Avian influenza outbreaks/Crossover to humans/Avian influenza as a biological weapon

[Guest guest]

KD Weber <wvadreaminUndisclosed-Recipient:; <Undisclosed-Recipient:;>Monday, 26 January 2004 10:29Avian influenza outbreaks/Crossover to humans/Avian influenza as a biological weapon

 

Workers throw bags containing chickens into a dump site in Soong Peenong district, Supanburi province, Thailand Sunday, Jan. 25, 2004.

 

Thailand's prime minister said Sunday that the government suspected for 'a couple of weeks' that the country was facing an outbreak of bird flu, but decided not to tell the public to avoid causing panic. (AP Photo/Apichart Weerawong) Bird Flu Vaccine Not Likely for 6 Months By DANIEL LOVERING, Associated Press Writer BANGKOK, Thailand - Asia's bird flu virus is resistant to key anti-influenza drugs, and an effective vaccine is probably more than six months away, the World Health Organization (news - web sites) said Sunday, as Indonesia confirmed it had become the seventh country in the region with an outbreak. The WHO said it would launch a massive funding appeal to help Asian nations destroy millions of chickens in an attempt to stem the disease. Experts warned that if the mass slaughter is improperly carried out, it might only help the virus' jump from fowl to humans. In Indonesia, bird flu has affected millions of chickes, said Sofjan Sudardjat, a senior Indonesian Department of Agriculture official. But the virus has not crossed over to humans, he said. Vietnam and Thailand are the only countries this year where humans have caught the avian flu, with six confirmed deaths in Vietnam and one suspected fatality in Thailand. But the virus has hit millions of chickens in five other countries as well — raising concerns it might mutate, link with regular influenza to create a form that can be transmitted from human to human, fostering the next human flu pandemic. World Health Organization spokesman Dick Thompson warned that the H5N1 virus in humans appears to be resistant to amantadine and rimantadine, the cheaper anti-viral drugs used to treat regular influenza. " This is a disease that's appearing in the developing world. So what you want is affordable drugs, " said Thompson in Geneva. " Should this move from human to human — and it hasn't yet, I want to stress that — then it's going to be a real challenge. " Last week, WHO influenza chief Dr. Klaus Stohr said other anti-viral drugs still appeared to work against the bird flu virus in humans. WHO also reported that the virus, thought to be highly adaptable, had already mutated — setting back hopes for creating a vaccine, which the organization had said might be ready within four weeks. " I don't think we're looking at a workable vaccine within six months. That's too late for the influenza season in Asia but it would be available, " regional WHO spokesman Peter Cordingley told The Associated Press in the Philippines. " It could be available for next winter's flu season ... It's not promising this year, " he added. On its Web site, a WHO statement said new strains that haved appeared were " significantly different from other H5N1 strains isolated in Asia in the recent past, thus necessitating the development of a new prototype strain for use in vaccine manufacturing. " Asia is on a region-wide health alert, with governments slaughtering millions of chickens to contain outbreaks in Thailand, Vietnam, Cambodia, South Korea (news - web sites), Japan and Taiwan. On Sunday, China — which has so far reported no cases of bird flu — banned all poultry from Thailand and Cambodia, two days after cases of the virus were confirmed in both Southeast Asian nations. China is eager to show its resolve in proactively battling bird flu, particularly after last year's severe acute respiratory syndrome epidemic brought the communist government under criticism for its initial guarded response. Hundreds of Thai soldiers, wearing rubber gloves, boots, colorful shower caps and safety masks, helped clear farms of chickens in Thailand's Suphanburi province — the area hardest hit by an outbreak of bird flu. " It's not dangerous, but don't be neglectful, " Deputy Agriculture Minister Newin Chidchob said as he briefed soldiers lined up at the village hall. " The safety masks may be uncomfortable because you're not used to them, but don't even think of taking them off. " Some 450 troops were joined in the operation by 60 prisoners from the provincial jail. In Thailand, prisoners are sometimes called out to dig ditches, repair sewage works and perform other manual public service labor. WHO backs a poultry cull in affected countries as the best way to wipe out the disease. But Thompson said that if the mass slaughter is not funded and handled properly it could make things worse, so the U.N. organization will appeal for international donations to ensure it's carried out correctly. " Safety's the key. You don't want the virus to start mixing in humans. If you send a lot of humans in to do culling you'd be exposing them, unless they wear protective clothing and goggles — something many poor nations can ill-afford, Thompson said. " It's going to be an enormous burden on the developing world to do safe culling, " he said. " We're also going to be asking for assistance for reimbursement to pay backyard farmers when we ask them to kill off their investment in their poultry stock and give them a reasonable incentive to do that. " Thai officials, following weeks of denial, acknowledged the virus' presence this week after poultry farmers claimed not enough was being done to stop the disease from spreading from nearby countries. In a weekly radio address, Thai Prime Minister Thaksin Shinawatra acknowledged Saturday that the onset of the virus in Thailand could devastate the country's chicken export sector — the world's fourth largest. Thailand shipped about 500,000 tons of chicken worth $1.3 billion in 2003. But the 15-nation European Union (news - web sites) and Japan — Thailand's biggest markets for poultry — and several other countries also have announced poultry bans. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

Thaksin admits human bird flu cases 'highly likely' - JAN 23, 2004... call several weeks ago to import bird-flu vaccine, much of ... of a government cover-upover bird flu, said on ... H5N1 swops genes with a common flu virus, creating a ... http://straitstimes.asia1.com/latest/story/0,4390,231395,00.html - Cached

Bird Flu Hits Indonesia, WHO Concerned Over Drug Resistance

 

Thailand admits hiding avian flu Concealed outbreak for 'a few weeks' to avoid public panic --New York Times

 

Nations Ban Poultry Imports to Contain Avian Flu Reported in Six Asian Countries

 

WHO Suggests Quarantine for Bird FluGENEVA (AP) -- The World Health Organization said Friday that people hit by the bird flu outbreak sweeping Asia should be quarantined to avoid contact with sufferers of regular influenza, because a combination of the two viruses may accelerate the spread of the disease....

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Avian influenza H5N1 infection in humans: urgent need to eliminate the animal reservoir - update 5 www.who.int/csr/don/2004_01_22/en/22 January 2004 Epidemics of highly pathogenic avian influenza, caused by various H5N1 strains, have been reported in parts of Asia since mid-December 2003. Millions of domestic poultry have either died or been destroyed as a result. Thousands of workers have been involved in the culling operations.The current situation is of serious concern for human health as well as for agriculture and the poultry industry. Rapid elimination of the H5N1 virus in bird populations should be given high priority as a matter of international public health importance.WHO is collaborating closely, at high levels, with FAO and the World Organisation for Animal Health (OIE) to ensure that appropriate measures in the agricultural sector are introduced as a matter of urgency, and in the interest of protecting public health at the international level. Joint investigations are currently under way in Viet Nam.Of all the avian influenza viruses, which normally cause infection in birds and pigs only, the H5N1 strain may have a unique capacity to cause severe disease, with high mortality, in humans.The simultaneous occurrence in several countries of large epidemics of highly pathogenic H5N1 influenza in domestic poultry is historically unprecedented. The present situation may grow worse. In bird populations, the disease is highly contagious and rapidly fatal, and spreads easily from farm to farm. Wild migratory waterfowl can spread infection to domestic flocks. The potential for further spread of ongoing poultry epidemics, both within affected countries and to other countries, is therefore great.For all these reasons, the H5N1 strain may be more widely established in bird populations and in the environment in this part of the world than presently appreciated. Studies have shown that infected birds can shed large amounts of the virus in their faeces. The virus can survive for long periods in the tissues and faeces of diseased birds and in water, especially when temperatures are low. In water, the virus can survive for up to four days at 22oC and more than 30 days at 0oC. The virus survives in frozen material indefinitely.The large epidemics of highly pathogenic avian influenza currently seen in poultry, and possible widespread presence of the virus in the environment, increase opportunities for human exposure and infection. They also increase opportunities for human and avian influenza viruses to exchange genes This can occur when humans are simultaneously infected by human and avian influenza viruses. The frequency of such co-infections increases the likelihood that a completely new influenza virus subtype might emerge, carrying sufficient human genes to allow efficient and sustainable person-to-person transmission.Research has shown that the risk of direct transmission of H5N1 infection from birds to humans is greatest in persons having close contact with live infected poultry. Contact with poultry kept in live markets is considered the source of infection for 17 of the 18 human cases of H5N1 infection that occurred in Hong Kong in 1997. The additional case – the first in the outbreak – has been linked to contact with poultry at farms experiencing epidemics of highly pathogenic avian H5N1 influenza. Six of the 18 cases were fatal.Occupational exposure can occur among poultry workers, and among workers involved in culling operations.Rapid elimination of the H5N1 virus in animal populations is an essential measure to prevent the emergence of a new influenza virus subtype with pandemic potential. This measure not only helps prevent further spread in bird populations, but also reduces opportunities for human infection. However, in the present situation, the problem of controlling all human exposures is compounded by the large number of “back yard” farms where chickens are kept in rural areas.While rapid culling of infected or exposed flocks is strongly recommended, prevention of infection during culling operations must also be given high priority. Culling operations can place large numbers of workers at risk of brief but intensive exposure to the virus.In 1997, Hong Kong authorities culled the entire poultry population, an estimated 1.5 million birds, within three days. This rapid and comprehensive action is thought by many experts to have averted an influenza pandemic. Culling operations were performed by trained government workers, most of whom wore protective masks, gloves, and gowns. Although subsequent investigation detected H5 antibodies, indicating exposure to the virus, in around 3% of persons involved in the culling of infected poultry, no case of severe respiratory disease was detected as a result of this exposure.In the Netherlands in 2003, an outbreak of highly pathogenic H7N7 avian influenza in poultry caused infection, with mild illness, in 83 persons, and fatal illness in a veterinarian. An estimated 30 million poultry were culled within a week.Further information about highly pathogenic avian influenza is available in a WHO fact sheet, at the FAO web site , and the OIE web site . Information on safety precautions during culling operations will be issued soon by the WHO Regional Office for the Western Pacific.Laboratory characterization of the 2004 H5N1 viruses Laboratories in the WHO Global Influenza Surveillance Network have today discussed results from the sequencing and antigenic characterization of H5N1 strains isolated from humans and poultry in Viet Nam. Initial results show significant differences between these viruses and strains obtained during outbreaks of H5N1 avian influenza in Hong Kong, in 1997 and 2003, indicating that the virus has mutated.Work continues on the updating of WHO diagnostic kits for the rapid detection of H5N1 infection in humans, and on the development of a prototype virus for use in vaccine manufacturing. Viruses from birds in other currently affected countries are urgently needed in order to conduct additional laboratory investigations. Such investigations are part of the information needed by WHO to recommend and develop a vaccine strain that can protect humans against circulating H5N1 strains.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~CDCInfluenza A (H5N1) Outbreak in Vietnam

www.cdc.gov/flu/about/h5n1outbreak.htmRecent Influenza A (H5N1) CasesThe Government of Vietnam has reported hospitalized cases of severe respiratory illness in people from provinces surrounding Hanoi beginning in October 2003. Avian influenza A (H5N1) virus infections have been confirmed is some of these patients. Deaths have been reported. (Visit www.who.int/en/ for updated case counts.)Influenza A (H5N1) viruses normally circulate among wild birds but can infect poultry and rarely have infected people in the past. In 1997, 18 persons in Hong Kong were hospitalized because of influenza A (H5N1) infections and six of them died. In 2003, two residents of Hong Kong who traveled to China developed influenza A (H5N1) virus infections and one of them died. In Vietnam, large outbreaks of influenza A (H5N1) have been reported among poultry in the southern and northern regions of the country. WHO has reported that the H5N1 strain implicated in the outbreak has now been sequenced. All genes are of avian origin, indicating that the virus that caused death in the three confirmed cases had not yet acquired human genes. The acquisition of human genes increases the likelihood that a virus of avian origin can be readily transmitted from one human to another.H5N1 Outbreak InvestigationThe World Health Organization (WHO) is coordinating an investigation in Vietnam. Staff from CDC have traveled to Vietnam to work with WHO and Vietnam’s human and animal health authorities to evaluate the situation, including patterns of transmission of the influenza A (H5N1) viruses. The investigation will focus on determining specific characteristics of influenza A (H5N1) viruses isolated from human cases and poultry and on determining how people became infected. In addition, increased surveillance will help investigators determine how many people in Vietnam already have been infected with the influenza A (H5N1) virus and whether other people are continuing to be infected.During December 2003, an outbreak of avian influenza A (H5N1) was reported among poultry in South Korea. In the second week of January, Japan reported the deaths of 6,000 chickens on a single farm in the western part of Honshu due to influenza A (H5N1) virus infection. No human cases of infection with the avian influenza virus have been reported in either of these outbreaks.CDC RecommendationsU.S. residents who are traveling outside the United States should consult their physician for advice about which vaccines they should obtain. In Vietnam and in other tropical regions, influenza can occur at any time during the year. Thus, persons who are at increased risk of developing influenza-related complications and healthy persons who wish to decrease their risk of becoming ill with influenza should receive the 2003-04 trivalent influenza vaccine. The vaccine will protect against three viruses and offers some protection against variants of them as well. At this time CDC and WHO have not issued any travel alerts or advisories for Vietnam. However, travelers to Vietnam are advised to avoid contact with animals in live food markets and any surfaces that appear to be contaminated with feces from poultry or other animals. For more information about topics related to travelers’ health, visit www.cdc.gov/travel/.Enhanced U.S. Influenza SurveillanceAt this time, CDC recommends enhanced surveillance efforts by state and local health departments, hospitals, and clinicians to identify patients who have been hospitalized with unexplained pneumonia, ARDS, or severe respiratory illness AND who have traveled to Vietnam, South Korea, and Japan within 10 days from onset of symptoms.CDC will make additional recommendations on enhanced surveillance if influenza A (H5N1) activity continues to evolve.More Information About InfluenzaFor further details about the reported cases of influenza A (H5N1) in Vietnam, see the WHO Web site www.who.int/en/. Additional information about influenza is available on the CDC Web site at www.cdc.gov.

 

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Experts Fear Global Bird Flu Outbreak story.news./news...he_big_oneBy DANIEL Q. HANEY, AP Medical Editor With luck, the world will escape the latest outbreak of bird flu with no more than the six human deaths already blamed on it and the loss of millions of chickens. But public health experts worry of a much greater disaster: A catastrophe they say is among the worst imaginable, a global outbreak of an entirely new form of human flu. There is no clear sign that will happen. Nevertheless, avian influenza's sudden sweep through Asia, along with its tendency for wholesale mutation, leave many wondering about the bug's potential for rampant spread among humans. It is a possibility the medical journal The Lancet calls " massively frightening. " " The question everybody is asking is, 'Is this the progenitor to a pandemic?' " says Dr. Gregory Poland, chief of vaccine research at the Mayo Clinic. Influenza pandemics typically strike three or four times a century. The worst in the past 100 years, the 1918-19 Spanish flu, caused an estimated 40 million to 50 million deaths. Another is considered inevitable and perhaps overdue, but when it will happen and how bad it will be are almost totally unpredictable. The nightmare this time would be a flu virus leaping from birds to people and spreading, introducing a disease for which humans have no natural defense. The potential source is the strain of bird flu that has moved rapidly through parts of Asia since December, infecting chickens in at least six countries. Millions of birds have died of the flu or were destroyed by workers trying to contain the outbreak. The World Health Organization (news - web sites) says eliminating this " animal reservoir " is urgent. Avian flu is naturally carried by wild ducks, and it ordinarily does not attack creatures other than birds or pigs, so experts are especially concerned that this bird flu is occasionally infecting people. (ED NOTE: See

LAKEPORT, CALIFORNIA: Massive avian cholera kill

http://www.record-bee.com/Stories/0,1413,255~26901~1912220,00.html

The effort to pick up hundreds of ruddy ducks killed by avian cholera continues. )Human cases have been reported in Vietnam and Thailand, including six deaths as of Saturday in Vietnam, the WHO said, and one suspected death in Thailand. Experts believe all caught the virus from chickens, not other people. " We know there are two possible ways a new pandemic strain can emerge, " said Dr. Steve Ostroff, deputy director of the National Center for Infectious Diseases at the Centers for Disease Control and Prevention (news - web sites). One is a human flu virus that resurfaces after years of dormancy, so people have no defense built up from earlier bouts. The other is a non-human variety acquiring the ability to infect people and spread. The latter may happen if somebody already infected with a human flu virus also catches the bird virus. Inside the body, these two may recombine into a new mutant, part-human virus, part-bird. The more people are around infected chickens and other birds, experts say, the more chances there are for such a disaster to occur. " If the virus continues to spread in chickens, it may adapt itself so it can grow in humans, " says Dr. Arnold Monto, a University of Michigan epidemiologist. " If it is transmitted human to human, then we are concerned this is the start of the great pandemic. " The first time an avian flu virus was found to have infected people was in Hong Kong in 1997. At least 18 people fell severely ill and six died. Experts believe a pandemic may have been averted that time by the rapid slaughter of Hong Kong's entire poultry supply — an estimated 1.5 million birds killed in three days. That flu virus was the H5N1 variety, one of 15 known subtypes of avian flu. The WHO calls it worrisome for several reason: It mutates rapidly and tends to acquire genes from flu viruses in other animal species; it is clearly dangerous to people; and it spreads quickly. Infected birds give off the virus for at least 10 days in their feces and oral secretions. H5N1 appeared again last February, when two members of a family returning to Hong Kong from China became ill. One died and the other recovered. How and where they got infected was never learned. The disease now circulating in Asia is the same H5N1, but it is so widespread that a quick purging, like Hong Kong accomplished seven years ago, is unlikely. Testing shows it has mutated but has not yet picked up any genes from human flu viruses. If a bird flu pandemic occurs, could it be stopped? Many experts fear not. Flu is so contagious that quarantining victims, a method that eventually contained SARS (news - web sites) last year, is unlikely to work. Studies suggest that prescription drugs used to treat human flu strains could also keep people from catching the bird flu. However, spot shortages were reported during this winter's U.S. flu outbreak, and supplies would quickly run out during a pandemic. No country has stockpiled the drugs, Tamiflu, Relenza and the older amantadine and rimantadine. The WHO is already working on a prototype vaccine against the bird flu. But even the standard annual flu shot takes six months to manufacture, and experts doubt a new vaccine could be ready in time. If there is evidence the bird flu is producing significant illness in humans, " there would be a full-bore effort to produce a vaccine, " says the CDC's Ostroff. " It's hard to predict the timeliness of it and how widely it could be put into people's arms. "

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Highly Pathogenic Avian Influenza (Fowl Plague)

Last updated January 23, 2004

http://www.cidrap.umn.edu/cidrap/content/biosecurity/ag-biosec/anim-disease/avianflu.html

AgentHostsEpidemiologyHPAI As a Biological WeaponClinical FeaturesDifferential DiagnosisLaboratory DiagnosisTreatmentPreventionOutbreak ControlPublic Health IssuesReferences

Agent

Avian influenza can occur in two forms: highly pathogenic avian influenza (HPAI), also known as fowl plague, and low-pathogenic avian influenza (LPAI). Both forms are caused by influenza type A virus. HPAI spreads rapidly among flocks and often is highly fatal. Conversely, LPAI generally does not cause severe disease and is more commonly seen in US poultry flocks.

Viral classification and genetic composition

 

Family: Orthomyxoviridae Genus: Influenza

Virions 80 to 120 nm in diameter May be filamentous Eight different segments of negative-stranded RNA; allows for genetic reassortments in single cells infected with more than one virus and may result in multiple strains that are different from the initial ones (see References: PHS, Voyles 2002)

Types: A, B, and C

Type designation is based on the antigenic character of the M protein located in the virus envelope and the nucleoprotein within the virus particle. Influenza A virus causes human, swine, equine, avian, and marine mammal influenza and is the type associated with pandemic disease in humans. Influenza B virus causes disease in humans only. Influenza C virus causes a relatively mild illness in both humans and swine and occurs uncommonly. HPAI and LPAI are caused by influenza A viruses.

The virus envelope glycoproteins have hemagglutinin (HA) and neuraminidase (NA) activity; these characteristics are used to subtype the A, B, and C viruses.

For influenza A viruses, there are 15 different HA antigens (H1 to H15) and nine different NA antigens (N1 to N9). Only subtypes H5 and H7 of influenza A virus have caused HPAI. The H5 and H7 strains also are identifiable according to a nucleic acid sequence at the hemagglutinin cleavage site (see References: PHS).

Environmental Survival of HPAI Virus

 

Influenza A virus remains viable at moderate temperatures for long periods in the environment and can survive indefinitely in frozen material. It can survive for 4 days in water at 22°C and for over 30 days at 0°C (see References: PHS). Inactivation of the virus occurs under the following conditions (see References: OIE 2002, PHS):

Temperatures of 56°C for 3 hours or 60°C or more for 30 minutes Acidic pH conditions Presence of oxidizing agents such as sodium dodecyl sulfate, lipid solvents, and B-propiolactone Exposure to disinfectants: formalin, iodine compounds

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Hosts

It is likely that all birds are susceptible to HPAI. Species that have been shown to be susceptible either experimentally or naturally include:

 

Chickens Turkeys Ducks Partridges Pheasants Quail Pigeons Ostriches and other ratites Geese Guinea fowl

Migratory waterfowl, sea birds, shore birds, and imported pet birds have been found to be carriers of highly-pathogenic influenza A viruses without clinical signs.

As noted above, influenza A viruses also cause illness in humans and other animal hosts (pigs, horses, sea mammals, and mustelids).

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Epidemiology

Transmission

 

Routes of infection include:

Oral Conjunctival Respiratory

Vertical transmission is not known to occur Common modes of infection include:

Direct transmission through secretions (feces, respiratory secretions) of infected birds Broken contaminated eggs in incubators infecting healthy chicks (see References: OIE 2002) Movement of infected birds between flocks Fomites such as contaminated equipment, egg flats, feed trucks, and clothing and shoes of employees and service crews (see References: APHIS, Beard 1998) Contact with wild birds and waterfowl, which appear to be natural reservoirs for the virus Fecal contamination of drinking water Garbage flies (suspected of transmitting the virus during the 1983-1984 epidemic in Pennsylvania) (see References: Beard 1998) Airborne transmission if birds are in close proximity

The disease is highly contagious. One gram of contaminated manure can contain enough HPAI virus to infect 1 million birds (see References: APHIS).

As stated above, waterfowl, ostriches and other ratites, shore birds, sea birds, and other wild birds can act as carriers of the virus. These birds may not show clinical signs but shed the virus.

Occurrence

Because HPAI usually arises from an LPAI virus that has mutated at its hemagglutinin surface proteins, it is difficult to define specific areas where the disease is endemic. HPAI types of virus have been isolated from free-living birds in Europe and other regions; however, there is no recognized wild bird reservoir for the HPAI subtypes of the virus.

 

Apathogenic and mildly pathogenic influenza A viruses occur worldwide. Some H5 and H7 viruses are of low pathogenicity. Because of a lack of appropriate laboratory facilities in many parts of the world, it is difficult to accurately determine the actual incidence of HPAI in the world's poultry flocks (see References: Beard 1998).

Outbreaks of HPAI have occurred throughout the world:

 

An H5 strain affected Pennsylvania in 1983 and caused severe clinical disease and high mortality rates in chickens, turkeys, and guinea fowl (see References: Beard 1998).

A serologically identical but apparently mild virus had been circulating in poultry in the area for 6 months (see References: Beard 1998). A total of 17 million birds were culled. Retail egg prices increased by 30 cents (see References: APHIS).

An H5N1 strain of AI was responsible for a significant outbreak of influenza in humans and domestic poultry in 1997 in Hong Kong.

Prior to this outbreak, H5N1 was not known to infect humans. Six human deaths were attributed to this strain. The virus was isolated from chickens, and mortality rates were high. A total of 1.5 million birds were culled in 3 days. A monitoring system was instituted for birds in live markets.

An H7N1 strain occurred in the Veneto region of Italy in December 1999.

A total of 30,000 turkeys died or were destroyed to contain the outbreak. In 1998, H5N2 strains of the virus were responsible for at least eight outbreaks on Italian farms (see References: APHIS).

Other countries that have had outbreaks include Australia (H7), England (H7), South Africa (H5), Scotland (H5), Ireland (H5), Mexico (H5), and Pakistan (H7). A Hong Kong man died in February 2003 from bird flu (H5N1), the first human case reported since 1997 (see below), and his son contracted the disease as well. Health officials are working to develop a vaccine to H5N1 in humans (see References: Cyranoski 2003). An outbreak of HPAI occurred in the Netherlands in 2003. Over 28 million birds out of a total 100 million birds in the country were killed. There were reports of over 80 human cases, and one veterinarian died. The disease spread to Belgium but was quite rapidly contained. An outbreak in Asia started in January 2004 and continues to spread. So far, it involves South Korea, Vietnam, Japan, Thailand, and Cambodia. Of special concern is that fact that in Vietnam and Thailand, the avian strain (H5N1) has now been confirmed in several cases of fatal human respiratory disease. Low-pathogenic avian influenza (H5N2) has been identified in Taiwan.

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HPAI As a Biological Weapon

HPAI is considered a potential biological weapon because of the following factors:

 

Extremely contagious High mortality rate Severe economic consequences of an outbreak:

Large numbers of birds are destroyed or die. Control measures disrupt trade of poultry products from affected areas. Prices of retail poultry products may increase significantly.

Virus has a high potential for genetic mutations and for new strains to arise and affect new species

The Hong Kong epidemic of 1997 and the associated human cases demonstrate the ability of the virus to affect humans and birds.

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Clinical Features

The clinical signs of HPAI are severe and result in high mortality rates in many species of birds, especially domestic fowl. As mentioned above, waterfowl, ratites, and other birds may not be as susceptible to clinical signs, but can act as carriers for the virus.

 

 

 

 

Clinical Features of Highly Pathogenic Avian Influenza in Animals

 

 

Feature

 

Characteristics

 

 

CHICKENS

 

 

Incubation Period

 

3-7 days

 

 

Clinical signs

 

—Sudden death—Severe depression with ruffled feathers—Inappetence —Drastic decline in egg production—Edema of head and neck—Swollen and cyanotic combs and wattles (see Gray Book figure 25 and figure 26 [References: Beard 1998]) —Petechial hemorrhages on internal membrane surfaces—Excessive thirst—Watery diarrhea that begins as bright green and progresses to white—Swollen and congested conjunctiva with occasional hemorrhage—Diffuse hemorrhage between hocks and feet (see Gray Book figure 27 [References: Beard 1998])—Respiratory signs are dependent on tracheal involvement—Nasal and ocular discharge—Mucus accumulation (varies)—Lack of energy—Coughing/sneezing—Incoordination—Nervous system signs such as paralysis

 

 

Complications

 

—Cessation of egg production, and eggs laid immediately prior to infection often soft-shelled and misshapen—Surviving birds are in poor condition and resume laying only after a period of several weeks

 

 

Case-fatality rate

 

—Can be as high as 100% —Death may occur prior to any symptoms or as late as a week after symptoms, though it is frequently within 48 hr

 

 

TURKEYS

 

 

Incubation period

 

3-7 days

 

 

Clinical signs

 

—Sudden death—Severe depression with ruffled feathers—Inappetence—Drastic decline in egg production—Edema of the head and neck—Swollen and cyanotic combs and wattles—Petechial hemorrhages on internal membrane surfaces—Excessive thirst and evidence of dehydration—Watery diarrhea that begins as bright green and progresses to white—Swollen and congested conjunctivae with occasional hemorrhage—Diffuse hemorrhage between hocks and feet—Respiratory signs are dependent on tracheal involvement—Nasal and ocular discharge—Mucus accumulation (varies)—Lack of energy—Coughing/sneezing—Incoordination—Nervous system signs such as paralysis—Sinusitis—Dehydration

 

 

Complications

 

—Decrease in egg production—Sudden death—Surviving birds are in poor condition and resume laying only after a period of several weeks

 

 

Case-fatality rate

 

—Can be as high as 100%—Most turkeys die within 3 to 10 days

 

 

DOMESTIC DUCKS AND GEESE

 

 

Incubation period

 

3-7 days

 

 

Clinical signs

 

—Signs of depression, inappetence, and diarrhea similar to those seen in layers—Swollen sinuses—Neurologic signs in younger birds—Sinusitis

 

 

Complications

 

—Decrease in egg production—Sudden death—Surviving birds are in poor condition and resume laying only after a period of several weeks

 

 

Case-fatality rate

 

As high as 100%

 

 

Adapted from Aeillo 1998, APHIS, Beard 1998, Capua 2001, OIE 2002, PHS) (see References).