Living With disease（The First Period）

    hybrids are dangerous because the body has never encountered them before，and the immune system is unprepared.
    “from studying the sequence we see that the sars virus is derived from a mouse coronavirus and an avian coronavirus，”said michael lai，a pioneer in coronavirus genetics at the university of southern california in los angeles.
    if the virus exists in a wild widespread host--like the west nile virus carried by mosquitoes—then sars could be a perennia11y recurring problem, according to lai.
    if the host is a domestic animal一like the chicken responsible for the avian f1u virus of 1997--then the source of the virus could be eliminated.the avian flu effectively stopped after the hong kong government ordered the slaughter of chickens in the area.
    lai suspects that the sars virus lurks in a wild animals. “it probably doesn’t bother domestic animals or we would have come across it before，”he said.
    1f people are the only carriers of sars，“honest reporting of sars cases and stringent quarantines could stop the virus in its tracks ,”lai said.
  knowing a virus，predicting an epidemic
  “making a vaccine could be quite straightforward，if it is needed。”lai said.
vaccines already exist for swine and chicken coronaviruses. but it isn’t easy to  gauge whether sars，or any virus.can trigger an epidemic.
  “we’ve been working with influenza for over 50 years and it can sti1l evade our best attempts.”
    “in many cases of the influenza virus we don’t understand the molecular properties that cause high mortality，”said nancy cox， chief of the influenza branch at the cdc.
    “outbreaks are like wildfires，”morse said.“some fires smolder and are easily extinguished.others rage out of control，destroying everything in their path.the who and the cdc are like the fire department and they need to investigate all outbreaks because you never know which way they could go.”
  morse points out our long history with influenza.sars is only a few months old.
tracking and containing viruses，and predicting what they will do，morse said，“it is as much an evolving science as an evolving art.”
    2.fight continues against hiv/aids
    a picture，a calendar or even a balloon may be the best way for millions of people living in china’s vast country areas to learn about aids，one of the biggest threats to public health in the world today.