. The evidence shows that they might be able to improve survival, if administered early, in cases of human infection with H5N1, despite the fact that clinical data are limited in that respect.

IS THERE ANY VACCINE FOR AVIAN FLU DISEASE IN HUMANS?

Currently, there is no vaccine available that can be used against H5N1 virus which emerged in Asia. Vaccine development is under research. However, news are available now about some success in the development of human vaccine against H5N1, for more information

HOW ABOUT THE RISK OF PANDEMIC FROM H5N1 VIRUS?

According to WHO (World Health Organization), pandemic risk would be high if 3 conditions are met namely:

A new influenza virus subtype emerges

It infects human, causing serious illness

It spreads easily and sustainably among humans.

Applying to the current situation, two conditions out of three are met. H5N1 is a new virus for humans that has never circulated widely among them, and it has infected more than 100 individuals with a mortality of > 50%. However, risk of sustained human-to-human transmission will be acquired by the virus as long as opportunities for human infections occur. Moreover, opportunities for human infections will continue as long as the virus continue to circulate in birds.

October 24, 2005

References:

World Health Organization

Center of Disease Control