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Bird flu (avian influenza)

Definition


Disease: Bird flu (avian influenza) Bird flu (avian influenza)
Category: Infectious diseases
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Disease Definition:

Hundreds of millions of wild and domestic birds along with a small number of people died due to bird flu. However, now it’s difficult for people to get this disease. Most cases of people having bird flu symptoms had close contact with sick birds. Yet, a few cases passed from one person to another. Health officials worry that a major bird flu crisis might occur to humans if the virus— H5N1 —changes into a more easy-spreading form.

The gloomiest scene would be an international outbreak to challenge the flu epidemic of 1918-1919 which killed millions of people worldwide.
Now, researchers are trying to develop a vaccine that would protect people from the event of bird flu epidemic.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

The incubation period of bird flu in humans is not clear, but the illness seems to develop within 1 to 5 days of exposure to the virus.

The common signs and symptoms of bird flu seem to resemble those of conventional influenza, such as:

  • Fever
  • Cough
  • Sore throat
  • Muscle pain
  • A comparatively mild eye infection (conjunctivitis) which is sometimes the only indication of the disease.

Viral pneumonia and acute respiratory distress, which is the most common cause of deaths from bird flu, are some of the life-threatening complications that may develop due to this disease.
 

Causes:

Three or four times every 100 years, an epidemic flu sweeps the earth taking millions of lives. The secret behind this misery-causing disease is its ability to change itself quickly, disappointing the best-guess vaccines and leaving the immune system scourged.

Influenza viruses:
There are three strains of influenza viruses, namely, influenza A, B and C.

  • Type A is responsible for deadly influenza epidemics.
  • Type B can lead to smaller more localized outbreaks.
  • Type C is less common and more stable than other strains, with milder symptoms.

Either A or B types can cause the flu that spreads every winter. Types B and C are found only in humans, whereas type A infects both people and animals, including birds, horses, pigs, whales and seals.
There are numerous subtypes of type A that can join with other subtypes to form more subtypes; some of which can affect certain animals. 15 flu subtypes can affect birds; the deadliest one is H5N1. Until recently, avian subtypes were rarely the cause of human or other animal flu; except for pigs.

There are more strains of type A influenza viruses, each of which is continuously developing. This huge ability of influenza viruses to alter their genetic constitution and switch genes makes them unanticipated and potentially fatal.

HOW DO HUMANS CONTRACT BIRD FLU??
Typically, avian (bird) flu does not affect humans. But in 1997, a flu outbreak in china (Hong Kong) affected 18 people and 6 of them died. Cases of bird flu have been reported in Asia, Europe and the middle east since then. Most of these cases were due to infected poultry or surfaces polluted by sick birds.

In areas that people live near chickens and pigs is where the flu viruses that cross the species barrier originate. Pigs are more apt to have infection from both the human and avian type of viruses and thus are an ideal “mixing pot” for genes.

Some bird flu viruses need no third party. Instead, they shamble and rearrange their genes in the human container. This is the case in most human-developed bird flu.
Chiefly, people become infected not from contact with other animals, but from contact with sick birds or surfaces that are contaminated by sick birds.

HOW DOES THE DIRECT BIRD-TO-HUMAN TRANSMISSION WORK??
Wild avian casts off the virus. Sick, migratory waterfowls, which are the natural carriers of bird flu virus, shed the virus in their dung, saliva and nasal secretions.  The virus expands to reach domesticated birds by direct contact with sick birds or through contaminated water, feed or soil. Bird flu spreads quickly among domesticated flocks and is unknowingly carried from a farm to another through equipments, cages or workers’ shoes and clothes. Heat can destroy the virus. Yet, it still can survive for long spans of time in a cool temperature environment.

The pathway to humans is offered by markets. Open-markets where eggs and chickens are sold in crowded and unhealthful conditions are good environment for infection and virus expansion. Humans can pick up the virus from sick birds, contaminated surfaces or simply touching the sick bird at any point along the way because sick birds can shed the virus through their feathers or droppings. The worldwide travel has the main possibility in spreading the disease around the world. Also, migratory birds can carry the virus along flyways from one continent to the other. Locally, outbreaks could spread through markets, contaminated clothing and equipment, and smuggled birds.

IS THIS THE BEGINNING OF A PANDEMIC??
Mutation of H5N1 happens quickly. Thus, it’s able to integrate large blocks of genetic codes from viruses that infect other species; a process called re-assortment. That’s why H5N1 has the possibility to combine with a human flu virus and create a new viral strain that spreads rapidly from one person to another. The outbreak of such a virus foretells a global crisis.

In October 2006, the ability of H5N1 to evolve quickly was evident when a new strain, called H5N1 Fujian-like, appeared in China and spread quickly throughout much of Southeast Asia. This new strain is immune to the vaccines given to birds to prevent H5N1 infections.
 

Complications

Complications:

Signs of traditional influenza show in people with bird flu. Some develop life jeopardizing complications like viral pneumonia and acute respiratory distress syndrome, which fills the air sacs in someone's lungs with fluid, leading to grave breathing difficulties.

More than half of the people carrying the virus died. Yet, the greatest complication of bird flu; that is the emergence of new viral breed spreading from a person to another is merely hypothetical. If a person had bird and human flu at the same time, the re-assortment of genes could produce an entirely new subtype with a majority of human genes. This makes the virus highly contagious and very lethal due to the little natural immunity in the world’s population.

Hopefully, this hasn't happened. A few person-to-person cases of infection have occurred, but they were bounded in importance. Still, some health officials worry that it's just a matter of time before avian viruses find out a path to pass among people easily.
 

Treatments:

The number one treatment option now remains flu drug oseltamivir , which stops the virus from breeding. Exactly how effective Oseltamivir will prove against H5N1 is still not clear. An alternative antiviral flu medication might be zanamivir .

These drugs should be taken within 2 days after symptoms appeare which may prove logically and systematically difficult on a worldwide scale, even if there were enough drugs for everyone. However, at some point, viruses may become immune to these drugs.
Being short supply, it's not clear how flu drugs would be apportioned if there were a worldwide epidemic.

Prognosis:

Not available

Expert's opinion

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