Overview
            Avian influenza is one of the most important viruses in the 21th century. The subtype A (H5N1) first appeared in Hong Kong in 19971 and has been founded in eight countries since then: Cambodia, Indonesia, China, Japan, Lao People's Democratic Republic, Republic of Korea, Thailand and Vietnam2.
            The virus, responsible for the bird flu, can be spread from the poultry to humans and until now, about 20 millions of chickens have been slaughtered in order to control the spread of the virus3. Since 1997, it has been reported more than 100 cases of the disease in humans, resulting in more than 50 deaths1. Experts are very concerned about the rising of a pandemic new strain of the virus because of the mixing between avian and human viruses. It’s suspected that the virus could infect someone who is already infected with a human flu virus like A, resulting in genetic rearrangement and a novel pathogen that could be highly virulent 4and easily transmitted human-to-human6.  
Transmission and symptoms.

            All birds are susceptible to the avian virus and some types of wild birds are natural reservoir of influenza type A virus. They have a large amount of avian virus in their secretion, saliva and feces that can contaminate domestic poultry when in contact. Furthermore, their dropping or saliva may contaminate water, rivers, feed and even human shoes1. Infected droplets may settle on conjunctival, nasopharyngeal or other respiratory mucosal epithelium in humans5 leading to symptons ranged from typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications6.
Virus characteristics and heat instability.

            Viruses aren’t considered living organisms, but they are very dependent on living cells to replicate. The structure of the virus includes the envelope which is constituted by proteins and the genetic material which can be DNA or RNA. All these components are thermosensible. The genetic material and the proteins have complex structures that are involved in their function and the change of their arrangements may result in lost of function. This process is called denaturation. There are two basic ways to do that: changing pH and temperature.

            The avian virus, H5N1, is a negative-sense, single-stranded RNA virus5, which has two types of proteins in its surface: hemagglutinin (HA) and neuraminidase (NA)6. It is known from the literature that the virus can be inactivated by 56oC in 3 hours and 60oC in 30 minutes1. Thus, only four degrees of temperature elevation reduced the time of inactivation exposure about 85%.

Bibliography

1. Shih-Wen Hung, I-Yin Lin, Tzong-Luen Wang. Emerging Infectious Disease (1): Avian Influenza. Med. 2005;3 Suppl 2:S40-S46).
2. Fleck, F. Avian flu virus could evolve into dangerous human pathogen, experts fear. Bull World Health Organ, mar. 2004; 82 (3):236-237. ISSN 0042-9686.
3. Abott A., Pearson H. Fear of human pandemic grows as bird flu sweeps through Asia. Nature, febr 2004; (427): 472-73.
4. Andresen M. Avian flu: WHO prepares for the worst. CMAJ. 2004 Mar 2;170(5):777.
5. KY Yuen, SSY Wong. Human infection by avian influenza A H5N1.Hong Kong Med J 2005;11:189-99

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