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The Human Immune System and Infectious Disease

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All living things are subject to attack from disease-causing agents. Even bacteria, so small that more than a million could fit on the head of a pin, have systems to defend against infection by viruses. This kind of protection gets more sophisticated as organisms become more complex.

Multicellular animals have dedicated cells or tissues to deal with the threat of infection. Some of these responses happen immediately so that an infecting agent can be quickly contained. Other responses are slower but are more tailored to the infecting agent.

Collectively, these protections are known as the immune system.

The human immune system is essential for our survival in a world full of potentially dangerous microbes, and serious impairment of even one arm of this system can predispose to severe, even life-threatening, infections.

Non-Specific (Innate) Immunity

The human immune system has two levels of immunity: specific and non-specific immunity.

Through non-specific immunity, also called innate immunity, the human body protects itself against foreign material that is perceived to be harmful.

Microbes as small as viruses and bacteria can be attacked, as can larger organisms such as worms. Collectively, these organisms are called pathogens when they cause disease in the host.

All animals have innate immune defenses against common pathogens. These first lines of defense include outer barriers the skin and mucous membranes. When pathogens breach the outer barriers, for example through a cut in the skin or when inhaled into the lungs, they can cause serious harm.

Some white blood cells (phagocytes) fight pathogens that make it past outer defenses. A phagocyte surrounds a pathogen, takes it in, and neutralizes it.

Specific Immunity

While healthy phagocytes are critical to good health, they are unable to address certain infectious threats. Specific immunity is a complement to the function of phagocytes and other elements of the innate immune system.

In contrast to innate immunity, specific immunity allows for a targeted response against a specific pathogen. Only vertebrates have specific immune responses.

Two types of white blood cells called lymphocytes are vital to the specific immune response. Lymphocytes are produced in the bone marrow, and mature into one of several subtypes. The two most common are T cells and B cells.

An antigen is a foreign material that triggers a response from T and B cells. The human body has B and T cells specific to millions of different antigens. We usually think of antigens as part of microbes, but antigens can be present in other settings. For example, if a person received a blood transfusion that did not match his blood type, it could trigger reactions from T and B cells.

A useful way to think of T cells and B cells is as follows: B cells have one property that is essential. They can mature and differentiate into plasma cells that produce a protein called an antibody. This protein is specifically targeted to a particular antigen.

However, B cells alone are not very good at making antibody and rely on T cells to provide a signal that they should begin the process of maturation. When a properly informed B cell recognizes the antigen it is coded to respond to, it divides and produces many plasma cells.

The plasma cells then secrete large numbers of antibodies, which fight specific antigens circulating in the blood.

T cells are activated when a particular phagocyte known as an antigen-presenting cell (APC) displays the antigen to which the T cell is specific. This blended cell (mostly human but displaying an antigen to the T cell) is a trigger for the various elements of the specific immune response.

A subtype of T cell known as a T helper cell performs a number of roles. T helper cells release chemicals to

  • Help activate B cells to divide into plasma cells
  • Call in phagocytes to destroy microbes
  • Activate killer T cells

Once activated, killer T cells recognize infected body cells and destroy them.

Regulatory T cells (also called suppressor T cells) help to control the immune response. They recognize when a threat has been contained and then send out signals to stop the attack.

Organs and Tissues

The cells that make up the specific immune response circulate in the blood, but they are also found in a variety of organs.

Within the organ, immune tissues allow for maturation of immune cells, trap pathogens and provide a place where immune cells can interact with one another and mount a specific response.

Organs and tissues involved in the immune system include the thymus, bone marrow, lymph nodes, spleen, appendix, tonsils, and Peyer’s patches (in the small intestine).

Infection and Disease

Infection occurs when a pathogen invades body cells and reproduces. Infection will usually lead to an immune response. If the response is quick and effective, the infection will be eliminated or contained so quickly that the disease will not occur.

Sometimes infection leads to disease. (Here we will focus on infectious disease, and define it as a state of infection that is marked by symptoms or evidence of illness.) Disease can occur when immunity is low or impaired, when virulence of the pathogen (its ability to damage host cells) is high, and when the number of pathogens in the body is great.

Depending on the infectious disease, symptoms can vary greatly.

Fever is a common response to infection: a higher body temperature can heighten the immune response and provide a hostile environment for pathogens.

Inflammation, or swelling caused by an increase in fluid in the infected area, is a sign that white blood cells are on the attack and releasing substances involved in the immune response.

Vaccination works to stimulate a specific immune response that will create memory B and T cells specific to a certain pathogen. These memory cells persist in the body and can lead to a quick and effective response should the body encounter the pathogen again.

For more on vaccination, see the activity How Vaccines Work.


“I was tired of fighting a disease”

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Cole Christopher spent twenty years living with chronic granulomatous disease (CDG), a hereditary immune disorder that required daily medication and frequent hospitalizations.

In 2014, Cole was losing his battle with a spinal infection when he came to NIH for a risky bone marrow transplant. Now recovered and healthy, he sat down with his long-time physician, Dr.

Buddy Creech, to reflect on his experiences and the transplant that saved his life.


Buddy Creech: What was it being in the hospital as a kid?

Cole Christopher: There’s multiple emotions and feelings, you know.  You’re not just diagnosed with this at a late age, you’re born with this.

  You grow up to living in the hospital; it is a normality.  But after puberty, teenage years, that’s when you start to realize things aren’t normal, so things got worse.

  You know, sometimes you would be in the hospital every month or every other month.

There was a time where I felt I didn’t need my meds anymore.  The way I told myself is, well, God gave me this so he’s going to fix it.  There was probably about, I’d say, a good chunk of five years I went against doctor’s advice and I wanted to be normal and I was tired of fighting a disease, so I’m going to be normal.

Buddy Creech: I don’t think I’ve ever gotten so angry with a patient, because I just knew how much I cared about you, and I just wanted to somehow get inside your brain and say, “If you’ll take these, you will feel so much better.”  Aww, I got so frustrated with you.

But maybe my favorite time was when we were sitting in the room and you had decided after getting pretty sick that getting a bone marrow transplant might be worth trying, knowing that it would be risky, especially since you had infection, and knowing that there was no complete promise that it would work.  And I let you know that there had been match found in the registry.  And I think that’s still one of my favorite moments with a patient, ever.

Cole Christopher: Really?

Buddy Creech: Oh yeah.  Because I saw you grow and I saw you struggle, rightly so, with a disease you didn’t ask for and didn’t create and that I couldn’t do anything about it.  And being able to walk in there and say, “There’s a match for you,” and watching your face and your mom’s face , are you kidding?  Do you remember that moment?

Cole Christopher: I remember the… I could probably do it now, the look: you’re…you’re kidding me.

Buddy Creech: That’s awesome.

Cole Christopher: You know with the 50 plus surgeries and, you know, CAT scans and lung biopsies, you know, I’ve got battle scars all over me, you know, from literally head to toe.

  When you came in there that day, my world lit up, I could begin to see hope, because after 20 years of fighting a disease, I did begin to lose hope.  I was severely ill.  I was literally on my deathbed.

Buddy Creech: You were.

Cole Christopher: I still look at the pictures and think, how was I even alive?

Buddy Creech: Well, you had lost so much weight and I remember calling the NIH to say, “Will you take him?”  And the question was not, let’s transplant him because things have been hard and we want to make things better, it was can we transplant him to save his life?  And them saying, “Yeah, this is going to be tough, but we’re happy to help and we’re happy to take him.”  This is the best I’ve seen you look in years.

Cole Christopher: Ever.

Buddy Creech: Yeah, really.  I mean, it’s amazing.

Cole Christopher: I feel I’ve accomplished a lot and overcome a lot.  Yes there was some bumps in the road, but with all the brilliant teamwork I’m able to say, I’m here today and not going anywhere.


Help fight disease with Folding@home on Chrome OS

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Distributed computing is at the core of many of the technologies that we use on a daily basis without even realizing it.

To simplify it into terms I can understand, the process involves multiple systems performing the same tasks in conjunction with each other but not dependent on any one device. The applications range from telecommunications to peer-to-peer networks and everything in between.

Some distributed computing projects rely on the computing power of individual users that allow portions of their PC’s CPU/GPU power to be delegated to whatever the project is attempting to achieve.

One such project, Folding@home, has gained the attention of the public eye as users joined the project in droves to help aid and assist in researching the COVID-19 virus that has created a worldwide pandemic.

What is Folding@home? Started in October 2000 by the Pande Laboratory at Stanford University, Folding@home is a distributed computing project that utilizes the power of volunteer computers to perform protein folding which is in turn used to research viruses and diseases in the search for causes, cures and vaccinations. From the Folding@home website:

Folding@home (FAH or F@h) is a distributed computing project for simulating protein dynamics, including the process of protein folding and the movements of proteins implicated in a variety of diseases.

It brings together citizen scientists who volunteer to run simulations of protein dynamics on their personal computers.

Insights from this data are helping scientists to better understand biology, and providing new opportunities for developing therapeutics.

Over the past two decades, Folding@home has grown into a massive community that puts forth excess computing power towards researching Alzheimer’s, Parkinson’s, Ebola virus and a number of other diseases that affect humanity on a global scale.

The latest addition to the research platform is COVID-19 along with other types of coronaviruses which has resulted in Folding@home becoming the fastest computing system in the world and the first to bread the exaFLOP barrier.

(One exaflop is a thousand petaflops or a quintillion, 1018, double-precision floating-point operations per second.

) Now, I can’t fathom how much that really is but in perspective, the Department of Energy is working on a single computer that will break the exaFLOP barrier and its cost is in excess of $600 million dollars. (My brain just exploded.)

I first heard of Folding@home a couple of years back when one of the participants contacted me about folding on a Chromebook.

At that time, the only real option was to do so using the Chrome browser client and the performance was so minimal, it was practically useless to try and contribute to the project. However, that changed when Chrome OS gained support for Linux apps.

Now, Chromebook users can get in on the action and help by adding their excess CPU power to the future research of these horrible diseases.

To get started, you will need to have a Chrome OS device that supports Linux apps and of course, you will need to be willing to sacrifice some of your CPU’s horsepower. Don’t worry about performance if you really want to help. The Folding@home client is customizable and you can lend as much or as little power as you choose.

I keep my Core i5 Pixelbook Go set to medium in the FaH Client and I see very little decline in performance unless I’m doing heavy work. Even then, you can disable FaH whenever you . The Folding@home client works by downloading work units that are portions of a model simulation.

Once your device completes the “folding” of the model, it is sent back to the server added to the larger model. If you join or create a team, your team will receive credits for work units that are completed. The credits are simply a way to track your contribution.

The project is strictly volunteer-based and the only compensation is the knowledge that you’re helping humanity. Now, let’s move on to installing FaH on Chrome OS.

First, head over to the FaH website and download the Debian packages for the client and the controller. You can also download the 3D viewer but it is not needed to run Folding@home. It just gives you a fancy, 3D model of the real-time work that your computer is doing for the project. You can get the .deb files here. You will want the .deb packages listed under Debian/Mint/Ubuntu.

There is an alternative method to install and run FaH from the command line but this will give you a user interface and much simpler control of the FaH client. Now that you have those downloaded, open your downloads folder and double-click the file named fahclient and wait for the installation to complete. (You won’t see the client in your applications list as it runs in the background.


Next, double-click the other FaH file named fahcontrol. Once that’s finished installing, you’re ready to launch the app and start folding. You should find the controller in your apps list labeled FAHControl. Click the icon and when the app launches, click the “fold” button to begin downloading your first work unit.

To the right of the fold/pause buttons, you will see the slider where you can set how much CPU power you wish to give. Deeper in the configuration settings, you will find spots where you can specify how many cores you wish to use as well as tweaks for GPU. I don’t think Chrome OS is lending GPU power and the default -1 setting for CPU will use what the application determines is best.

It’s probably best to just leave that alone unless you know what you’re doing.

As I mentioned, FaH is now dedicating a lot of work researching COVID-19.

While you can’t choose which project your device is folding for, you can click the project number in the controller to see which one your computer is currently working on.

FaH has stated that COVID-19 and coronavirus research is being prioritized at the moment and I’ve found each project on my respective devices are all focused on that research at the moment.

Join our team

Chrome Unboxed is dedicating some excess Chrome power to aiding in this research and we have a team if you’d to join us. Again, this is just to keep track of our contribution and it would be cool to see the Chrome OS community unite and help move this project even further into the future.

If you’d to join the team, open the configuration panel of the controller and add the team number 234120 and save before you start folding. Additionally, you can add a unique user name so you can see your contribution to the project on the team stats board that can be found here.

To learn more about protein folding and how you can contribute, head over to the Folding@home website here.


Measles Makes Your Immune System Forget How to Fight Other Diseases, a New Study Says

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Not so long ago, coming down with measles was seen almost as a rite of passage. Before measles vaccination began in the U.S.

in the early 1960s, millions of Americans, many of them children, contracted the virus each year—forcing them to weather a flu- illness and telltale skin rash, but also bestowing lifelong immunity.

As a result, some Americans still view measles as relatively harmless—which, in addition to a dangerous uprising of anti-vaccine sentiment, has led some parents to decline shots for their children, contributing to a resurgence of preventable illness in the U.S. and overseas.

A pair of related studies published in Science and Science Immunology, however, busts the myth that measles isn’t dangerous. In addition to being a serious disease in its own right, measles can also virtually wipe out a person’s immune system, leaving them with “immune amnesia” that makes them more susceptible to other diseases, according to the research.

Doctors have long known that measles predisposes sufferers to other illnesses. Measles can lead to serious complications neurological damage, but many of the approximately 110,000 global measles-related deaths each year actually come from concurrent infections pneumonia. The new studies are among the first to demonstrate why that happens.

“Every time we see a pathogen, our immune system recognizes this pathogen, builds immunity to it and then stores it in the form of immune memory,” explains Velislava Petrova, a postdoctoral fellow in immunogenetics at the Wellcome Sanger Institute in the U.K.

and first author of the report published in Science Immunology.

The measles virus, however, seems to attack these memory cells, effectively leaving sufferers with an immune system that no longer remembers the pathogens to which it has already built up immunity, and thus an impaired ability to fight them off.

Petrova and her colleagues conducted their research in a part of the Netherlands with very low measles vaccination rates.

They analyzed blood samples from a group of 26 children ages 4 to 17 who were unvaccinated and had never had measles—meaning they could develop the infection organically—both when they were healthy, and again after a measles outbreak in the community. They also used three unvaccinated children who did not develop measles as a control group.

Blood sample testing revealed the children who had recovered from measles had the right number of white blood cells, crucial to mounting an immune response and fighting off disease. But sequencing revealed that the types of white blood cells weren’t right. “Our immune cells recover back to normal numbers [after getting measles],” Petrova says, “but they are no longer the same memory cells.”

In the related Science study, researchers analyzed the kids’ antibody activity before and after measles infection, and found that, two months after recovery, they had lost up to 73% of their antibody diversity.

Not only did the virus wipe out memory cells, it also replaced them with new cells that provide immunity against future measles infection, Petrova says. So, while people who come down with measles are protected from future bouts of that virus, they seem to be left unprotected from other, previously known pathogens and ill-equipped to respond to new ones.

The researchers confirmed that finding by infecting flu-vaccinated ferrets with a measles- illness. After suffering from measles, the animals no longer had immunity against the flu, and experienced more severe flu symptoms, compared to animals that had the flu before contracting measles.

Measles “makes our immune system more baby-,” Petrova says. “Babies are more vulnerable to infections because their immune system is still maturing. That’s what measles does.”

Future research, Petrova says, will focus on learning how, exactly, measles—”an immunological paradox”—manages this feat. The answer may lie in the virus’ ability to infiltrate and alter bone marrow, the body’s reservoir for immune cells, she says.

More research may be needed, but Petrova emphasizes that there’s plenty of evidence to support measles vaccination now. “Measles is not as harmless of a disease as many people think. The disease itself is a dangerous,” she says. “But what this study shows is vaccination is really important not only to protect us from the disease itself, but also to protect us from other diseases.”

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Immune System: Diseases, Disorders & Function

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The role of the immune system — a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body's own healthy tissue, according to Merck Manuals.

Innate vs. adaptive immunity

The immune system can be broadly sorted into categories: innate immunity and adaptive immunity.

Innate immunity is the immune system you're born with, and mainly consists of barriers on and in the body that keep foreign threats out, according to the National Library of Medicine (NLM).

Components of innate immunity include skin, stomach acid, enzymes found in tears and skin oils, mucus and the cough reflex.

There are also chemical components of innate immunity, including substances called interferon and interleukin-1.

Innate immunity is non-specific, meaning it doesn't protect against any specific threats.

Adaptive, or acquired, immunity targets specific threats to the body, according to the NLM. Adaptive immunity is more complex than innate immunity, according to The Biology Project at The University of Arizona.

In adaptive immunity, the threat must be processed and recognized by the body, and then the immune system creates antibodies specifically designed to the threat.

After the threat is neutralized, the adaptive immune system “remembers” it, which makes future responses to the same germ more efficient.

Major components

Lymph nodes: Small, bean-shaped structures that produce and store cells that fight infection and disease and are part of the lymphatic system — which consists of bone marrow, spleen, thymus and lymph nodes, according to “A Practical Guide To Clinical Medicine” from the University of California San Diego (UCSD). Lymph nodes also contain lymph, the clear fluid that carries those cells to different parts of the body. When the body is fighting infection, lymph nodes can become enlarged and feel sore.

Spleen: The largest lymphatic organ in the body, which is on your left side, under your ribs and above your stomach, contains white blood cells that fight infection or disease. According to the National Institutes of Health (NIH), the spleen also helps control the amount of blood in the body and disposes of old or damaged blood cells.

Bone marrow: The yellow tissue in the center of the bones produces white blood cells.

This spongy tissue inside some bones, such as the hip and thigh bones, contains immature cells, called stem cells, according to the NIH.

Stem cells, especially embryonic stem cells, which are derived from eggs fertilized in vitro (outside of the body), are prized for their flexibility in being able to morph into any human cell. 

Lymphocytes: These small white blood cells play a large role in defending the body against disease, according to the Mayo Clinic.

The two types of lymphocytes are B-cells, which make antibodies that attack bacteria and toxins, and T-cells, which help destroy infected or cancerous cells.

Killer T-cells are a subgroup of T-cells that kill cells that are infected with viruses and other pathogens or are otherwise damaged. Helper T-cells help determine which immune responses the body makes to a particular pathogen.

Thymus: This small organ is where T-cells mature.

This often-overlooked part of the immune system, which is situated beneath the breastbone (and is shaped a thyme leaf, hence the name), can trigger or maintain the production of antibodies that can result in muscle weakness, the Mayo Clinic said.

Interestingly, the thymus is somewhat large in infants, grows until puberty, then starts to slowly shrink and become replaced by fat with age, according to the National Institute of Neurological Disorders and Stroke. 

Leukocytes: These disease-fighting white blood cells identify and eliminate pathogens and are the second arm of the innate immune system. A high white blood cell count is referred to as leukocytosis, according to the Mayo Clinic. The innate leukocytes include phagocytes (macrophages, neutrophils and dendritic cells), mast cells, eosinophils and basophils. 

Diseases of the immune system

If immune system-related diseases are defined very broadly, then allergic diseases such as allergic rhinitis, asthma and eczema are very common. However, these actually represent a hyper-response to external allergens, according to Dr.

Matthew Lau, chief, department of allergy and immunology at Kaiser Permanente Hawaii. Asthma and allergies also involve the immune system.

A normally harmless material, such as grass pollen, food particles, mold or pet dander, is mistaken for a severe threat and attacked.

Other dysregulation of the immune system includes autoimmune diseases such as lupus and rheumatoid arthritis.

“Finally, some less common disease related to deficient immune system conditions are antibody deficiencies and cell mediated conditions that may show up congenitally,” Lau told Live Science.

Disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer, according to the NIH.

Immunodeficiency occurs when the immune system is not as strong as normal, resulting in recurring and life-threatening infections, according to the University of Rochester Medical Center.

  In humans, immunodeficiency can either be the result of a genetic disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS, or through the use of immunosuppressive medication.

On the opposite end of the spectrum, autoimmunity results from a hyperactive immune system attacking normal tissues as if they were foreign bodies, according to the University of Rochester Medical Center.

Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and systemic lupus erythematosus.

Another disease considered to be an autoimmune disorder is myasthenia gravis (pronounced my-us-THEE-nee-uh GRAY-vis).

Diagnosis and treatment of immune system diseases

Even though symptoms of immune diseases vary, fever and fatigue are common signs that the immune system is not functioning properly, the Mayo Clinic noted. 

Most of the time, immune deficiencies are diagnosed with blood tests that either measure the level of immune elements or their functional activity, Lau said. 

Allergic conditions may be evaluated using either blood tests or allergy skin testing to identify what allergens trigger symptoms.

In overactive or autoimmune conditions, medications that reduce the immune response, such as corticosteroids or other immune suppressive agents, can be very helpful.

“In some immune deficiency conditions, the treatment may be replacement of missing or deficiency elements,” Lau said. “This may be infusions of antibodies to fight infections.”

Treatment may also include monoclonal antibodies, Lau said. A monoclonal antibody is a type of protein made in a lab that can bind to substances in the body.

They can be used to regulate parts of the immune response that are causing inflammation, Lau said. According to the National Cancer Institute, monoclonal antibodies are being used to treat cancer.

They can carry drugs, toxins or radioactive substances directly to cancer cells.

Milestones in the history of immunology

1718: Lady Mary Wortley Montagu, the wife of the British ambassador to Constantinople, observed the positive effects of variolation — the deliberate infection with the smallpox disease — on the native population and had the technique performed on her own children.

1796: Edward Jenner was the first to demonstrate the smallpox vaccine.

1840: Jakob Henle put forth the first modern proposal of the germ theory of disease.

1857-1870: The role of microbes in fermentation was confirmed by Louis Pasteur.

1880-1881: The theory that bacterial virulence could be used as vaccines was developed. Pasteur put this theory into practice by experimenting with chicken cholera and anthrax vaccines. On May 5, 1881, Pasteur vaccinated 24 sheep, one goat, and six cows with five drops of live attenuated anthrax bacillus.

1885: Joseph Meister, 9 years old, was injected with the attenuated rabies vaccine by Pasteur after being bitten by a rabid dog. He is the first known human to survive rabies.

1886: American microbiologist Theobold Smith demonstrated that heat-killed cultures of chicken cholera bacillus were effective in protecting against cholera.

1903: Maurice Arthus described the localizing allergic reaction that is now known as the Arthus response. 

1949: John Enders, Thomas Weller and Frederick Robbins experimented with the growth of polio virus in tissue culture, neutralization with immune sera, and demonstration of attenuation of neurovirulence with repetitive passage.

1951: Vaccine against yellow fever was developed.

1983: HIV (human immunodeficiency virus) was discovered by French virologist Luc Montagnier.

1986: Hepatitis B vaccine was produced by genetic engineering.

2005: Ian Frazer developed the human papillomavirus vaccine.

Additional resources:

This article is for informational purposes only and is not meant to offer medical advice. This article was updated Oct. 17, 2018 by Live Science Health Editor, Sarah Miller.


9 Ways to Prevent Disease

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Health. It’s the way to enjoy your life. Our experts offer nine ways to take care of yourself and partner up with your doctor.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Eat a champion

For good health, avoid saturated fats, cholesterol, refined carbs and sugars and trans fats. These foods can cause chronic inflammation — a normal bodily process gone awry that can contribute to heart disease, diabetes and even cancer. Also, choose good cooking oils and read food labels carefully. Even so-called “diet foods” can be bad for you.

Get your cholesterol checked

A little-known fact: diet isn’t the most important factor in determining your cholesterol level. Only 20% of your body’s cholesterol comes from your diet, while the other 80% is made by your liver. That’s why it is so hard to lower cholesterol through diet alone and why you need to get it checked. It should be 200 mg/DL or lower.

Watch your blood pressure

Do you have high blood pressure? Even if you don’t think so, keep reading. One three American adults has high blood pressure, diagnosed with a reading above 140/90. However, experts say if you are consistently over 120/80, you also have high blood pressure. Help your heart by keeping your weight and salt intake down and your activity level up.

Pursue an ideal body mass

Dare to be different from the average American, who is more ly to be obese than adults in any other developed nation. To see if you are at a good weight for your height, calculate your Body Mass Index (BMI) and check out this BMI calculator from the BBC to see how your BMI stacks up against people from around the world. Need to lose?

Keep safe blood sugar levels

For good preventive health, cut back on soda, candy and sugary desserts, which can cause blood sugar to rise. If you have diabetes, this can damage your heart, kidneys, eyes and nerves over time. Managing blood sugar is 1 of 7 metrics for heart health, according to the American Heart Association. These same metrics make it less ly to be diagnosed with cancer.

Get moving

Exercise doesn’t have to be in a gym or structured environment. Experts say frequency (how often), intensity (how hard) and time (how long) are what matter. Find just 30 minutes, which don’t have to be consecutive minutes. You could take short and brisk walks two to three times a day. Or do three 10-minute spurts (or two 15-minute spurts) of activity that make your heart happy.

Quit smoking

If you smoke, there is probably no other single choice you can make to help your health more than quitting. While a recent study found that smokers lose at least 10 years of life expectancy compared with people who never smoked, it also found that people who quit by age 40 reduce their risk of smoking-related death by 90%. 

Sleep well

Sleep restores us and has a huge effect on how we feel. Have trouble sleeping? Your diet may be a culprit.

Food relates directly to serotonin, a key hormone that — along with Vitamin B6, B12, and folic acid — promotes healthy sleep.

For more restful sleep, focus your diet on the “big three”: complex carbohydrates, lean proteins and unsaturated fats. Exercise yoga, can also help. Find other sleep tips.

Keep pace with health screenings

It’s no exaggeration: health screenings can save your life. They are designed to catch cancers and serious problems early for more successful treatment. There are screening recommendations for adults and women specifically, and varied screenings depending on your family history. Some screening recommendations have changed, so talk to your doctor. Find more on women’s screenings.


Using Disease to Fight Disease

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Swatting Mosquitoes

Using Disease to Fight Disease

Using Disease to Fight Disease

By Bill Gates


February 16, 2012

Most people probably wouldn’t want to visit a mosquito research lab on their family vacation, but Melinda and I were in Australia recently and were excited to see some amazing work in molecular biology that could lead to a breakthrough in controlling mosquito-borne diseases such as dengue fever.

Mosquitoes are a plague in much of the developing world, not just because they are a nuisance, but because they are transmission agents for some truly terrible diseases.

The scientists we met with in Cairns have discovered a way to infect mosquitoes that are normally capable of carrying diseases dengue and yellow fever with a bacterium called Wolbachia. Wolbachia is naturally present in many types of insects, but not in these mosquitoes.

 Although it is harmless to humans and most other animals, when placed in these mosquitoes Wolbachia shortens their lifespan by about 50 percent and inhibits the development of dengue virus and several other pathogens.

If mosquitoes with the Wolbachia strain can be successfully introduced into wild mosquito populations, it could greatly reduce the transmission of infectious diseases to humans because most mosquitoes would die off before the viruses that cause human disease could replicate in their body.

 Another plus for Wolbachia is that it alters the mosquitoes’ reproductive biology, so that when female mosquitoes that do not carry Wolbachia mate with male mosquitoes that do carry Wolbachia nearly all of their embryos die off.

 Since Wolbachia is passed through the mother mosquito to her offspring, this means that Wolbachia can spread very rapidly through a mosquito population.

Some of these discoveries were a surprise to scientists. If they can be proven in field trials, Wolbachia could create a cheap, natural, and self-sustaining method of control that dramatically reduces dengue fever and other major infectious diseases such as yellow fever and malaria.

The research, led by Professor Scott O’Neill of Monash University, has been funded since 2005 by the Foundation for the National Institutes of Health (FNIH) under the Grand Challenges in Global Health initiative, which encourages innovation to solve persistent health problems in the developing world. Diseases spread by mosquitoes are definitely at the top of that list.

O’Neill’s work is mainly focused on preventing mosquitoes from transmitting the virus that causes dengue fever, an infectious tropical disease that causes 22,000 deaths—mostly among children—and results in 500,000 cases of severe illness each year. Scientists are optimistic that this approach could also work with other insect-transmitted diseases such as malaria, which kills nearly 1 million people annually, mostly children under 5 years of age.

Historically, the battle against disease-carrying mosquitoes has relied on repellants, insecticides, bed nets and eliminating stagnant water breeding sites. More recently, scientists have been working on vaccines that would prevent people from getting infected with mosquito-borne diseases.

To do his current research, O’Neill has had to convince people in Cairns that releasing mosquitoes in their neighborhoods is a good thing. Melinda and I participated in one release of about 20 jars of mosquitoes—probably 1,000 mosquitoes in all.

I was bitten by several dozen, but was safe from getting dengue fever because the mosquitoes being released were lab-reared and not infected with dengue. I have a lot of respect for the volunteers who go into mosquito cages and allow themselves to be bit in the name of science.

The average number of bites they get is over 50!

It was fascinating to see the project first-hand. There’s a real possibility that this approach will get deployed broadly and could really help reduce a lot of disease transmission. But as exciting as it was for Melinda and me, our kids said they definitely didn’t mind not going along.

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