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Avian H5N1 influenza: In or out flew-enza?

Bioengineered bugs 05/2012; 3(3):145-6. DOI:10.4161/bbug.20190
Source: PubMed
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    ABSTRACT: Highly pathogenic avian influenza (HPAI) has been recognized as a serious viral disease of poultry since 1878. The number of outbreaks of this disease globally has increased in the past 10 years culminating in 2004 with the unprecedented outbreak of H5N1 HPAI involving nine countries in East and South East Asia. Apart from the geographical extent of this outbreak and apparent rapid spread, this epidemic has a number of unique features, among which is the carriage of highly pathogenic AI viruses by asymptomatic domestic waterfowl. When this disease first emerged it was recognized almost simultaneously in a number of countries for the first time. This created considerable concern among both veterinary and public health authorities especially as the virus was also shown to cause fatal disease in humans. This article brings together a range of information on H5N1 HPAI viruses in Asia that were collected by FAO during the past year through field projects and explores possible reasons for the emergence of the disease in late 2003 and early 2004. Key epidemiological features of the disease in different Asian countries are described in an attempt to look for, and where possible, explain similarities and differences. This includes assessment of factors that could have contributed to the spread of the disease. Molecular aspects of the viruses are examined to assess relationships between isolates from different locations and times so as to gain insights into the origins of viruses in various countries. It is apparent that the coincidence and grouping of the reports declaring the outbreaks of HPAI did not truly reflect the time course of disease emergence, which was widespread well before the outbreak. The factors that could have led to a change from infection to emergence of widespread disease in 2003-2004 are discussed. There are still some questions that remain unanswered regarding the origins of the 2004 outbreak. This article does not provide answers to all of these, but brings together what is currently known about these outbreaks and the viruses that have caused them.
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    ABSTRACT: The pandemic influenza virus of 1918-1919 killed an estimated 20 to 50 million people worldwide. With the recent availability of the complete 1918 influenza virus coding sequence, we used reverse genetics to generate an influenza virus bearing all eight gene segments of the pandemic virus to study the properties associated with its extraordinary virulence. In stark contrast to contemporary human influenza H1N1 viruses, the 1918 pandemic virus had the ability to replicate in the absence of trypsin, caused death in mice and embryonated chicken eggs, and displayed a high-growth phenotype in human bronchial epithelial cells. Moreover, the coordinated expression of the 1918 virus genes most certainly confers the unique high-virulence phenotype observed with this pandemic virus.
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    ABSTRACT: The influenza pandemic of 1918-20 is recognized as having generally taken place in three waves, starting in the northern spring and summer of 1918. This pattern of three waves, however, was not universal: in some locations influenza seems to have persisted into or returned in 1920. The recorded statistics of influenza morbidity and mortality are likely to be a significant understatement. Limitations of these data can include nonregistration, missing records, misdiagnosis, and nonmedical certification, and may also vary greatly between locations. Further research has seen the consistent upward revision of the estimated global mortality of the pandemic, which a 1920s calculation put in the vicinity of 21.5 million. A 1991 paper revised the mortality as being in the range 24.7-39.3 million. This paper suggests that it was of the order of 50 million. However, it must be acknowledged that even this vast figure may be substantially lower than the real toll, perhaps as much as 100 percent understated.
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