H5N1

From Wikipedia, the free encyclopedia.

Jump to: navigation, search
 This article documents a current event.
Information may change rapidly as the event progresses.

H5N1 is a highly pathogenic strain of avian influenza (bird flu). The first known appearance of this type of influenza in humans was in Hong Kong during 1997. The infection of humans coincided with an epidemic of avian influenza, caused by the same strain, in Hong Kong’s poultry population. The outbreak was stopped by total elimination of poultry population within the territory. The name H5N1 refers to the subtypes of surface antigens present on the virus: hemagglutinin type 5 and neuraminidase type 1.

Influenza A virus, the virus that causes Avian flu. Transmission electron micrograph of negatively stained virus particles in late passage. (Source: Dr. Erskine Palmer, Centers for Disease Control and Prevention Public Health Image Library).
Enlarge
Influenza A virus, the virus that causes Avian flu. Transmission electron micrograph of negatively stained virus particles in late passage. (Source: Dr. Erskine Palmer, Centers for Disease Control and Prevention Public Health Image Library).

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 culled.

Normally, avian flu viruses are transported worldwide in the intestines of wild birds, and are non-lethal. However, this variant has mutated into the most lethal strain of avian influenza ever recorded. Such mutations are natural and have happened in the past, as in the influenza pandemic caused by the 1918 Spanish flu, a variant of H1N1.

Contents

Transmission and infection

[Image:Bird Migration Patterns] 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 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.

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 travellers to areas of Asia where outbreaks of H5N1 have occurred to avoid poultry farms and animals in live food markets[1]. Travellers should also avoid surfaces that appear to be contaminated by feces from any kind of animal, especially poultry.

At present there is no H5N1 flu vaccine, although development efforts are under way according to the World Health Organization. In August 2005, scientists said they had successfully tested in people a vaccine that they believe can protect against the strain of avian influenza that is spreading in birds through Asia and Europe [2].

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[3], unlike human cases of infection by the H7 virus.

Treatment

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 [4], 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 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 immune to the medication and hence significantly more dangerous to humans[5]. 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.

Increasing virulence

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" [6] 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.

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. Because the virus is more likely to survive along with the patients in this scenario, it means that the virus could infect a larger number of people, 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% [7] yet killed more people than World War I.

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. [8] 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 disease 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 [9]. 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. [10]

Global spread 2004/2005

Bird Flu Spread on October 26th, 2005
Enlarge
Bird Flu Spread on October 26th, 2005

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 40 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 23 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 bird flu free [11].

An outbreak of avian influenza in January 2005 affected 33 out of 64 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 were 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 the original carrier, who received the disease from a bird, was held by her mother for roughly 5 days as the young girl died. Shortly afterwards, the mother became ill and perished as well. In March 2005, it was revealed that two nurses who had cared for avian flu patients have 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) [12]. As of July 20, the outbreak had claimed at least 58 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% [13]. Also, in July 2005, it was confirmed H5N1 had appeared in Russia's Novosibirsk region, probably carried by migratory birds [14]. On July 28th, avian influenza was reported to have killed two more people in Vietnam, raising the death toll to 60 [15]. 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 influenza A(H5N1) was confirmed in Kazakhstan and Mongolia, suggesting further spread of the virus [16]. 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.[17] 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. [18]

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[19]. 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 bird flu 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 bird flu 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. [20]

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 21 October/22 October 2005, The British Government announced that a parrot from South America had died in quarantine from the deadly H5N1 strain of Avian Influenza (Bird Flu). However because the parrot died in quarantine, the United Kingdom is still considered free of Bird 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 [21].

Wikinews
Wikinews has news related to this article:

On 31 October 2005, Russia confirmed previously suspected H5N1 bird flu in 10 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. [22]

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. [23]

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. [24]

Human cases

Cumulative number of confirmed human cases of H5N1 avian influenza infection
edit
Country Date of onset
26 December 2003
10 March 2004
19 July 2004
8 October 2004
16 December 2004
to date
Total
Cambodia cases 0 0 4 4
deaths 0 0 4 4
Indonesia cases 0 0 9 9
deaths 0 0 5 5
Thailand cases 12 5 3 20
deaths 8 4 1 13
Vietnam cases 23 4 64 91
deaths 16 4 21 41
Total cases 35 9 80 124
deaths 24 8 31 63
Fatality rate: 50.8%
Source: Communicable Disease Surveillance & Response (CSR), WHO.  



Human Cases and Deaths of H5N1
Enlarge
Human Cases and Deaths of H5N1

Worst Case Scenario

The worst case scenario for a H5N1 pandemic is 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.

"[I]nfluenza 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 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 five and a half percent, it’s 160 million dead. Either way it’s a big number." Pandemic Influenza Risk

See also

References

  1. ^  Interim Guidance about Avian Influenza A (H5N1) for U.S. Citizens Living Abroad from the U.S. Centers for Disease Control and Prevention.
  2. ^  Oseltamivir (Tamiflu) information from United States National Institutes of Health.
  3. ^  Full text article online: "Avian Influenza A (H5N1) Infection in Humans" by The Writing Committee of the World Health Organization (WHO) Consultation on Human Influenza A/H5 in New England Journal of Medicine (29 September 2005) Volume 353 pages 1374-1385.
  4. ^  Bird Flu Drug Rendered Useless: Chinese Chickens Given Medication Made for Humans By Alan Sipress in the Washington Post Saturday, June 18, 2005.
  5. ^  "AVIAN INFLUENZA: 'Pandemic Vaccine' Appears to Protect Only at High Doses" by Martin Enserink in Science, volume 309, page 996, 12 August 2005 DOI:10.1126/science.309.5737.996b
  6. ^  H5N1 Bird Flu Information Used under the fair use policy of the United States copyright law, and under Wikipedia fair use policy See also: What is "Fair Use" in Copyright Law?


External links and sources

Official

Research

News

General information

Personal tools