In the simplest of terms, a virus is an infectious agent. It operates like a computer virus, replicating and dispersing itself in all directions, while crippling the normal function of the host. A virus has genes, but no cellular structure, so it's not considered a living organism. And like parasites, viruses can't survive on their own. Bacteria, on the other hand, are tiny cells that reproduce and can survive independently, with the ability to transport dangerous toxins.
Epidemiologists generally rely on an international but informal network of colleagues to get wind of a disease outbreak fast, even when it starts in a remote corner of the world. But while patients may be lining the hospital corridors in Jakarta, Veracruz or Pittsburgh, activating a worldwide emergency response protocol is not instantaneous. Laboratory tests must first isolate the virus, microbe, toxin or other mechanism of injury. Usually, scientists in the field must collaborate with researchers in other countries to identify the culprit. And only when the team is absolutely sure about the agent and its cause will entities like the Centers for Disease Control (CDC) and World Health Organization (WHO) spring into action. That's when the country alerts go out, a vaccine (or other remedy) gets developed, and the counterattack begins.
Getting Ahead of The Curve
In 1999, the CDC initiated the Laboratory Response Network (LRN), a group of local, state, federal, and international labs that can test for disease agents and develop vaccines in a fast, efficient manner. An estimated ninety percent of the U.S. population now live within a 100 miles of a designated lab. This close proximity insures a quick turnaround as evidence in the field is procured, then shipped to epidemiologists ready to analyze it.
To help get a jump on the next global pandemic, the CDC also dispatches scientists worldwide each year to sniff out virulent strains that may be on the prowl. The Epidemic Intelligence Service (EIS) recruits 70-80 college graduates annually for two-year, post-graduate assignments performing surveillance and study in the field.
Influenza viruses that affect humans are divided into two basic groups. "A" viruses have pandemic potential. "B" viruses don't. To qualify as a pandemic, an "A" virus must also be "novel", which means there's no pre-disposed immunity to it and no existing vaccines. Furthermore, the bug must have the potential for human to human transmission.
Diagram of the 1918 H1N1 Spanish Flu Virus. Photo: University of Washington School of Medicine
Other things to note about pandemic virus:
According to the U.S. Department of Health and Human Services, the continued spread of the avian H5N1 virus across much of eastern Asia, Russia, and eastern Europe represents the most significant pandemic threat out there today. Human avian H5N1 influenza infection was first recognized in 1997 when it infected 18 people in Hong Kong, causing 6 deaths. Concern has increased in recent years as avian H5N1 infections have killed poultry flocks in countries throughout Asia and in parts of Europe. Since 2003, over 100 human H5N1 cases have been diagnosed in Thailand, Vietnam, Cambodia, and Indonesia. HHS believes the virus is worrisome because:
Reports of new cases worldwide have continued to pour in through 2011. In March alone, Egypt reported its 131th case, Bangladesh reported its 67th outbreak, while public health officials in Japan, Myanmar, South Korea, India, Israel and Gaza all discovered its presence in poultry and other species. See the timeline (PDF) prepared by WHO.
While cases of human infection are rare, avian influenza is very contagious among birds and some of these viruses can sicken certain domesticated species, like chickens, ducks, and turkeys.
While H5N1 remains the top pandemic threat today, additional avian flu subtypes are entering the fray. In 1999, H9N2 infections were identified in Hong Kong; in 2003, H7N7 infections occurred in the Netherlands; and in 2004, H7N3 infections occurred in Canada. Such outbreaks have the potential to generate a pandemic, the CDC claims, reinforcing the need for continued surveillance and ongoing vaccine research.
In the case of a major nationwide pandemic, the CDC has established the following priority groups for vaccine distribution:
Vaccines are produced by pharmaceutical companies, often under a contract from the U.S. Government. Over 200 million doses, for instance, were ordered at the start of the H1N1 pandemic. In addition to pandemic vaccines, drug manufacturers produce the annual flu shot vaccine and chilhood immunization drugs for polio, chicken pox, German measles, etc. Immunizations for adults include hepatitus, malaria and tetanus. Some of these shots have only a short-term effectiveness. In the case of tetanus, for instance, a "booster" shot is recommended every ten years.
Vaccines are divided into other categories based on how the drug intends to destroy the targetted microbe or pathogen. Since viruses, bacteria and toxins attack the body in different ways, the epidemiologist must design a solution that works best for the circumstances. Here are his choices:
Live, attenuated vaccines
These contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. Like firefighters setting small fires in advance of a mega-blaze, this small dose of the killer pathogen is easy for the immune system to fight off, thereby achieving lifelong immunity with one or two doses. However, people with compromised immune systems are considered too weak to overcome a live vaccine. Besides that, the microbe that's injected may on occasion morph into something worse than it was initially. These vaccines are likewise not suitable for some geographical locations, since a "live" vaccine must be kept alive through refrigeration.
Samples of the disease-causing microbe are first destroyed with chemicals, heat, or radiation. These vaccines are more stable and safer than live vaccines, since the dead microbes can’t mutate back to their disease-causing state. Inactivated vaccines usually don’t require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries. On the down side, they trigger a weaker immune system response and therefore require multiple doses over time or booster shots to be effective.
These use only parts of the killer microbe, specifically the antigens, which are responsible for triggering the production of antibodies to fight the microbe. It takes a long time to develop a subunit vaccine, but once it's perfected, adverse reactions are much lower than with live or inactivated vaccines. These vaccines are a good choice for people with compromised immune systems.
Some bacteria secrete toxins or harmful chemicals, which can cause a serious illness all by themselves. The toxins can in some cases be neutralized by treating them with formalin, which is a solution of formaldehyde and sterilized water. Such “detoxified” toxins are called toxoids and are safe for use as vaccines.When injected, the toxoid causes the immune system to fight off the natural toxin and produce antibodies that will block the real toxin. Diphtheria and tetanus are examples of diseases that toxoid vaccines can prevent.
The immature immune systems of infants and younger children don't always recognize or respond to certain types of coatings around bacteria, so this special type of subunit vaccine has been developed to address the problem.
Still in the experimental stages, these vaccines show great promise (according to NIH), and several types are currently being tested in humans. These vaccines dispense with the microbe and its parts, and instead use the genes of those all-important antigens.
Recombinant vector vaccines
Also in the experimental stage, these are similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body. “Vector” refers to the virus or bacterium used as the disease carrier. (For instance, mosquitoes carry malaria, so it's considered a "vector-bourne" disease.)
In addition to antigens that alert the immune system to an infectious agent, vaccines may also contain substances called adjuvants, which NIH says improve the immune response produced by the vaccines. Currently, the only adjuvant licensed for human use in the United States is an “alum” adjuvant, which is composed of aluminum salts.
Vaccines may also contain substances to prevent contamination, as well as maintain a vaccine’s potency at less-than-optimal temperatures, or act as a preservative. One such controversial ingredient in this catgegory is a compound call thimerosal.
Autism advocacy organizations oppose the use of thimerasol and other mercury-based additives in vaccines. They allege that autism is caused in part by these ingredients when multiple childhood immunizations are administered at one time. The claim is virulently rejected by the CDC and much of the western medical establishment. In recent years, however, thimerasol use in vaccines has been reduced. Autism advocates urge parents to observe the following cautions when getting vaccines for their kids or themselves:
For information on specific bacterial diseases and viruses, please check the second column on this page.
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"New Strain of Bird Flu Causing Deaths in China." Asian Pacific Post 4/17/13.
"Sri Lanka Red Rain may have a cosmic connection." Sinhalaya News 11/18/12
"Yosemite tourist dies after contracting hantavirus." Associated Press 8/17/12
"Amid severe outbreak, is it time for a whooping cough booster?"Los Angeles Times 7/20/12.
"Sepsis: An Infection, Unnoticed, Turns Unstoppable." By Jim Dwyer. New York Times 7/9/12.
"How the Swine Flu Pandemic Got Started." by Michael Friscolanti and Charlie Gillis. Macleans 5/1/09.
"1918 Influenza: the Mother of All Pandemics." By Jeffery K. Taubenberger and David M. Morens (2006)
"Health officials issue alert about Valley fever in County." Stockton Record 6/12/12.
Omaha sees outbreak of flesh-eating bacteria cases." Radio Iowa 6/11/12
Epidemics and Plagues
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Emergency Preparedness for Pandemic - Eight-week Supply List (PDF)
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Mega Disasters: "Pandemics and Alien Infection" - Season 2, Episode 7. The History Channel At Amazon...
After Armageddon. 2-hour docudrama examines the potential of a lethal flu virus spreading quickly across the United States.
The History Channel At Amazon...
The Plague. 2-hour documentary tracks the 15th Century pandemic that killed tens of millions.
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How A Virus Invades Your Body
H1N1 virus and the 1918 pandemic
The Bubonic Plague
Epidemics - Old and New
The Plague, which still claims thousands of victims each year, has been traced not to a virus but to a bacteria called Yersinia pestis. It typically originates in the Indian rat flea, known scientifically as Xenopsylla cheopsis, of which only the adult females live off their hosts. This dreaded world traveler can survive up to a year on a host (especially rodunts), in dung, an abandoned rodent's nest or in textile bales.
Xenopsylla cheopsis, the killer flea.
Historically, human infection has occurred in three different ways:
Bubonic Plague - Caused when the victim gets bit by an infected flea. Here, the trademark symptom is painful swelling of the lymph glands in the armpits, groin or neck. The swelling creates ball-like buboes, hence the name bubonic plague. Red spots also appear on the skin and eventually turn black. Victims usually vomit blood and die within about three days without antibiotics.
Pneumonic Plague - The bacteria in this case is transmitted primarily through air, usually coughing, thus entering the respiratory tract. People who dissect or handle contaminated animal tissue are also susceptible. Symptoms include fever, coughing up blood and pneumonia leading to respiratory failure and shock within a few days. Most modern cases have occurred in Africa.
Septicemic Plague - Most often transmitted to humans through the bite of an infected rodent or bug, or through an opening in the skin or by cough from another infected human. This is the rarest type of Plague but the deadliest, as it causes sepsis. Cities along trade routes, especially Venice and Florence, were hit hardest during the Medieval epidemic. Symptoms include stomach ache, diarrhea, fever, nausea, vomiting, low blood pressure and lack of blood clotting.
Today, most cases of Plague occur in Africa, but 10-15 reports are logged in the United States annually, mostly in rural areas of the western states. Bats and rats are known to carry the flea.
Now for the big epidemics caused by viruses:
1918 Spanish Influenza - Still cloaked in mystery, this virus was responsible for infecting half a billion people worldwide, killing 50 million. Unlike other pandemics, this one struck on multiple continents on the same day. The infectious agent triggers an overreaction in the human immune system of mostly young, healthy adults. Like the simultaneous appearance, this feature of H1N1 (1918) also also diverges from the usual pattern. The lungs often became inflamed, leading to death. The original virus struck remote corners of the world, especially Alaska, leading a few researchers to suggest that it must have passed down through the atmosphere from outer space.
A theory known as Panspermia alleges that microbes are transmitted onto Earth via passing comets. Microbes may even be the source of all biological life on the planet. Professor Chandra Wickramasinghe of the Buckingham Centre for Astrobiology is the leading authority on comet-based microbes and viruses. (For more on his work, here's the school's website.)
Smallpox - An estimated 300 million deaths were recorded in the 20th Century alone. Because naturally occurring smallpox was wiped out worldwide by the 1970's, vaccinations stopped. According to the CDC, a case of smallpox today would be the result of an intentional act. Strains of the virus are kept in two approved labs in the U.S. and Russia. The CDC also states that "credible concern exists that the virus was made into a weapon by some countries and that terrorists may have obtained it. "
Polio - Largely unrecorded until the 19th century, recurring epidemics of the Poliomyelitis virus continued into the 20th until a vaccine was discovered. The disease is also known as infantile paralysis, but affects adults as well as children. In a typical case, a fever and other flu symptoms set in, followed eventually by paralysis in the lower half of the body.
Viral Hemorrhagic Fevers - A mostly rodunt-borne set of viruses made its first curtain call in the latter twentieth century, appearing on all continents. However cases usually remain localized. Ticks and mosquitoes may also carry the bug, which targets the vascular system, along with several organs in the body. The bleeding for which the disease is named is itself rarely life-threatening. Slaughterhouse workers have a much greater chance of contracting the virus than others.
HIV - Human Immunodeficiency Virus is a retrovirus discovered in the 1980s by Robert Gallo, but that identification was immediately surrounded in controversy. In particular, the so-called "father of retroviruses" Peter Duesberg dismissed Gallo's conclusions, claiming there was no virological evidence to back-up the HIV-AIDS connection. (This led many African governments to ban the use of anti-HIV drugs.) Duesberg believes HIV is biochemically inactive and harmless, and that the cause of AIDS may be toxicological (i.e. a toxic substance). There is still no satisfactory treatment, although a variety of new drugs has vastly reduced the number of fatalitiies.
West Nile Virus - Carried by mosquitoes, this virus first appeared in the United States in 1999, but got its start seventy years earlier in Uganda. It can produce a mild fever and other flu symptoms, and sometimes a rash, but 80 percent of those infected have no adverse reaction. In severe cases, encephalitis or meningitis may develop, but only one person out of every 150 infected falls into this category. Here's a CDC map of most recently reported cases.
SARS - Severe acute respiratory syndrome started in Hong Kong in 2002 and eventually infected a relatively small number of individuals in 37 countries. It targetted the lungs, caused fever and low white blood cell counts. There were appoximately 8,500 cases and 900 deaths. SARS is considered contained and there's no screening for it.
H1N1 Swine Flu - First appearing in Veracruz, Mexico, this 2009 version of an H1N1virus is thought to be a mutation or combination of previous bird, swine and human flu viruses. A Eurasian pig flu virus was also involved, hence the term "Swine Flu". H1N1 was not spread through eating pork products, however, but contracted through respiratory droplets circulating in the air (like other most other forms of influenza). In a small percentage of people exposed, the virus caused pneumonia or acute respiratory problems. The widespread public emergency surrounding it was offically put to rest by WHO in 2010.
Valley Fever - While not a contagion, Valley fever is carried by spores of the fungus Coccidioides immitis, found in soils of the southwestern United States and Central Valley of California, as well as parts of Africa, Central and South America. Wind is generally credited with transporting the spores, but digging, construction work or farming can likewise cause the spores to become airborne.
Dust containing the spores enters a person's lungs, which can sometimes lead to illness. Exposure is most common in the dry, late summer months, with most cases reported to medical personnel in the fall and early winter. It takes 5-21 days on average for flu-like symptoms to show up.
Those exposed to dust while working outside should consider wearing a close-fitting mask. Early recognition and treatment of Valley fever's flu-like symptoms is important to avert more serious complications.
Flesh-Eating Bacteria - Formally known as necrotizing fasciitis, it's caused by a toxin found in several types of bacteria. Infection is rare, with 500-1,000 cases per year reported in the United States. Aimee Copeland, a young Georgia woman, recently put this dirge on the map after a zipline accident and 22 stitches led to an infection. Open wounds and hospital surgery are the prime vehicles, with 25 percent of victims dying.
If you get a cut or wound that becomes increasingly painful, red and swollen, the bacteria may be present. Go to the emergency room immediately, as time is of the essence. First aid for any wound should always include thorough washing of the exposed area with soap and water, and if possible, application of an anti-biotic ointment.
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