Asian bird flu, bird flu, Avian flu virus.

  Is Asian Bird Flu the Next Pandemic?

When a top World Health Organization official warned late last month that the bird flu virus that has plagued Asian countries might unleash a pandemic that could kill up to 50 million people, one thing that did not break out was mass panic. After all, it's hardly the first time such a catastrophic prediction has been issued. Last year it was the SARS virus, now the potential mass killer is the H5N1 avian flu virus. While most health experts agree that the bird flu virus represents a grave danger and is highly likely to spread unless urgent steps are taken, some virologists caution that alarmist warnings could harm preparedness plans. "The danger is that people might get blasé about the message," said Ian Jones, a virology professor at the University of Reading in England. "They'll think, Yeah, yeah, I've heard it before. It didn't come then, and it won't come this time."

Genetic Change

The H5N1 virus, a subtype of the avian influenza virus, is found in poultry. Scientists at first believed it was impossible for birds to directly infect humans with the virus. But an outbreak in Hong Kong in 1997 that killed 6 of 18 people infected with the virus proved the contrary. Since then outbreaks have forced the slaughter of millions of chickens, ducks, and other birds across Asia. This year there have been 44 confirmed human cases of H5N1 flu in Thailand and Vietnam. Of these, 32 people died. There is not yet a vaccine for the disease. Meanwhile the virus has undergone huge genetic changes and become even more pathogenic. It now affects not only birds, but also cats, pigs, and even tigers. Experts fear the disease will mutate into a form that can leap between humans and sweep populations with no immunity. The adaptation could occur through a few genetic changes or what is known as "re-assortment" of the genes of the avian strain and the human strain. Domestic ducks and pigs are seen as likely transmitters. "All virologists agree that this is a very dangerous time for H5N1" .

Virologists say domesticated ducks and pigs would be the likely carriers if avian flu H5N1 were to genetically mutate into a form that could leap between humans.

There is some evidence that influenza pandemics occur on a regular cycle, with one every 20 to 30 years. The notorious Spanish flu killed at least 20 million people worldwide in 1918. Outbreaks in the late 1950s and late 1960s resulted in tens of thousands of deaths in the United States alone. Now the world may be due for another outbreak. "Almost everyone in the field feels that an influenza pandemic is virtually inevitable, and that we need to be prepared for it," said Stephen Morse, the director of the Center for Public Health Preparedness at Columbia University in New York. The World Health Organization estimates the H5N1 virus could infect up to 30 percent of the world's population. Shigeru Omi, the WHO official who issued last month's warning, said that estimates of 2-7 million deaths were "conservative" and that the maximum range could go as high as 50 million deaths. Some virologists, however, take issue with his warning. "This alarmist warning is irresponsible in using this language to rouse the public's fear," said Michael Lai, a virologist at the University of Southern California in Los Angeles. He says the warnings of an impending flu pandemic have circulated since the Hong Kong outbreak in 1997, but no major outbreak among humans has yet happened. Furthermore no one actually knows what would happen to the virus if it adapted to grow in humans. It might be as lethal as it is now, or it might become far less pathogenic.

Hot topic - Avian flu (bird flu).

A number of Asian countries have been affected by avian flu (bird flu) infecting their poultry stocks. In some of these countries, a small number of people have contracted the avian flu virus from chickens. Scientists are concerned by these events because it is feared that the avian flu virus could merge with a human flu virus. The result of this merging might result in a new, highly infectious, rapidly fatal flu virus. Such a new virus would be transmitted rapidly from person to person with potentially devastating results. To keep the outbreak of avian flu virus under control, many of the Asian countries are culling their poultry stocks to prevent further spread of the virus.

What is avian flu?

Avian flu is used to describe the influenza viruses that infect birds - for example wild birds such as ducks and domestic birds such as chickens. In fact, birds appear to a natural reservoir of flu viruses - 15 subtypes influenza A virus are known to be circulating in bird populations. Many forms of avian flu virus cause only mild symptoms in the birds, or no symptoms at all. However, some of the viruses produce a highly contagious and rapidly fatal disease, leading to severe epidemics. These virulent viruses are known as "highly pathogenic avian influenza" and it is these viruses that cause particular concern. One such avian flu virus is currently infecting chickens in Asian countries.

Why are scientists and governments so concerned about avian flu?

Until 1997 avian flu was believed to only infect birds, however in 1997 it was discovered that the virus can occasionally infect people who have been in close contact with live birds in markets or farms. This rare ability of avian flu viruses to infect humans (known as "species jumping") throws up a worrying possibility. It is possible that a highly pathogenic avian flu virus could merge with a human flu virus and create a new virus that could be easily passed between humans and was rapidly fatal. If this happens, the result could be the next flu pandemic.

What is a flu pandemic?

When a new, highly infectious form of a flu virus is formed it can rapidly infect a large number of people. The result is a illness that rapidly spreads round the world and may cause widespread loss of life. An example is the Spanish flu pandemic of 1918-1919 which caused an estimated 40-50 million deaths worldwide.

How would an avian flu virus merge with a human flu virus to produce a new, highly infectious flu virus?

There are two circumstances in which an avian flu virus could merge with a human flu virus: In humans - if a person who already has flu is comes into close contact with birds who have highly pathogenic avian flu, there is a tiny chance that the person could become infected with the avian flu virus. If this happens, the person would now be carrying both the human flu virus and the avian flu virus. The two viruses could meet in the person's body and swap genes with each other. If the new virus had the avian flu's genes that made it rapidly fatal and the human flu's genes to allow it to be passed from person to person, a flu pandemic could result. In pigs - pigs are susceptible to both human and bird flu viruses. If a pig became infected with both viruses at the same time, it could act as a "mixing vessel", allowing the two viruses to swap genes and produce a new virus.

Has such a new flu virus happened yet?

No. There is no evidence that the people who have been infected with avian flu have passed the disease on to other people. This suggests that a new, highly infectious, flu virus has not been produced yet. However, every time an avian flu virus jumps from a bird to a person, the risk of a new flu virus being produced increases. For this reason, governments are keen to prevent the spread of avian flu among birds and this is why they are culling their poultry stocks.

How is the avian flu virus transmitted?

When a bird is infected with avian flu, it sheds the flu virus in its faeces, saliva and mucus. Other birds become infected by eating or inhaling the virus. Very rarely, the virus can infect people who are in close contact with infected birds - for example by people inhaling dried faeces that have become trampled into dust. People cannot catch avian flu from eating cooked chickens. It is suggested that travellers to Asian countries affected by avian flu should avoid poultry markets and farms to minimise any risk of becoming infected.

What are the symptoms of human flu?

Human flu symptoms are:

• fever
• cough
• sore throat
• muscle aches
• conjunctivitis

Cases of bird flu are more likely to cause breathing problems and pneumonia, and can be fatal.

Are there any treatments available for avian flu?Antiviral medications used to treat human flu viruses appear to be effective in treating avian flu.

How dangerous is avian flu?

Avian flu appears to have a high mortality rate among people who get it. There have been a number of small outbreaks of avian flu since 1997:

Hong Kong 1997 - during this outbreak, 18 people were infected and 6 people died.

Hong Kong 2003 - in a family that had visited southern China, there were two cases of the disease and one death.

Far East 2004 - up to 10 deaths have been linked to this latest outbreak of the disease in a number of Asian countries.

What is the current travel advice for visitors travelling to Asian ountries affected by avian flu?

The UK Department of Health (DoH) advises:
"Although there is no restriction on travel to any of the areas where avian flu is being reported, travellers are advised to take sensible precautions such as avoiding bird markets, farm or contact with live poultry." The US Centers for Disease Control and Prevention (CDC) advises:
"At this time CDC and WHO [the World Health Organisation] have not issued any travel alerts or advisories for the region in response to the H5N1 [avian flu virus] outbreak. However, travellers to countries in Asia with documented H5N1 outbreaks are advised to avoid poultry farms, contact with animals in live food markets and any surfaces that appear to be contaminated with faeces from poultry or other animals."

Avian influenza (“bird flu”) and the significance of its transmission to humans

The disease in birds: impact and control measures

Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than 100 years ago, occurs worldwide. All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics. The latter is known as “highly pathogenic avian influenza”. This form is characterized by sudden onset, severe illness, and rapid death, with a mortality that can approach 100%. Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations. To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7. Migratory waterfowl – most notably wild ducks – are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza. Direct or indirect contact of domestic flocks with wild migratory waterfowl has been implicated as a frequent cause of epidemics. Live bird markets have also played an important role in the spread of epidemics. Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1983–1984 epidemic in the United States of America, the H5N2 virus initially caused low mortality, but within six months became highly pathogenic, with a mortality approaching 90%. Control of the outbreak required destruction of more than 17 million birds at a cost of nearly US$ 65 million. During a 1999–2001 epidemic in Italy, the H7N1 virus, initially of low pathogenicity, mutated within 9 months to a highly pathogenic form. More than 13 million birds died or were destroyed. The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing spread to other farms and eventual establishment of the virus in a country’s poultry population. Apart from being highly contagious, avian influenza viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. Stringent sanitary measures on farms can, however, confer some degree of protection. In the absence of prompt control measures backed by good surveillance, epidemics can last for years. For example, an epidemic of H5N2 avian influenza, which began in Mexico in 1992, started with low pathogenicity, evolved to the highly fatal form, and was not controlled until 1995.

A constantly mutating virus: two consequences

All type A influenza viruses, including those that regularly cause seasonal epidemics of influenza in humans, are genetically labile and well adapted to elude host defenses. Influenza viruses lack mechanisms for the “proofreading” and repair of errors that occur during replication. As a result of these uncorrected errors, the genetic composition of the viruses changes as they replicate in humans and animals, and the existing strain is replaced with a new antigenic variant. These constant, permanent and usually small changes in the antigenic composition of influenza A viruses are known as antigenic “drift”. The tendency of influenza viruses to undergo frequent and permanent antigenic changes necessitates constant monitoring of the global influenza situation and annual adjustments in the composition of influenza vaccines. Both activities have been a cornerstone of the since its inception in 1947. Influenza viruses have a second characteristic of great public health concern: influenza A viruses, including subtypes from different species, can swap or “reassort” genetic materials and merge. This reassortment process, known as antigenic “shift”, results in a novel subtype different from both parent viruses. As populations will have no immunity to the new subtype, and as no existing vaccines can confer protection, antigenic shift has historically resulted in highly lethal pandemics. For this to happen, the novel subtype needs to have genes from human influenza viruses that make it readily transmissible from person to person for a sustainable period. Conditions favourable for the emergence of antigenic shift have long been thought to involve humans living in close proximity to domestic poultry and pigs. Because pigs are susceptible to infection with both avian and mammalian viruses, including human strains, they can serve as a “mixing vessel” for the scrambling of genetic material from human and avian viruses, resulting in the emergence of a novel subtype. Recent events, however, have identified a second possible mechanism. Evidence is mounting that, for at least some of the 15 avian influenza virus subtypes circulating in bird populations, humans themselves can serve as the “mixing vessel”.

Human infection with avian influenza viruses: a timeline

Avian influenza viruses do not normally infect species other than birds and pigs. The first documented infection of humans with an avian influenza virus occurred in Hong Kong in 1997, when the H5N1 strain caused severe respiratory disease in 18 humans, of whom 6 died. The infection of humans coincided with an epidemic of highly pathogenic avian influenza, caused by the same strain, in Hong Kong’s poultry population. Extensive investigation of that outbreak determined that close contact with live infected poultry was the source of human infection. Studies at the genetic level further determined that the virus had jumped directly from birds to humans. Limited transmission to health care workers occurred, but did not cause severe disease. Rapid destruction – within three days – of Hong Kong’s entire poultry population, estimated at around 1.5 million birds, reduced opportunities for further direct transmission to humans, and may have averted a pandemic. That event alarmed public health authorities, as it marked the first time that an avian influenza virus was transmitted directly to humans and caused severe illness with high mortality. Alarm mounted again in February 2003, when an outbreak of H5N1 avian influenza in Hong Kong caused 2 cases and 1 death in members of a family who had recently travelled to southern China. Another child in the family died during that visit, but the cause of death is not known. Two other avian influenza viruses have recently caused illness in humans. An outbreak of highly pathogenic H7N7 avian influenza, which began in the Netherlands in February 2003, caused the death of one veterinarian two months later, and mild illness in 83 other humans. Mild cases of avian influenza H9N2 in children occurred in Hong Kong in 1999 (two cases) and in mid-December 2003 (one case). H9N2 is not highly pathogenic in birds. The most recent cause for alarm occurred in January 2004, when laboratory tests confirmed the presence of H5N1 avian influenza virus in human cases of severe respiratory disease in the northern part of Viet Nam.

Why H5N1 is of particular concern

Of the 15 avian influenza virus subtypes, H5N1 is of particular concern for several reasons. H5N1 mutates rapidly and has a documented propensity to acquire genes from viruses infecting other animal species. Its ability to cause severe disease in humans has now been documented on two occasions. In addition, laboratory studies have demonstrated that isolates from this virus have a high pathogenicity and can cause severe disease in humans. Birds that survive infection excrete virus for at least 10 days, orally and in faeces, thus facilitating further spread at live poultry markets and by migratory birds. The epidemic of highly pathogenic avian influenza caused by H5N1, which began in mid-December 2003 in the Republic of Korea and is now being seen in other Asian countries, is therefore of particular public health concern. H5N1 variants demonstrated a capacity to directly infect humans in 1997, and have done so again in Viet Nam in January 2004. The spread of infection in birds increases the opportunities for direct infection of humans. If more humans become infected over time, he likelihood also increases that humans, if concurrently infected with human and avian influenza strains, could serve as the “mixing vessel” for the emergence of a novel subtype with sufficient human genes to be easily transmitted from person to person. Such an event would mark the start of an influenza pandemic.

Influenza pandemics: can they be averted?

Based on historical patterns, influenza pandemics can be expected to occur, on average, three to four times each century when new virus subtypes emerge and are readily transmitted from person to person. However, the occurrence of influenza pandemics is unpredictable. In the 20th century, the great influenza pandemic of 1918–1919, which caused an estimated 40 to 50 million deaths worldwide, was followed by pandemics in 1957–1958 and 1968–1969. Experts agree that another influenza pandemic is inevitable and possibly imminent. Most influenza experts also agree that the prompt culling of Hong Kong’s entire poultry population in 1997 probably averted a pandemic. Several measures can help minimize the global public health risks that could arise from large outbreaks of highly pathogenic H5N1 avian influenza in birds. An immediate priority is to halt further spread of epidemics in poultry populations. This strategy works to reduce opportunities for human exposure to the virus. Vaccination of persons at high risk of exposure to infected poultry, using existing vaccines effective against currently circulating human influenza strains, can reduce the likelihood of co-infection of humans with avian and influenza strains, and thus reduce the risk that genes will be exchanged. Workers involved in the culling of poultry flocks must be protected, by proper clothing and equipment, against infection. These workers should also receive antiviral drugs as a prophylactic measure. When cases of avian influenza in humans occur, information on the extent of influenza infection in animals as well as humans and on circulating influenza viruses is urgently needed to aid the assessment of risks to public health and to guide the best protective measures. Thorough investigation of each case is also essential. While WHO and the members of its global influenza network, together with other international agencies, can assist with many of these activities, the successful containment of public health risks also depends on the epidemiological and laboratory capacity of affected countries and the adequacy of surveillance systems already in place. While all these activities can reduce the likelihood that a pandemic strain will emerge, the question of whether another influenza pandemic can be averted cannot be answered with certainty.

Clinical course and treatment of human cases of H5N1 avian influenza .

Published information about the clinical course of human infection with H5N1 avian influenza is limited to studies of cases in the 1997 Hong Kong outbreak. In that outbreak, patients developed symptoms of fever, sore throat, cough and, in several of the fatal cases, severe respiratory distress secondary to viral pneumonia. Previously healthy adults and children, and some with chronic medical conditions, were affected. Tests for diagnosing all influenza strains of animals and humans are rapid and reliable. Many laboratories in the WHO global influenza network have the necessary high-security facilities and reagents for performing these tests as well as considerable experience. Rapid bedside tests for the diagnosis of human influenza are also available, but do not have the precision of the more extensive laboratory testing that is currently needed to fully understand the most recent cases and determine whether human infection is spreading, either directly from birds or from erson to person. Antiviral drugs, some of which can be used for both treatment and prevention, are clinically effective against influenza A virus strains in otherwise healthy adults and children, but have some limitations. Some of these drugs are also expensive and supplies are limited. Experience in the production of influenza vaccines is also considerable, particularly as vaccine composition changes each year to match changes in circulating virus due to antigenic drift. However, at least four months would be needed to produce a new vaccine, in significant quantities, capable of conferring protection against a new virus subtype.

Colds and flu

The runny nose, sore throat or "bunged up" feeling of a cold is caused by one of many viruses, called rhinoviruses, that can infect the upper part of the breathing system (upper respiratory tract). Influenza - or flu - has similar symptoms but tends to be a more severe illness. In vulnerable people it can be dangerous.

Fighting flu

Although a cold can make you feel miserable, colds are usually "self limiting". This means the body fights off the infection and the cold is cured without the need for specific medical treatment.

How do you catch colds and flu?

The viruses responsible for colds are spread from person to person as droplets in the air. Sneezing or coughing produces more droplets and helps to spread the infection. Touching infected surfaces, such as door handles or when shaking hands, and then passing the virus from the hands to the mouth is another route of infection for viruses. Infected people can spread the viruses from two days before the symptoms of the illness start and up to four days afterwards. Colds can occur all year round but are more common in the winter months. On average, adults catch two to three colds each year. School age children can have twelve or more colds in a year.

Complications of flu

To most healthy adults, flu can be just like a nasty cold. However, young children, the elderly and people with certain chronic medical conditions are susceptible to potentially serious complications. These are mostly related to a bacterial infection of the lungs (pneumonia) or of the ears, nose and throat. In children under about six years, fits – known as febrile convulsions – can occur as a result of the high body temperature. People living in residential or nursing homes and people with the following conditions are at greater risk of complications:

• asthma
• chronic chest problems such as chronic obstructive pulmonary disease
• diabetes
• heart disease
• kidney diseases and kidney failure
• people with reduced immunity, such as people with HIV or people who have had their spleen removed.

Antiviral medicines

For people in general good health, who are not elderly, no specific medical treatment – apart from the home care suggested above – is required for flu. For vulnerable groups, where it is important to prevent complications or spread of the virus, prescription only medicines may be needed. There are several antiviral treatments, taken as tablets or as an inhaler (similar to the ones used for asthma). They have been shown to reduce the duration of flu but only by around one day, and then only if treatment is started within two days of the onset of the illness. GPs do not routinely prescribe antiviral medicines for flu. Antibiotics may be given to treat any secondary bacterial infections such as a chest infection, ear infection or sinusitis.

Prevention

There are a few steps that can be taken to help prevent colds and flu:

• Isolation of people with colds and flu to prevent it spreading to other people, if practical.
• Regular hand washing and immediate disposal of used tissues.
• A healthy lifestyle – a balanced diet, rich in fruit and vegetables, and regular (preferably daily) physical activity.
• Not smoking – smokers are more likely to catch colds.

Immunisation

Having a flu jab each year significantly reduces the chance of catching flu. The immunisation provides protection against the flu virus for the whole flu season - the vaccination lasts for one year. It is available free for everyone over 65 and is recommended for people at risk from the complications of flu. Your GP will be able to advise you further. Flu jabs may also be offered to some employees by their company. Alternatively, they are available from private clinics.

Avian influenza A H5 and H7 viruses can be distinguished as “low pathogenic” and “high pathogenic” forms on the basis of genetic features of the virus and the severity of the illness they cause in poultry; influenza H9 virus has been identified only in a “low pathogenicity” form. Each of these three avian influenza A viruses (H5, H7, and H9) theoretically can be partnered with any one of nine neuraminidase surface proteins; thus, there are potentially nine different forms of each subtype (e.g., H5N1, H5N2, H5N3, H5N9).

Summary information follows about these three prominent subtypes of avian influenza A viruses:

Influenza A H5N1

• Potentially nine different subtypes
• Can be highly pathogenic or low pathogenic
• H5 infections have been documented among humans, sometimes causing severe illness and death

Influenza A H7N1

• Potentially nine different subtypes
• Can be highly pathogenic or low pathogenic
• H7 infection in humans is rare, but can occur among persons who have direct contact with infected birds; symptoms may include conjunctivitis and/or upper respiratory symptoms

Influenza A H9N1

• Potentially nine different subtypes
• Documented only in low pathogenic form
• At least three H9 infections in humans have been confirmed .

 

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