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Elephantiasis

Elephantiasis

Definition

The word elephantiasis is a vivid and accurate term for the syndrome it describes: the gross (visible) enlargement of the arms, legs, or genitals to elephantoid size.

Description

True elephantiasis is the result of a parasitic infection caused by three specific kinds of round worms. The long, threadlike worms block the body's lymphatic systema network of channels, lymph nodes, and organs that helps maintain proper fluid levels in the body by draining lymph from tissues into the bloodstream. This blockage causes fluids to collect in the tissues, which can lead to great swelling, called "lymphedema." Limbs can swell so enormously that they resemble an elephant's foreleg in size, texture, and color. This is the severely disfiguring and disabling condition of elephantiasis.

There are a few different causes of elephantiasis, but the agents responsible for most of the elephantiasis in the world are filarial worms: white, slender round worms found in most tropical and subtropical places. They are transmitted by particular kinds (species) of mosquitoes, that is, bloodsucking insects. Infection with these worms is called "lymphatic filariasis" and over a long period of time can cause elephantiasis.

Lymphatic filariasis is a disease of underdeveloped regions found in South America, Central Africa, Asia, the Pacific Islands, and the Caribbean. It is a disease that has been present for centuries, as ancient Persian and Indian writings clearly described elephant-like swellings of the arms, legs, and genitals. It is estimated that 120 million people in the world have lymphatic filariasis. The disease appears to be spreading, in spite of decades of research in this area.

Other terms for elephantiasis are Barbados leg, elephant leg, morbus herculeus, mal de Cayenne, and myelolymphangioma.

Other situations that can lead to elephantiasis are:

  • a protozoan disease called leishmaniasis
  • a repeated streptococcal infection
  • the surgical removal of lymph nodes (usually to prevent the spread of cancer )
  • a hereditary birth defect

Causes and symptoms

Three kinds of round worms cause elephantiasis filariasis: Wuchereria bancrofti, Brugia malayi, and Brugia timori. Of these three, W. bancrofti makes up about 90% of the cases. Man is the only known host of W. bancrofti.

Culex, Aedes, and Anopheles mosquitoes are the carriers of W. bancrofti. Anopheles and Mansonia mosquitoes are the carriers of B. malayi. In addition, Anopheles mosquitoes are the carriers of B. timori.

Infected female mosquitoes take a blood meal from a human, and in doing so, introduce larval forms of the particular parasite they carry to the person. These larvae migrate toward a lymphatic channel, then travel to various places within the lymphatic system, usually positioning themselves in or near lymph nodes throughout the body. During this time, they mature into more developed larvae and eventually into adult worms. Depending upon the species of round worm, this development can take a few months or more than a year. The adult worms grow to about 1 in (2.5 cm) to 4 in (10 cm) long.

The adult worms can live from about three to eight years. Some have been known to live to 20 years, and in one case 40 years. The adult worms begin reproducing numerous live embryos, called microfilariae. The microfilariae travel to the bloodstream, where they can be ingested by a mosquito when it takes a blood meal from the infected person. If they are not ingested by a mosquito, the microfilariae die within about 12 months. If they are ingested by a mosquito, they continue to mature. They are totally dependent on their specific species of mosquito to develop further. The cycle continues when the mosquito takes another blood meal.

Most of the symptoms an infected person experiences are due to the blockage of the lymphatic system by the adult worms and due to the substances (excretions and secretions) produced by the worms.

The body's allergic reactions may include repeated episodes of fever, shaking chills, sweating, headaches, vomiting, and pain. Enlarged lymph nodes, swelling of the affected area, skin ulcers, bone and joint pain, tiredness, and red streaks along the arm or leg also may occur. Abscesses can form in lymph nodes or in the lymphatic vessels. They may appear at the surface of the skin as well.

Long-term infection with lymphatic filariasis can lead to lymphedema, hydrocele (a buildup of fluid in any saclike cavity or duct) in the scrotum, and elephantiasis of the legs, scrotum, arms, penis, breasts, and vulvae. The most common site of elephantiasis is the leg. It typically begins in the ankle and progresses to the foot and leg. At first the swollen leg may feel soft to the touch but eventually becomes hard and thick. The skin may appear darkened or warty and may even crack, allowing bacteria to infect the leg and complicate the disease. The microfilariae usually don't cause injury. In some instances, they cause "eosinophilia," an increased number of eosinophils (a type of white blood cells) in the blood.

This disease is more intense in people who never have been exposed to lymphatic filariasis than it is in the native people of tropical areas where the disease occurs. This is because many of the native people often are immunologically tolerant.

Diagnosis

The only sure way to diagnose lymphatic filariasis is by detecting the parasite itself, either the adult worms or the microfilariae.

Microscopic examination of the person's blood may reveal microfilariae. But many times, people who have been infected for a long time do not have microfilariae in their bloodstream. The absence of them, therefore, does not mean necessarily that the person is not infected. In these cases, examining the urine or hydrocele fluid or performing other clinical tests is necessary.

Collecting blood from the individual for microscopic examination should be done during the night when the microfilariae are more numerous in the bloodstream. (Interestingly, this is when mosquitoes bite most frequently.) During the day microfilariae migrate to deeper blood vessels in the body, especially in the lung. If it is decided to perform the blood test during the day, the infected individual may be given a "provocative" dose of medication to provoke the microfilariae to enter the bloodstream. Blood then can be collected an hour later for examination.

Detecting the adult worms can be difficult because they are deep within the lymphatic system and difficult to get to. Biopsies usually are not performed because they usually don't reveal much information.

Treatment

The drug of choice in treating lymphatic filariasis is diethylcarbamazine (DEC). The trade name in the United States is Hetrazan.

The treatment schedule is typically 2 mg/kg per day, three times a day, for three weeks. The drug is taken in tablet form.

DEC kills the microfilariae quickly and injures or kills the adult worms slowly, if at all. If all the adult worms are not killed, remaining paired males and females may continue to produce more larvae. Therefore, several courses of DEC treatment over a long time period may be necessary to rid the individual of the parasites.

DEC has been shown to reduce the size of enlarged lymph nodes and, when taken long-term, to reduce elephantiasis. In India, DEC has been given in the form of a medicated salt, which helps prevent spread of the disease.

The side effects of DEC almost all are due to the body's natural allergic reactions to the dying parasites rather than to the DEC itself. For this reason, DEC must be given carefully to reduce the danger to the individual. Side effects may include fever, chills, headache, dizziness, nausea and vomiting, itching, and joint pain. These side effects usually occur within the first few days of treatment. These side effects usually subside as the individual continues taking the drug.

There is an alternate treatment plan for the use of DEC. This plan is designed to kill the parasites slowly (to reduce allergic reactions to the dead microfilariae and dying adult worms within the body). Lower doses of DEC are taken for the first few days, followed by the higher dose of 2 mg/kg per day for the remaining three weeks. In addition, steroids may be prescribed to prevent the individual's body from reacting severely to the dead worms.

Another drug used is Ivermectin. Early research studies of Ivermectin show that it is excellent in killing microfilariae, but the effects of this drug on the adult worms are still being investigated. It is probable that patients will need to continue using DEC to kill the adult worms. Mild side effects of Ivermectin include headache, fever, and myalgia.

Other means of managing lymphatic filariasis are pressure bandages to wrap the swollen limb and elastic stockings to help reduce the pressure. Exercising and elevating a bandaged limb also can help reduce its size.

Surgery can be performed to reduce elephantiasis by removing excess fatty and fibrous tissue, draining the swelled area, and removing the dead worms.

Prognosis

With DEC treatment, the prognosis is good for early and mild cases of lymphatic filariasis. The prognosis is poor, however, for heavy parasitic infestations.

Prevention

The two main ways to control this disease are to take DEC preventively, which has shown to be effective, and to reduce the number of carrier insects in a particular area.

Avoiding mosquito bites with insecticides and insect repellents is helpful, as is wearing protective clothing and using bed netting.

Much effort has been made in cleaning the breeding sites (stagnant water) of mosquitoes near people's homes in areas where filariasis is found.

Before visiting countries where lymphatic filariasis is found, it would be wise to consult a travel physician to learn about current preventative measures.

Resources

ORGANIZATIONS

National Lymphedema Network. 2211 Post St., Suite 404, San Francisco, CA 94115. (800) 541-3259. http:// www.hooked.net.

National Organization for Rare Disorders. PO Box 8923, New Fairfield, CT 06812-8923. (800) 999-6673. http://www.rarediseases.org.

KEY TERMS

Antigen Any substance (usually a protein) that causes an immune response by the body to produce antibodies.

Filarial Threadlike. The word "filament" is formed from the same root word.

Host A person or animal in which a parasite lives, is nourished, grows, and reproduces.

Lymph A watery substance that collects in the tissues and organs of the body and eventually drains into the bloodstream.

Lymphatic system A network composed of vessels, lymph nodes, the tonsils, the thymus gland, and the spleen. It is responsible for transporting fluid and nutrients to the bloodstream and for maturing certain blood cells that are part of the body's immune system.

Lymphedema The unnatural accumulation of lymph in the tissues of the body, which results in swelling in that area.

Protozoa (Plural form of protozoan) Single-celled organisms (not bacteria) of which about 30 kinds cause disease in humans.

Streptococcal Pertaining to any of the Streptococcus bacteria. These organisms can cause pneumonia, skin infections, and many other diseases.

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elephantiasis

elephantiasis (ĕl´əfăntī´əsĬs), abnormal enlargement of any part of the body due to obstruction of the lymphatic channels in the area (see lymphatic system), usually affecting the arms, legs, or external genitals. In tropical countries the most common cause is filariasis, infestation with certain filaria, small parasitic roundworms (see worm) of the genera Wuchereria bancrofti or Brugia malayi that are introduced into the body by many species of mosquitoes. The adult worms live in the lymphatic system, causing local inflammation, fibrosis, and obstruction, and resulting in the characteristic enlargement and thickening of the skin. The initial damage done by the worms can be greatly worsened by secondary bacterial and fungal infections.

Recovery from filariasis is possible and surgery sometimes helps, but any elephantiasis that develops during the disease cannot be cured. Ivermectin, an antifilarial drug, has been effective with a single dose. Diethylcarbamazine often kills the adult worms or impairs their reproductive capabilities, and the antibiotic doxycycline, which works by killing symbiotic bacteria that live inside the worms, also eliminates adult worms. Albendazole, in combination with others drugs, is being used in a program of mass drug administration undertaken under the auspices of the World Health Organization in an attempt to eliminate filariasis. Begun in 1999 the program treats an entire population in an attempt to eradicate the worm. Control of mosquitoes also is instrumental in holding down the incidence of the disease. Careful hygiene and other measures that prevent and control subsequent bacterial and fungal infections in limbs or genitals in which the lymphatic system has been damaged can reduce disfigurement and suffering. Blocking of the lymph channels and elephantiasis can also result from lymphogranuloma venereum, a sexually transmitted disease.

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Elephantiasis

Elephantiasis

The Mosquito Carrier

What Happens to People with Elephantiasis?

Resource

Elephantiasis (el-e-fan-TY-a-sis) is the result of a tropical worm infection called filariasis (fil-a-RY-a-sis). When infected mosquitoes transmit the parasitic worm Wuchereria bancrofti to people, the worm blocks the lymphatic system. The blockage causes swelling in the legs or other parts of the body, making these body parts appear large and puffy, or elephant-like. Elephantiasis is not elephant man disease, which is an inherited condition with completely different causes and symptoms.

KEYWORDS

for searching the Internet and other reference sources

Filariasis

Infestation

Lymphatic system

Mosquitoes

Nematodes

Parasites

Tropical diseases

Wuchereria bancrofti

Elephantiasis was known to the early Greeks and Romans. It is a tropical or subtropical disease, occurring where many kinds of disease-carrying mosquitoes are found: South America, Cuba, Puerto Rico, West Indies, Africa, Spain, Turkey, Asia, Australia, and many South Pacific Islands. About 100 million people worldwide are affected.

The Mosquito Carrier

Insects that carry diseases are known as vectors*, and several species of mosquito are vectors of Wuchereria bancrofti, the nematode worm that causes elephantiasis. When a Culex (KYU-lex), Anopheles (a-NOF-e-LEEZ), Aedes (ay-EE-deez), or Mansonia (man-SO-ne-a) mosquito carrying the Wuchereria bancrofti organism bites a human, the mosquito may inject worm larvae* into the body. The tiny larvae then may make their way into the lymph glands and the lymphatic system.

* vectors
are animals or insects that carry diseases and transfer them from one host to another.
* larvae
are worms at an intermediate stage of the life cycle between egg and adult.

Lymphedema

The lymphatic system is a complicated network of very fine tubes, about the diameter of a needle, which criss-cross body tissues to collect a fluid known as lymph. Lymph is a milk-like substance (containing white blood cells, proteins, and fats) that plays an important role in absorbing fats from the intestine, in fighting infections, and in the proper functioning of the immune system. Lymph is returned to the bloodstream via many vessels known as lymphatics. At various points, the lymphatics drain into masses of tissue known as lymph nodes or glands. If a blockage occurs, fluid may collect in the tissues, causing a type of swelling known as lymphedema (limf-e-DEE-ma). In the lymph system draining the legs, for example, few connections exist, and the legs often are a site of swelling when lymphedema occurs.

Lymphatic filiariasis

Worm larvae that make their way into lymph vessels can mature into adult worms. Male worms are long and slender, about 4 to 5 cm long, and 0.1 mm in diameter. Female worms are much larger, 6 to 10 cm long, and about three times wider than the males. The adults make their home mostly near the lymph glands in the lower part of the body. The adult female releases eggs enclosed within an egg membrane (microfllariae), and the microfllariae (mi-kro-fi-LAR-ee-i) develop into larvae to continue the life cycle.

In most parts of the world, microfllariae are at their peak in the blood during the night. The worms restrict the normal flow of lymph, resulting in swelling, thickening of the skin, and discoloration. This is what can cause the appearance of an elephants leg. However, the swelling of elephantiasis usually does not occur until a person has been bitten by the disease-carrying mosquitoes many times and has had years of exposure to infected mosquitoes.

What Happens to People with Elephantiasis?

Symptoms

In addition to the characteristic swelling, people with this disorder sometimes have bouts of fever and headache. Sometimes their swollen limbs become infected.

Diagnosis

Microfilariae sometimes can be seen in blood under a microscope. Often the doctor diagnoses the disorder based on the symptoms and a medical history, after ruling out other disorders with similar symptoms.

The Elephant Man

Joseph John Cary Merrick was known as the Elephant Man, but he did not have elephantiasis.

Born in 1862 in Leicester, England, Merrick became a human attraction in circus side shows. His appearance was normal at birth, but when he was about age 5, he developed extensive overgrowths of skin that affected his face, head, torso, arms, and legs. He was reported to have had a 12-inch wrist and a fin-like hand.

For many years, researchers believed that Merrick had neurofibromatosis (neur-o-fib-ro-ma-TO-sis), a genetic condition that causes large growths on the skin and in tissues. Recent research using x-ray studies, however, suggests that Merrick in fact had Proteus syndrome, a condition so rare that only 100 cases in history have been reported.

Treatment

Medications are not very effective against adult worms. New microfllariae produced by the adult worms often continue to show up months after treatment.

Prevention

Because elephantiasis is found mainly in poorer countries, money for research into the cure and prevention of the disease has been limited. Effective treatment and preventive efforts would include:

  • spraying to kill mosquitoes
  • giving antibiotics to prevent infection
  • giving medications to kill microfllariae circulating in the blood
  • applying pressure bandages to reduce swelling
  • surgically removing infected tissue.

See also

Parasitic Diseases

Worms

Resource

World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland. WHO posts a fact sheet about lymphatic filariasis at its website. http://www.who.org/home/map_ht.html

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elephantiasis

elephantiasis (el-i-făn-ty-ă-sis) n. gross enlargement of the skin and underlying connective tissues caused by obstruction of the lymph vessels. Obstruction is commonly caused by the parasitic filarial worms Wuchereria bancrofti and Brugia malayi. The parts most commonly affected are the legs but the scrotum, breasts, and vulva may also be involved. See also filariasis.

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elephantiasis

el·e·phan·ti·a·sis / ˌeləfənˈtīəsis/ • n. Med. a condition in which a limb or other part of the body becomes grossly enlarged due to obstruction of the lymphatic vessels, typically by the nematode parasites that cause filariasis.

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elephantiasis

elephantiasis Condition in which there is gross swelling of the tissues due to blockage of lymph vessels. It is usually caused by parasitic worms, as in filariasis.

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elephantiasis

elephantiasisglacis, Onassis •abscess •anaphylaxis, axis, praxis, taxis •Chalcis • Jancis • synapsis • catharsis •Frances, Francis •thesis • Alexis • amanuensis •prolepsis, sepsis, syllepsis •basis, oasis, stasis •amniocentesis, anamnesis, ascesis, catechesis, exegesis, mimesis, prosthesis, psychokinesis, telekinesis •ellipsis, paralipsis •Lachesis •analysis, catalysis, dialysis, paralysis, psychoanalysis •electrolysis • nemesis •genesis, parthenogenesis, pathogenesis •diaeresis (US dieresis) • metathesis •parenthesis •photosynthesis, synthesis •hypothesis, prothesis •crisis, Isis •proboscis • synopsis •apotheosis, chlorosis, cirrhosis, diagnosis, halitosis, hypnosis, kenosis, meiosis, metempsychosis, misdiagnosis, mononucleosis, myxomatosis, necrosis, neurosis, osmosis, osteoporosis, prognosis, psittacosis, psychosis, sclerosis, symbiosis, thrombosis, toxoplasmosis, trichinosis, tuberculosis •archdiocese, diocese, elephantiasis, psoriasis •anabasis • apodosis •emphasis, underemphasis •anamorphosis, metamorphosis •periphrasis • entasis • protasis •hypostasis, iconostasis

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Elephantiasis

Elephantiasis

How lymphatic filariasis is spread

Symptoms and progression of filarial disease

Diagnosis

Treatment

Prevention

Resources

Elephantiasis is an extreme symptom of human infection by a type of roundworm or nematode. It involves massive swelling of a limb or of the scrotum. The leg of an individual suffering from elephantiasis can become enlarged to two or three times normal diameter.

The disease or infection that causes elephantiasis is lymphatic filariasis, an important parasitic infection (a parasite is any organism that survives by living within another organism) in Africa, Latin America, the Pacific Islands, and Asia. It infects about 250 million individuals (more than the number suffering from malaria). At one time, there was a small focus of infection that occurred in South Carolina, but this ended in the 1920s.

How lymphatic filariasis is spread

Lymphatic filariasis is caused by infestation by one of three nematodes (Wucheria bancrofti, Brugia malayi, or Brugia timori). These nematodes are spread to humans through mosquito bites. The mosquitoes are considered vectors, meaning that they spread the nematode, and therefore the disease. Humans are considered hosts, meaning that actual reproduction of the nematode occurs within the human body.

The nematode has a rather complicated life cycle. The larval form lives within the mosquito, and it is this form that is transmitted to humans through the bite of an infected mosquito. The larvae pass into the human lymphatic system, where they mature into the adult worm. Adult worms living within the human body produce live offspring, known as microfilariae, which find their way into the bloodstream.

Microfilariae are released into the bloodstream primarily during the night, a property called nocturnal periodicity. Therefore, the vectors (carriers) of filariasis, which deliver the infective worm larvae to the human host, tend to be the more nocturnal (active at night) species of mosquito.

Symptoms and progression of filarial disease

The majority of the suffering caused by filarial nematodes occurs because of blockage of the

lymphatic system. The lymphatic system is made up of a network of vessels that drain tissue fluid from all the major organs of the body, including the skin, and from all four limbs. These vessels pass through lymph nodes on their way to empty into major veins at the base of the neck and within the abdomen. While it was originally thought that lymph flow blockage occurred due to the live adult worms coiling within the lymphatic vessels, it is now thought that the worst obstructions occur after the adult worms die.

While the worm is alive, the human immune system attempts to rid itself of the foreign invader by sending a variety of cells to the area, causing the symptoms of inflammation (redness, heat, swelling) in the infected node and lymph channels. The skin over these areas may become thickened and rough. In some cases, the host will experience systemic symptoms as well, including fever, headache, and fatigue. This complex of symptoms lasts seven to ten days, and may reappear as often as ten times in a year.

After the worms death, the inflammatory process is accelerated, and includes the formation of tough fibrous tissue that ultimately blocks the lymphatic vessel. Lymph fluid cannot pass through the blocked vessel, and the fluid backup results in swelling (also called edema) below the area. Common areas to experience edema are arms, legs, and the genital area (especially the scrotum). These areas of edema are also prone to infection from bacterial agents. When extreme, lymphatic obstruction to vessels within the abdomen and chest can rupture those vessels, spilling lymph fluid into the abdominal and chest cavities.

An individual who picks up filarial disease while traveling does not tend to experience the more extreme symptoms of elephantiasis that occur in people who live for longer periods of time in areas where the disease is common. It is thought that people who live in these areas receive multiple bites by infected mosquitoes over a longer period of time, and are therefore host to many, many more nematodes than a traveler who is just passing through. The larger worm load, as the quantity of nematodes present within a single individual is called, contributes to the severity of the disease symptoms suffered by that individual.

Diagnosis

An absolutely sure diagnosis (called a definitive diagnosis) of filarial disease requires that the actual nematode be identified within body tissue or fluid from an individual experiencing symptoms of infection. This is not actually easy to accomplish, as the lymph nodes and vessels in which the nematodes dwell are not easy to access. Sometimes, blood samples can be examined to reveal the presence of the microfilariae. Interestingly enough, because of the nocturnal periodicity of these microfilariae, the patients blood must be drawn at night to increase the likelihood of the sample actually containing the parasite.

Many times, however, diagnosis is less sure, and relies on the patients history of having been in an area where exposure to the nematode could have occurred, along with the appropriate symptoms, and the presence in the patients blood of certain immune cells which could support the diagnosis of filarial disease.

Treatment

A drug called diethylcarbamazine (DEC) is quite effective at killing the microfilariae as they circulate in the blood, and injuring or killing some of the adult worms within the lymphatic vessels. An individual may require several treatment with DEC, as any

KEY TERMS

Host An animal or plant within which a parasite lives.

Microfilariae Live offspring produced by adult nematodes within the hosts body.

Nocturnal Occurring at night.

Periodicity The regularity with which an event occurs.

Vector Any agent, living or otherwise, that carries and transmits parasites and diseases.

adult worms surviving the original DEC treatment will go on to produce more microfilariae offspring.

As the nematodes die, they release certain chemicals that can cause an allergic-type reaction in the host, so many individuals treated with DEC will also need treatment with potent anti-allergy medications such as steroids and antihistamines. Tissue damage caused by elephantiasis is permanent, but the extreme swelling can be somewhat reduced by surgery or the application of elastic bandages or stockings.

Prevention

Prevention of lymphatic filariasis is very difficult, if not impossible, for people living in the areas where the causative nematodes are commonly found. Travelers to such areas can minimize exposure to the mosquito vectors by using insect repellant and mosquito netting. Work is being done to determine whether DEC has any use as a preventive measure against the establishment of lymphatic filariasis.

See also Roundworms.

Resources

BOOKS

Andreoli, Thomas E., et al. Cecil Essentials of Medicine. Philadelphia: W. B. Saunders Company, 1993.

Berkow, Robert, and Andrew J. Fletcher. The Merck Manual of Diagnosis and Therapy. Rahway, NJ: Merck Research Laboratories, 1992.

Cormican, M.G. and M.A. Pfaller. Molecular Pathology of Infectious Diseases, in Clinical Diagnosis and Management by Laboratory Methods 20th ed. Philadelphia: W. B. Saunders, 2001.

Isselbacher, Kurt J., et al. Harrisons Principles of Internal Medicine. New York: McGraw Hill, 1994.

Mandell, Douglas, et al. Principles and Practice of Infectious Diseases. New York: Churchill Livingstone, 1995.

Prescott, L., J. Harley, and D. Klein. Microbiology. 5th ed. New York: McGraw-Hill, 2002.

OTHER

Davidson College. Dan Heerens Elephantiasis Page <http://www.bio.davidson.edu/Courses/immunology/Students/spring2006/Heeren/eleph.html> (accessed November 21, 2006).

University of Texas Medical Branch, Graduate School of Biomedical Sciences. Medical Microbiology, 4th ed.: Filarial Nematodes <http://www.gsbs.utmb.edu/microbook/ch092.htm> (accessed November 21, 2006).

Rosalyn Carson-DeWitt

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Elephantiasis

Elephantiasis

Elephantiasis is an extreme symptom of human infection by a type of roundworm or nematode. It involves massive swelling of a limb or of the scrotum. The leg of an individual suffering from elephantiasis can become enlarged to two or three times normal diameter.

The actual name of the disease or infection which causes elephantiasis is lymphatic filariasis. Lymphatic filariasis is an important parasitic infection (a parasite is any organism which survives by living within another organism) in Africa , Latin America, the Pacific Islands, and Asia , and causes infection in about 250 million individuals (more than the number suffering from malaria ). At one time, there was a small focus of infection that occurred in South Carolina, but this ended in the 1920s.


How lymphatic filariasis is spread

Lymphatic filariasis is caused by infestation by one of three nematodes (Wucheria bancrofti, Brugia malayi, or Brugia timori). These nematodes are spread to humans through the bite of mosquitoes . The mosquitoes are considered vectors, meaning that they spread the nematode, and therefore the disease. Humans are considered hosts, meaning that actual reproduction of the nematode occurs within the human body.

The nematode has a rather complicated lifecycle. The larval form lives within the mosquito, and it is this form which is transmitted to humans through the bite of an infected mosquito. The larvae pass into the human lymphatic system , where they mature into the adult worm. Adult worms living within the human body produce live offspring, known as microfilariae, which find their way into the bloodstream.

Microfilariae have interesting properties which cause them to be released into the bloodstream primarily during the night; this property is called nocturnal periodicity. Therefore, the vectors (carriers) of filariasis, which deliver the infective worm larvae to the human host, tend to be the more nocturnal (active at night) species of mosquito.


Symptoms and progression of filarial disease

The majority of the suffering caused by filarial nematodes occurs because of blockage of the lymphatic system. The lymphatic system is made up of a network of vessels which serve to drain tissue fluid from all the major organs of the body, including the skin, and from all four limbs. These vessels pass through lymph nodes on their way to empty into major veins at the base of the neck and within the abdomen. While it was originally thought that blockage of lymph flow occurred due to the live adult worms coiling within the lymphatic vessels, it is now thought that the worst obstructions occur after the adult worms die.

While the worm is alive, the human immune system attempts to rid itself of the foreign invader by sending a variety of cells to the area, causing the symptoms of inflammation (redness, heat, swelling) in the infected node and lymph channels. The skin over these areas may become thickened and rough. In some cases, the host will experience systemic symptoms as well, including fever, headache, and fatigue. This complex of symptoms lasts seven to ten days, and may reappear as often as ten times in a year.

After the worm's death, the inflammatory process is accelerated, and includes the formation of tough, fibrous tissue which ultimately blocks the lymphatic vessel. Lymph fluid cannot pass through the blocked vessel, and the back up of fluid results in swelling (also called edema ) below the area of blockage. Common areas to experience edema are arms, legs, and the genital area (especially the scrotum). These areas of edema are also prone to infection with bacterial agents. When extreme, lymphatic obstruction to vessels within the abdomen and chest can lead to rupture of those vessels, with spillage of lymph fluid into the abdominal and chest cavities.

An individual who picks up filarial disease while traveling does not tend to experience the more extreme symptoms of elephantiasis that occur in people who live for longer periods of time in areas where the disease is common. It is thought that people who live in these areas receive multiple bites by infected mosquitoes over a longer period of time, and are therefore host to many, many more nematodes than a traveler who is just passing through. The larger worm load, as the quantity of nematodes present within a single individual is called, contributes to the severity of the disease symptoms suffered by that individual.


Diagnosis

An absolutely sure diagnosis (called a definitive diagnosis) of filarial disease requires that the actual nematode be identified within body tissue or fluid from an individual experiencing symptoms of infection. This is not actually easy to accomplish, as the lymph nodes and vessels in which the nematodes dwell are not easy to access. Sometimes, blood samples can be examined to reveal the presence of the microfilariae. Interestingly enough, because of the nocturnal periodicity of these microfilariae, the patient's blood must be drawn at night to increase the likelihood of the sample actually containing the parasite.

Many times, however, diagnosis is less sure, and relies on the patient's history of having been in an area where exposure to the nematode could have occurred, along with the appropriate symptoms, and the presence in the patient's blood of certain immune cells which could support the diagnosis of filarial disease.


Treatment

A drug called diethylcarbamazine (DEC) is quite effective at killing the microfilariae as they circulate in the blood, and injuring or killing some of the adult worms within the lymphatic vessels. An individual may require several treatment with DEC, as any adult worms surviving the original DEC treatment will go on to produce more microfilariae offspring.

As the nematodes die, they release certain chemicals which can cause an allergic-type reaction in the host, so many individuals treated with DEC will also need treatment with potent anti-allergy medications such as steroids and antihistamines . The tissue damage caused by elephantiasis is permanent, but the extreme swelling can be somewhat reduced by surgery or the application of elastic bandages or stockings.


Prevention

Prevention of lymphatic filariasis is very difficult, if not impossible, for people living in the areas where the causative nematodes are commonly found. Travelers to such areas can minimize exposure to the mosquito vectors through use of insect repellant and mosquito netting. Work is being done to determine whether DEC has any use as a preventive measure against the establishment of lymphatic filariasis.

See also Roundworms.

Resources

books

Andreoli, Thomas E., et al. Cecil Essentials of Medicine. Philadelphia: W. B. Saunders Company, 1993.

Berkow, Robert, and Andrew J. Fletcher. The Merck Manual ofDiagnosis and Therapy. Rahway, NJ: Merck Research Laboratories, 1992.

Cormican, M. G. and M. A. Pfaller. "Molecular Pathology of Infectious Diseases." In Clinical Diagnosis and Management by Laboratory Methods. 20th ed. Philadelphia: W. B. Saunders, 2001.

Isselbacher, Kurt J., et al. Harrison's Principles of InternalMedicine. New York: McGraw Hill, 1994.

Mandell, Douglas, et al. Principles and Practice of InfectiousDiseases. New York: Churchill Livingstone, 1995.

Prescott, L., J. Harley, and D. Klein. Microbiology. 5th ed. New York: McGraw-Hill, 2002.


Rosalyn Carson-DeWitt

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Host

—An animal or plant within which a parasite lives.

Microfilariae

—Live offspring produced by adult nematodes within the host's body.

Nocturnal

—Occurring at night.

Periodicity

—The regularity with which an event occurs.

Vector

—Any agent, living or otherwise, that carries and transmits parasites and diseases.

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"Elephantiasis." The Gale Encyclopedia of Science. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"Elephantiasis." The Gale Encyclopedia of Science. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/elephantiasis-0

"Elephantiasis." The Gale Encyclopedia of Science. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/elephantiasis-0

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Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.