It’s hard to be a happy camper when you’ve got diarrhea!

Joseph Dean Nestor

Hey there, outdoorsy types!

Whether you get a wild hair for the woods one day or even if you are a chronic adventurer, you can ruin your excursion with just one swallow. 

Consuming unsanitary, fecal-contaminated water or food can lead to diarrhea causing parasitic infections and other serious health risks.

“Hang on now, mister,” you interject, “I boil my water or only drink from clear mountain streams!”

Well, easy there big fella’.  Did you know that at high elevations the boiling point of water is lowered, meaning some disease causing critters may still be viable, and even if water looks clean and cold from a stream, disease-causing protozoa (animal-like microscopic organisms [1]) like Giardia lambia may survive for up to 6 months when encysted (think dormant and protected from environment) [2].

“Fine. I’ll just purchase some of those chemical tablets,” say you.

Ah, determined to go a-hiking are you? Well, some critters are tenacious; our newest friend Giardia lamblia and another protozoan Cryptosporidium parvum are resistant to halogen chemical treatments and remain safe in their cysts ready to give you some uncomfortable results. Those tablets may eliminate bacterial risks, but you’re still at risk for diarrhea causing parasites [2]. The chlorine dioxide and silver ion tablets can kill G. lamblia and C. parvum but the process can take up to 4 hours to be determined safe to drink. Additionally, frequent use of a product containing silver may cause a buildup of silver in your body causing a permanent grey-blue coloring of skin and eyes [3].

“What about those portable filter-y thingies?” you demand.

Those can be very helpful in removing the cysts of parasitic protozoa as they are very large, but viruses, bacteria, and harmful solutes remain in the filtered product. You may have realized the safest way to provide yourself with clean, drinkable water while in the wilds is to use more than one approach to ensure cleanliness and safety of the water you drink. A good example is to first filter your water using a carbon/ceramic filter with very small pores. 0.2-0.4 micron pores are an effective way to filter out parasitic cysts as they are much larger than the pores, and then boil the water thoroughly to eliminate any harmful flora that remain.
“Is there any other way; I don’t like to carry more than I have to?” you ask.

You could set up a few solar distillation systems at your camp. These effectively remove all critters and harmful particulates in water at the cost of taking up time to set up and even longer to produce drinkable water. They can be as simple as a single sheet of plastic, and a cup or complex glass and metal framing. Here’s a fun video of the “Mythbusters” fellows using just duct tape and plastic wrap to create a solar distillation unit: http://dsc.discovery.com/tv-shows/mythbusters/videos/jamies-solar-still.htm

Although admittedly a silly premise, you can see the set up and the condensation process involved. This yields drinkable water from even dirty, salty water. Additionally, if there isn't any water you can use it over moist earth. This is quite the handy survival skill to have.

“I don't think I want to go anymore,” you mutter.

Cheer up! You can go, just remember there are always other options for turning possibly contaminated water (portable UV, 3 step filters, etc) or you can make sure you have enough water in tow. Enjoy and try not to become too paranoid.

Here's some pictures of the protozoan critters ready and waiting to give you diarrhea:

Picture 1: Each G. lamblia cyst ingested yields two feeding parasites.

Picture 2: Each feeding form of G. lamblia is capable of asexual replication by binary fission.

Picture 3: G. lamblia attaches to the wall of your small intestine.

Picture 4: Each Cryptosporidium oocyst yields four feeding parasites.

Picture 5: Cryptosporidium feed and reproduce in your small intestine.

These are just two of many possible organisms that can turn your vacation adventure into a stay-cation in the porcelain throne room. Stay safe.

Edutainment links:

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/travelersdiarrhea_g.htm/

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001333/

http://www.cdc.gov/parasites/giardia/

http://www.cdc.gov/parasites/crypto/

http://www.motherearthnews.com/Renewable-Energy/1974-09-01/How-To-Build-and-Use-A-Solar-Still.aspx

In text citations:

[1] Edward Alcamo; Jennifer M. Warner (28 August 2009). Schaum's Outline of Microbiology. McGraw Hill Professional. 144.

[2] Huang DB, White AC (2006). "An updated review on Cryptosporidium and Giardia". Gastroenterol. Clin. North Am. 35 (2): 291–314.

[3] Lansdown AB (2006). "Silver in health care: antimicrobial effects and safety in use". Current Problems in Dermatology. Current Problems in Dermatology 33: 17–34.

Picture sources:

Title.http://licleanwater.com/blog/wp-content/uploads/2010/09/dirtywater.jpg

In-text Link.http://jimhalterman.com/wp-content/uploads/2012/03/23568_IMG_1729.jpg

1.http://www.btinternet.com/~ukneqas.parasitologyscheme/Faecal_Scheme/Teaching_Information/Protozoa/Flagellates/Giardia_lamblia/giardia1.JPG

2.http://theonlyhopeformeisart.tumblr.com/

3.http://cfb.unh.edu/phycokey/Choices/Amoebae_Flagellates_Ciliates/Flagellates/GIARDIA/Giardia_Image_page.html

4.http://www.k-state.edu/parasitology/546tutorials/PROTFIG02.JPG

5.http://www.avianbiotech.com/diseases/Images/cryptosporidium_3.gif

Student Posts

As part of my summer course in parasitology my students have prepared a selection of posts centered on water borne disease. Some are entertaining and some are informative. Some are both. Check them out. I hope that by reading them you will gain a greater appreciation for the privelege of clean water that we enjoy here in the United States and that you will become more aware of the challenges faced by people throughout the developing world.

• BALROG, APOPHIS, OR SLUGULIS ERUCTO?         
• CHOLERA
• Dirty Water and Its Impact on Global Health
• Guinea Worm Disease
• It's Hard to Be a Happy Camper When You Have Dirty Water
• Naegleria fowleri: Think before you leap 
• Onchocerca volvulus 
• Project Clear Water 
• Recreational fun leading to the runs or an untimely death 
• Schistosomiasis: A disease among travellers
• Swimmer’s itch 
• The Creation of Sea Monsters: Limb Malformation inAmphibians  
• “The Fiery Serpent”
• Vittaforma corneae 
• What would you do if worms ate up your income?

FYI, I am running a contest to see which post gets the most "likes" on Facebook. The winner gets their pick of a Giant Microbe.

“The Fiery Serpent”

by Kezhan E. Khazaw

 

            Hello there, my name is Dracunculus medinensis but most people know me as the Guinea worm. I am a parasite that likes to live off of an organism (in this case it is these strange creatures called humans). My job is to feed, grow, reproduce, and find a host to use as my own personal house. It is a wonderful place to live because I have lots of room to roam around and oh yes there is also plenty of food for me not to go hungry. I usually live in the subcutaneous tissues and I cause ulcerated blisters in the tissue around the vulva. It is a nifty place and I like it very much. However, the person that I am in does not seem to like me very much. I do not know why. I mean I just form this blister so that way I can get my babies, larvae children, out into the fresh water. Now these humans are stubborn and will not let us out easily so I secrete my wrath toxins so they feel this burning sensation. My children absolutely love the water! While they are in the water, my babies get eaten by copepods which are these small crustaceans that live in the fresh water also. This where these strange creatures come and drink the water. As a result some of the copepods are ingested and my three week baby larvae come out and penetrate through their small intestines. Humans are wonderful creatures because their body allows for my children to reproduce and become parents themselves. Who does not love grandchildren? I know I do, I love seeing my own daughter becoming a mother and continuing our generation into the future. You see I usually travel down to the lower extremities (you know their legs and feet) so that way I can have better access to the water. Most often I do not like to show or indicate my presence until at least a year later after I am really and healthy. That way I am ready to release my children into the water to continue the life cycle process once again. It is crazy, for some reason when I do make my appearance the human’s body starts to go through some changes. I have heard rumors that I, the Guinea worm, cause a slight fever, itchy rash, nausea, vomiting, diarrhea, and dizziness. After all those symptoms I form a blister, so that I can escape and let children breath.  When I stick my head out, these humans want to get rid of me. Can you believe such a thing? These humans are kicking me out of my own home, for what reason- I do not know. There is no specific drug to kill me. No, they want to take me through this long journey of tying me to a stick and each day they slowly expose me until I am out in a few weeks. Oh the process is so tedious; I mean I get so bored just dangling there, while starving to death. Humans are very inconsiderate of my feelings. They are so mean!

 Humans are trying to eradicate my family and me. They are filtering their water so that way they do not drink the copepods; they kill my babies by using larvicide, and for some reason these humans tell their human friends that I am dangerous and they should stay away from me and my children. It is just awful, and I hate it! The main organization behind all of this eradicating business is the Carter Center; created by Jimmy Carter and his wife Rosaland Carter. The eradication program is successful, reducing the number of my guinea worm friends from 3.5 million cases in 21 countries in Africa and Asia to only 1058 cases in four African countries in 2011. I still have friends living in South Sudan, Mali, and Ethiopia. Recently, there was an isolated outbreak in Chad. Well, my fellow reader I must leave you now. My children are anxious for the water, I must go and get prepared because I believe this human I am occupying is about put his foot in the water. Until next time drink some contaminated fresh water and help my family live and prosper for generations to come. 

 

Resources:

http://www.cdc.gov/parasites/guineaworm/

http://www.scientificamerican.com/article.cfm?id=what-is-guinea-worm-disease

http://www.cartercenter.org/about/index.html

Guinea Worm Disease

By Raphael Valdivia

Ever wonder about those worms that are able to pierce through the skin and are able to visibly be seen with the naked eye? Guinea worm disease also classified as dracunculiasis, is caused by a nematode roundworm called Dracunculus medenisis. These worms are acquired through drinking contaminated water that is at a standstill. This water contains water fleas which are referred to as copepods which contain the Guinea worm larvae in an ineffective stage. Once this larva is inside the abdomen of a host the gastric juices digest the water flea and the male and female larvae are released. They mature and mate with some growing as much as 3 feet in length about 3 weeks after an individual is infected! After mating the male will eventually die off and the female will then proceed to move to connective tissues more commonly found in longer bones in extremities. Upon a year of the infection blisters form and are usually located on the leg, this is the sight of rupture where the worm can be seen causing a symptom associated with a burning feeling of the local area. It takes around 10 days for the whole worm to exit the host and the individual cannot walk if it is on the leg or foot. Removing this worm is tricky and can be dangerous if the worm gets agitated. Usually people take a risk of wrapping the worm around a stick and pulling the worm every other day until the worm is able to be pulled out. The problem is when the worm resists this procedure, it can pull back inside of the body and calcify cutting the hosts blood supply or even causing paralysis.  The only way to alleviate the sensation of burning is by placing the location of the blister under water and this is the primary way of further contaminating a water supply because the female release millions of eggs under this condition. The cycle further continues because water fleas of copepods eat these worms followed by humans drinking the water associated with infected water fleas.

http://cartercenter.org/health/guinea_worm/mini_site/facts.html

There are several simple and effective ways that waterborne diseases can be controlled such as keeping the public, sewage, and rain water separated. The flow of stagnant water should always be in constant motion to keep water from becoming sessile and accumulating various types of agents that can cause disease. Land should be checked periodically for any sources of contaminants such as fuel or oil spills, along with highly populated areas where abandoned buildings and rodents might be present. Cities with high density populations are especially susceptible to parasitic diseases and should be highly monitored.

The good news is that this disease is on the verge of eradication, the carter center began its aid in 1986 partnering with the international Guinea worm disease eradication campaign, the Centers for Disease Control, and the World Health Organization. Due to simple and effective procedures to help get rid of this disease these organizations have dropped the number of cases from 3.5 million in 1986 to under 5,000 cases worldwide with Africa containing the most cases due to elevated poverty.

Facts to keep in mind!

1.     Guinea worm disease is also known as Dracunculiasis caused by Dracunculus medinensis which is a nematode roundworm.

2.     The guinea worm has the capacity to grow up to 3 feet long!

3.     Guinea worm ulcers that are put under water cause the female to release thousands of eggs further contaminating a water supply.

4.     Symptoms only occur a year after a person is infected! A rather long process if you ask me, and to add to this most of the time ulcers will develop on the leg

5.     Symptoms that include fever, pain, and swelling can occur hours before the worm leaves the ulcer

6.     No medication! There is no type of medicine available to kill the worm or hinder its parasitic process. The only way to eliminate the worm is through surgical removal or by wrapping the worm around a stick and slowly pulling on it. This process is lengthy and can take as much as 3 months to remove the worm depending on length.

7.     This disease does not kill but will suppress daily activities due a weak immune system and cause lethargic behavior.

8.     The disease has been highly eliminated from 3.5 million cases in 1986 to fewer than 5,000 cases throughout the world

                                         

What would you do if worms ate up your income?

By Tiffany S. Schluter

We who don’t live in tropical and subtropical regions of the world, especially those who have high poverty rates, don’t worry about things like getting WORMS from just going outside, swimming, bathing, drinking water, and NORMAL EVERYDAY THINGS for us. Can you even imagine? We take it all for granted. If it even was a risk for us, we have the means to go to the doctor and be diagnosed and treated before the more serious complications occur, but what about other countries? What happens to them? What happens to people that can’t get rid of their worms and not just right now… for the rest of their lives??? First, we will talk about a major worm, Schistosoma, and all of its facts then we’ll talk about what it causes.
Schistosomiasis is a Neglected Tropical Disease (NTD) caused by parasitic worms (trematodes to be specific). This disease is also called bilharzia. The only parasitic disease that is more devastating than Schistosomiasis is Malaria. Over 230 MILLION people are treated for Schisto yearly according to the World Health Organization. Basically, it is a HUGE problem.
There are 5 different species of Schistosoma that affect different areas of the world. The United States is not affected. The areas of the world that are affected by each type of Schistosoma are:
1)  S. mansoni: Africa, South American and the Caribbean.
2) S. haematobium: Africa and the Middle East.
3) S. japonicum: Indonesia, China and Southeast Asia
4) S. mekongi:  Cambodia and Laos
5) S. intercalatum: Central and West Africa.
How do you get it?? The stage of the parasite life cycle that infects people, called cercariae, emerges from snails, which are the intermediate hosts, to INFECT THE FRESHWATER that they’re in. The cercariae can only survive alone in the water for 48hours. The way that the water gets infected to begin with is by poor sanitation such as people peeing or pooping in the water, because the eggs come out in the urine and feces.  Once the cercariae get into your system, all they have to do is come in to contact with your skin, they migrate to the blood vessels then to the liver, they mature. After they mature, the worms pair up and go to the intestine or bladder for the female to lay eggs. The eggs either leave in the pee or poop or they can stay in the tissue, which is what causes the problems associated with the disease.

Symptoms of Schisto vary, and they aren’t caused by the worms but rather they are the body’s response to the eggs aren’t excreted, which cause an immune response (Like allergies).
Commonly, people don’t have symptoms at first, but after a few days people sometimes get an itchy rash. After a few months, flu-like symptoms can occur such as fever, chills, cough and muscle aches. If the disease becomes chronic, it can cause complications such as kidney failure, bloody pee or poop, enlarged spleen, liver damage, colon inflammation, bladder obstruction, which causes trouble passing urine, and leads to increased risk for CANCER. In rare cases, eggs can get into the brain or spine, which can inflame the spine or cause seizures or paralysis. Kids that are repeatedly infected can suffer anemia, malnutrition, and LEARNING DIFFICULTIES!!! On average, this disease takes up to TEN YEARS off of people’s lives!!!
So, how is it detected? By a simple microscopic examination of stool or urine for eggs. Also, a blood test can be done. What’s so hard about that?
Treatment: It’s treated by a drug called praziquantel, which is used in a lot of de-worming stuff that we give our pets, and if the disease is severe corticosteroids are also administered.  Also, the antimalarial drug artemesinin (this drug is old) has proven to work on the immature stages of all 5 species of Schistosoma.
So, what will be the result when Schisto, and NTDs altogether, are gone from a population? With decreased worm burdens on poor populations, people are HEALTHIER, have the chance to fully develop, can raise their own families, and are PRODUCTIVE in their community. The lack of productivity in countries that have heavy worm loads help to keep impoverished countries in a cycle of poverty. So, decreasing worm loads one LITTLE step at a time is a GIANT step towards helping impoverished countries break free of the chains of poverty and improving their lives, communities, and countries as a whole.
So, how could we help PREVENT this ghastly disease? Just IMPROVED SANITATION could lessen/eradicate transmission!  KEEP THE WATER CLEAN!!! One control measure that has been, and is being, used is mass drug treatment of entire communities and targeted treatment of school-age children, but drugs cost money so people and children in affected countries would have NO WAY of getting these meds WITHOUT HELP. Donations to charities are a great way to do your part in trying to better our world by improving at least one person’s life! You can do this by helping to give them the opportunity to either have CLEAN WATER to drink/swim/bathe in or, if they’re already infected, to be able to take medicine to kick these worms OUT!! We de-worm our pets without a second thought; it’s just something you do, right? The SAME MEDICINE can cure the people afflicted with this disease! So, how about next time you go to get your dog’s meds you think about the people with this disease and throw a little bit of spare change their way. Every cent counts. Can you imagine living this way, and with no way out? Your help can help to give them that push in the right direction towards a better life for themselves, their families, their communities and eventually their countries.
Sites to donate to the Schistosomiasis Control Initiative (SCI) to help control this disease are http://www.givewell.org/international/top-charities/schistosomiasis-control-initiative and http://www3.imperial.ac.uk/schisto.

For more information about Schistosomiasis:

https://gsa.confex.com/gsa/2011AM/finalprogram/abstract_194053.htm

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002298/

http://www.cdc.gov/parasites/schistosomiasis/index.html

http://www.who.int/mediacentre/factsheets/fs115/en/index.html

http://www.medicalecology.org/water/schistosomiasis/schistosomiasis.htm

Vittaforma corneae

By Benjamin J. Pitts 

Overview

            Vittaforma corneae is a human-infecting microsporidia species. V. corneae can cause eye infections in immunocompetent individuals, and has also been linked to causing infections in immunocompromised AIDS patients. V. corneae is a member of the microsporidia family. Microsporidia are extremely widespread and they infect nearly every organism on earth from honey-bees and silkworm to mammals and birds. Relatively little is known about the epidemiology of microsporidia, as transmission and infection pathways are still somewhat unclear. Though active spores have been found in water sources in developed and developing nations, microsporidiosis remains primarily a disease of HIV and AIDS patients. Despite the relatively recent discovery of this pathogen, the infection among AIDS patients is remarkable and the parasite will be of growing importance in the future as HIV continues to spread and more research is undertaken to understand the role microsporidia play in the human health. Microsporidia are described as intracellular parasites that infect a wide variety of vertebrate and invertebrate hosts.          

Life Cycle

            Microsporidia are characterized by the production of resistant spores that vary in size. The infective form of microsporidia is the resistant spore and it can survive for extended periods of time in the environment. The spore pokes out its polar tubule and infects the host cell. The spore is injected into the sporoplasm into the eukaryotic host cell through the polar tubule. Inside the cell, the sporoplasm undergoes extensive multiplication either by binary fission or multiple fissions. This development can occur either in direct contact with the host cell cytoplasm or inside a vacuole termed parasitophorous vacuole. Either free in the cytoplasm or inside a parasitophorous vacuole, microsporidia develop by sporogony to mature spores. During sporogony, a thick wall is formed around the spore, which provides resistance to adverse environmental conditions. When the spores increase in number and completely fill the host cell cytoplasm, the cell membrane is disrupted and releases the spores to the surroundings. These free mature spores can infect new cells thus continuing the cycle.

Diagnosis

            The methods of diagnosis typically involve identifying spores in feces, urine, other bodily fluids or body tissues. Transmission electron microscopy  is the top notch way for identifying specific species and diagnosing microsporidiosis but is often too expensive and time consuming. Another way to view V. corneae is with light microscopy using various stains including gram stains, which the V. corneae are gram-positive. V. corneae is said to cause urinary tract infections as well as ocular infections. One of the prominent conditions related to V. corneae is keratitis. Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.

Treatment

            One treatment is with albendazole and is the most common for all species and is coupled with topical Fumagillin for ocular infections. However, most drug treatments will not fully eradicate the parasites. New, more effective drugs for microsporidiosis are still being discovered and tested.

Conclusion

            The widespread location of microsporidia is a reason concern. With not much being known about the species and its devastating affects on the immunocompetent. The world should switch its funding to help combat these dangerous parasites that cause one to lose their eyesight.

Above is a map of the places that Microsporidia have been reported.

 

           

References

http://dpd.cdc.gov/dpdx/html/Frames/M-R/Microsporidiosis/body_Microsporidiosis_page2.htm

http://www.stanford.edu/class/humbio103/ParaSites2006/Microsporidiosis/microsporidia1.html

http://dpd.cdc.gov/dpdx/html/Microsporidiosis.htm

Swimmer’s itch

By Joshua D. Peugh

            Summer time is finally here, with the heat setting record breaking temperatures each day.  These phenomenal temperatures are leading more and more families to local recreational water areas like water parks and lakes.  What lies beyond the unseen eye in these mysterious waters? Parasites, of course!

            Many people at these recreational facilities are susceptive to any type of water-borne parasite infection unknowingly. A common water-borne parasite, known as schistosomatidae, causes an immune reaction occurring on the skin of humans.  The immune reaction is caused by an allergic reaction to certain parasites that infect some mammals and birds.  This water-borne infection is known as Swimmer’s itch, also called cercarial dermatitis, and the symptoms include itchy, raised papules, generally occurring within a few hours of the infection.  The infection does not generally last for more than a week.

            Once an egg of a schistosomatidae is submerged into a lake or pond, a free-living stage known as the miracidium is appears.  This stage is a short-lived non-feeding stage, where the miracidium uses cilia to follow physical and chemical cues.  These cues are thought to increase the opportunities of finding the first intermediate host in its life cycle, an aquatic snail.  When the miracidium has infected the aquatic snail, it develops into a mother sporocyst.  This will cause asexual reproduction in the organism, yielding very large number of daughter sporocysts, which asexually produce another short-lived, free-living stage, the cercaria.  This stage known as the cercariae is the stage that causes swimmer’s itch. In this stage the cercariae uses a tail-like appendage to swim to the top of the water, along with other chemical and physical cues, in order to target the final host in its life cycle, a bird.  After infecting a bird, the parasite develops into a schistosomulum.  Then the schistosomulum migrates through the host’s circulatory system to the final location within the host body where it matures and, if it encounters a mate, sheds eggs to start the life cycle over again.

            However, a bird is the preferred final host, but what happens when the host comes into contact with a human?  Once the parasite is in the infective stage, upon contact with a human the cercaria burrows through the skin.  Inside the skin, the parasite goes into its next stage the schistomulum, where it then migrates to the lungs and liver to form into an adult.  As an adult worm, depending on its species the parasite migrates to its preferred body part.  These body parts include the bladder, rectum, intestines, liver, portal venous system, spleen, and lungs.

            The symptoms that come from swimmer’s itch will depend on the type of parasite and how heavy the infestation is.  There may be fever, chills, and lymph node enlargement, along with liver and spleen enlargement.  The initial invasion by the parasite may cause itching and a rash.  If a rash occurs, this stage is known as swimmer’s itch and the parasite is being destroyed by the body.  Furthermore, if the parasite is not destroyed intestinal symptoms may occur with diarrhea and urinary symptoms with blood in the urine.

            Treatment before considerable damage or severe complications occur usually produces superior results.  Swimmer’s itch is usually treated with the drug praziquantel.  If the infection gets too severe or involves the central nerve system, corticosteroids may be given.  Prevention measures can be taken to avoid Swimmer’s itch all together.  First, do not swim in any water that may be contaminated and do not go in any water that may be unsafe.  Secondly, the aquatic snail is the intermediate host for schistosomiasis; therefore, controlling the snail population and getting rid of them in water used by humans would help prevent infections.

            The schistosomatidae that is frequently related with swimmer’s itch in humans are Trichobilharzia and Gigantobilharzia.  Schistosomiasis is not commonly found in the United States, it tends to reside in many tropical and subtropical areas worldwide.  There are currently no funds for swimmer’s itch; however research for schistomiasis is currently being held, but young scientist and investors are greatly needed to increase future funds.

For more information please visit:

http://en.wikipedia.org/wiki/Swimmer's_itch

http://www.ncbi.nlm.nih.gov/pubmed/15117691

http://www.cdc.gov/parasites/swimmersitch/

http://usf.academia.edu/DavidLewis/Papers/1216898/A_survey_of_swimmers_itch-causing_cercariae_and_their_intermediate_snail_host_species_in_Devils_Lake_Wisconsin

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002298/