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Let me give a brief on Avian Influenza (H5N1) or Commonly termed as Bird Flu

Transmission
Human influenza is transmitted by inhalation of infectious droplets and droplet nuclei, by direct contact, and perhaps, by indirect (fomite) contact, with self-inoculation onto the upper respiratory tract or conjunctival mucosa.4,5 The relative efficiency of the different routes of transmission has not been defined. For human influenza A (H5N1) infections, evidence is consistent with bird-to-human, possibly environment-to-human, and limited, nonsustained human-to-human transmission to date.
Animal to Human
In 1997, exposure to live poultry within a week before the onset of illness was associated with disease in humans, whereas there was no significant risk related to eating or preparing poultry products or exposure to persons with influenza A (H5N1) disease. Exposure to ill poultry and butchering of birds were associated with seropositivity for influenza A (H5N1). Recently, most patients have had a history of direct contact with poultry, although not those who were involved in mass culling of poultry. Plucking and preparing of diseased birds; handling fighting cocks; playing with poultry, particularly asymptomatic infected ducks; and consumption of duck's blood or possibly undercooked poultry have all been implicated. Transmission to felids has been observed by feeding raw infected chickens to tigers and leopards in zoos in Thailand and to domestic cats under experimental conditions. Transmission between felids has been found under such conditions. Some infections may be initiated by pharyngeal or gastrointestinal inoculation of virus.
Human to Human
Human-to-human transmission of influenza A (H5N1) has been suggested in several household clusters and in one case of apparent child-to-mother transmission. Intimate contact without the use of precautions was implicated, and so far no case of human-to-human transmission by small-particle aerosols has been identified. In 1997, human-to-human transmission did not apparently occur through social contact, and serologic studies of exposed health care workers indicated that transmission was inefficient. Serologic surveys in Vietnam and Thailand have not found evidence of asymptomatic infections among contacts. Recently, intensified surveillance of contacts of patients by reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assay has led to the detection of mild cases, more infections in older adults, and an increased number and duration of clusters in families in northern Vietnam, findings suggesting that the local virus strains may be adapting to humans. However, epidemiologic and virologic studies are needed to confirm these findings. To date, the risk of nosocomial transmission to health care workers has been low, even when appropriate isolation measures were not used. However, one case of severe illness was reported in a nurse exposed to an infected patient in Vietnam.
Environment to Human
Given the survival of influenza A (H5N1) in the environment, several other modes of transmission are theoretically possible. Oral ingestion of contaminated water during swimming and direct intranasal or conjunctival inoculation during exposure to water are other potential modes, as is contamination of hands from infected fomites and subsequent self-inoculation. The widespread use of untreated poultry feces as fertilizer is another possible risk factor.

Here's a link from where you can download the WHO (World Health Organization) published report on Bird Flu and it's possible treatments.