Flu
Return to Library
 |
NewsRx Bundle
A quick and inexpensive way to view the most recent articles for a one-time project.
Custom Reports on Flu
Tired of prepackaged reports that just don't meet your needs? Target your needs!
|
 |
A flu virus is roughly round, but it can also be elongated or irregularly shaped. Inside are eight segments of single-strand RNA containing the genetic instructions for making new copies of the virus. Flu's most striking feature is a layer of spikes projecting from its surface. There are two different types of spikes: one is the protein hemagglutinin (HA), which allows the virus to stick to a cell and initiate infection, the other is a protein called neuraminidase (NA), which enables newly formed viruses to exit the host cell.
What Yypes of Flu Are There?
Influenza viruses are classified as type A, B, or C based upon their protein composition. Type A viruses are found in many kinds of animals, including ducks, chickens, pigs, whales, and also in humans. The type B virus widely circulates in humans. Type C has been found in humans, pigs, and dogs and causes mild respiratory infections, but does not spark epidemics.
Type A influenza is the most frightening of the three. It is believed responsible for the global outbreaks of 1918, 1957 and 1968. Type A viruses are subdivided into groups based on two surface proteins, HA and NA. Scientists have characterized 16 HA subtypes and 9 NA subtypes.
Type A subtypes are classified by a naming system that includes the place the strain was first found, a lab identification number, the year of discovery, and, in parentheses, the type of HA and NA it possesses, for example, A/Hong Kong/156/97 (H5N1). If the virus infects non-humans, the host species is included before the geographical site, as in A/Chicken/Hong Kong/G9/97 (H9N2). There are no type B or C subtypes.
Where Does The Flu Virus Comes From?
In nature, the flu virus is found in wild aquatic birds such as ducks and shore birds. It has persisted in these birds for millions of years and does not typically harm them. But the frequently mutating flu viruses can readily jump the species barrier from wild birds to domesticated ducks and then to chickens. From there, the next stop in the infectious chain is often pigs.
Pigs can be infected by both bird (avian) influenza and the form of influenza that infects humans. In a setting such as a farm where chickens, humans and pigs live in close proximity, pigs act as an influenza virus mixing bowl. If a pig is infected with avian and human flu simultaneously, the two types of virus may exchange genes. Such a reassorted flu virus can sometimes spread from pigs to people.
Depending on the precise assortment of bird-type flu proteins that make it into the human population, the flu may be more or less severe.
In 1997, for the first time, scientists found that bird influenza skipped the pig step and infected humans directly. Alarmed health officials feared a worldwide epidemic (a pandemic). But, fortunately, the virus could not pass between people and thus did not spark an epidemic. Scientists speculate that chickens may now also have the receptor used by human-type viruses.
Drifting and Shifting
Influenza virus is one of the most changeable of viruses. These genetic changes may be small and continuous or large and abrupt.
Small, continuous changes happen in type A and type B influenza as the virus makes copies of itself. The process is called antigenic drift. The drifting is frequent enough to make the new strain of virus often unrecognizable to the human immune system. For this reason, a new flu vaccine must be produced each year to combat that year's prevalent strains.
Type A influenza also undergoes infrequent and sudden changes, called antigenic shift. Antigenic shift occurs when two different flu strains infect the same cell and exchange genetic material. The novel assortment of HA or NA proteins in a shifted virus creates a new influenza A subtype. Because people have little or no immunity to such a new subtype, their appearance tends to coincide with very severe flu epidemics or pandemics.
Source: National Institutes of Health
New data from National University of Singapore illuminate research in bird flu
2009 AUG 4 - (NewsRx.com) -- Researchers detail in 'Avian influenza and South Jakarta primary healthcare workers: a controlled mixed-method study,' new data in bird flu. "To study the attitudes, concerns, perceived impact, coping strategies, knowledge on avian influenza (AI) and personal protection measures, and institutional and personal preparedness for AI among all Indonesian primary healthcare workers (PHW). Questionnaire survey of PHW from four public primary healthcare clinics in South Jakarta (n=333), with Singaporean PHW from 18 such clinics as controls (n=1321)," scientists writing in the journal Tropical Medicine & International Health report. "Twelve focus group discussions with 51 South Jakarta PHW were also conducted. Quantitative and qualitative data were analysed separately with statistical and thematic analysis, respectively, then combined. South Jakarta PHW had positive attitudes but major concerns about contracting AI, difficulties in diagnosing human AI and inadequacy of personal protection provided. South Jakarta PHW are less knowledgeable about AI and use of personal protection equipment, and reported poorer awareness, availability and participation in AI preparation activities. Only 3% of South Jakarta PHW received influenza vaccination in the preceding 6 months and few felt prepared for AI. South Jakarta primary healthcare workers are not well prepared for avian influenza," wrote G.C. Koh and colleagues, National University of Singapore. The researchers concluded: "There is an urgent need to build their primary healthcare capacity to protect them and contain this global health threat." Koh and colleagues published their study in Tropical Medicine & International Health (Avian influenza and South Jakarta primary healthcare workers: a controlled mixed-method study. Tropical Medicine & International Health, 2009;14(7):817-29). Additional information can be obtained by contacting G.C. Koh, National University of Singapore, Dept. of Epidemiology and Public Health, Singapore. The publisher of the journal Tropical Medicine & International Health can be contacted at: Blackwell Publishing Inc., 350 Main St., Malden, MA 02148, USA. Keywords: Singapore, Singapore, Avian Flu, Avian Influenza, Bird Flu. This article was prepared by Health Risk Factor Week editors from staff and other reports. Copyright 2009, Health Risk Factor Week via NewsRx.com.
|
