**3. Avian influenza in birds**

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 highly pathogenic avian influenza virus [12].

Some species of birds are more disease resistant than others. For example, domestic poultry is more susceptible to H5N1 HPAIV infection than wild ducks. Wild ducks spread the disease to other susceptible hosts [2].

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 tracheal or fecal swabs of suspected birds [14].

#### **4. Transmission of disease from birds**

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 problem [1].

#### **5. Transmission of disease to humans**

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

**57**

*Prologue: Avian Influenza - An Overview from Endemic to Pandemic*

level are more prone to exposure than other people [16]. Meat workers, poultry farmworkers, and bird sellers are under constant threat. Veterinarians are also at higher risk due to their contact with different types of birds [17]. Direct human to human transmission is also possible at mass gatherings such as airports, concerts,

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

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

The first influenza A virus pandemic in humans was recorded almost a century ago, in 1918, which resulted in the death of around 20–50 million humans worldwide [20, 21]. So far, three other pandemics of influenza A virus in humans that have caused considerable loss include the 1957 H2N2 pandemic, the 1968 H3N2 pandemic, and the 2009 H1N1 pandemic [22]. From East Asia to Southeast Asia, sporadic human infection of H5N1 viruses was reported in 2003–2004 along with

H5N1 viruses have been reported from domesticated poultry and wild birds in Asia, North Africa, Central Africa, and Europe [23]. The transmission of HPAI H5N1 viruses from poultry to humans was first documented in 1997 in Hong Kong. Some subtypes of avian influenza virus such as H5, H7, H9, and H10 have the capability of interspecies transmission [18]. According to the World Health Organization, the total confirmed human cases of H5N1 infection to date are 860 with 454 fatal cases [24]. In 2013, a LPAI H7N9 virus caused an outbreak in China with a 36% case fatality [25]. Influenza viruses are a permanent threat for humans

effective vaccination can limit the H5N1 HPAI virus spread [18].

*DOI: http://dx.doi.org/10.5772/intechopen.90328*

and funeral ceremonies [18].

**6. Prevention and control**

**7. One health perspective**

outbreaks in the poultry [21].

as well as birds.

outbreak of AI [16].

level are more prone to exposure than other people [16]. Meat workers, poultry farmworkers, and bird sellers are under constant threat. Veterinarians are also at higher risk due to their contact with different types of birds [17]. Direct human to human transmission is also possible at mass gatherings such as airports, concerts, and funeral ceremonies [18].
