20 Jan 2006

Scientists studying virus samples from the human outbreak of avian influenza in Turkey have identified 3 mutations in the virus's sequence. They say that at least 2 of these look likely to make the virus better adapted to humans.

The Turkey outbreak is unusual, because of the large family clusters of cases; the fact that many of those infected have only mild symptoms; and the speed with which infections have arisen -- 20 cases, including 4 deaths, in less than 2 weeks. So scientists are urgently trying to establish whether the virus is behaving differently in this outbreak from previous ones in Asia. In particular, international teams are investigating the possibility that the virus is moving between people. "With such a large number of cases within such a short period of time, human-to-human transmission is something that we've had to consider," says Maria Cheng, a spokeswoman at World Health Organization (WHO) headquarters in Geneva.

As Nature went to press, samples from the first 2 teenagers in the country to die had been sequenced by a WHO collaborating centre at the National Institute of Medical Research (NIMR) in London. The results so far are not comforting. The 1st mutation found, announced last week, involves a substitution in one sample of an amino acid at position 223 of the haemoagglutinin protein. This protein allows the flu virus to bind to the receptors on the surface of its host's cells. This mutation has been observed twice before -- in a father and son in Hong Kong in 2003, and in one fatal case in Viet Nam during 2005. It increases the virus's ability to bind to human receptors, and decreases its affinity for poultry receptors, making strains with this mutation better adapted to infecting humans.

The same sample also contained a mutation at position 153 of the haemagglutinin protein, Nature has learned. Cheng says this information was not included in WHO statements, because "it is not clear what role this particular change plays".

Finally, both samples from the Turkish teenagers show a substitution of glutamic acid with lycine, at position 627 of the polymerase protein, which the virus uses to replicate its genetic material. This mutation has been seen in other flu sequences from Eurasian poultry over the past year. It was also present in the one person who died during an outbreak of H7N7 in the Netherlands in 2003, and in a few people in Viet Nam and Thailand. The polymerase mutation is one of the 10 genetic changes that gave rise to the 1918 pandemic flu virus.

Like the 223-haemagglutinin mutation, it signals adaptation to humans, says Alan Hay, Director of a WHO influenza laboratory at the NIMR. "There is this glutamic acid/lysine flip," he explains. "Glutamic acid is associated with flu-virus replication in birds, and lycine is in primates."

The Turkey strains are the first in which the polymerase and receptor-binding mutations have been found together. They could make it easier for humans to catch the virus from poultry. But they might also favour human-to-human transmission. This is because the polymerase change helps the virus to survive in the cooler nasal regions of the respiratory tract, and the haemagglutinin mutation encourages the virus to target receptors in the nose and throat, rather than lower down in the lungs. The virus is thought to be more likely to spread through droplets coughed from the nose and throat than from infections lower down. Hay points out, however, that it is difficult to predict how the mutations will actually influence the virus's behaviour. He adds that just 2 changes are unlikely to create efficient human-to-human transmission on their own.

Establishing what effects these changes are having on the epidemiology of the current outbreak is a top priority for research teams working in Turkey. "We must learn more about the mild cases and be absolutely sure of whether these viruses are behaving differently from those we have seen elsewhere," says Hay. "It is early days in terms of what we know about the viruses causing these infections."

Researchers are sequencing more strains from the Turkish cases, to see whether they share the mutations and to check for further changes. Samples were expected to arrive in London on Wed 18 Jan 2006, after being held up for more than a week in Turkey because of the Eid-ul-Adha holiday period.

12 Jan 2006

Laboratory tests conducted in Turkey have confirmed detection of the H5 subtype of avian influenza virus in samples from an additional two patients. The patients are residents of Sanliurfa Province, near the southern border with Syria, and Siirt Province, which is adjacent to Van in the eastern part of the country. Human cases have now been reported from nine of the country’s 81 provinces.

Both patients are young children, aged four and six years, and both have a documented history of direct contact with diseased birds. In Sanliurfa Province, outbreaks in backyard poultry are now thought to date back to late November 2005. Altogether, agricultural officials have confirmed poultry outbreaks in 11 provinces and are investigating possible outbreaks in an additional 14 provinces across the country...

...All available evidence indicates that no sustained human-to-human transmission has occurred. As in Asia, contact with infected birds is the principal source of infection. The risk of infection for travellers to Turkey is negligible provided direct contact with dead or diseased domestic and wild birds is avoided.

Gene sequencing information on human viruses

The WHO Collaborating Centre for Reference and Research on influenza at the MRC National Institute for Medical Research in Mill Hill, London, has today completed genetic and antigenic analyses of viruses recovered from the first two fatal human cases in the Turkish outbreak.

Information provided to WHO indicates that these viruses are very similar to current avian H5N1 viruses isolated from birds in Turkey. They are also closely related to viruses isolated from the large outbreak in migratory birds that occurred at the Qinghai Lake nature reserve in China, beginning in late April of last year.

These analyses indicate that the Turkish viruses are sensitive to both classes of antiviral drugs, including oseltamivir and amantadine. WHO and collaborating experts will review the data on amantadine sensitivity. Oseltamivir remains the drug of first choice recommended by WHO.

Virus from one of the patients shows mutations at the receptor-binding site. One of the mutations has been seen previously in viruses isolated from a small outbreak in Hong Kong in 2003 (two cases, one of which was fatal) and from the 2005 outbreak in Viet Nam. Research has indicated that the Hong Kong 2003 viruses bind preferentially to human cell receptors more so than to avian cell receptors. Researchers at the Mill Hill laboratory anticipate that the Turkish virus will also have this characteristic.

Interpretation of the significance of this finding for human health will depend on clinical and epidemiological data now being gathered in Turkey.

All available evidence indicates that no sustained human-to-human transmission is occurring in any country experiencing human cases.

The present WHO level of pandemic alert remains at phase 3: human infections with a new virus subtype are occurring, but the vast majority of these infections are acquired directly from animals.

The first case was a 37-year-old female nurse in QEH with encephalitis The diagnosis was immune-mediated encephalitis. This case showed a temporal relation with influenza vaccination, with onset of mild neurological symptoms resolving spontaneously 1 week following vaccination, and neck pain, fever, blurred vision and involuntary upper limb movement 3 weeks after vaccination. The Working Group also noted another case report of encephalitis following influenza vaccination reported in PMH in 2003. On the other hand, other causes of encephalitis in this patient cannot be excluded… …While it is difficult to prove or disprove influenza vaccination as causing this patient’s illness, the Working Group opines that a causal relationship between encephalitis and influenza vaccination in general cannot be established on the basis of current evidence. The second case was a 26-year-old female teacher reported by PWH The diagnosis was suspected Guillain-Barre Syndrome (GBS). The Working Group opines that further tests (e.g. nerve conduction test) repeated over the next few weeks will be useful to confirm the diagnosis of GBS. This case showed a temporal relation with influenza vaccination, with sudden onset of weakness and numbness about 3 weeks following vaccination. However, the patient also had symptoms of upper respiratory tract infection 1-2 weeks before onset which might serve as the triggering event (two-thirds of GBS patients report antecedent infectious illnesses)… …it is difficult to prove or disprove influenza vaccination as causing this patient¡¦s illness, the Working Group concurs with WHO’s assessment and opines that this case alone does not prove a general causal relationship between GBS and influenza vaccination.

The 2004 outbreaks of highly pathogenic avian influenza H5N1 disease in China led to a great poultry loss and society attention. A survey of avian influenza viruses was conducted on tree sparrows (Passer montanus) collected in China in 2004. Four viruses were isolated from free-living tree sparrows. The results of the whole-genome analysis indicated that an H5N1 virus with a new genotype is circulating among tree sparrows. The hemagglutinin and neuraminidase genes of the new genotype were derived from Gs/Gd/96-like viruses and the nuclear protein gene descended from the 2001 genotype A H5N1 viruses, while the other inner genes originated from an unknown influenza virus. In experimental infection, all four viruses were highly pathogenic to chickens but not pathogenic to ducks or mice. The four tree sparrow viruses were different from the 2003 tree sparrow strain (genotype Z) in Hong Kong. The results suggested that H5N1 viruses might be distributed widely in tree sparrows.

Current phase of alert in the WHO global influenza preparedness plan: Experts at WHO and elsewhere believe that the world is now closer to another influenza pandemic than at any time since 1968, when the last of the previous century's three pandemics occurred. WHO uses a series of six phases of pandemic alert as a system for informing the world of the seriousness of the threat and of the need to launch progressively more intense preparedness activities. The designation of phases, including decisions on when to move from one phase to another, is made by the Director-General of WHO. Each phase of alert coincides with a series of recommended activities to be undertaken by WHO, the international community, governments, and industry. Changes from one phase to another are triggered by several factors, which include the epidemiological behaviour of the disease and the characteristics of circulating viruses. The world is presently in phase 3: a new influenza virus subtype is causing disease in humans, but is not yet spreading efficiently and sustainably among humans.

28 Oct 05 - The WHO Global Influenza Programme has been closely monitoring the antigenic and genetic evolution of circulating H5N1 viruses, especially human isolates. Recent investigations have indicated that H5 haemagglutinins (HA) genes of viruses from birds in China, Indonesia, Japan, Mongolia, Russia, South Korea and Turkey, and 3 viruses from humans in Indonesia are genetically distinguishable from the prototype strains selected last year for influenza pandemic vaccine development. There is also evidence of antigenic variation among the HA of recent viruses. However, their geographical spread and pathogenicity in human populations remain unclear. At present WHO does not recommend changing the previously selected H5N1 prototype strains for ongoing pandemic vaccine development...

27 Oct 05 - Outbreaks of avian influenza in poultry, when caused by highly pathogenic viruses of the H5 or H7 subtypes, are of great concern for the agricultural sector and can have considerable economic consequences. Such outbreaks are also of concern for human health. WHO therefore recommends, for certain avian influenza viruses, a series of protective measures aimed at preventing human infections in persons at high risk of exposure. These measures are particularly important during veterinary investigations and extensive and urgent culling operations...

During January 2004 to October 10, 2005, a total of 117 human cases of avian influenza A (H5N1) were reported in Asia, according to the World Health Organization (WHO); of these 60 (51%) were fatal. Human cases have been reported in Cambodia (4 cases, all fatal), Indonesia (5 cases, 3 fatal), Thailand (17 cases, 12 fatal), and Vietnam (91 cases, 41 fatal).

Today (24 Aug 05), the World Health Organization (WHO) welcomes Roche's donation of three million treatment courses of the antiviral oseltamivir to a WHO international antiviral stockpile. WHO would use this stockpile to respond quickly to an emerging influenza pandemic... ...Roche has agreed to reserve three million treatment courses (30 million capsules) for up to five years. The first one million treatment courses (10 million capsules) will be ready early next year, with the remaining two million (20 million capsules) ready before mid-2006. The timing and severity of a flu pandemic is uncertain, but experts predict a pandemic will occur. Therefore WHO continues to urge countries to develop preparedness plans. Planning must include international cooperation between wealthy and poor countries to reduce the opportunity for national and international spread, and to reduce the death, illness and social disruption which have been a feature of all previous influenza pandemics.

Beginning in late July 2005, official reports to the OIE from government authorities indicate that the H5N1 virus has expanded its geographical range. Both Russia and Kazakhstan reported outbreaks of avian influenza in poultry in late July, and confirmed H5N1 as the causative agent in early August. Deaths in migratory birds, infected with the virus, have also been reported. Outbreaks in both countries have been attributed to contact between domestic birds and wild waterfowl via shared water sources. These are the first outbreaks of highly pathogenic H5N1 avian influenza recorded in the two countries. Both countries were previously considered free of the virus... ...The expanding geographical presence of the virus is of concern as it creates further opportunities for human exposure. Each additional human case increases opportunities for the virus to improve its transmissibility, through either adaptive mutation or reassortment. The emergence of an H5N1 strain that is readily transmitted among humans would mark the start of a pandemic.

The WHO H5 Reference Laboratory Network and WHO Collaborating Centres and Reference Laboratories have reviewed available data to assess the suitability of the H5N1 prototype strains selected by WHO last year for influenza A/H5N1 pandemic vaccine development. The results of genetic and antigenic analyses of 2004 and 2005 human and animal A/H5N1 viruses received from affected countries, did not provide any convincing evidence to change the WHO recommended A/H5N1 influenza vaccine prototype strains. Therefore, the WHO recommendations from April 2004 are still valid...