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Global spread of H5N1

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Highly pathogenic H5N1
Highly pathogenic H5N1
 →  Countries with poultry or wild birds killed by H5N1.
 →  Countries with human cases of H5N1.
H5N1

WHO pandemic phases
1. Low risk
2. New virus
3. Self limiting
4. Person to person
5. Epidemic exists
6. Pandemic exists
The global spread of (highly pathogenic) H5N1 in birds is considered a significant pandemic threat.

While prior H5N1 strains have been known, they were significantly different from the current H5N1 strain on a genetic level, making the global spread of this new strain unprecedented. The current H5N1 strain is a fast-mutating, highly pathogenic avian influenza virus (HPAI) found in multiple bird species. It is both epizootic (an epidemic in non-humans) and panzootic (a disease affecting animals of many species especially over a wide area). Unless otherwise indicated, "H5N1" in this article refers to the recent highly pathogenic strain of H5N1.

"Since 1997, studies of H5N1 indicate that these viruses continue to evolve, with changes in antigenicity and internal gene constellations; an expanded host range in avian species and the ability to infect felids; enhanced pathogenicity in experimentally infected mice and ferrets, in which they cause systemic infections; and increased environmental stability." [NEJM]

Tens of millions of birds have died of H5N1 influenza and hundreds of millions of birds have been slaughtered and disposed of to limit the spread of H5N1. Countries that have reported one or more major highly pathogenic H5N1 outbreaks in birds (causing at least thousands but in some cases millions of dead birds) are (in order of first outbreak occurrence): Korea, Vietnam, Japan, Thailand, Cambodia, Laos, Indonesia, China, Malaysia, Russia, Kazakhstan, Mongolia, Turkey, Romania, Croatia, Ukraine, Cyprus, Iraq, Nigeria, Egypt, India, France, Niger, Bosnia, Azerbaijan, Albania, Cameroon, Myanmar, Afghanistan, Israel, Pakistan, Jordan, Burkina Faso, Germany, Sudan, Ivory Coast, Djibouti. Highly pathogenic H5N1 has been found in birds in the wild in numerous other countries: Austria, Bulgaria, Czech Republic, Denmark, Greece, Hungary, Iran, Italy, Kuwait, Poland, Serbia and Montenegro, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom. Countries with massive bird die offs that do not confirm H5N1 include: Ethiopia. Surveillance of H5N1 in humans, poultry, wild birds, cats and other animals remains very weak in many parts of Asia and Africa. Much remains unknown about the exact extent of its spread.

H5N1 has low pathogenic varieties endemic in birds in North America. H5N1 has a highly pathogenic variety that is endemic in dozens of species of birds throughout south Asia and is threatening to become endemic in birds in west Asia and Africa. So far, it is very difficult for humans to become infected with H5N1. The presence of highly pathogenic (deadly) H5N1 around the world in both birds in the wild (swans, magpies, ducks, geese, pigeons, eagles, etc.) and in chickens and turkeys on farms has been demonstrated in millions of cases with the virus isolate actually sequenced in hundreds of cases yielding definitive proof of the evolution of this strain of this subtype of the species Influenzavirus A (bird flu virus).

H5N1 caused flu outbreaks in 1959 and in 1991 but these strains were very different from the current highly pathogenic strain of H5N1. Evolution from 1999 to 2002 created the Z genotype which became the dominant strain of highly pathogenic H5N1 in 2004.

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 China. In October 2004 researchers discovered H5N1 is far more dangerous than previously believed because waterfowl were directly spreading the highly pathogenic strain of H5N1 to chickens, crows, pigeons, and other birds and that it was increasing its ability to infect mammals as well. From this point on, avian flu experts increasingly refer to containment as a strategy that can delay but not prevent a future avian flu pandemic.

The spread of avian influenza in the eastern hemisphere.
Enlarge
The spread of avian influenza in the eastern hemisphere.

In January 2005 an outbreak of avian influenza 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. In April 2005 there begins an unprecedented die-off of over 6,000 migratory birds at Qinghai Lake in central China over three months. This strain of H5N1 is the same strain as is spread west by migratory birds over at least the next ten months. In August 2005 H5N1 spread to Kazakhstan, Mongolia and Russia. 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. David Nabarro later stated that as the virus had spread to migratory birds, an outbreak could start in Africa or the Middle East. Later in 2005 H5N1 spread to Turkey, Romania, Croatia and Kuwait.

In the first two months of 2006 H5N1 spread to Africa and Europe in wild bird populations possibly signaling the beginning of H5N1 being endemic in wild migratory bird populations on multiple continents for decades, permanently changing the way poultry are farmed.

By April 2006 scientists had concluded that containment had failed due to the role of wild birds in transmitting the virus and were now emphasizing far more comprehensive risk mitigation and management measures. [International Institute for Sustainable Development (IISD)] SCIENTIFIC SEMINAR ON AVIAN INFLUENZA, THE ENVIRONMENT AND MIGRATORY BIRDS ON 10-11 APRIL 2006 published 14 April 2006.

As of July 142006
Cumulate Human Cases of and Deaths from H5N1

Source World Health Organization>WHO [Confirmed Human Cases of H5N1]
The smooth curve represents an exponential regression, fitting a function of the form y = a + ek x to the actual number of deaths.

Contents

Human and bird cases

As of July 142006
Confirmed human cases and Transmission and infection of H5N1#Mortality rate>mortality rate of avian influenza (H5N1)
Country Report dates [ edit ]

Total
2003 2004 2005 2006
cases deaths cases deaths cases deaths cases deaths cases deaths
  8 5 63% 8 5 63%
  4 4 100% 2 2 100% 6 6 100%
 People's Republic of China   8 5 63% 11 7 64% 19 12 63%
  1 0 0% 1 0 0%
  14 6 43% 14 6 43%
  17 11 65% 36 30 83% 53 41 77%
  2 2 100% 2 2 100%
  17 12 71% 5 2 40%   22 14 64%
  12 4 33% 12 4 33%
3 3 100% 29 20 69% 61 19 31%   93 42 45%
Total 3 3 100% 46 32 70% 95 41 43% 86 56 65% 230 132 57%
Source World Health Organization (WHO) :
[Communicable Disease Surveillance & Response (CSR)].

1959-2003

A highly pathogenic strain of H5N1 caused flu outbreaks with significant spread to numerous farms, resulting in great economic losses in 1959 in Scotland in chickens and in 1991 in England in turkeys. [WHO] These strains were somewhat similar to the current pathogenic strain of H5N1 in two of its ten genes, the gene that causes it to be type H5 and the gene that causes it to be N1. The other genes can and have been reassorted from other subtypes of the bird flu species (their ease at exchanging genes is part of what makes them all one species). Evolution by reassortment of H5N1 from 1999 to 2002 created the Z genotype which became the dominant strain of highly pathogenic H5N1 in 2004 and is now spreading across the entire world in both wild and domestic birds.

"The precursor of the H5N1 influenza virus that spread to humans in 1997 was first detected in Guangdong, China, in 1996, when it caused a moderate number of deaths in geese and attracted very little attention." [CDC]

In 1997, in Hong Kong, 18 humans were infected and 6 died in the first known case of H5N1 infecting humans. [WHO]

"Human disease associated with influenza A subtype H5N1 re-emerged in January 2003, for the first time since an outbreak in Hong Kong in 1997." Three people in one family were infected after visiting Fujian province in mainland China and 2 died. [NCBI]

By midyear of 2003 outbreaks of poultry disease caused by H5N1 occurred in Asia, but were not recognized as such. That December animals in a Thai zoo died after eating infected chicken carcasses. Later that month H5N1 infection was detected in 3 flocks in the Republic of Korea. [WHO]

H5N1 in China in this and later periods is less than fully reported. Blogs have described many discrepancies between official China government announcements concerning H5N1 and what people in China see with their own eyes. Many reports of total H5N1 cases exclude China due to widespread disbelief in China's official numbers. [WHO] [WHO] [CBC] [WHO] [WHO]

2004

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 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.

February 2004: "The Ministry of Public Health in Thailand has confirmed the country’s tenth case of H5N1 infection." [WHO]

July 2004: Fresh outbreaks in poultry were confirmed in Ayutthaya and Pathumthani provinces of Thailand, and Chaohu city in Anhui, China. Research identifies the dominant strain of H5N1 as the "Z genotype". [WHO timeline]

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 bird flu free [Yahoo news].

September 2004: More cases of H5N1 in humans in Thailand. [WHO]

October 2004: Researchers discover H5N1 is far more dangerous than previously believed. "In the past, outbreaks of highly pathogenic avian influenza in poultry began following the primary introduction of a virus, of low pathogenicity, probably carried by a wild bird. The virus then required several months of circulation in domestic poultry in order to mutate from a form causing very mild disease to a form causing highly pathogenic disease, with a mortality approaching 100%. Only viruses of the H5 and H7 subtypes are capable of mutating to cause highly pathogenic disease. In the present outbreaks, however, asymptomatic domestic ducks can directly introduce the virus, in its highly pathogenic form, to poultry flocks." [WHO] Limiting this conclusion to domestic waterfowl proved to be wishful thinking, as in later months it became clear that nondomestic waterfowl were also directly spreading the highly pathogenic strain of H5N1 to chickens, crows, pigeons, and other birds and that it was increasing its ability to infect mammals as well. From this point on, avian flu experts increasingly refer to containment as a strategy that can delay but not prevent a future avian flu pandemic.

November 2004: The U.S.'s National Institutes of Health's (NIH) National Institute of Allergy and Infectious Diseases's (NIAID) Influenza Genome Sequencing Project to provide complete sequence data for selected human and avian influenza isolates begins. [Nature article: "Race against time"]

December 2004: "[F]irst human case of H5N1 [is] detected in Viet Nam since early September" [WHO].

2005

January 2005: An outbreak of avian influenza 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.

February 2005: "Surveillance stepped up in province where Cambodia's first human avian influenza case was detected" [WHO].

March 2005: Vietnam and Thailand have seen several isolated cases where human-to-human transmission of the virus has been suspected in care-givers of H5N1 patients, including a mother of a girl who died from H5N1 and two nurses.

April 2005: "The Ministry of Health in Vietnam has provided WHO with official confirmation of an additional eight human cases of H5N1 avian influenza. Two of the cases were recently detected, between 2 and 8 April, in Hung Yen and Ha Tay Provinces, respectively. Both patients are alive. The other six cases are thought to have been detected prior to 2 April. WHO is seeking further details from the authorities on this six cases." [WHO] There is an unprecedented die-off of over 6,000 migratory birds at Qinghai Lake in central China during April, May and June. This strain of H5N1 is the same strain as is spread west by migratory birds over at least the next ten months. "The RNA sequence of the Qinghai virus reveals that three of its eight genes are almost identical to those of a virus isolated from a chicken in Shantou in 2003. The other five genes resemble those of viruses found in southern China earlier in 2005, which belong to the "Z genotype" virus circulating across east Asia." [New Scientist] [Alert Net].

May 2005: "Since January 2004, when human cases of H5N1 avian influenza were first reported in the current outbreak, 97 cases and 53 deaths have been reported in Vietnam, Thailand and Cambodia. Vietnam, with 76 cases and 37 deaths, has been the most severely affected country, followed by Thailand, with 17 cases and 12 deaths, and Cambodia, with 4 cases and 4 deaths." [WHO]

June 2005: "[T]esting of clinical specimens by international experts working in Vietnam provided further suggestive evidence of more widespread infection with the virus, raising the possibility of community-acquired infection" but "the detection of H5N1 in clinical specimens is technically challenging and prone to errors" so team members and supplies from "institutes in Australia, Canada, Hong Kong SAR, Japan, the United Kingdom, and the United States of America having extensive experience in the testing of avian influenza viruses in human clinical specimens" investigated and concluded that "no laboratory evidence suggesting that human infections are occurring with greater frequency or that the virus is spreading readily among humans." [WHO]

July 2005: A death in Jakarta was the first confirmed human fatality in Indonesia. On July 28, avian influenza was reported to have killed two more people in Vietnam, raising the death toll to sixty [Washington Post].

August 2005: On August 3 2005, 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. [United Nations] In early August, an avian outbreak of H5N1 flu was confirmed in Kazakhstan and Mongolia, suggesting further spread of the virus [flu.org news]. 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. [BBC] EU officials chose not to impose a similar policy on member countries.

September 2005: 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. [United Nations] David Nabarro stated that as the virus had spread to migratory birds, an outbreak could start in Africa or the Middle East. Agricultural ministers of Association of South East Asian Nations announced a three-year plan to counter the spread of the disease. [BBC]

October 2005: 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 15 October 2005, the British Veterinary Laboratory in Weybridge confirmed that the virus detected in Ciamurlia, Romania is H5N1. On 19 October 2005, China announced a fresh outbreak of bird flu, 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 26 October 2005, Croatia announced H5N1 strain was found in dead swans [DW-World]. On 31 October 2005, Russia confirmed previously suspected H5N1 bird flu 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. [Rian.ru]

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 [source] reports, it was killed by authorities and did not die from the virus.

December 2005: "China confirms its third human death from bird flu. That brings the death toll [...] to 74, comprising 14 victims in Thailand, four in Cambodia, 11 in Indonesia, 42 in Vietnam and three in China." [Reuters]

2006

January

January 5 2006 January 7 2006 January 8 2006 January 10 2006 January 16 2006 January 18 2006 January 21 2006 January 29 2006 January 30 2006
The Ministry of Health in Iraq has confirmed the country’s first case of human infection with the H5N1 avian influenza virus. The case occurred in a 15-year-old girl who died on 17 January following a severe respiratory illness. Her symptoms were compatible with a diagnosis of H5N1 avian influenza. Preliminary laboratory confirmation was provided by a US Naval Medical Research Unit located in Cairo, Egypt. The girl’s 39-year-old uncle, who cared for her during her illness, developed symptoms on 24 January and died of a severe respiratory disease on 27 January. Both patients resided in the town of Raniya near Sulaimaniyah in the northern part of the country, close to the border with Turkey. Poultry deaths were recently reported in their neighbourhood, but H5N1 avian influenza has not yet been confirmed in birds in any part of the country. Poultry samples have been sent for testing at an external laboratory. A history of exposure to diseased birds has been found for the girl. The uncle’s source of infection is under investigation. The Ministry of Health has further informed WHO of a third human case of respiratory illness that is under investigation for possible H5N1 infection. The patient is a 54-year-old woman, from the same area, who was hospitalized on 18 January. Specimens are on their way to a WHO collaborating laboratory in the United Kingdom for diagnostic confirmation and further analysis. An international team, including representatives of other UN agencies, is being assembled to assist the Ministry of Health in its investigation of the situation and its planning of an appropriate public health response. WHO staff within Iraq have been directly supporting the government’s operational response, which was launched shortly after the girl’s death. Iraq is the seventh country to report human H5N1 infection in the current outbreak. The first human case occurred in Viet Nam in December 2003. [WHO]

February

February 4 2006 February 6 2006 February 7 2006 February 8 2006 February 9 2006 February 10 2006 February 11 2006 February 12 2006 February 13 2006 February 14 2006 February 15 2006 February 17 2006 February 18 2006 [Times of India online edition]

February 19 2006

[Times of India online edition]

February 20 2006

[CroEos .net - Znanstveni portal] February 21 2006 [CroEos .net - Znanstveni portal]
"This is a disease which doesn't go away so we are going to be living with H5N1 in Western Europe, I believe, in wild bird populations - even endemic in wild bird populations - for decades perhaps, or even sporadically in those populations every year." [BBC online article: Bird flu planning]
  • The respected science journal Nature says:
    • "The virus is highly likely to become endemic, says Peter Openshaw, head of the respiratory viral infections section at the National Heart and Lung Institute in London, UK. We have to change the way poultry are farmed. [...] Jan Slingenbergh, an animal health expert at the United Nation's Food and Agriculture Organization (FAO) in Rome, Italy, points out that H5N1 may survive in icy lake waters over European winters, potentially infecting any migratory birds that subsequently arrive. The virus could also become established in permanently resident European birds; Openshaw notes that H5N1 has so far been able to infect a wide range of species. If this happens, farming practices will have to be changed, says Neil Ferguson, an epidemiologist at Imperial College London, UK, who is advising the British government on how to deal with possible future outbreaks." [Natue magazine online's article: Bird flu here to stay? Experts warn that H5N1 could become entrenched in Europe.]
    February 23 2006 [CroEos .net - Znanstveni portal - Avian Influenza complete coverage]

    February 25 2006

    February 27 2006 [Reuters]

    February 28 2006

    March

    March 1 2006 March 2 2006 March 3 2006 March 4 2006 March 5 2006 March 6 2006 March 8 2006 March 9 2006 March 10 2006 March 12 2006 March 14 2006 March 15 2006 March 16 2006 March 17 2006 March 18 2006 March 19 2006 [Aljazeera]

    March 20 2006

    March 21 2006 March 24 2006 March 26 2006 March 29 2006 March 31 2006

    April

    April 4 2006 April 5 2006 April 6 2006 April 7 2006 April 10 2006 April 11 2006 April 12 2006 April 18 2006 April 27 2006

    May

    May 11 2006 May 13 2006 May 15 2006 May 16 2006 May 21 2006 May 23 2006 May 25 2006 May 30 2006

    June

    June 2 2006 June 17 2006 June 23 2006 June 30 2006
    1. The number of new countries reporting human cases increased from 4 to 9 after October 2005, following the geographical extension of outbreaks among avian populations.
    2. Half of the cases occurred in people under the age of 20 years; 90% of cases occurred in people under the age of 40 years.
    3. The overall case-fatality rate was 56%. Case fatality was high in all age groups but was highest in persons aged 10 to 39 years.
    4. The case-fatality profile by age group differs from that seen in seasonal influenza, where mortality is highest in the elderly.
    5. The overall case-fatality rate was highest in 2004 (73%), followed by 63% to date in 2006, and 43% in 2005.
    6. Assessment of mortality rates and the time intervals between symptom onset and hospitalization and between symptom onset and death suggests that the illness pattern has not changed substantially during the three years.
    7. Cases have occurred all year round. However, the incidence of human cases peaked, in each of the three years in which cases have occurred, during the period roughly corresponding to winter and spring in the northern hemisphere. If this pattern continues, an upsurge in cases could be anticipated starting in late 2006 or early 2007." [Avian influenza – epidemiology of human H5N1 cases reported to WHO]

    July

    July 5 2006 July 7 2006 Spain detects H5N1 bird flu for first time'' published July 7, 2006

    Pig cases

    Pigs can harbor influenza viruses adapted to humans and others that are adapted to birds, allowing the viruses to exchange genes and create a pandemic strain.
    Enlarge
    Pigs can harbor influenza viruses adapted to humans and others that are adapted to birds, allowing the viruses to exchange genes and create a pandemic strain.

    Avian influenza virus H3N2 is endemic in pigs ("swine flu") in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment) with H5N1, passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000 humans. The dominant strain of annual flu in humans in January 2006 is H3N2. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans has increased to 91% in 2005. A combination of these two subtypes of the species known as the avian flu virus in a country like China is a worst case scenario. In August 2004, researchers in China found H5N1 in pigs. [WHO timeline]

    ''
    Domestic cats can get H5N1 from eating birds, and can transmit it to other cats and possibly to people.
    Enlarge
    Domestic cats can get H5N1 from eating birds, and can transmit it to other cats and possibly to people.

    October 2004: Variants have been found in a number of domestic cats, leopards and tigers in Thailand, with high lethality. [NCBI] "The Thailand Zoo tiger outbreak killed more than 140 tigers, causing health officials to make the decision to cull all the sick tigers in an effort to stop the zoo from becoming a reservoir for H5N1 influenza (ProMED-mail, 2004i; ProMED-mail, 2004w). A study of domestic cats showed H5N1 virus infection by ingestion of infected poultry and also by contact with other infected cats (Kuiken et al., 2004)." [NAP] The initial OIE report reads: "the clinical manifestations began on 11 October 2004 with weakness, lethargy, respiratory distress and high fever (about 41-42 degrees Celsius). There was no response to any antibiotic treatment. Death occurred within three days following the onset of clinical signs with severe pulmonary lesions." [link]

    On February 28 2006 a dead cat infected with the H5N1 bird flu virus was found in Germany. [Reuters]

    On March 6 2006 Hans Seitinger, the top agriculture official in the southern state of Styria, Austria announced that several still living cats in Styria have tested positive for H5N1. [ABC News]

    The spread to more and more types and populations of birds and the ability of felidae (cats) to catch H5N1 from eating this natural prey means the creation of a reservoir for H5N1 in cats where the virus can adapt to mammals is one of the many possible pathways to a pandemic.

    Mammals in general

    Martens and an unknown number of other mammals can catch H5N1, illustrating the unprecedented ability of H5N1 to survive and spread.
    Enlarge
    Martens and an unknown number of other mammals can catch H5N1, illustrating the unprecedented ability of H5N1 to survive and spread.

    H5N1 has been transmitted in laboratories to many species including mice and ferrets to study its effects.

    H5N1 was transmitted in the wild to three civet cats in Vietnam in August 2005 and a stone marten in Germany in March 2006. [AP news report] [Science daily]

    The BBC reported that a stray dog in Azerbaijan died from the disease on March 15 2006. [BBC]

    Experts believe more work is needed to determine the role of mammals in the epidemiology of H5N1. Officials are not doing enough to monitor cats, dogs and other carnivores for their possible role in transmitting H5N1. People living in areas where the A(H5N1) virus has infected birds are advised to keep their cats indoors. "Cats can be infected through the respiratory tract. Cats can also be infected when they ingest the virus, which is a novel route for influenza transmission in mammals. But cats excrete only one-thousandth the amount of virus that chickens do [...] The concern is that if large numbers of felines and other carnivores become infected, the virus might mutate in a series of events that could lead to an epidemic among humans. Dogs, foxes, seals and other carnivores may be vulnerable to A(H5N1) virus infection, Dr. Osterhaus said. Tests in Thailand have shown that the virus has infected dogs without causing apparent symptoms." [New York Times] Article on Bird Flu Criticizes Effort to Monitor Cats and Dogs - By Altman - Published: April 6, 2006

    Expected mortality from pandemic

    If H5N1 mutates so that it can jump from human to human, while maintaining a relatively high level of mortality, how many people could die? Risk communication analysts Peter M. Sandman and Jody Lanard give a round-up of the various estimates:

    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 1000 million deaths (the bird flu 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 hale 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 Communication The Teachable Moment]

    Perhaps the most extreme maximum has come from renowned virus expert, Robert Webster, who believes H5N1 has the capacity to mutate into a form that could kill a third of the human population [link] In 2003 world renowned virologist Robert Webster published The world is teetering on the edge of a pandemic that could kill a large fraction of the human population in American Scientist saying "a third of the human population" could die from H5N1. In [ABC News] article on March 14, 2006 he is quoted as saying "Society just can't accept the idea that 50 percent of the population could die. And I think we have to face that possibility". .

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