Bird Flu Tips

Bird flu is an infection caused by avian (bird) influenza(flu) viruses. These flu virusesoccur naturally among birds. Wild birds worldwide carry the virusesin their intestines, but usually do not get sick from them.

However, bird flu is very contagious among birds andcan make some domesticated birds, including chickens, ducks, and turkeys,very sick and kill them.

Last Updated - 12th November 2005

Do bird flu viruses infect humans?

Bird flu viruses do not usually infect humans, but several cases ofhuman infection with bird flu viruses have occurred since 1997.

How are bird flu viruses different from humanflu viruses?

There are many different subtypes of type A influenza viruses. Thesesubtypes differ because of certain proteins on the surface of the influenzaA virus (hemagglutinin [HA] and neuraminidase [NA] proteins). Thereare 16 different HA subtypes and 9 different NA subtypes of flu A viruses.Many different combinations of HA and NA proteins are possible. Eachcombination is a different subtype. All known subtypes of flu A virusescan be found in birds. However, when we talk about “bird flu”viruses, we are referring to influenza A subtypes chiefly found in birds.They do not usually infect humans, even though we know they can. Whenwe talk about “human flu viruses” we are referring to thosesubtypes that occur widely in humans. There are only three known A subtypesof human flu viruses (H1N1, H1N2, and H3N2); it is likely that somegenetic parts of current human influenza A viruses came from birds originally.Influenza A viruses are constantly changing, and they might adapt overtime to infect and spread among humans.

What are the symptoms of bird flu in humans?

Symptoms of bird flu in humans have ranged from typical flu-like symptoms(fever, cough, sore throat and muscle aches) to eye infections, pneumonia,severe respiratory diseases (such as acute respiratory distress), andother severe and life-threatening complications. The symptoms of birdflu may depend on which virus caused the infection.

How does bird flu spread?

Infected birds shed flu virus in their saliva, nasal secretions, andfeces. Susceptible birds become infected when they have contact withcontaminated excretions or surfaces that are contaminated with excretions.It is believed that most cases of bird flu infection in humans haveresulted from contact with infected poultry or contaminated surfaces.The spread of avian influenza viruses from one ill person to anotherhas been reported very rarely, and transmission has not been observedto continue beyond one person.

How is bird flu in humans treated?

Studies done in laboratories suggest that the prescription medicinesapproved for human flu viruses should work in preventing bird flu infectionin humans. However, flu viruses can become resistant to these drugs,so these medications may not always work. Additional studies are neededto prove the effectiveness of these medicines.

What is the risk to humans from bird flu?

The risk from bird flu is generally low to most people because theviruses occur mainly among birds and do not usually infect humans. However,during an outbreak of bird flu among poultry (domesticated chicken,ducks, turkeys), there is a possible risk to people who have contactwith infected birds or surfaces that have been contaminated with excretionsfrom infected birds. The current outbreak of avian influenza A (H5N1)among poultry in Asia and Europe is an example of a bird flu outbreakthat has caused human infections and deaths. In such situations, peopleshould avoid contact with infected birds or contaminated surfaces, andshould be careful when handling and cooking poultry. In rare instances,limited human-to-human spread of H5N1 virus has occurred, and transmissionhas not been observed to continue beyond one person.

What is an avian influenza A (H5N1) virus?

Influenza A (H5N1) virus – also called “H5N1 virus”– is an influenza A virus subtype that occurs mainly in birds.Like all bird flu viruses, H5N1 virus circulates among birds worldwide,is very contagious among birds, and can be deadly.

What is the H5N1 bird flu that has been reportedin Asia and Europe?

Outbreaks of influenza H5N1 occurred among poultry in eight countriesin Asia (Cambodia, China, Indonesia, Japan, Laos , South Korea , Thailand, and Vietnam) during late 2003 and early 2004. At that time, more than100 million birds in the affected countries either died from the diseaseor were killed in order to try to control the outbreak. By March 2004,the outbreak was reported to be under control. Beginning in late June2004, however, new outbreaks of influenza H5N1 among poultry were reportedby several countries in Asia (Cambodia, China [ Tibet ], Indonesia,Kazakhastan, Malaysia, Mongolia, Russia [ Siberia ], Thailand, and Vietnam).It is believed that these outbreaks are ongoing. Most recently, influenzaH5N1 has been reported among poultry in Turkey and Romania. Human infectionsof influenza A (H5N1) have been reported in Cambodia, Indonesia, Thailand,and Vietnam.

What is the risk to humans from the H5N1 virusin Asia and Europe?

The H5N1 virus does not usually infect humans. In 1997. However, thefirst case of spread from a bird to a human was seen during an outbreakof bird flu in poultry in Hong Kong, Special Administrative Region.The virus caused severe respiratory illness in 18 people, 6 of whomdied. Since that time, there have been other cases of H5N1 infectionamong humans. Recent human cases of H5N1 infection that have occurredin Cambodia, Thailand, and Vietnam have coincided with large H5N1 outbreaksin poultry. The World Health Organization (WHO) also has reported humancases in Indonesia. Most of these cases have occurred from contact withinfected poultry or contaminated surfaces; however, it is thought thata few cases of human-to-human spread of H5N1 have occurred.

So far, spread of H5N1 virus from person to person has been rare andhas not continued beyond one person. However, because all influenzaviruses have the ability to change, scientists are concerned that theH5N1 virus one day could be able to infect humans and spread easilyfrom one person to another. Because these viruses do not commonly infecthumans, there is little or no immune protection against them in thehuman population. If the H5N1 virus were able to infect people and spreadeasily from person to person, an influenza pandemic (worldwide outbreakof disease) could begin. No one can predict when a pandemic might occur.However, experts from around the world are watching the H5N1 situationin Asia very closely and are preparing for the possibility that thevirus may begin to spread more easily and widely from person to person.

How is infection with H5N1 virus in humanstreated?

The H5N1 virus currently infecting birds in Asia that has caused humanillness and death is resistant to amantadine and rimantadine, two antiviralmedications commonly used for influenza. Two other antiviral medications,oseltamavir and zanamavir, would probably work to treat flu caused bythe H5N1 virus, but additional studies still need to be done to provetheir effectiveness.

Is there a vaccine to protect humans fromH5N1 virus?

There currently is no commercially available vaccine to protect humansagainst the H5N1 virus that is being seen in Asia and Europe . However,vaccine development efforts are taking place. Research studies to testa vaccine to protect humans against H5N1 virus began in April 2005,and a series of clinical trials is underway.

What is the risk to people in the United Statesfrom the H5N1 bird flu outbreak in Asia and Europe ?

The current risk to Americans from the H5N1 bird flu outbreak in Asiais low. The strain of H5N1 virus found in Asia and Europe has not beenfound in the United States . There have been no human cases of H5N1flu in the United States . It is possible that travelers returning fromaffected countries in Asia could be infected if they were exposed tothe virus. Since February 2004, medical and public health personnelhave been watching closely to find any such cases.

Instances of Avian Influenza Infections inHumans

Confirmed instances of avian influenza viruses infecting humans since1997 include:

Symptoms of Avian Influenza in Humans

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

Antiviral Agents for Influenza

Four different influenza antiviral drugs (amantadine, rimantadine,oseltamivir, and zanamivir) are approved by the U.S. Food and Drug Administration(FDA) for the treatment of influenza; three are approved for prophylaxis.All four have activity against influenza A viruses. However, sometimesinfluenza strains can become resistant to these drugs, and thereforethe drugs may not always be effective. For example, analyses of someof the 2004 H5N1 viruses isolated from poultry and humans in Asia haveshown that the viruses are resistant to two of the medications (amantadineand rimantadine). Monitoring of avian influenza A viruses for resistanceto influenza antiviral medications is ongoing.

Which viruses cause highly pathogenic disease?

Influenza A viruses1 have 16 H subtypes and 9 N subtypes2. Only virusesof the H5 and H7 subtypes are known to cause the highly pathogenic formof the disease. However, not all viruses of the H5 and H7 subtypes arehighly pathogenic and not all will cause severe disease in poultry.

On present understanding, H5 and H7 viruses are introduced to poultryflocks in their low pathogenic form. When allowed to circulate in poultrypopulations, the viruses can mutate, usually within a few months, intothe highly pathogenic form. This is why the presence of an H5 or H7virus in poultry is always cause for concern, even when the initialsigns of infection are mild.

Do migratory birds spread highly pathogenicavian influenza viruses?

The role of migratory birds in the spread of highly pathogenic avianinfluenza is not fully understood. Wild waterfowl are considered thenatural reservoir of all influenza A viruses. They have probably carriedinfluenza viruses, with no apparent harm, for centuries. They are knownto carry viruses of the H5 and H7 subtypes, but usually in the low pathogenicform. Considerable circumstantial evidence suggests that migratory birdscan introduce low pathogenic H5 and H7 viruses to poultry flocks, whichthen mutate to the highly pathogenic form.

In the past, highly pathogenic viruses have been isolated from migratorybirds on very rare occasions involving a few birds, usually found deadwithin the flight range of a poultry outbreak. This finding long suggestedthat wild waterfowl are not agents for the onward transmission of theseviruses.

Recent events make it likely that some migratory birds are now directlyspreading the H5N1 virus in its highly pathogenic form. Further spreadto new areas is expected.

What is special about the current outbreaksin poultry?

The current outbreaks of highly pathogenic avian influenza, which beganin South-east Asia in mid-2003, are the largest and most severe on record.Never before in the history of this disease have so many countries beensimultaneously affected, resulting in the loss of so many birds.

The causative agent, the H5N1 virus, has proved to be especially tenacious.Despite the death or destruction of an estimated 150 million birds,the virus is now considered endemic in many parts of Indonesia and VietNam and in some parts of Cambodia, China, Thailand, and possibly alsothe Lao People’s Democratic Republic. Control of the disease inpoultry is expected to take several years.

The H5N1 virus is also of particular concern for human health, as explainedbelow.

Which countries have been affected by outbreaksin poultry?

From mid-December 2003 through early February 2004, poultry outbreakscaused by the H5N1 virus were reported in eight Asian nations (listedin order of reporting): the Republic of Korea, Viet Nam, Japan, Thailand,Cambodia, Lao People’s Democratic Republic, Indonesia, and China.Most of these countries had never before experienced an outbreak of highlypathogenic avian influenza in their histories.

In early August 2004, Malaysia reported its first outbreak of H5N1in poultry, becoming the ninth Asian nation affected. Russia reportedits first H5N1 outbreak in poultry in late July 2005, followed by reportsof disease in adjacent parts of Kazakhstan in early August. Deaths ofwild birds from highly pathogenic H5N1 were reported in both countries.Almost simultaneously, Mongolia reported the detection of H5N1 in deadmigratory birds. In October 2005, H5N1 was confirmed in poultry in Turkeyand Romania. Outbreaks in wild and domestic birds are under investigationelsewhere.

Japan, the Republic of Korea, and Malaysia have announced control oftheir poultry outbreaks and are now considered free of the disease.In the other affected areas, outbreaks are continuing with varying degreesof severity.

What are the implications for human health?

The widespread persistence of H5N1 in poultry populations poses twomain risks for human health.

The H5N1 virus amply meets the first two conditions: it is a new virusfor humans (H5N1 viruses have never circulated widely among people),and it has infected more than 100 humans, killing over half of them.No one will have immunity should an H5N1-like pandemic virus emerge.

All prerequisites for the start of a pandemic have therefore been metsave one: the establishment of efficient and sustained human-to-humantransmission of the virus. The risk that the H5N1 virus will acquirethis ability will persist as long as opportunities for human infectionsoccur. These opportunities, in turn, will persist as long as the viruscontinues to circulate in birds, and this situation could endure forsome years to come.

What changes are needed for H5N1 to becomea pandemic virus?

The virus can improve its transmissibility among humans via two principalmechanisms. The first is a “reassortment” event, in whichgenetic material is exchanged between human and avian viruses duringco-infection of a human or pig. Reassortment could result in a fullytransmissible pandemic virus, announced by a sudden surge of cases withexplosive spread.

The second mechanism is a more gradual process of adaptive mutation,whereby the capability of the virus to bind to human cells increasesduring subsequent infections of humans. Adaptive mutation, expressedinitially as small clusters of human cases with some evidence of human-to-humantransmission, would probably give the world some time to take defensiveaction.

What is the significance of limited human-to-humantransmission?

Though rare, instances of limited human-to-human transmission of H5N1and other avian influenza viruses have occurred in association withoutbreaks in poultry and should not be a cause for alarm. In no instancehas the virus spread beyond a first generation of close contacts orcaused illness in the general community. Data from these incidents suggestthat transmission requires very close contact with an ill person. Suchincidents must be thoroughly investigated but – provided the investigationindicates that transmission from person to person is very limited –such incidents will not change the WHO overall assessment of the pandemicrisk. There have been a number of instances of avian influenza infectionoccurring among close family members. It is often impossible to determineif human-to-human transmission has occurred since the family membersare exposed to the same animal and environmental sources as well asto one another.

How serious is the current pandemic risk?

The risk of pandemic influenza is serious. With the H5N1 virus nowfirmly entrenched in large parts of Asia, the risk that more human caseswill occur will persist. Each additional human case gives the virusan opportunity to improve its transmissibility in humans, and thus developinto a pandemic strain. The recent spread of the virus to poultry andwild birds in new areas further broadens opportunities for human casesto occur. While neither the timing nor the severity of the next pandemiccan be predicted, the probability that a pandemic will occur has increased.

Are there any other causes for concern?

Yes. Several.

Why are pandemics such dreaded events?

Influenza pandemics are remarkable events that can rapidly infect virtuallyall countries. Once international spread begins, pandemics are consideredunstoppable, caused as they are by a virus that spreads very rapidlyby coughing or sneezing. The fact that infected people can shed virusbefore symptoms appear adds to the risk of international spread viaasymptomatic air travellers.

The severity of disease and the number of deaths caused by a pandemicvirus vary greatly, and cannot be known prior to the emergence of thevirus. During past pandemics, attack rates reached 25-35% of the totalpopulation. Under the best circumstances, assuming that the new viruscauses mild disease, the world could still experience an estimated 2million to 7.4 million deaths (projected from data obtained during the1957 pandemic). Projections for a more virulent virus are much higher.The 1918 pandemic, which was exceptional, killed at least 40 millionpeople. In the USA, the mortality rate during that pandemic was around2.5%.

Pandemics can cause large surges in the numbers of people requiringor seeking medical or hospital treatment, temporarily overwhelming healthservices. High rates of worker absenteeism can also interrupt otheressential services, such as law enforcement, transportation, and communications.Because populations will be fully susceptible to an H5N1-like virus,rates of illness could peak fairly rapidly within a given community.This means that local social and economic disruptions may be temporary.They may, however, be amplified in today’s closely interrelatedand interdependent systems of trade and commerce. Based on past experience,a second wave of global spread should be anticipated within a year.

As all countries are likely to experience emergency conditions duringa pandemic, opportunities for inter-country assistance, as seen duringnatural disasters or localized disease outbreaks, may be curtailed onceinternational spread has begun and governments focus on protecting domesticpopulations.

What are the most important warning signalsthat a pandemic is about to start?

The most important warning signal comes when clusters of patients withclinical symptoms of influenza, closely related in time and place, aredetected, as this suggests human-to-human transmission is taking place.For similar reasons, the detection of cases in health workers caringfor H5N1 patients would suggest human-to-human transmission. Detectionof such events should be followed by immediate field investigation ofevery possible case to confirm the diagnosis, identify the source, anddetermine whether human-to-human transmission is occurring.

Studies of viruses, conducted by specialized WHO reference laboratories,can corroborate field investigations by spotting genetic and other changesin the virus indicative of an improved ability to infect humans. Thisis why WHO repeatedly asks affected countries to share viruses withthe international research community.

What is the status of vaccine developmentand production?

Vaccines effective against a pandemic virus are not yet available.Vaccines are produced each year for seasonal influenza but will notprotect against pandemic influenza. Although a vaccine against the H5N1virus is under development in several countries, no vaccine is readyfor commercial production and no vaccines are expected to be widelyavailable until several months after the start of a pandemic.

Some clinical trials are now under way to test whether experimentalvaccines will be fully protective and to determine whether differentformulations can economize on the amount of antigen required, thus boostingproduction capacity. Because the vaccine needs to closely match thepandemic virus, large-scale commercial production will not start untilthe new virus has emerged and a pandemic has been declared. Currentglobal production capacity falls far short of the demand expected duringa pandemic.

What drugs are available for treatment?

Two drugs (in the neuraminidase inhibitors class), oseltamivir (commerciallyknown as Tamiflu) and zanamivir (commercially known as Relenza) canreduce the severity and duration of illness caused by seasonal influenza.The efficacy of the neuraminidase inhibitors depends on their administrationwithin 48 hours after symptom onset. For cases of human infection withH5N1, the drugs may improve prospects of survival, if administered early,but clinical data are limited. The H5N1 virus is expected to be susceptibleto the neuraminidase inhibitors.

An older class of antiviral drugs, the M2 inhibitors amantadine andrimantadine, could potentially be used against pandemic influenza, butresistance to these drugs can develop rapidly and this could significantlylimit their effectiveness against pandemic influenza. Some currentlycirculating H5N1 strains are fully resistant to these the M2 inhibitors.However, should a new virus emerge through reassortment, the M2 inhibitorsmight be effective.

For the neuraminidase inhibitors, the main constraints – whichare substantial – involve limited production capacity and a pricethat is prohibitively high for many countries. At present manufacturingcapacity, which has recently quadrupled, it will take a decade to produceenough oseltamivir to treat 20% of the world’s population. Themanufacturing process for oseltamivir is complex and time-consuming,and is not easily transferred to other facilities.

So far, most fatal pneumonia seen in cases of H5N1 infection has resultedfrom the effects of the virus, and cannot be treated with antibiotics.Nonetheless, since influenza is often complicated by secondary bacterialinfection of the lungs, antibiotics could be life-saving in the caseof late-onset pneumonia. WHO regards it as prudent for countries toensure adequate supplies of antibiotics in advance.

Can a pandemic be prevented?

No one knows with certainty. The best way to prevent a pandemic wouldbe to eliminate the virus from birds, but it has become increasinglydoubtful if this can be achieved within the near future.

Following a donation by industry, WHO will have a stockpile of antiviralmedications, sufficient for 3 million treatment courses, by early 2006.Recent studies, based on mathematical modelling, suggest that thesedrugs could be used prophylactically near the start of a pandemic toreduce the risk that a fully transmissible virus will emerge or at leastto delay its international spread, thus gaining time to augment vaccinesupplies.

The success of this strategy, which has never been tested, dependson several assumptions about the early behaviour of a pandemic virus,which cannot be known in advance. Success also depends on excellentsurveillance and logistics capacity in the initially affected areas,combined with an ability to enforce movement restrictions in and outof the affected area. To increase the likelihood that early interventionusing the WHO rapid-intervention stockpile of antiviral drugs will besuccessful, surveillance in affected countries needs to improve, particularlyconcerning the capacity to detect clusters of cases closely relatedin time and place.

Is the world adequately prepared?

No. Despite an advance warning that has lasted almost two years, theworld is ill-prepared to defend itself during a pandemic. WHO has urgedall countries to develop preparedness plans, but only around 40 havedone so. WHO has further urged countries with adequate resources tostockpile antiviral drugs nationally for use at the start of a pandemic.Around 30 countries are purchasing large quantities of these drugs,but the manufacturer has no capacity to fill these orders immediately.On present trends, most developing countries will have no access tovaccines and antiviral drugs throughout the duration of a pandemic.