**6. Prevention and control**

*Viruses and Viral Infections in Developing Countries*

Kong, strain 156, and isolated in 1997 [1].

highly pathogenic avian influenza virus [12].

tracheal or fecal swabs of suspected birds [14].

**4. Transmission of disease from birds**

**5. Transmission of disease to humans**

**3. Avian influenza in birds**

of the virus along with the alteration of the host range [10].

Wild ducks spread the disease to other susceptible hosts [2].

A nomenclature system for influenza viruses has been established by the World Health Organization (WHO) and FAO. This system contains the type of influenza, the first place of isolation of virus, strain, and year of isolation. For example, A/ Hong Kong/156/97 would be interpreted as influenza type A, isolated in Hong

Hemagglutinin mediates binding of the virus to sialic acid receptors at the cell surface. Neuraminidase plays its role in the detachment of the virus from the cell surface [8]. A specific type of hemagglutinin binds with a specific type of cell surface that further clarifies the difference host range for different influenza virus types [9]. Mutation of genes coding hemagglutinin and neuraminidase affects the transmission

Healthy birds can become affected by the avian influenza virus by direct contact with an infected bird. Avian influenza virus has the capability to infect more than 100 species of birds worldwide [11]. Reservoir hosts of the virus include waterfowls and shorebirds. Low pathogenic avian influenza infection does not cause any clinical disease. But, the virus survives in the host and sometimes mutates to produce

Some species of birds are more disease resistant than others. For example, domestic poultry is more susceptible to H5N1 HPAIV infection than wild ducks.

HPAI infection in susceptible birds can cause systemic infection including damage to the nervous and circulatory system that ultimately leads to death. HPAI virus inhabits and multiplies in the respiratory and gastrointestinal tracts [13]. Clinical signs and symptoms of HPAI infection in birds include loss of appetite, diarrhea, nasal discharge, respiration problem, misshapen eggs, ataxia, and incoordination [10]. The maximum mortality rate in poultry due to HPAI infection can be up to 95%. Confirmatory diagnosis of HPAI can be done by performing PCR analysis of

Waterfowls and shorebirds are natural reservoirs of the influenza virus, and these birds spread the virus to domestic poultry by contaminating the water source, feed, and housing of domestic poultry [15]. Influenza virus secreted in feces can survive up to 35 days at 4°C. Aerosol transmission of the virus is also possible. Indirect contamination via shoes, clothing, and contaminated feathers is also reported [2]. Interspecies transmissions of the avian influenza virus are also possible. In Europe and the United States, H1N1 and H3N2 are commonly prevalent in swine population, and outbreaks have been reported by the transmission of these viruses to susceptible turkeys and chickens [11]. In another case, an outbreak in turkey flock has been reported in Canada from a poultry worker having a respiratory

In most cases of human infection with the influenza virus, the previous contact with alive or dead bird was recorded. People who are involved with poultry at any

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problem [1].

For the control of avian influenza in commercial and rural poultry, risk management is the most important point [18]. Implementation of good agricultural practices such as strict biosecurity measures, training of poultry workers, availability of non-contaminated water, disinfection of equipment, and decontamination of farm premises before the introduction of the new flock can decrease the chance of an outbreak of AI [16].

In case of an outbreak, rapid culling and depopulation are recommended. Rapid culling can reduce the spread of the virus and minimize economic loss [19]. Poultry and their products infected with HPAI are banned to enter the food chain in developed countries [1], whereas in developing countries, HPAI-infected meat and products are consumed as feed after cooking at high temperatures. The use of effective vaccination can limit the H5N1 HPAI virus spread [18].
