Vaccination as Part of an Avian Influenza Control Strategy

Introduction Influenza Control Strategy

Avian influenza is a disease capable of causing extremely high mortality amongst infected poultry. Influenza viruses have a worldwide distribution and although not endemic in commercial poultry sporadic outbreaks do occur.

In recent times these outbreaks have been occurring with increasing regularity. Outbreaks are typically of a low pathogenic form of avian influenza (LPAI). Past experience indicates that in a susceptible domestic poultry population, circulating LPAI (especially H5- and H7- subtypes) has the ability to mutate into a more devastating high pathogenic avian influenza (HPAI) resulting in Fowl Plague.

HPAI is an OIE List A disease, hence the accepted control measure is implementing a "stamping out" procedure. All poultry that are infected, suspected of being infected or suspected of being contaminated are culled. This is accompanied by severe restrictions on the movement of poultry, personnel and related industry activities within the designated quarantine area. However in areas with high poultry density these stringent control measures may not be sufficient in curtailing the spread of the virus as has been experienced with the current HPAI outbreak in The Netherlands.

During a nine-week period (01/03/2003 . 02/05/2003) the virus has spread from an initial outbreak involving six poultry farms to a total of 243 confirmed cases, with new cases being confirmed daily. This is despite culling more than 21 million poultry during this time period and all efforts at strictly controlling movement within the industry. With the virus now jumping the border into Belgium questions must be asked whether there are not more effective strategies to control such an epidemic. 

Avian Influenza Vaccination

Vaccination as an additional control tool has been used with success in controlling LPAI⁵ outbreaks as well as HPAI outbreaks in the past (1995 - Utah, USA; 2000 - Italy³ & California, USA; 2001 - Hong Kong; 2002 - Colorado, USA). At the Fifty-Second Western Poultry Disease Conference held in Sacramento, California during March 2003 Capua and Marangon² proposed a scheme, summarised in Diagram 1, whereby vaccination is included in the control strategy in certain scenarios.

The concept of vaccination in the face of HPAI is however met with much resistance based on the arguments that it is not in line with OIE or EU control strategies, would have an negative impact on export trade agreements and potentially masks the symptoms of the disease thus removing the most significant early warning signal for HPAI - acute increase in mortality. 

Trade Regulations

As a list A disease (OIE) an HPAI outbreak has serious trade implications, such as a possible export ban on poultry products. The document International Animal Health Code (2002) of the office International des Epizooties (OIE) defines a country as HPAI free:

·         when it has been shown that HPAI has not been present in the country for the past 3 years, or

·         six months after the slaughter of the last affected animal for countries in which a stamping-out policy is practised with or without vaccination.

Claiming this free status is achieved by the lack of fresh outbreaks and sufficient proof that repopulated flocks remain AI seronegative. AI vaccinated flocks test seropositive, thus effectively complicating the surveillance required to declare a region free of HPAI. However, by vaccinating with a heterologous vaccine and applying the DIVA (Differentiating Infected from Vaccinated Animals) monitoring strategy it is possible to demonstrate that there is no circulating virus in the vaccinated population. This principle was successfully used to lift trade bans in Italy during the 2000 Italian AI outbreak.

Commission Decision of 30 November 2001 amending for the third time to modify the Italian avian influenza vaccination programme and current trade restrictions for fresh meat originating from vaccinated turkeys.

DIVA Strategy

The DIVA strategy4 is based on the use of an inactivated oil emulsion vaccine containing the same haemagglutinin (H) subtype as the field virus, but a different neuramidase (N). The homologous H group ensures protection while it is possible to differentiate vaccinated from infected birds based on the serological response to the N group using an indirect immunofluorescence test. Vaccinated birds should only test positive to the N group used in the vaccine, a positive reaction to the N group of the prevailing infective virus would indicate a field challenge. 

Reduction of Virus Excretion

What is the advantage of vaccination? The most significant benefit of vaccination is the dramatic reduction in virus shedding from infected birds, reducing the load of environmental contamination and consequently containing the spread of the virus. In a published article by Swayne et. al.6, SPF chickens vaccinated at day old or 3 weeks of age with an inactivated whole AI vaccine (H5N2) were challenged 4 weeks later with the HP A/Hong Kong/156/97 (H5N1) influenza virus. Two days post challenge Swayne demonstrated a reduction in the re-isolation rate of the challenge strain from vaccinated birds in comparison to unvaccinated controls. Of more significance though was a significant reduction in the titre of virus re-isolated from vaccinated chickens in comparison to unvaccinated controls.

Diagnosis

How to Recognise Avian Influenza

What to look for

·         Ruffled feathers

·         Soft-shelled eggs

·         Depression and droopiness

·         Sudden drop in egg production

·         Loss of appetite

·         Cyanosis (purplish-blue coloring) of wattles and comb

·         Edema and swelling of head, eyelids, comb, wattles, and hocks

·         Green diarrhoea

·         Blood-tinged discharge from nostrils

·         Incoordination, including loss of ability to walk and stand

·         Pin-point hemorrhages (most easily seen on the feet and shanks)

·         Respiratory distress

·         Increased death losses in a flock

·         Sudden death

·         Nasal discharges

Avian influenza Outbreaks

Outbreaks of avian influenza in the poultry industry cause devastating economic losses and is generally controlled through extensive culling of infected birds. Alternative strategies also use vaccination as a supplementary control measure during avian influenza outbreaks.

Advantages of Vaccination

·         Vaccination reduces susceptibility to infection.

·         A higher dose of virus is necessary to infect the vaccinated birds.

·         Vaccinated birds shed less virus.
- Decreased contamination of the environment.
- Decreased risk of human infection

·         Used strategically vaccination compliments a stamping out strategy by slowing/stopping the spread of the virus

TREATMENT AND VACCINATION FOR H5N1 VIRUS IN HUMANS

Recommendations from management aspects

The H5N1 virus that was found to be major cause of human illness and death in Asia is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat influenza caused by H5N1 virus, but additional studies still need to be done to demonstrate their safety and effectiveness.Treatment modalities recommended for the clinical management of human H5N1 virus infection is shown in table.

When there is evidence for sustained human-to-human transmission of H5N1 or another novel avian influenza virus emerges, strict recommendations need to be developed. Whenever feasible, sequential clinical data collection and virological sampling (for analysis at WHO-designated laboratories) should be performed during treatment or should apparent failures of chemoprophylaxis occur. Self-medication in the absence of appropriate clinical or public health advice is discouraged. When considering chemoprophylaxis for H5N1 infection, priority should be given to standard infection control practices. This includes protection of health care workers and individuals involved in eradication of animals infected with H5N1 virus as well as household contacts of H5N1 patients.

For treatment of patients with confirmed or strongly suspected human infection with the H5N1 virus, where neuraminidase inhibitors are available for therapy:

Clinicians should administer oseltamivir treatment (strong recommendation); zanamivir might be used as an alternative (weak recommendation).
In these patients, clinicians should not administer amantadine or rimantadine alone as a first-line treatment (strong recommendation).

Clinicians might administer a combination of a neuraminidase inhibitor and an M2 inhibitor if local surveillance data show that the H5N1 virus is known or likely to be susceptible (weak recommendation), but this should only be done in the context of prospective data collection.

For treatment of patients with confirmed or strongly suspected H5N1 infection, where neuraminidase inhibitors are not available for therapy:

Clinicians might administer amantadine or rimantadine as a first-line treatment if local surveillance data show that the H5N1 virus is known or likely to be susceptible to these drugs (weak recommendation).
In general, decisions to initiate antiviral chemoprophylaxis should be guided by the risk stratification described below. Stratification is based on observational data for reported cases of human H5N1 infection and on high quality data from studies of seasonal influenza.

High risk exposure groups are currently defined as:

• Household or close family contacts of a strongly suspected or confirmed H5N1 patient, because of potential exposure to a common environmental or poultry source as well as exposure to the index case.

Moderate risk exposure groups are currently defined as:

• Personnel involved in handling sick animals or decontaminating affected environments (including animal disposal) if personal protective equipment may not have been used properly.
• Individuals with unprotected and very close direct exposure to sick or dead animals infected with the H5N1 virus or to particular birds that have been directly implicated in human cases.
• Health care personnel in close contact with strongly suspected or confirmed H5N1 patients, for example during intubation or performing tracheal suctioning, or delivering nebulised drugs, or handling inadequately screened/sealed body fluids without any or with insufficient personal protective equipment. This group also includes laboratory personnel who might have an unprotected exposure to virus containing samples.

Low risk exposure groups are currently defined as:

• Health care workers not in close contact (distance greater than 1 metre) with a strongly suspected or confirmed H5N1 patient and having no direct contact with infectious material from that patient.
• Health care workers who used appropriate personal protective equipment during exposure to H5N1 patients.
• Personnel involved in culling non-infected or likely non-infected animal populations as a control measure.
• Personnel involved in handling sick animals or decontaminating affected environments (including animal disposal), who used proper personal protective equipment.

Where neuraminidase inhibitors are available:

• In high risk exposure groups, including pregnant women, oseltamivir should be administered as chemoprophylaxis, continuing for 7–10 days after the last exposure (strong recommendation); zanamivir could be used in the same way (strong recommendation) as an alternative.
• In moderate risk exposure groups, including pregnant women, oseltamivir might be administered as chemoprophylaxis, continuing for 7-10 days after the last exposure (weak recommendation); zanamivir might be used in the same way (weak recommendation).
• In low risk exposure groups oseltamivir or zanamivir should probably not be administered for chemoprophylaxis (weak recommendation). Pregnant women in the low risk group should not receive oseltamivir or zanamivir for chemoprophylaxis (strong recommendation).
• Amantadine or rimantadine should not be administered as chemoprophylaxis (strong recommendation).

Where neuraminidase inhibitors are not available:

• In high or moderate risk exposure groups, amantadine or rimantadine might be administered for chemoprophylaxis if local surveillance data show that the virus is known or likely to be susceptible to these drugs (weak recommendation).
• In low risk exposure groups, amantadine and rimantadine should not be administered for chemoprophylaxis (weak recommendation).
• In pregnant women, amantadine and rimantadine should not be administered for chemoprophylaxis (strong recommendation).
• In the elderly, people with impaired renal function and individuals receiving neuropsychiatric medication or with neuropsychiatric or seizure disorders, amantadine should not be administered for chemoprophylaxis (strong recommendation).

We recommend that countries develop their own guidelines for the assessment of human patients in whom there is a suspicion of influenza A (H5N1) infection. These should include the criteria required to initiate treatment pending confirmatory laboratory testing. Such guidelines will reflect geographical location with respect to recent outbreaks of avian influenza H5N1 in birds and the locally available resources.

SELF-CARE GUIDELINES

Self Medication

To prevent avian influenza:

• If you are in an area where avian influenza is a risk, protect yourself by practicing good hand hygiene.
• If you will be handling birds known or thought be infected, protect yourself with gloves, goggles, a medical gown, shoe covers, and a mask designed for very small particles, such as a tuberculosis mask.
• There is little known about transmission of avian influenza between humans, but to be on the safe side, do not allow secretions, sneezing, or coughing to contaminate other humans, particularly children, the elderly, and the immunocompromised.

When to Seek Medical Care Contact your doctor for any illness with high fever (ie, temperature greater than 39°C [102°F]), inability to tolerate foods or liquids, or bad abdominal pain.

TREATMENTS YOUR PROVIDER MAY PRESCRIBE

Treatment for Avian Influenza





There is no certain treatment for avian influenza. Some drugs (antivirals) that are used to treat human influenza may be helpful for patients with avian influenza, but for both, these drugs are designed to shorten the duration and severity of symptoms; the illness must run its course. The earlier in the course of illness these drugs are started, the better. If one person in a family develops avian influenza, the other family members may receive an antiviral in order to protect against illness (although at this time the disease is not thought to be contagious person to person). There is a specific vaccine for one strain of avian influenza; the vaccine will be made available to the public in the event of an outbreak. The human influenza vaccine that the Centers for Disease Control and Prevention makes public every year does not protect against avian influenza.

A GLOBAL FLU PANDEMIC

The 1918 Flu Pandemic

In 1918 and 1919, a deadly strain of influenza killed 50 million people worldwide. The virus appeared first in Kansas and spread to the rest of the world through soldiers fighting in World War I. Scientist have recently reconstructed the virus and now believe that it may have originated in birds Sources: National Geographic: Bird Flu and National Geographic: Spanish Flu.

Some people wonder whether scientists are overreacting to bird flu. After all, the virus has infected under 200 people, as compared to millions of birds. It also can't easily move from birds to people, and it's even less able to move from person to person. But public health officials have several concerns about avian flu:

• It has an extremely high mortality rate and kills previously healthy young adults.
• Since many wild, migrating birds carry it, controlling its spread is difficult.
• There's no vaccine for the virus, which appears to be developing a resistance to the few drugs that can limit its severity. Scientists are also investigating whether use of amantadine - a drug intended for humans - in Chinese poultry may have caused additional resistance.

Right now, avian flu H5N1 is most threatening to birds, especially in Asia. The biggest threat to human health and potential for the spread of the disease is also in Asia, where many rural families have at least a few chickens that typically roam free instead of living in an enclosure. But health officials report that the disease has gotten hardier and more infectious, and they worry that it may mutate and become a bigger threat to people.

TRIAL OF EXPERIMENTAL AVIAN INFLUENZA VACCINE

Influenza Vaccine

Fast-track recruitment has begun for a trial to investigate the safety of a vaccine against the H5N1 strain of avian influenza, the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), announced today.

Sites in Rochester, NY, Baltimore and Los Angeles will enroll a total of 450 healthy adults. The clinical sites are part of the NIAID-sponsored Vaccine and Treatment Evaluation Units (VTEU). While there have been relatively few cases worldwide of H5N1 avian influenza infection in humans, the public health community is concerned that the H5N1 strain of avian influenza virus will develop the capability of efficiently spreading from human to human and thus create a risk for a worldwide pandemic.

NIAID has supported research on H5N1, the strain responsible for this deadly form of avian influenza, since 1997 when the first cases in humans were reported. The initiation of this vaccine trial marks a key advance in our efforts to prepare to respond to an avian influenza pandemic.

Sanofi pasteur, Swiftwater, PA, manufactured the trial vaccine, which is an inactivated vaccine made from an H5N1 virus isolated in Southeast Asia in 2004. Sanofi pasteur, formerly Aventis Pasteur, was awarded a contract by NIAID to manufacture the H5N1 vaccine in May 2004.

This Phase I trial will test the avian influenza vaccines safety and ability to generate an immune response in 450 healthy adults aged 18 to 64. If the vaccine is shown to be safe in adults, there are plans to test it in other populations, such as the elderly and children.

H5N1 avian influenza leads to severe disease in both birds and humans. Between January 2004 and March 11, 2005, there were 69 confirmed cases of and 46 deaths from H5N1 infection in humans reported to the World Health Organization. To date, there has been a small number of cases where human-to-human transmission of the virus may have occurred. However, public health experts fear that the virus may evolve into one that is more easily transmitted between people. If this were to happen, a worldwide pandemic could follow.

Influenza pandemics are global outbreaks that emerge infrequently and unpredictably and involve strains of virus to which humans have little or no immunity. H5N1 is one such Avian Influenza virus strain. The last influenza pandemic swept the globe in 1968; many public health officials believe the world is overdue for another one.

Avian Influenza Infection in Humans

Although avian influenza A viruses usually do not infect humans, more than 100 confirmed cases of human infection with avian influenza viruses have been reported since 1997. For example, the World Health Organization (WHO) maintains situation updates and cumulative reports of human cases of avian influenza A (H5N1). Most cases of avian influenza infection in humans are thought to have resulted from direct 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. (For more information, see �Low Pathogenic versus Highly Pathogenic Avian Influenza Viruses� on the CDC Influenza Viruses Web page.

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 A viruses detected since 1997 have not resulted in sustained human-to-human transmission. However, because influenza A 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.

HUMAN CASES AND DEATHS OF H5N1

Worst case scenario

The worst case scenario for a H5N1 pandemic is somewhere around 150,000,000 human deaths directly due to H5N1 infection (or two to three percent of the world's human population). No one knows what the chances are for this worst case scenario.

"Influenza viruses keep changing. They mutate. And they exchange genetic material with other flu viruses, a process called reassortment. All that's needed is a mutation or reassortment that produces a new variant of H5N1 one that's as deadly as the current strain but as easily transmitted from human to human as lots of other flu strains. Most virologists believe something like this will happen sooner or later, and many believe it will happen soon. When it does, H5N1 will inevitably spread throughout the world. Worldwide mortality estimates range all the way from 2-7.4 million deaths (the "conservatively low" pandemic influenza calculation of a flu modeling expert at the U.S. Centers for Disease Control and Prevention) to 1 billion deaths (the avian influenza pandemic prediction of one Russian virologist). The estimates of most H5N1 experts range less widely but still widely. In an H5N1 pandemic, the experts guess that somewhere between a quarter of us and half of us would get sick, and somewhere between one percent and five percent of those who got sick would die the young and frail as well as the old and frail. If it's a quarter and one percent, that's 16 million dead; if it's a half and five percent, it's 160 million dead. Either way it's a big number." Pandemic Influenza Risk.

H5N1 Avian Influenza, Bird Flu. Some developments for a human vaccine.

On August 6, 2005, government scientists at UNIAID, (US National Institute of Allergy and Infectious Diseases), announced results from the first clinical trials of a vaccine being developed to protect humans against H5N1 avian influenza ( bird Flu ). Preliminary tests show that the experimental vaccine evoked an immune response in a small group of healthy adults.

Although more tests are needed, this is at least a good sign that developing a H5N1 specific vaccine is possible.

Currently it is believed that the next pandemic will be caused by the H5N1, Avian Influenza ( bird flu ) virus. The increasing spread of the H5N1 virus, especially in asia, have brought the world much closer to to another pandemic then at any time since 1968, when the last of the 1900's three pandemics began.

Vaccines are the main ammunition in the fight against pandemic influenzas, especially ones of the Avian Influenza (bird flu) type. If available to the public in a timely manner and in great enough quanities they can reduce the morbidity and mortality that have traditionally made pandemics such socially disruptive as well as deadly events.

However many obstacles need to be overcome before vaccines can even help alleviate some of the effects of the next pandemic.One of, if not the most important is to find vaccine formulations that make the greatest use of the limited supply of antigens we have.

Antigen is the component of the vaccine that elicits an immune response. The US trial provides important insight into possible vaccine formulations. It used doses that are higher than the amount of virus antigen contained in influenza vaccines produced yearly for normal seasonal epidemics.

Strategies for stretching limited antigen supplies

By adding an adjuvant to the vaccine formulation or injecting the vaccine into the skin rather than into muscle, have been proposed. Adjuvants are chemicals that can be added to the vaccine formulation to boost the immune response, theoretically allowing the use of smaller doses of antigen to achieve an immune response. Such antigen-sparing strategies using adjuvants are currently being tested by several manufacturers, and preliminary results are expected within the next three months.

At present, 90% of production capacity for all influenza vaccines is concentrated in Europe and North America in countries that account for only 10% of the world�s population. Current global manufacturing capacity (estimated at 300 million doses of regular trivalent influenza vaccine per year) is inadequate to meet the expected global needs during a pandemic and cannot be rapidly augmented.

Influenza pandemics are unique infectious disease events that can spread to every country in the world within months, resulting in a high and universal demand for preventive and treatment measures. Pandemics thus throw into sharp relief inequities in global access to vaccines and other medical interventions during an emergency. Based on past experience, countries with local manufacturing capacity are likely to meet domestic demand for vaccines and other critical resources fully before freeing supplies for the export market.

Because the present total global manufacturing capacity for influenza vaccine is limited, any decision to manufacture a pandemic vaccine in large quantities prior to the start of a pandemic would, of necessity, compromise the capacity to produce vaccines for seasonal influenza. Seasonal epidemics of influenza predictably cause an estimated 250,000 to 500,000 deaths each year. In the current situation, the capacity to respond to seasonal influenza must be balanced against preparations for pandemic influenza. However, once a pandemic has been declared, all manufacturers would stop production of seasonal vaccines and produce only the pandemic vaccine.

AVIAN VIRUS IN ASIA

Avian / human cases, Asia

In January 2004, a major new outbreak of H5N1 surfaced in Vietnam and Thailand's poultry industry, and within weeks spread to ten countries and regions in Asia, including Indonesia, South Korea, Japan and mainland China. Intensive efforts were undertaken to slaughter chickens, ducks and geese (over forty million chickens alone were slaughtered in high-infection areas), and the outbreak was contained by March, but the total human death toll in Vietnam and Thailand was twenty three people.

In July 2004, fresh outbreaks in poultry were confirmed in Ayutthaya and Pathumthani provinces of Thailand, and Chaohu city in Anhui, China.

In August 2004, avian flu was confirmed in Kampung Pasir, Kelantan, Malaysia. Two chickens were confirmed to be carrying H5N1. As a result Singapore has imposed a ban on the importation of chickens and poultry products. Similarly the EU has imposed a ban on Malaysian poultry products. A cull of all poultry has been ordered by the Malaysian government within a 10km radius of the location of this outbreak. These moves appear to have been successful and since then, Singapore has lifted the ban and Malaysia has requested the OIE declare Malaysian poultry avian influenza free .

An outbreak of avian influenza in January 2005 affected thirty three out of sixty four cities and provinces in Vietnam, leading to the forced killing of nearly 1.2 million poultry. Up to 140 million birds are believed to have died or been killed because of the outbreak.

Vietnam and Thailand have seen several isolated cases where human-to-human transmission of the virus has been suspected. In one case a young girl, who received the disease from a bird, was held by her mother for roughly five days until she died. Shortly afterwards, the mother also died. In March 2005, it was revealed that two nurses who had cared for avian flu patients had tested positive for the disease.

In July 2005, a death in Jakarta was the first confirmed human fatality in Indonesia. The deaths of the man's two children, neither of whom were reported to have had close contact with poultry, further raised concerns of human-to-human transmission (although infection by eating undercooked poultry may be a more likely explanation) [16]. As of July 20, the outbreak had claimed at least fifty eight human lives mostly in Vietnam. What concerns health researchers now is that the virus mortality rate in Vietnam has dropped significantly lately, from more than 65% to about 35% in a year. This might be a sign that the virus is able to infect a larger number of people (i.e., the virus is able to spread more easily) and possibly develop into a global pandemic with millions of deaths despite the lower reported percentage of deaths. For example, the mortality rate of 1918 Spanish flu (H1N1) pandemic was less than 5% . Also, in July 2005, it was confirmed H5N1 had appeared in Russia's Novosibirsk region, probably carried by migratory birds .

On July 28, avian influenza was reported to have killed two more people in Vietnam, raising the death toll to sixty . As of July 2005, most human cases of avian influenza in East Asia have been attributed to consumption of diseased poultry. Person-to-person transmission has not been unequivocally confirmed in the outbreaks in East Asia.

Asia and beyond

Also in early August, an avian outbreak of H5N1 flu was confirmed in Kazakhstan and Mongolia, suggesting further spread of the virus . Later in August, the virus was found in western Russia, marking its appearance in Europe. As a result, Dutch authorities ordered that free-range chickens would have to be kept indoors. EU officials chose not to impose a similar policy on member countries.

Chinese government officials have said more than 1,000 migratory birds have been found dead during 2005.

In late September 2005, the UN health representative responsible for coordinating a response to an outbreak, David Nabarro, stated that a flu pandemic could happen at any time, and kill from five to 150 million people. He further stated that as the virus had spread to migratory birds, an outbreak could start in Africa or the Middle East, rather than southeast Asia as has been widely assumed. At the same time, agricultural ministers of Association of South East Asian Nations announced a three-year plan to counter the spread of the disease.

In early October 2005, Romanian officials quarantined Ceamurlia de Jos, a Danube delta village of about 1,200 people, after three dead ducks there tested positive. However, there have been no immediate reports of sickness in the village. The Agriculture Minister said the virus found in the farm-raised ducks came from migrating birds from Russia. Pending scientific clarification, this is the first time the virus had been detected in Europe. Six villages have been put under quarantine following the deaths of domestic birds and over 6000 birds have been killed.

On 13 October 2005 the EU Health Commissioner Markos Kyprianou confirmed that tests on the dead turkeys found on farms in Kiziksa, Turkey, showed that they had died from the H5N1 strain. Even before the test results were available, some 5,000 birds and poultry have been culled in the area. It is believed that the disease had spread from migratory birds that land at the Manyas bird sanctuary (a few miles from the infected farm) on their way to Africa.

On 14 October 2005, European health officials confirmed what many had long feared -- the arrival of the H5N1 strain on Europe's doorstep. The European Commission said the avian influenza outbreak in Turkey was indeed H5N1, and advised Europe to prepare for a pandemic. It has also been reported in Romania.

On 15 October 2005, the British Veterinary Laboratory in Weybridge confirmed that the virus detected in Ciamurlia, Romania is H5N1.

On 17 October 2005, a avian influenza outbreak occurred in Chios, Greece. The mayor of Chios said a farmer on Oinousses who raised turkeys and chickens noted the previous week that some of his birds had died. Two state veterinarians were sent in to look at nine turkeys. They also took blood samples from some chickens. The mayor said a state lab in Athens confirmed that one of the nine samples proved positive. Authorities have yet to announce what measures they will be taking. The farmer was taken to a hospital for observation.

On 19 October 2005, China announced a fresh outbreak of avian influenza, saying 2,600 birds have died from the disease in Inner Mongolia. The deaths, at a farm near the region's capital of Hohhot, were due to the H5N1 strain, the Xinhua news agency said.

On 21 October/22 October 2005, the British Government announced that a parrot from South America had died in quarantine from H5N1 . Because the parrot died in quarantine, the United Kingdom is still considered free of avian flu. The staff that had been in contact with the parrots were immediately given anti-viral drugs.

On 26 October 2005, Croatia announced H5N1 strain was found in dead swans .

On 31 October 2005, Russia confirmed previously suspected H5N1 avian influenza in ten rural communities across Russia. The confirmed outbreak sites are in the central areas of Tula and Tambov, as well as in the Urals province of Chelyabinsk and in Omsk and Altai, in Siberia.

On 31 October 2005, Canada has discovered a strain of H5 avian flu in wild birds and is now checking whether it is the same H5N1 killer strain which has spread to Europe.

On 11 November 2005, Kuwait has reported positive testing of two birds, one infected with H5N1, and the other with the H5N2 virus, making them the first cases of infection in the Middle East. A flamingo holding the H5N1 virus was found dead by the sea, as the scource reports, it was killed by authorities and did not die from the virus, however, it does not report why it was killed. The second bird, a falcon, was found at the Kuwait airport, holding the H5N2 virus.

On 19 November 2005, Wild birds in Manitoba, Canada have tested positive for a low-pathogenic subtype of the H5N1 avian flu virus.

On Sunday November 20, CTV News reported H5N1 strain was found in a farm in the Fraser Valley area of British Columbia, Canada. The Canadian Food Inspection Agency has ordered a precautionary cull of 65,000 birds.

Pig cases

In February 2004, avian influenza virus was detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. In May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported ("swine flu"). Along with the continuing pattern of virus circulation in poultry, the occurrence in swine raises the level of concern about the possible evolution of the virus into a strain capable of causing a global human influenza pandemic. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment.) with the avian virus, swap genes and mutate into a form which can pass easily among humans.

Tiger and leopard cases

Variants have been found in leopards and tigers in Thailand, with high lethality.

Human cases

RESEARCH ABOUT THE INFLUENZA VIRUS

Mutations and Strains

"The influenza virus genome has remarkable plasticity because of a high mutation rate and its segmentation into 8 separate RNA molecules. This segmentation allows frequent genetic exchange by segment reassortment in hosts co-infected with 2 different influenza viruses."

In July 2004, researchers led by H. Deng of the Harbin Veterinary Research Institute, Harbin, China and Professor Robert Webster of the St Jude Children's Research Hospital, Memphis, Tennessee, reported results of experiments in which mice had been exposed to 21 isolates of confirmed H5N1 strains obtained from ducks in China between 1999 and 2002. They found "a clear temporal pattern of progressively increasing pathogenicity" Results reported by Dr. Webster in July 2005 reveal further progression toward pathogenicity in mice and longer virus shedding by ducks.

In May 2005, the occurrence of avian influenza in pigs ("swine flu") in Indonesia was reported. Along with the continuing pattern of virus circulation in poultry, the occurrence in swine raises the level of concern about the possible evolution of the virus into a strain capable of causing a global human influenza pandemic. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment.) with the avian virus, swap genes and mutate into a form which can pass easily among humans.

In July 2005, a death in Jakarta was the first confirmed human fatality in Indonesia. The deaths of two children, neither of whom were reported to have had close contact with poultry, further raised concerns of human-to-human transmission.  As of July 2005, most human cases of avian influenza in East Asia have been attributed to consumption of diseased poultry. Person-to-person transmission has not been unequivocally confirmed in the outbreaks in East Asia.

On August 3, 2005, the WHO said it was following closely reports from China that at least 38 people have died and more than 200 others have been made ill by a swine-borne virus in Sichuan Province. Sichuan Province, where infections with Streptococcus suis have been detected in pigs in a concurrent outbreak, has one of the largest pig populations in China. The outbreak in humans has some unusual features and is being closely followed by the WHO. At that time, Chinese authorities say they have found no evidence of human-to-human transmission . On September 29, 2005, David Nabarro, the newly appointed Senior United Nations System Coordinator for Avian and Human Influenza, warned the world that an outbreak of avian influenza could kill 5 to 150 million people. Also, due to a bipartisan effort of the United States Senate, $4 billion dollars was appropriated to develop vaccines and treatments for Avian influenza.

In 2004 and 2005, 118 people are known to have been infected with the H5N1 virus and 61 of them died. The mortality rate of this virus is as high as that of the virus H1N1 that caused the Spanish Flu of 1918, which killed over 20 million people world wide. One of the major differences between H1N1 of 1918 and the current H5N1 is the fact that the latter is not (yet) transmissible between humans. Until recently, that prevented the H5N1 virus from becoming a pandemic. Recent research of Taubenberger et al {Taubenberger JK, Reid AH, Lourens RM, Wang R, Jin G, Fanning TG. Characterization of the 1918 influenza virus polymerase genes. Nature. 2005 Oct 6;437(7060):889-893} showed that the 1918 virus like H5N1 was an avian virus. Furthermore, Tumpey and colleagues {Tumpey TM, Basler CF, Aguilar PV, Zeng H, Solorzano A, Swayne DE, Cox NJ, Katz JM, Taubenberger JK, Palese P, Garcia-Sastre A. Characterization of the reconstructed 1918 Spanish influenza pandemic virus. Science. 2005 Oct 7;310(5745):77-80} who reconstructed the H1N1 virus of 1918 come to the conclusion that it is especially the polymerase genes and the HA and NA genes that caused the extreme virulence of this virus. The sequences of the polymerase proteins (PA, PB1, and PB2) of the 1918 virus and subsequent human viruses differ by only 10 amino acids from the avian influenza viruses. Human forms of seven of the ten amino acids have already been identified in currently circulating H5N1. It is not unlikely that also the other mutations eventually will surface and make the H5N1 virus better suited for human-to-human transmission.

Another important factor is the change of the HA protein to a binding preference for alpha 2,6 sialic acid (the major form in the human respiratory tract). In avian virus the HA protein preferentially binds to alpha 2,3 sialic acid, which is the major form in the avian enteric tract. It has been shown that only a single amino acid change can result in the change of this binding preference. Altogether it seems that only a few mutations are needed to make the H5N1 avian influenza virus a pandemic virus like the one of 1918.

"In Vietnam, scientists at the Ho Chi Minh Pasteur Institute who have been studying the genetic make up of H5N1 samples taken from people and poultry said it had undergone several mutations. 'There has been a mutation allowing the virus to (replicate) effectively in mammal tissue and become highly virulent.

TRANSMISSION AND INFECTION

Infected birds pass on H5N1

Infected birds pass on H5N1 through their saliva, nasal secretions, and feces. Other birds may pick up the virus through direct contact with these excretions or when they have contact with surfaces contaminated with this material. Because migratory birds are among the carriers of the H5N1 virus it may spread to all parts of the world. Past outbreaks of avian flu have often originated in crowded conditions in southeast and east Asia, where humans, pigs, and poultry live in close quarters. In these conditions a virus can mutate into a form that more easily infects humans.

The majority of H5N1 flu cases have been reported in southeast and east Asia. Once an outbreak is detected, local authorities often order a mass slaughter of birds or animals affected. If this is done promptly, an outbreak of avian flu may be prevented. However, the United Nations (UN) World Health Organization (WHO) has expressed concern that not all countries are reporting outbreaks as completely as they should. China, for example, is known to have officially denied past outbreaks of severe acute respiratory syndrome (SARS) and HIV.

H5N1 infections in humans are generally caused by bird to human transmission of the virus. A few isolated cases of suspected human to human transmission exist, but there is no proof either way in those cases.

Prevention

The current method of prevention in animal populations is to destroy infected animals as well as animals suspected of being infected. In southeast Asia, millions of domestic birds have been slaughtered to prevent the spread of the virus.

The probability of a "humanized" form of H5N1 emerging through recombination in the body of a human co-infected with H5N1 and another influenza could be reduced by influenza vaccination of at-risk workers. It is not clear at this point whether vaccine production could be stepped up sufficiently to meet this demand.

If an outbreak of pandemic flu does occur, its spread might be slowed by increasing hygiene in aircraft, and by examining airline cabin air filters for presence of H5N1 virus.

The American Centers for Disease Control and Prevention advises travelers to areas of Asia where outbreaks of H5N1 have occurred to avoid poultry farms and animals in live food markets. Travelers should also avoid surfaces that appear to be contaminated by feces from any kind of animal, especially poultry.

There are several H5N1 vaccines for several of the H5N1 varieties. H5N1 continually mutates rendering them, so far for humans, of little use.

Symptoms

Since H5N1 is an influenza virus, symptoms similar to those of the common flu, such as fever, cough, sore throat, and sore muscles, can develop in infected humans. However, in more severe cases, pneumonia and respiratory failure can develop and eventually cause death. Patients with H5N1 avian influenza have rarely had conjunctivitis, unlike human cases of infection by the H7 virus.

"The H5N1 virus causes an exaggerated response of cytokines (such as TNF-a), and this could result in a toxic-shock-like syndrome (including fever, chills, vomiting and headache), which ultimately results in death "In many diseases (including H5N1 in humans), a 'cytokine storm' [also called hypercytokinemia (sometimes spelled hypercytokinaemia)] is triggered by the infection. Cytokines are hormones that regulate the immune sytem. When released at the right time in the proper amounts, cytokines can help fight infections and regulate processes through out the body. But many cytokines are inflammatory and are damaging to the body if present in too high levels, or for too long. But whatever it is called, this phenomenon is a type of inflammatory cascade.  Many inflammatory cascades have self limiting components - the release of an inflammatory agent often leads to the production of both anti-inflammatory and inflammatory compounds. But as microbes evolve, they sometimes begin producing a mix of toxins that interfere with the control mechanisms of the immune system. This seems to be the case for the deadly strains of avian influenza. The H5N1 virus is not only partially resistant to the cytokines that are involved in fighting viruses, but it also reduces the production of anti-inflammatory cytokines - in essence, it enhances the accelerator while impairing the brakes, and the immune system goes out of control and crashes."

Treatment

"The 3 viral envelope proteins of influenza A virus are most medically relevant. The hemagglutinin (HA), neuraminidase (NA), and M2 are essential viral proteins targeted by host antibodies or antiviral drugs such as oseltamivir and rimantadine. The HA glycoprotein forms spikes at the surface of virions, mediating attachment to host cell sialoside receptors and subsequent entry by membrane fusion. The NA forms knoblike structures on the surface of virus particles and catalyzes their release from infected cells, allowing virus spread. The M2 is a transmembrane protein that forms an ion channel required for the uncoating process that precedes viral gene expression."

Neuraminidase inhibitors are a class of drugs which act on a protein conserved in all influenza A viruses. Drugs of this type include zanamivir and oseltamivir, the latter being licensed for prophylaxis treatment in the United Kingdom. Oseltamivir, which "attacks the influenza virus and stops it from spreading" inside the user's body, is marketed by Roche as Tamiflu, and this brand has become the drug of choice for governments and organizations in their preparations for a possible H5N1 pandemic. In August 2005, Roche agreed to donate three million courses of Tamiflu to the World Health Organization, to be deployed by the WHO to contain a pandemic in its region of origin. Although Tamiflu is patented, international law gives governments wide freedom to issue compulsory licenses for life-saving drugs.

A further class of drugs, which include amantadine and rimantadine, target M2 protein, a proton channel found in the viral membrane. Unlike zanamivir and oseltamivir, these drugs are inexpensive and widely available and the WHO had initially planned to use them in efforts to combat a H5N1 pandemic. However, the potential of these drugs was considerably lessened when it was discovered that farmers in China has been administering amantadine to poultry with government encouragement and support since the early 1990s, against international livestock regulations; the result has been that the strain of the virus now circulating in South East Asia is largely resistant to the medication and hence significantly more dangerous to humans. However, the strain of H5N1 spread throughout Northern China, Mongolia, Kazakhstan, Russia and Europe by wild birds in the summer of 2005 is not amantadine resistant.

AVIAN INFLUENZA MUTATION, H5N1

Humans coincided with an epizootic

H5N1 is a type of avian influenza virus (bird flu virus) that has mutated through antigenic drift into dozens of highly pathogenic varieties. The first of these appeared in China in 1996 in birds and in Hong Kong in 1997 in Humans.

This infection of humans coincided with an epizootic (an epidemic in nonhumans) of H5N1 influenza in Hong Kong's poultry population. This panzootic (a disease affecting animals of many species esp. over a wide area outbreak was stopped by the killing of the entire domestic poultry population within the territory. The name H5N1 refers to the subtypes of surface antigens present on the virus.

Influenza A virus, the virus that causes Avian flu. Transmission electron micrograph of negatively stained virus particles in late passage.

Colorized transmission electron micrograph of H5N1 (golden) grown in Madin-Darby canine kidney cells (green). As of November 1, 2005, 122 cases of infections in humans, resulting in 62 deaths, have been confirmed outside of China (see Human cases). Thirteen countries across Asia and Europe have been affected. Additionally, more than 120 million birds have died from infection or been killed to prevent further infections.

H5N1 Epidemic across several Countries

Conclusions

 

The simultaneous resurgence of the H5N1 epidemic across several countries during the summer of 2004 indicated that the virus has become endemic in Asian poultry. This situation represents an increasing threat for public health since constant multiplication and circulation of the virus might help selecting mutations that adapt the virus to new hosts. This continuous evolution is supported by our study, which showed that, although the A/crested eagle/Belgium/01/2004 virus still belongs to the Z genotype, an amino acid change was observed in the HA cleavage site. The exchange of an arginine by a lysine conserved 6 basic amino acids in the cleavage site, a molecular structure demonstrated by reverse genetics studies as being the optimal sequence for highly pathogenic bird flu virus cleavability and pathogenicity.

Although Spizaetus nipalensis, a CITES2-listed species (Convention on International Trade in Endangered Species), is well distributed in the H5N1 affected regions in Thailand, no details are currently available that might explain how the birds got infected. One possibility is that they were fed infected chicken carcasses before their departure to Europe. The birds may thus have been infected very shortly before their transportation. This scenario might explain why no clinical symptoms were found. Alternatively, avian wildlife may have a higher resistance to the disease before they exhibit clinical signs and then die suddenly. Preliminary quantitative real-time RT-PCR data collected in our laboratory (data not shown) support this explanation as they show a viral load in the eagles similar to poultry infected with highly pathogenic bird flu . In a zoo in Cambodia, a variety of free-flying and captive birds, including raptors, were reported as being infected with the H5N1 version of the bird flu virus . The disease appeared first in raptors, including hawk-eagles, in the first 2 to 3 days, indicating their high susceptibility. They were most probably fed infected chicken carcasses. The only other report of H5N1 in wild raptors consists of a single peregrine falcon found dead in Hong Kong . Unfortunately, no histopathologic confirmation of the cause of death or viral load assessment studies about this case have been communicated. There have also been 2 reports of bird flu infections of falcons with H7 highly pathogenic bird flu virus. Manvell et al. reported the isolation of a highly pathogenic bird flu virus of H7N3 subtype from a peregrine falcon dying in the United Arab Emirates. During the highly pathogenic bird flu virus outbreaks in Italy in 2000, an H7N1 virus was isolated from a Saker Falcon that died 3 days after normal hunting activity . The raptor had a sudden onset of depression, weakness, and anorexia the day after normal hunting activity and died 2 days later without further clinical signs.

This study demonstrates that international air travel and smuggling represent major threats for introducing and disseminating H5N1 version of the bird flu virus worldwide. Hunting with falcons is practiced in several countries around the world. Here, the falconer who ordered the birds already owned 4 other eagles of the same species. The 2 birds detected by customs may reflect a much larger underlying problem of bird smuggling. Such birds easily remain undetected because customs officers are essentially focused on metal objects, although airport scanners can theoretically detect bones of animals. Specific methods for systematically detecting live animals (e.g., trained dogs) should be considered at airports and borders. This method is now under evaluation in Belgium.