Cybermed Update August 2004

H5N1 Avian Flu


Drink! for you know not whence you came nor why: / Drink! for you know not why you go, nor where.
  —
Omar Khayym

My first article on Influenza A H5N1 a.k.a Avian Flu a.k.a as Bird Flu was way back on 13th December 1997. It was in my tenth article for Berita MMA. How time fly's! This is my sixty-fourth.....anyway who is counting? Avian Influenza includes not only the H5N1 strain but also the H9N2, H7N2, H7N7 and H7N3 strains.

A chronology of events so far can be viewed at ...well where else...H5N1 avian influenza: a chronology of key events a WHO site. Unfortunately it lists events in 2003 and 2004 only. My web page on the Avian Flu, gives an overview from 10th December 1997. The first reported outbreak occurred in Hong Kong. A visit to Pro-Med site shows so far 447 reports have been posted. Countries most recently affected are Vietnam and Thailand and well in Malaysia although at the moment it appears to be contained. The posting on Malaysia was on 19th August 2004. An excerpt is below.

Malaysia confirms outbreak of fatal strain of bird flu virus World Health Organization / Western Pacific Region

Malaysian agricultural officials have confirmed that a deadly strain of bird flu virus has infected poultry in the country. The announcement Thursday came 24 hours after it was revealed that bird flu had been found in chickens in a northern Malaysian village. Officials say tests showed the flu strain to be H5N1, which killed 27 people in Thailand and Vietnam earlier in 2004. Officials have ordered the slaughter of all poultry in the village to halt the potential spread of the disease. But Malaysian officials have reversed an earlier decision to suspend poultry exports.

Recently, there has been news that the virus strain was found in pigs in Fujian province in China. Any virus that jumps species and infects man can be deadly. The virus can mutate and make difficult to treat. We had first hand experience with the Nipah virus. This makes it paramount that we have in place a good surveillance system and our public health system are ever ready.

Below is information from CDC site on Avian Influenza .

Avian Influenza Viruses

Influenza viruses that infect birds are called “ avian influenza viruses.” Only influenza A viruses infect birds. All known subtypes of influenza A virus can infect birds. However, there are substantial genetic differences between the subtypes that typically infect both people and birds. Within subtypes of avian influenza viruses there also are different strains (described in “Strains”).

Below is summary information about these three prominent subtypes of avian influenza virus:

Influenza A H5

Influenza A H7

Influenza A H9

Types, Subtypes and Strains

There are three types of influenza viruses: A, B, and C.

Influenza Type A
Influenza type A viruses can infect people, birds, pigs, horses, seals, whales, and other animals, but wild birds are the natural hosts for these viruses. Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are called hemagglutinin (HA) and neuraminidase (NA). There are 15 different HA subtypes and 9 different NA subtypes. Many different combinations of HA and NA proteins are possible. Only some influenza A subtypes (i.e., H1N1, H1N2, and H3N2) are currently in general circulation among people. Other subtypes are found most commonly in other animal species. For example, H7N7 and H3N8 viruses cause illness in horses.
Subtypes of influenza A virus are named according to their HA and NA surface proteins. For example, an “H7N2 virus” designates an influenza A subtype that has an HA 7 protein and an NA 2 protein. Similarly an “H5N1” virus has an HA 5 protein and an NA 1 protein.

Influenza Type B
Influenza B viruses are normally found only in humans. Unlike influenza A viruses, these viruses are not classified according to subtype. Although influenza type B viruses can cause human epidemics, they have not caused pandemics.

Influenza Type C
Influenza type C viruses cause mild illness in humans and do not cause epidemics or pandemics. These viruses are not classified according to subtype.

Strains
Influenza B viruses and subtypes of influenza A virus are further characterized into strains. There are many different strains of influenza B viruses and of influenza A subtypes. New strains of influenza viruses appear and replace older strains. This process occurs through a type of change is called “drift.”When a new strain of human influenza virus emerges, antibody protection that may have developed after infection or vaccination with an older strain may not provide protection against the new strain. Thus, the influenza vaccine is updated on a yearly basis to keep up with the changes in influenza viruses.

Human Influenza Viruses versus Avian Influenza Viruses

Humans can be infected with influenza types A, B, and C. However, the only subtypes of influenza A virus that normally infect people are influenza A subtypes H1N1, H1N2, and H3N2. Between 1957 and 1968, H2N2 viruses also circulated among people, but currently do not.

Only influenza A viruses infect birds. Wild birds are the natural host for all subtypes of influenza A virus. Typically wild birds do not get sick when they are infected with influenza virus. However, domestic poultry, such as turkeys and chickens, can get very sick and die from avian influenza, and some avian viruses also can cause serious disease and death in wild birds.

Low Pathogenic versus Highly Pathogenic Avian Influenza Viruses
H5 and H7 subtypes of avian influenza A viruses can be further classified as either highly pathogenic avian influenza (HPAI) or low pathogenic avian influenza (LPAI). This distinction is made on the basis of genetic features of the virus. HPAI is usually associated with high mortality in poultry. It is not certain how the distinction between “low pathogenic” and “highly pathogenic” is related to the risk of disease in people. HPAI viruses can kill 90 to 100% of infected chickens, whereas LPAI viruses cause less severe or no illness if they infect chickens. Because LPAI viruses can evolve into HPAI viruses, outbreaks of H5 and H7 LPAI are closely monitored by animal health officials

Avain Influenza among Birds

Avian influenza viruses circulate among birds worldwide. Certain birds, particularly water birds, act as hosts for influenza viruses by carrying the virus in their intestines and shedding it. Infected birds shed virus in saliva, nasal secretions, and feces. Susceptible birds can become infected with avian influenza virus when they have contact with contaminated nasal, respiratory, or fecal material from infected birds. Fecal-to-oral transmission is the most common mode of spread between birds.

Most often, the wild birds that are host to the virus do not get sick, but they can spread influenza to other birds. Infection with certain avian influenza A viruses (for example, some H5 and H7 strains) can cause widespread disease and death among some species of domesticated birds.

Avian Influenza Outbreaks in Poultry

Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with virus. People, vehicles, and other inanimate objects such as cages can be vectors for the spread of influenza virus from one farm to another. When this happens, avian influenza outbreaks can occur among poultry.

Low pathogenic forms of avian influenza viruses are responsible for most avian influenza outbreaks in poultry. Such outbreaks usually result in either no illness or mild illness (e.g., chickens producing fewer or no eggs), or low levels of mortality.

When highly pathogenic influenza H5 or H7 viruses cause outbreaks, between 90% and 100% of poultry can die from infection. Animal health officials carefully monitor avian influenza outbreaks in domestic birds for several reasons:

When avian influenza outbreaks occur in poultry, quarantine and depopulation (or culling) and surveillance around affected flocks is the preferred control and eradication option.

Avian Influenza Infection in Humans

Although avian influenza A viruses do not usually infect humans, several instances of human infections and outbreaks of avian influenza have been reported since 1997. Most cases of avian influenza infection in humans are thought to have resulted from contact with infected poultry or contaminated surfaces. However, there is still a lot to learn about how different subtypes and strains of avian influenza virus might affect humans. For example, it is not known how the distinction between low pathogenic and highly pathogenic strains might impact the health risk to humans. Of the documented cases of human infection with avian influenza viruses, illnesses caused by highly pathogenic viruses appear to be more severe.

Because of concerns about the potential for more widespread infection in the human population, public health authorities closely monitor outbreaks of human illness associated with avian influenza. To date, human infections with avian influenza viruses detected since 1997 have not resulted in sustained human-to-human transmission. However, because influenza viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person-to-person transmission is important.

Instances of Avian Influenza Infections in Humans

Confirmed instances of avian influenza viruses infecting humans since 1997 include:

Symptoms of Avian Influenza in Humans

The reported symptoms of avian influenza in humans have ranged from typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.

So finally, the million dollar question, "What if we eat infected poultry or its products?" For this I refer you to "Avian influenza A(H5N1) in humans and in poultry in Asia: food safety considerations", another WHO link. An abstract of it is appended below.

WHO is aware of recent concern over the possibility that the avian influenza in addition to direct contact with live infected animals could spread through contact with contaminated poultry products. WHO is therefore working to determine if there is any evidence to suggest that avian influenza could be spread through contaminated foods. To date there is no epidemiological information to suggest that the disease can be transmitted through contaminated food or that products shipped from affected areas have been the source of infection in humans.

WHO has reviewed studies and reports received regarding the transmission of the disease. In the present outbreaks, in addition to chickens, reports indicate that pigs and ducks have also been infected. Infected chicken flocks would rapidly develop symptoms and should be destroyed before having any possibility of entering the food-chain. Ducks have been reported to be asymptomatic carriers and duck products could be contaminated with the virus. In one recent study, a highly pathogenic strain of avian influenza H5N1 has been isolated from imported frozen duck meat. The public health significance of such findings is not well understood but believed to be very limited since further processing would inactivate the virus. In general, good hygiene practices during handling of raw poultry meat and usual recommended cooking practices for poultry products would lower any potential risk to insignificant levels. Eggs from infected poultry could also be contaminated with the virus and therefore care should be taken in handling shell eggs or raw egg products.

Some knowledge is available about the effect of food handling and treatment on the influenza virus. While freezing and refrigeration would not substantially reduce the concentration or virulence of viruses on contaminated meat, proper cooking kills such viruses. In general, WHO recommends that foods should be cooked to reach an internal temperature of 70C.

While trade restriction have been put in place by some countries to protect animal health, on the basis of presently available data, WHO does not at present conclude that any processed poultry products (whole refrigerated or frozen carcasses and products derived from these) and eggs in or arriving from areas currently experiencing outbreaks of avian influenza H5N1 in poultry pose a risk to public health. WHO continuously emphasizes the importance of good hygiene practices during handling including hand washing, prevention of cross-contamination and thorough cooking of poultry products. WHO will continue to closely monitor the evolution of the current outbreaks, in collaboration with Ministries of Health and our partner agencies.

Finally, some frequent questions asked from the WHO site.

Why so much concern about the current outbreaks?

Public health officials are alarmed by the unprecedented outbreaks in poultry for several reasons. First, most – but not all – of the major outbreaks recently reported in Asia have been caused by the highly pathogenic H5N1 strain. There is mounting evidence that this strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in humans.

A second and even greater concern is the possibility that the present situation could give rise to another influenza pandemic in humans. Scientists know that avian and human influenza viruses can exchange genes when a person is simultaneously infected with viruses from both species. This process of gene swapping inside the human body can give rise to a completely new subtype of the influenza virus to which few, if any, humans would have natural immunity. Moreover, existing vaccines, which are developed each year to match presently circulating strains and protect humans during seasonal epidemics, would not be effective against a completely new influenza virus.

If the new virus contains sufficient human genes, transmission directly from one person to another (instead of from birds to humans only) can occur. When this happens, the conditions for the start of a new influenza pandemic will have been met. Most alarming would be a situation in which person-to-person transmission resulted in successive generations of severe disease with high mortality.

This was the situation during the great influenza pandemic of 1918–1919, when a completely new influenza virus subtype emerged and spread around the globe, in around 4 to 6 months. Several waves of infection occurred over 2 years, killing an estimated 40–50 million persons.

Is there evidence of efficient human-to-human transmission now?

No. WHO teams in Viet Nam and Thailand are supporting governments in the design and conduct of studies needed to detect the earliest stage of human-to-human transmission. In parallel activities, laboratories in the WHO Global Influenza Surveillance Network are urgently conducting studies on both human and avian viruses, obtained in the current outbreaks. These studies are also expected to shed some light on the origins and characteristics of the currently circulating H5N1 strain.

Moreover, a new virus adapted for efficient human-to-human transmission would spread very rapidly, and health authorities would know very quickly that a completely new virus had emerged. There is no evidence, to date, that this has occurred.

Does human infection with H5N1 happen often?

No. Only very rarely. The first documented human infections with the H5N1 avian strain occurred in Hong Kong in 1997. In that first outbreak, 18 persons were hospitalized and 6 of them died. The source of infection in all cases was traced to contact with diseased birds on farms (1 case) and in live poultry markets (17 cases).

The human cases coincided with outbreaks of highly pathogenic H5N1 avian influenza in poultry. Very limited human-to-human transmission of the H5N1 strain was documented in health care workers, family members, poultry workers, and workers involved in culling operations. Though H5 antibodies were detected in these groups, indicating infection with the virus, no cases of severe disease occurred as a result. Antibodies were detected in 10% of the poultry workers studied, and in 3% of the cullers.

In February 2003, the H5N1 strain again jumped from birds to infect two members of a family (a father and his son) when they returned to Hong Kong following travel in southern China. The father died but the son recovered. A third member of the family, the boy’s sister, died of a severe respiratory illness in China. No samples were available for determining the cause of her death.

Are all of the currently reported outbreaks in birds equally dangerous for humans?

No. Outbreaks caused by the H5N1 strain are presently of the greatest concern for human health.

In assessing risks to human health, it is important to know exactly which avian virus strains are causing the outbreaks in birds. For example, the outbreak of avian influenza recently reported in Taiwan, China is caused by the H5N2 strain, which is not highly pathogenic in birds and has never been known to cause illness in humans. The outbreak recently announced in Pakistan is caused by H7 and H9 strains, and not by H5N1.

However, urgent control of all outbreaks of avian influenza in birds – even when caused by a strain of low pathogenicity – is of utmost importance. Research has shown that certain avian influenza virus strains, initially of low pathogenicity, can rapidly mutate (within 6 to 9 months) into a highly pathogenic strain if allowed to circulate in poultry populations.

Can a pandemic be averted?

No one knows for sure. Influenza viruses are highly unstable and their behaviour defies prediction. However, WHO remains optimistic that, if the right actions are taken quickly, an influenza pandemic can be averted. This is WHO’s foremost objective at present.

The first priority, and the major line of defence, is to reduce opportunities for human exposure to the largest reservoir of the virus: infected poultry. This is achieved through the rapid detection of poultry outbreaks and the emergency introduction of control measures, including the destruction all infected or exposed poultry stock, and the proper disposal of carcasses.

All available evidence points to an increased risk of transmission to humans when outbreaks of highly pathogenic avian H5N1 influenza are widespread in poultry. As the number of human infections grows, the risk increases that a new virus subtype could emerge, triggering an influenza pandemic. This link between widespread infection in poultry and increased risk of human infection is being demonstrated right now in Asia. All human cases and deaths detected so far are in two countries – Viet Nam and Thailand – with very widespread outbreaks in poultry.

WHO stresses the urgency of the situation and the need for rapid action in the animal and agricultural sectors. For example, the culling in 1997 of Hong Kong’s entire bird population – an estimated 1.5 million chickens and other birds – was done in 3 days. Again in 2003, the culling of nearly 30 million birds (out of a total bird population of 100 million) in the Netherlands was done within a week. Rapid action in both of these situations is thought by many influenza experts to have averted an influenza pandemic in humans.

Is it reassuring that so few human cases have occurred?

Yes. WHO has some evidence that the H5N1 strain may have been circulating in birds since April 2003. The detection so far of only a few human cases suggests that the virus may not be easily transmitted from birds to humans at present. However, the situation could change quickly, as the H5N1 strain has been shown to mutate rapidly and has a documented propensity to exchange genes with influenza viruses from other species.

In situations that could favour the emergence of a new pandemic strain of influenza virus, every case of human infection is one too many. In addition to the rapid destruction of infected animals, another opportunity to prevent human cases is through the protection of workers involved in culling operations. WHO has issued guidelines for conducting these operations safely.

Are the right control measures being applied?

In some cases, yes. Japan and the Republic of Korea appear to have controlled their outbreaks in poultry, quickly and safely. Studies of workers involved in culling operations have been conducted, and no cases of human infection have been detected. The situation in other countries is more problematic.

WHO is fully aware that governments in several countries with serious poultry outbreaks do not have the resources needed to introduce recommended protective measures for cullers or carry out the very rapid destruction of poultry flocks. In some of these countries, the practice of raising poultry on backyard farms in remote rural areas, which may not be registered with agricultural authorities, further complicates rapid and systematic elimination of the animal reservoir.

WHO, FAO, and OIE have jointly issued an urgent appeal to the international community to make adequate resources and other forms of support available quickly in the interest of protecting international public health.

Apart from H5N1, have other avian influenza viruses ever infected humans?

Yes. Two other avian strains have caused illness in humans, but the outbreaks were not as severe as those caused by the H5N1 strain

The H9N2 strain, which is not highly pathogenic in birds, caused mild cases of illness in two children in Hong Kong in 1999 and in one child in mid-December 2003, also in Hong Kong.

An outbreak of highly pathogenic H7N7 avian influenza in birds, which began in the Netherlands in February 2003, caused the death of one veterinarian (from acute respiratory distress syndrome) two months later, and mild illness in 83 poultry workers and members of their families.

This is primary a disease in poultry and if not well contained,could become an occupational health disease among workers and a potential threat of a global pandemic. Therefore health measures should be focused along these areas. There are numerous guidelines and recommendations at the sites below but I would like you'll to pay a visit to OSHA (Occupational Safety and Health Administrative site USA) site, "GUIDANCE FOR PROTECTING WORKERS AGAINST AVIAN FLU".

Some useful links for more information:


The links to URL mentioned above are valid at the time of writing (24th August 2004).

Last updated 15 January 2006.

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