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Symptoms of the Bird Flu in Humans

The severity of symptoms upon human contraction of avian influenza depends again on both the condition of the victim and the form of bird flu contracted. Certain symptoms developed by the patient will be similar to that of an ordinary flu infection but bird flu also further triggers much more critical, potentially life-threatening conditions. Characteristic symptoms include:

• Cough
• Sore throat
• Muscle aches
• Headaches
• Fever (above 38°C)
• Sleepiness
• Diarrhea
• Respiratory complications
• Chest Pains
• Conjunctivitis (More common to H7 viruses)
• Pneumonia

A study of human bird flu patients has suggested that diarrhea is likely to arise among the first symptoms of avian influenza, a key difference that may distinguish it from the ordinary flu viruses. Symptoms involving areas of the upper respiratory tract (the nose and throat) are also less likely to occur during bird flu infection compared to the common runny noses and sneezing, which are characteristic to human influenza. Furthermore, the lower respiratory tract (lungs and bronchi) is affected relatively early on during contraction, generally causing a shortness of breath in bird flu victims and ultimately, more severe respiratory problems.

Younger children and the elderly have weaker immune systems that make them particularly susceptible to contracting influenza (including bird flu) and fighting against the symptoms it produces. Patients of heart or respiratory disorders are also at high risk of the disease in light of the impact it causes on the heart and lungs.

Period of Time Before Symptoms Emerge

The incubation period of a virus refers to the time it requires for symptoms of an infection to first emerge after initially contracting the virus. In the case of avian influenza, the virus possesses a longer incubation period than that of ordinary human flu and the latest reports have indicated an average incubation period of 8 days. This is considerably longer than the average 2 days required for ordinary flu symptoms to appear.

In rare cases where bird flu has occurred within a household, there have been roughly 2-5 days (and at most 17 days) in between the diagnosis of each consecutive victim. There is however, no fixed incubation period for avian influenza, largely as a result of the constant alteration of influenza viruses and the different pathogenicities of each subtype. (See Influenza)

Symptoms of Avian Influenza in Bird Species

Since different types of birds have different levels of natural resistance against flu virus subtypes, the severity of symptoms during infection also varies accordingly. Wild birds commonly carry avian influenza viruses without actually falling ill from them, yet domestic fowl become easily infected upon active virus contact. In domestic poultry, typical symptoms of highly pathogenic avian influenza include:

• Depression
• Nervousness
• A decline and eventually a cease of egg production
• Appetite loss
• Extreme thirst
• Coughing
• Sneezing
• Inflammation and discoloring of blue combs/wattles
• Hemorrhages on featherless parts of skin
• Diarrhea (Runny and abundant)
• Sudden death

Unfortunately, a number of domestic ducks that have contracted bird flu have been known to display no symptoms whatsoever and make it extremely difficult to visually detect. Chicken and turkeys are known to have the severest onsets of bird flu symptoms and hens often die within the first 48 hours of illness while the majority of turkeys die within the first 3-10 days. Poultry may also abruptly die from the disease without displaying any of the above symptoms depending on the initial condition of the bird and the surrounding environment.

Low pathogenic bird flu produces much weaker symptoms in poultry, typically:

• Mild respiratory disease
• Depression
• A decline in egg production

These symptoms can easily go unnoticed in few or individual chickens within large flocks.

Emergence of Symptoms in Poultry

The incubation period of avian influenza is difficult to determine in domestic poultry. It may range from several hours to as long as 18 days, dependent on the pathogenicity, dose and species of the virus. In highly pathogenic species, a theoretical average of 3-5 days is estimated for its incubation period.

Recovery Period of Poultry

Poultry that recover from bird flu are often left in a feeble state and do not generally begin any further egg-laying within the first few weeks. The survival rate of birds that contract highly pathogenic avian influenza tends to be less than 10% and may drop as low as 0%.