Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997, due to the global spread of H5N1 that constitutes a pandemic threat.
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 is more likely to mutate into a form that more easily infects humans. A few isolated cases of suspected human to human transmission exist, with the latest such case in June 2006 (among members of a family in Sumatra). No pandemic strain of H5N1 has yet been found.
H5N1 vaccines for chickens exist and are sometimes used, although there are many difficulties, and it's difficult to decide whether it helps more or hurts more. H5N1 pre-pandemic vaccines exist in quantities sufficient to inoculate a few million people and might be useful for priming to "boost the immune response to a different H5N1 vaccine tailor-made years later to thwart an emerging pandemic". H5N1 pandemic vaccines and technologies to rapidly create them are in the H5N1 clinical trials stage but can not be verified as useful until after there exists a pandemic strain.
Environmental survival Avian flu virus can last indefinitely at a temperature dozens of degrees below freezing, as is found in the northernmost areas that migratory birds frequent.
Heat kills H5N1 (i.e. inactivates the virus).
Influenza A viruses can survive: Over 30 days at 0 °C (32.0 °F) (over one month at freezing temperature) 6 days at 37 °C (98.6 °F) (one week at human body temperature) decades in permanently frozen lakes on hard non-porous surface such as plastic or stainless steel for 24–48 hours on clothes, paper and tissues for 8–12 hours
While cooking poultry to 70 °C (158 °F) kills the H5N1 virus, it is recommended to cook meat to 74 °C (165 °F) to kill all foodborne pathogens.CIDRAP article Germany finds H5N1 in frozen duck meat published September 10, 2007
Inactivation of the virus also occurs under the following conditions: 30 minutes 60 °C (140.0 °F) (half-hour at a temperature that causes first and second degree burns in humans in ten seconds) Acidic pH conditions Presence of anti-microbial surfactants such as sodium dodecyl sulfate and lipid solvents Exposure to disinfectants: B-propiolactone, formalin, and iodine compounds
Ordinary levels of chlorine in tap water kill H5N1 in public water systems.
To kill avian flu viruses,Source of quotation:
H5N1 "can remain infectious in municipal landfills for almost 2 years. [...] The two factors that most reduced influenza survival times were elevated temperature and acidic or alkaline pH."physorg.com Reprint from: American Chemical Society; article "Bird flu virus remains infectious up to 600 days in municipal landfills" published May 27th, 2009
Avian flu in birds
According to Avian Influenza by Timm C. Harder and Ortrud Werner: Following an incubation period of usually a few days (but rarely up to 21 days), depending upon the characteristics of the isolate, the dose of inoculum, the species, and age of the bird, the clinical presentation of avian influenza in birds is variable and symptoms are fairly unspecific. Therefore, a diagnosis solely based on the clinical presentation is impossible. The symptoms following infection with low pathogenic AIV may be as discrete as ruffled feathers, transient reductions in egg production or weight loss combined with a slight respiratory disease. Some LP strains such as certain Asian H9N2 lineages, adapted to efficient replication in poultry, may cause more prominent signs and also significant mortality. In its highly pathogenic form, the illness in chickens and turkeys is characterised by a sudden onset of severe symptoms and a mortality that can approach 100% within 48 hours. 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.
Poultry farming practices There have been a number of farming practices that have changed in response to outbreaks of the H5N1 virus, including:
vaccinating poultry against bird flu vaccinating poultry workers against human flu limiting travel in areas where H5N1 is found increasing farm hygiene reducing contact between livestock and wild birds reducing open-air wet markets limiting workers contact with cock fighting reducing purchases of live fowl improving veterinary vaccine availability and cost.
For example, after nearly two years of using mainly culling to control the virus, the Vietnamese government in 2005 adopted a combination of mass poultry vaccination, disinfecting, culling, information campaigns and bans on live poultry in cities.
Dealing with outbreaks The majority of H5N1 flu cases have been reported in southeast and east Asia. Once an outbreak is detected, local authorities often order a mass slaughter of birds or animals infected or suspected to be infected.
Use of vaccines Dr. Robert G. Webster et al. write
Transmission of highly pathogenic H5N1 from domestic poultry back to migratory waterfowl in western China has increased the geographic spread. The spread of H5N1 and its likely reintroduction to domestic poultry increase the need for good agricultural vaccines. In fact, the root cause of the continuing H5N1 pandemic threat may be the way the pathogenicity of H5N1 viruses is masked by cocirculating influenza viruses or bad agricultural vaccines."
Webster speculates that substandard vaccines may be preventing the expression of the disease in the birds but not stopping them from carrying or transmitting the virus through feces, or the virus from mutating.
In order to protect their poultry from death from H5N1, China reportedly made a vaccine based on reverse genetics produced with H5N1 antigens, that Dr Wendy Barclay, a virologist at the University of Reading believes have generated up to six variations of H5N1.
Transmission
According to the United Nations FAO, wild water fowl likely plays a role in the avian influenza cycle and could be the initial source for AI viruses, which may be passed on through contact with resident water fowl or domestic poultry, particularly domestic ducks. A newly mutated virus could circulate within the domestic and possibly resident bird populations until highly pathogenic avian influenza (HPAI) arises. This new virus is pathogenic to poultry and possibly to the wild birds that it arose from.
Wild birds found to have been infected with HPAI were either sick or dead. This could possibly affect the ability of these birds to carry HPAI for long distances. However, the findings in Qinghai Lake-China, suggest that H5N1 viruses could possibly be transmitted between migratory birds. Additionally, the new outbreaks of HPAI in poultry and wild birds in Russia, Kazakhstan, Western China and Mongolia may indicate that migratory birds probably act as carriers for the transport of HPAI over longer distances. Short-distance transmission between farms, villages or contaminated local water bodies is likewise a distinct possibility.
The AI virus has adapted to the environment in ways such as using water for survival and to spread, and creating a reservoir (ducks) strictly tied to water. The water in turn influences movement, social behavior and migration patterns of water bird species. It is therefore of great importance to know the ecological strategy of influenza virus as well, in order to fully understand this disease and to control outbreaks when they occur. Most research is needed concerning HPAI viruses in wild birds. For example, small birds like sparrows and starlings can be infected with deadly H5N1 strains and they can carry the virus from chicken house to chicken house causing massive epidemics among the chickens. However, pigeons do not present a risk as they neither catch nor carry the virus.
Avian flu in humans
Human to human transmission
As of 2005, the WHO believed that another influenza pandemic is as likely to occur at any time since 1968, when the last century's third of three pandemics took place. The WHO describes a series of six phases, starting with the inter-pandemic period, where there are no new influenza virus subtypes detected in humans, and progressing numerically to the pandemic period, where there is efficient and sustained human-to-human transmission of the virus in the general population. According to WHO, the world has been at phase 3 on the scale, meaning a new influenza virus subtype is causing disease in humans, but has not yet spread efficiently and sustainably among humans.
So far, H5N1 infections in humans are attributed to bird-to-human transmission of the virus in most cases. Until May 2006, the WHO estimate of the number of human to human transmission had been "two or three cases". In May 2006, Julie L. Gerberding, director of the United States Centers for Disease Control and Prevention in Atlanta, estimated that there had been "at least three." Maria Cheng, a WHO spokeswoman, said there were "probably about half a dozen," but that no one "has got a solid number." A few isolated cases of suspected human to human transmission exist. with the latest such case in June 2006 (among members of a family in Sumatra). No pandemic strain of H5N1 has yet been found.
Prevention Notwithstanding possible mutation of the virus, the probability of a "humanized" form of H5N1 emerging through genetic recombination in the body of a human co-infected with H5N1 and another influenza virus type (a process called reassortment) could be reduced by widespread seasonal influenza vaccination in the general population. It is not clear at this point whether vaccine production and immunization could be stepped up sufficiently to meet this demand.
If an outbreak of pandemic flu does occur, its spread might be slowed by increasing hygiene in aircraft, and by examining airline cabin air filters for presence of H5N1 virus.
The American Centers for Disease Control and Prevention advises travelers to areas of Asia where outbreaks of H5N1 have occurred to avoid poultry farms and animals in live food markets. Travelers should also avoid surfaces that appear to be contaminated by feces from any kind of animal, especially poultry.
There are several H5N1 vaccines for several of the avian H5N1 varieties. H5N1 continually mutates rendering them, so far for humans, of little use. While there can be some cross-protection against related flu strains, the best protection would be from a vaccine specifically produced for any future pandemic flu virus strain. Daniel R. Lucey, co-director of the Biohazardous Threats and Emerging Diseases graduate program at Georgetown University has made this point, "There is no H5N1 pandemic so there can be no pandemic vaccine." However, "pre-pandemic vaccines" have been created; are being refined and tested; and do have some promise both in furthering research and preparedness for the next pandemic.Promising research into vaccines includes:
Vaccine manufacturing companies are being encouraged to increase capacity so that if a pandemic vaccine is needed, facilities will be available for rapid production of large amounts of a vaccine specific to a new pandemic strain.
It is not likely that use of antiviral drugs could prevent the evolution of a pandemic flu virus. Revised on January 10, 2001.
Symptoms