H5N1 bird flu: Symptoms, causes, and diagnosis

Avian flu, or bird flu, refers to a group of infectious diseases caused by influenza viruses that infect birds and make them ill. One subtype of bird flu is H5N1.

H5N1 is a severe infection with a high mortality rate.

The first outbreak of H5N1 bird flu was in December 2003.

Since then, over 700 cases have been reported, in Africa, Asia, and Europe. The highest numbers have been in Indonesia, Vietnam, and Egypt.

The most recent case of H5N1 was reported in Malaysia in March 2017. It killed a number of chickens, but no human cases were reported.

It is not easy for humans to catch it, but it is fatal in 60 percent of cases.

Fast facts about H5N1 avian flu

Here are some facts about avian flu. More detail is in the main article.

Avian flu affects birds. In some cases, it can transfer to humans.

It can be fatal in 60 percent of cases.

Symptoms include blood in the sputum, a high fever, headache, and an upset stomach. Deterioration can be rapid.

Antiviral medication can help increase the chances of survival and reduce the impact of the disease.

A pandemic is unlikely unless the disease learns to spread between people.

What is H5N1?

[Avian flu eggs]
Avian flu is transferred from birds to humans and is fatal in 60 percent of cases.

Type A strains of the influenza virus cause H5N1 avian flu.

H5N1 affects several types of birds. It has mostly been reported in farmed poultry, such as chickens, geese, turkeys, and ducks.

However, in January 2015 it was found in a wild duck in the United States (U.S.), and it has also been isolated in pigs, cats, dogs, stone martens, and lions and tigers in captivity.

The virus passes easily between birds, through their saliva, nasal secretions, feces, and feed. They can get the virus from tainted surfaces, such as cages and other farming equipment.

Most people with the virus have had direct contact with infected poultry or objects contaminated with bird feces or secretions.

Until now, very few cases of human-to-human transmission have occurred. However, if H5N1 were to mutate so that it can pass easily between humans, a pandemic could result.

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A person with H5N1 will develop serious symptoms.

The incubation period is from 2 to 8 days, and it can take up to 17 days. This is compared with 2 to 3 days for human seasonal flu.

Initial symptoms include a high fever, over 38 degrees centigrade, lower respiratory tract symptoms, and, less commonly, upper respiratory tract symptoms.

The following signs and symptoms may occur:

a cough, usually dry

hoarse voice

a high fever, over 38 degrees centigrade

a blocked or runny nose

aching bones, joints, and muscles

bleeding from the nose

chest pain

cold sweats and chills



loss of appetite

sleeping difficulties

upset stomach, sometimes involving diarrhea

bleeding from the gums

bloody sputum

Some patients develop pneumonia and breathing difficulties. This occurs around 5 days after the first symptoms appear.

The patient’s condition can deteriorate rapidly, resulting in pneumonia, multiple organ failure, and death.

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Humans can become infected and ill after coming into contact with infected birds.

The following have been linked to human illness:

touching or defeathering infected birds

touching or breathing in feces and other secretions of infected birds

preparing infected poultry for cooking

slaughtering or butchering infected poultry

handling birds for sale

attending markets selling live birds

Eating cooked poultry or eggs does not cause infection.

However, people should cook poultry until the internal temperature is at least 165 degrees Fahrenheit or 74 degrees centigrade, and eggs until both the white and yolk are firm.

Bird droppings can contain the virus, and they can contaminate feed, equipment, vehicles, shoes, clothing, soil, dust and water. The feet and bodies of animals can also carry the H5N1 virus.


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