Saturday Cimema: How mushrooms can save the world

Rocketboom: Fighting Malaria in Kenya

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Guinea Worm Disease

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Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa, some derived from our primate ancestors and some acquired from the animals we have domesticated or come into contact with during our history (History of human parasitology. Clin Microbiol Rev 2002 15: 595-612). The best-documented parasitic disease known from ancient times is caused by the nematode worm Dracunculus medinensis. The earliest description is from an Egyptian papyrus from 1500 BC that refers to both the nature of the infection and to techniques for removing the worm. Confirmation of the presence of this worm in ancient Egypt comes from the finding of a well-preserved worms in Egyptian mummies. Dracunculiasis, or Guinea worm disease, is one of the few diseases unambiguously described in the Bible, and most parasitologists accept that the “fiery serpents” that struck down the Israelites in the region of the Red Sea after the Exodus from Egypt somewhere between 1250 to 1200 BC were actually Guinea worms.

The adult worms live in the subcutaneous connective tissues of their victims, from which the females emerge to release thousands of larvae into water, where they are taken up by intermediate hosts, tiny aquatic crustaceans called Cyclops. In these hosts they mature into infectious larvae that infect humans when the crustaceans are accidentally swallowed in contaminated drinking water. On maturity, the large female worm, up to nearly a metre in length, protrudes from the skin, usually of the leg, and causes intense inflammation and irritation. The effects of the disease are crippling. Its victims develop large ulcers, usually in the lower leg. The ulcers swell, sometimes to the size of a tennis ball, and burst, releasing the spaghetti-like parasitic worm. Victims experience a pain so excruciating that they say it feels as if their leg is on fire. The searing pain compels people to jump into water, often the community’s only source of drinking water, to relieve the pain. When the infected person immerses his or her leg in the water, the worm in the leg releases thousands of larvae. The larvae are then ingested by Cyclops that live in the water. Thus the cycle begins again - when people drink the water, they are in effect drinking in the disease.

The most common way to treat Guinea worm disease involves wrapping the worm around a stick. This treatment has been employed for millennia and may have inspired the Rod of Asclepius which historically has symbolized the medical profession. As the adult worm begins to emerge from the patient’s skin, it is wound around a stick, then further extracted by a few centimeters per day. This slow process can take days or even weeks, but it is required to avoid breakage and leaving behind a portion of the worm. Leaving a portion of the dead worm remain within the host’s body increases the risk of infection, and can trigger immune responses resulting in pain and swelling. In many countries, a broken worm is immediately removed surgically, or the worm can be excised surgically from the very beginning if health care facilities are available. Antihelminthic drugs such as metronidazole or thiabendazole are sometimes used in conjunction with physical extraction. However, one study found that antihelminthic therapy was associated with aberrant migration of worms, resulting in infection in areas other than the lower extremity.

Dracunculiasis is a classic example of a neglected tropical disease, a symptom of poverty and disadvantage. Those most affected are the poorest populations often living in remote, rural areas, urban slums or in conflict zones. With little political voice, neglected tropical diseases have a low profile and status in public health priorities. In 1997 the World Health Assembly pledged to completely eradicate Guinea worm disease. This is no small task, but there are several factors which make eradication a possibility. Dracunculiasis is the first parasitic disease targeted for eradication because:

• Diagnosis is easy and unambiguous (presence of an emerging adult worm).
• The transmission agent, Cyclops, is not a mobile vector as is a mosquito.
• The incubation period in both Cyclops and humans is of limited duration.
• Interventions are effective, low cost, and relatively simple to implement.
• The disease has a limited geographic distribution and is seasonal in nature.
• Success in eliminating the disease has been demonstrated in several countries in Asia and the Middle East.
• There is no known animal reservoir.

Is Dracunculiasis eradication close? In 2007 the WHO announced that Guinea worm disease now affects around 25,000 people in nine countries, compared with an estimated 3 million people were infected in over 20 countries in the early 1980s. Twelve countries were declared Guinea worm-free in early March. If progress continues at this rate, the disease could be eradicated in less than two years. It is probable that complete eradication will take quite a few years yet, although it should be possible to eliminate the disease from seven countries in a couple of years, leaving only two endemic countries, Sudan and Ghana (Dracunculiasis eradication by 2009: will endemic countries meet the target? Tropical Medicine & International Health 2007 12: 1403-1408). One lesson to be drawn from the problems of local ownership and the experience of cash rewards is that there are dangers in throwing money at the problem. While the eradication initiative badly needs additional resources, it needs them at such a level and managed in such a way that they do not distort the priorities of the health care system, or exceed the capacity of local staff to manage them. The amounts needed are not large, but their continuity and flexibility is important. Given the highly seasonal transmission of dracunculiasis, the resources must be available at very specific times of the year, which is not always achieved. In spite of the difficulties, complete worldwide eradication of this ancient disease is drawing nearer.

Studying the structure of HIV

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The structure of all retroviruses is similar, although there are some minor differences. Virus particles are far too small to see, the closest we can come to are electron micrographs. To make transmission electron micrographs, the specimen (containing virus particles) are fixed and stained with a metal-containing dye. The more dye different areas of the specimen take up, the darker they appear in the electron micrograph.

In the centre of an HIV particle, there are two molecules of RNA which together make up the genome of the virus. Associated with the RNA are two enzymes, reverse transcriptase and integrase. The genome is enclosed in a conical core consisting of the nucleocapsid proteins. Outside this is an icosahedral protein capsid, which in turn is enclosed by the matrix protein layer. The whole particle is surrounded by a lipid bilayer known as the virus envelope. The transmembrane protein penetrates through the envelope and anchors the surface glycoprotein on the outside of the particle.

To see more detail in virus particles, special imaging techniques are needed. Cryo-electron tomography makes a three dimensional reconstruction from a series of two dimensional transmission electron micrographs taken at extremely low temperatures in order to preserve the structure of the particle. The individual micrographs represent slices though the virus particle which are put together on a computer to construct a three dimensional representation with false colours added for additional clarity.

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Related:

• I’m stuck on you
• T Cell Responses to Human Endogenous Retroviruses in HIV-1 Infection
• Cytopathic mechanisms of HIV-1 - is the envelope glycoprotein a viroporin?

E. coli O157:H7 - getting to the bottom of the burger bug

The Zoonotic and Animal Pathogens Research Laboratory at the University of Edinburgh has worked with a UK-based animation company to produce a full-length animation representing the key stages of E. coli O157:H7 interaction within the gastrointestinal tract. This movie was featured in the August 2004 issue of Microbiology Today, published by the Society for General Microbiology.

Biological Sciences at the University of Leicester

Find out more about the School of Biological Sciences at the University of Leicester and life in Leicester as a student:

Find out more, or read our Alternative Prospectus, written by the students.

 

 

Saturday Cinema: Cyanobacteria

Cyanobacteria are the oldest bacteria, having evolved around 3.8 billion years ago. The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing environment which dramatically changed the life forms on Earth and provoked an explosion of biodiversity. And they’re still here:

Video Credit: WLanier

Today’s Video: Different types of bacteria

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• Getting bacteria into shape
• The Gram Stain

Antonie van Leeuwenhoek

QuickTime

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Around the year 1590, two Dutch spectacle makers, Hans and Zaccharias Janssen were experimenting with glass lenses. They put several lenses in a tube and discovered that an object near the end of the tube could be viewed at much larger magnification than a simple magnifying glass could achieve. This was the invention of the microscope.

In 1648 while working for a cloth merchant in Amsterdam, Antonie van Leeuwenhoek saw his first simple microscope, which was only capable of magnifying a few times but was useful for counting the threads in cloth. He acquired a microscope for his own use and became so interested that he went on to learn how to make his own lenses.

During his lifetime van Leeuwenhoek ground more than 500 optical lenses and created over 400 microscopes, only nine of which still exist today. His microscopes consisted of silver or copper frames rather than a tube to hold the lenses. By grinding and polishing, he was able to make small lenses with large curvatures. These fat lenses produced greater magnifications, and his microscopes were eventually able to magnify up to 270 times. Van Leeuwenhoek never published his method of how to make these superb lenses.

Robert Hooke also spent much of his life working with microscopes and improved their design. In 1664 he published a book entitled Micrographia in which he described and illustrated small insects such as fleas, but which also contained the first description of plant cells. It is believed that van Leeuwenhoek read Hooke’s book in 1665 and that this stimulated him to use his microscopes for the purpose of investigating the natural world.

In 1674 van Leeuwenhoek discovered protists (which he called animalcules from the Latin for “little animal”) in lake water, and in 1676 was the first person to observe bacteria scraped from the film between his own teeth. In 1677 he also became the first person to observe spermatozoa. But van Leeuwenhoek’s work went far beyond merely observing micro-organisms. For example, in 1676 he described his methods of making infusion cultures of micro-organisms (so the next time anyone tries to tell you Louis Pasteur was the “Father of Microbiology”, remind them that van Leeuwenhoek got there 200 years earlier!).

Van Leeuwenhoek began to send of his microscopic observations to the Royal Society in England, and in 1676 he sent his first observations of microscopic single celled organisms. Such was the quality of his microscopes that other scientists were initially unable to repeat his observations, and his credibility was questioned. Eventually, in 1680, van Leeuwenhoek’s work was accepted by the Royal Society.

Van Leeuwenhoek has rightly become known as “the Father of Microbiology”, and the Federation of European Microbiology Societies (FEMS) has it’s headquarters in Delft, the birthplace of the science of microbiology.

Thonis Leeuwenhoek (16321723), was born and died in Delft in The Netherlands, and was known in his adult life as Antonie. He adopted “van” to precede his surname as a mark of social status in 1686.

• How To Make a Van Leeuwenhoek Microscope Replica

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Merry Christmas from MicrobiologyBytes

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