The Swine Flu Virus
Swine Flu Virus Update--Where We Stand and How We Got Here
May 06, 2009
During the last week, virologists have been sequencing and analyzing swine flu cells, and have decided that for the time being, the new strain of flu--called H1N1--is not as virulent as was originally feared, even though it continues to spread throughout the world.
We're not out of the woods yet, though, officials say. Sweden and Poland say citizens there have been infected. Sweden says a woman in her 50s who visited Chicago had tested positive for the virus, Reuters reported on Wednesday.
As of Wednesday afternoon, there have been 1,516 officially reported cases in 22 countries, the World Health Organization says, with 642 confirmed cases in the U.S.
Meanwhile, the virus has spread to Britain, Spain, Italy and Germany. If it continues to spread throughout Europe, it could be labeled a pandemic. (A pandemic simply means the virus has spread around the world. It doesn't mean it will kill people en mass, experts say.)
"Those numbers will go up, we anticipate, and unfortunately there are likely to be more hospitalizations and more deaths," said Health and Human Services Secretary Kathleen Sebelius.
WHO officials will meet next week to decide whether vaccine makers should switch from seasonal to pandemic flu production. Currently, CDC is telling manufacturers to continue making traditional flu vaccines.
Meanwhile, in Mexico City, security guards at a tower checked office workers with a heat scanner to make sure they didn't have fever when they returned to work, Reuters reports.
The Mexican government last week ordered most businesses to close to rapidly contain the virus and now says it appears to be ebbing. Officials around the world have congratulated Mexico for its swift response to the outbreak.
On Alert but Business as Usual
While preparing for a pandemic, CDC now says that even when a student is infected with the H1N1, schools should remain open. And the agency was certainly not in agreement with Vice President Joe Biden's advice last week that people should steer clear of airplanes. (Biden's remarks were quickly corrected.)
Most reassuring is the fact that people who are getting H1N1 are contracting mild cases and are responding to flu-fighters, Roche's Tamifu and GSK's Relenza. What's more, officials speculate that this year's flu vaccine might be conferring protection on people who would have otherwise been harder hit.
But the virus could thrive during a tropical summer and return in a more virulent incarnation during the winter, experts say.
Origins of the Virus: Wisconsin?
The new strain of flu--"do not call it swine flu, call it H1N1," the pork lobby insists, "since you can't get it from eating bacon or ham"--is an unusual, triple hybrid virus, composed not only of swine RNA, but bird and human RNA, as well.
Newsweek, reporting on the origins of H1N1 in its May 11/May 18 issue, says the first case of H1N1 was discovered around Thanksgiving 2005, when a 17-year old boy helped butcher 31 pigs at a Wisconsin slaughterhouse. A week later the teen killed another pig, the magazine reported.
In early December, in preparation for Christmas, his family bought a chicken and kept it in the house, to protect it from the fierce Wisconsin winter. On December 7, the teenager contracted flu. His illness lasted three days and he fully recovered, without spreading it to anyone around him. The virus was the first known case of H1N1, Newsweek says. (See the post below from the Wisconsin Department of Health regarding this case.)
Nine months ago, the Texas Department of State Health Services reported another case to the CDC. An individual who was exposed to infected pigs contracted a virus and was well within a few days.
CDC researchers found the same virus that infected the Wisconsin teenager, Newsweek reports.
In March of this year, the number of influenza cases in Mexico suddenly jumped.
Replication and Reassortment
Scientists say the new influenza strain is a continually mutating microbe, whose genetic code is in the form of RNA. (While some viruses use DNA cells to grow, this one uses RNA.)
The virus invades animals by attaching itself to a receptor in the nose or throat. The virus is then engulfed by a host cell, where its chromosomes reproduce, enter the bloodstream and spread throughout the body. While the virus is spreading, other genetic material may also be enveloped into the thousands of viral cells being copied. For example, if the virus is replicating inside a human cell, it will pick up human genetic material as well as avian genes from a chicken and swine RNA when it enters a pig.
When two types of flu virus get into an animal cell at the same time, they trade entire chromosomes. This is called reassortment and may be the major culprit in generating new strains of viruses.
Viruses spread through coughs or sneezes, though the majority of viruses don't adapt to their host and die. That's why it's rare when a new strain of virus is discovered.
What was infecting the teenager who slaughtered pigs in Wisconsin was a triple reassortment; he was infected with genes from three species of animals: pigs, birds and human beings.
Flu Treatments and Face Masks
Meanwhile, companies that make viral treatments like Tamiflu, say product is flying off pharmacy shelves.
And Cardinal Health spokesman Troy Fitzpatrick, told DOTmed News that as far back as last year, Cardinal had sold thousands of ventilators to several states, such as New York, Washington, D.C., and California, so that hospitals in the U.S. would be prepared in the event of any sort of emergency.
"Although there have been no new orders for ventilators since the new flu surfaced, demand for masks and gloves that Cardinal manufactures and flu testing kits that Cardinal distributes are way up," Kirkpatrick says.
DOTmed users in Mexico have also reported that they are out of facemasks and surgical masks.
Read DOTmed's exclusive reporting on the vaccine production challenges at DM8975 and DM8964. Just paste the story numbers into any DOTmed.com search box.
Read the latest from CDC:
Read CDC guidance for healthcare professionals:
National Swine Flu Situation Page
(View a comprehensive flu-tracking dashboard):
Wisconsin Health Official Explains the Sheboygan Case:
Below is a response to the 2005 Sheboygan Case from Dr. Jeff Davis at the Wisconsin Department of Health Services:
In Wisconsin, state and local health officials take the protection of the health and safety of the citizens of our state very seriously and we take expeditiously take action to help prevent and control the spread of infectious diseases.
We have a strong influenza surveillance system in Wisconsin, and in 2005, we detected an unusual strain of swine influenza virus that was isolated from one individual. We took aggressive action and this case was fully investigated along with partners from a local health department and the Centers for Disease Control and Prevention. The findings were published in a medical journal. Briefly, the individual was infected with a swine influenza A virus that was a triple reassortant H1N1 virus. The individual acquired his infection directly from exposure to freshly killed pigs at a slaughterhouse. No other individuals exposed to the same pigs or in the patient's household were infected with the virus.
Triple reassortant swine influenza viruses have been isolated from pigs in the United States since 1998. Surveillance data suggest that triple reassortant subtype H1N1 swine influenza A viruses are the predominant genotype of subtype H1N1 viruses in North American pigs. While it is prudent to compare strains of influenza virus to monitor relatedness of strains and other important factors, it would be incorrect to infer that the virus isolated from a human in Wisconsin in 2005 is the same virus as the H1N1 virus currently circulating.