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La Crosse encephalitis See encephalitis.

lassa fever A recently discovered viral infection found in the tropical regions of the world, especially West Africa; epidemics have been recognized in Nigeria, Sierra Leone, and Zaire. The disease is a major public health concern because it is highly contagious and can cause a severe or fatal illness. The rapid spread of the infection has been clearly identified in the case of hospital outbreaks.

Due to the highly contagious nature of this illness and because the mode of transmission is not understood, strict isolation precautions must be followed when this fever is suspected.

Cause The lassa virus has been found in one species of rodent, but the exact mode of transmission to humans is unclear. The virus is found in all body fluids of an infected person and remains in urine for several weeks after recovery.

Symptoms One to three weeks after infection, the symptoms begin with an increasingly high fever, vomiting, cough, and general weakness that lasts for several days.

Diagnosis If a person has traveled to West Africa and has a severe fever within three weeks of the return, the illness should be reported to a physician who would test for lassa fever.

Treatment At the present time there is no known treatment for lassa fever. Symptoms are treated and patients should be made as comfortable as possible. Strict isolation procedures must be maintained.

Legionella pneumophilia A small gram-negative bacterium that causes legionnaires' disease.

Legionellosis Another name for legionnaires' disease.

Legionnaires' disease A bacterial infection that can take one of two distinct forms: Legionnaires' disease or Pontiac fever. Legionnaires' disease is the more severe form of infection, which includes pneumonia; Pontiac fever is a milder illness.

An estimated 10,000 to 15,000 people are diagnosed with Legionnaire's disease each year; an additional unknown number are infected with the Legionella bacterium but rarely have any symptoms. Cases have been identified throughout the United States and in several foreign countries and is believed to occur worldwide.

Outbreaks usually occur in the summer and early fall, but cases may occur year-round. Between 5 and 15 percent of known cases of Legionnaires' disease have been fatal.

Throughout the spring of 1994, about 30 passengers on weekly cruises from New York City to Bermuda came down with the disease; after the cruise ship stopped sailing, the source of infection was discovered to be sand filters used in the whirlpool baths.

People of any age may contract the disease, but it usually affects middle-aged or older people (especially those with chronic lung disease and smokers). Anyone with an impaired immune system or who takes drugs that impair the immune system are at higher risk. Pontiac fever, on the other hand, commonly occurs in healthy individuals and resembles a flulike illness more than pneumonia.

The disease was named for its first identified outbreak, which occurred in 1976 during a Legionnaire convention at the Bellevue-Strat-ford Hotel in Philadelphia; 182 Legionnaires became ill and 29 died. Most of them had pneumonia, and because doctors didn't know what the men had, they called it "legionnaire's disease." In January 1977, scientists identified the bacterium that causes the disease and realized it had also caused outbreaks before 1976; nevertheless, the name remained.

Cause Legionnaires' disease (and a separate variety called Pontiac fever) is caused by the bacterium Legionella pneumophila transmitted by breathing in bacteria carried in water droplets through the air. The bacteria live in water and get into air-conditioning cooling towers and circulate throughout a building.

Outbreaks have occurred after persons have inhaled spray from a contaminated water source (such as air-conditioning cooling towers, whirlpool spas, or showers) in workplaces, hospitals, or other public places. Infection isn't spread from one person to another, and there is no evidence of people becoming infected from auto air conditioners or household window air conditioners.

Legionella can be found in many different water systems, but the bacteria reproduce best in warm, stagnant water such as is found in some plumbing systems and hot water tanks, cooling towers and condensers of large air-conditioning systems, and whirlpool spas.

Symptoms Between 2 and 10 days after exposure, symptoms of fever, chills, and cough appear. The cough may be dry or produce sputum; some patients may also experience muscle aches, headache, fatigue, loss of appetite, and diarrhea.

Symptoms in Pontiac fever usually appear within a few hours to two days.

Diagnosis It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone. Other tests are needed for diagnosis. Lab tests may show decreased kidney function; chest X-rays reveal pneumonia.

A diagnosis requires special tests not normally performed on suspected cases of pneumonia: looking for bacteria in sputum, finding antigens in urine, and comparing antibody levels in two blood samples three to six weeks apart. Experienced doctors are the most important diagnostic tool, since lab tests take several days to months.

Treatment Erythromycin is the recommended antibiotic for Legionnaires' disease; sometimes, rifampin may be used in severe cases. Pontiac fever does not require medication.

Prevention Outbreaks must be reported to the health department. The disease can be prevented by better design and maintenance of cooling towers and plumbing systems in order to limit the growth and spread of bacteria.

After the 1994 outbreaks on a cruise ship, public health officials met with industry representatives and issued more strict health guidelines. The new rules require changing hot tub filters more often, testing the water hourly, raising the chlorination level, and improving maintenance intervals. Consumers booking a cruise can ask their booking agent whether the cruise ship adheres to the new guidelines. It is also possible to find out how a ship scored on its most recent sanitary inspection by writing to the U.S. Public Health Service, 1015 N. America Way, Ste. 107, Miami, FL 33132. A score of more than 86 is acceptable.

Leishmania A genus of protozoan parasite transmitted to humans by any of several species of sand flies. Infestation causes one of a variety of diseases called LEISHMANIASIS.

leishmaniasis A variety of diseases that affect the skin and mucous membranes caused by infection with single-celled parasites. More than 350 million people in 88 countries of the world are presently at risk; 12 million people are already affected by the disease, which is fatal in one form.

At least three types of the disease affect the skin, one is common in the Middle East,

North Africa, and the Mediterranean; the others are found in Central and South America.

Cause The parasites that transmit the infection belong to the genus Leishmania, a protozoa transmitted by the bite of a tiny insect called the phlebotomine sand fly. Of 500 known species, only 30 of them carry the disease, and only the female sand fly transmits the protozoan, infecting itself with the parasites contained in the blood it sucks from its host. During a period of 4 to 25 days, the parasite continues its development inside the sand fly, where it is transformed. When the infectious female sand fly feeds on a fresh source of blood, its sting inoculates its new victim with the parasite.

The sand fly is found throughout the tropical and temperate regions of the world. The female lays its eggs in the burrows of rodents, in the bark of old trees, ruined buildings, cracks in house walls, and in rubbish.

Symptoms There are several types of this disease, with a wide range of symptoms. The visceral type—also known as kala azar—is characterized by irregular bouts of fever, weight loss, swelling of spleen and liver, and anemia. Untreated, this form of leishmaniasis is fatal almost 100 percent of the time. In mucocutaneous leishmaniasis, lesions can partially or completely destroy the mucous membranes of the nose, mouth, and throat and can cause severe disfigurement. The cutaneous form of the disease produces skin ulcers on exposed parts of the body such as the arms, legs, and face, causing many lesions (sometimes up to 200) and severe disability. Most of the time the patient is permanently scarred.

Treatment It is essential to understand the different geographic strains of the different parasites in order to properly treat the disease. All forms of this disease can be treated effectively with drugs (such as sodium stibogluconate or glucantime) given by injection. All types of this disorder with secondary bacterial infection should also be treated with antibiotics.

Prevention No effective vaccine currently exists. Insect control is important in the control of the disease.

leprosy A chronic bacterial infection (also called Hansen's disease) that damages nerves in the skin, limbs, face, and mucous membranes. Untreated leprosy can lead to severe complications, which can include blindness and disfigurement, but leprosy can be cured with proper medication. Contrary to popular belief, it is not highly contagious. While the disease still carries a significant stigma, patient care has become integrated with routine health care. Anti-leprosy organizations have fought to repeal stigmatizing laws and practices; patients are no longer referred to as "lepers."

Although leprosy is one of the oldest diseases in human history, it was not until 1873 that Armauer Hansen first identified the bacilli under a microscope. Today there are about 20 million leprosy patients in 87 countries, primarily in Asia, Central and South America, and Africa, but probably fewer than 20 percent have access to treatment. India has the highest prevalence of leprosy, followed by Brazil. In the United States, there are more than 6,000 known cases. Most are found in California, Florida, Hawaii, Louisiana, New York, and Texas. There are about 200 new cases each year in the United States, and 12,000 new cases each week around the world. Approximately 16 percent of the new cases of leprosy are children.

History Ancient religious traditions associated with leprosy continued to influence social policy well into the 20th century. Leprosy was first mentioned as a curse in Shinto prayers of 1250 B.C.; it was also mentioned in some Egyptian legends to explain the exodus of the Hebrews. For hundreds of years, those with leprosy were taken to a priest, not a doctor, and were found "guilty," not sick.

These customs led to the forcible confinement of patients in "leprosaria" or leper colonies; their children, whether infected or not, were denied an education in community schools. In eighth-century France, leprosy was considered grounds for divorce, and the Roman empire enforced banishment. Some countries passed legislation providing for the compulsory sterilization of leprosy patients because of fears that the condition was hereditary. Others would not permit patients to handle the nation's currency. Others "steam treated" patients' letters before allowing them in the mail, and some countries did not allow patients to vote. In medieval Europe, leprosy patients had to carry a "clapper" to warn others that a person with leprosy was approaching. Even as late as 1913, state Senator G. E. Willett of Montana was forced to give up his seat after he was diagnosed with leprosy.

Religious customs also affected many treatments for leprosy. In 250 B.C., Chinese patients pricked their swollen limbs to let out the "foul air." Ramses II of Egypt believed that people with leprosy who used his water wells would be cured. And in medieval Europe, it was believed that leprosy could be cured by the touch of a king.

Historically, topical treatments ranged from turtle soup, whiskey, and various poultices (onion, sea salt, and urine in Egypt; arsenic and powdered snake bones in China; water mixed with blood of dogs and infants under age two in Scotland; elephants' teeth; the flesh of crocodiles, snakes, lions, and bears). Other ingredients ranged from carbolic acid, creosote, phosphorus, mercury, and iodine, and plant extracts included madar, cashew-nut oil, gurjum oil, or chaulmoogra.

The idea of caring for patients with leprosy became popular among missionaries following Biblical directives and the teachings of Jesus; this service became fashionable about A.D. 1100 in Europe, after Crusaders (including a king) returned with the disease. Special hospitals were built, operated, and supported by cathedrals, but when the outbreak of Bubonic Plague in the 1300s wiped out entire populations, patients with leprosy began to be segregated again. Some countries seized the property of those with leprosy before burning them alive.

Leprosy is erroneously associated with the Old Testament, where references to tsara'ath, a term that most closely translates to "leprosy," actually refers to a broad spectrum of problems that affected cloth, leather, linen, and house walls as well as humans. Most medical historians doubt that leprosy even existed among the Hebrews in Moses' time. Biblical scholars also have problems with the translation of the Greek term lepra partly because the Greeks had a specific term for leprosy. The Greek word lepra was most likely used to mean a variety of severe skin diseases. Greek medical writings later than the third century B.C. provide the earliest clinical references to modern leprosy. No mention of leprosy occurs in the New Testament after the Gospels.

Cause Leprosy is caused by a rod-shaped bacterium, MYCOBACTERIUM LEPRAE, that is spread in droplets of nasal mucus. A person is infectious only during the first phase of the disease, and only those living in prolonged close contact with the infected person are at risk. Leprosy is probably spread by droplet infection through sneezing and coughing. In those with untreated leprosy, large amounts of bacteria are found in nasal discharge; the bacteria travel through the air in these droplets. They can survive three weeks or longer outside the human body, in dust or on clothing.

Although relatively infectious, leprosy is still one of the least contagious of all diseases. This—together with the fact that only 3 percent of the population are susceptible to leprosy—means that there is no justification for the practice (still prevalent in some countries) of isolating patients. Only a few people are susceptible because most people acquire a natural immunity when exposed to the disease.

Most of the body's destruction is caused not by bacterial growth but by a reaction of the body's immune system to the organisms as they die. In lepromatous leprosy, damage is widespread, progressive, and severe. Tuberculoid leprosy is a milder form of the disease.

Symptoms Damage is first confined to the nerves supplying the skin and muscles, destroying nerve endings, sweat glands, hair follicles, and pigment-producing cells. It first causes a lightening (or darkening) of the skin, with a loss of feeling, and sweating. Some types of the disease produce a rash of bumps or nodules on the skin. As the disease progresses, bacilli also attack peripheral nerves; at first patients may feel an occasional "pins and needles" sensation or have a numb patch on the skin. Next, patients become unable to feel sensations such as a light touch or temperature. Gradually, even hands, feet, and facial skin eventually become numb as muscles become paralyzed. Delicate connections between nerve cells and nerve endings are severed, and whole sections of the body become totally numb. For example, if the nerve above the elbow is affected, part of the hand becomes numb and small muscles become paralyzed, leading to curled fingers.

When a patient can no longer sense pain, the body loses the automatic withdrawal reflex that protects against trauma from sharp or hot objects, leading to extensive scarring or even loss of fingers and toes. Muscle paralysis can lead to further deformity, and damage to the facial nerve means eyelids can't close, leading to ulceration and blindness. Direct invasion of bacteria may also lead to inflammation of the eyeball, also leading to blindness.

Treatment Several antibiotic agents are effective against leprosy and are best used in combinations of two or three. This multidrug therapy is the current preferred treatment: it combines dapsone, clofazimine, and rifampin. Multi-drug therapy was developed as leprosy bacilli became resistant to the sulfone drug dapsone alone after decades of constant use.

The most powerful of these three drugs is rifampin, a drug first used against tuberculosis and found to be effective against leprosy in 1968. Particular combinations of these drugs were recommended in 1984 by the World Health Organization as standard treatment for mass campaigns against leprosy.

The three drugs are often distributed in blister packs containing a month's supply of pills; dapsone is taken daily, clofazimine is taken every other day, and rifampin is taken monthly. Now there are more than 1 million people receiving these drugs worldwide, and more than 1 million others who have already completed treatment.

While the medication can usually cure leprosy within six months to two years, patients are no longer contagious within a few days after treatment begins. To prevent a relapse, treatment needs to be administered for at least two years after the last signs of the disease have disappeared. In the United States, patients are eligible for treatment by the Public Health Service at special clinics and hospitals, or at the Gillis W. Long Hansen's Disease Center in Louisiana, the only institution in the United States devoted primarily to treatment, research, training, and education related to leprosy. Eleven regional centers, located primarily in major urban areas, treat those with leprosy on an outpatient basis.

No vaccine for leprosy is available because scientists have not been able to grow cultures in lab environments. However, about 95 percent of the population is immune to leprosy, which occurs naturally in armadillos.

Post-treatment care After leprosy is cured, patients must learn to watch for wounds and injuries they cannot feel and must wear special shoes to protect insensitive feet.

leptospirosis A bacterial disease characterized by a skin rash and flulike symptoms caused by a spirochete bacterium excreted by rodents. Also known as autumn fever, there are about 100 cases and a few deaths reported in the United States each year. Leptospirosis is considered to be a disease that is reemerging in this country and is possibly the most common disease that rats carry and transmit to humans in the United States. There are several strains of the organism; infection with one usually provides immunity to that organism alone, but not to other strains.

Although the disease is not new in the United States, it is hard to diagnose and its prevalence may be unknown. Those especially at risk are urban patients who complain of flulike symptoms (especially during the summer) and who could have been exposed to rat urine or to pools of infected water in alleys and parks of the inner city.

Unrecognized leptospirosis might be common in city dwellers; one 1992 Baltimore study found 16 percent of blood samples taken at an STD clinic were positive for leptospirosis. An earlier study found that about a third of children tested in Detroit also had been exposed. None of the inner-city patients had been diagnosed with leptospirosis.

Cause The infectious disease is caused by the spirochete Leptospira interrogans transmitted in the urine of wild or domestic animals, especially rats, livestock, and dogs. People get the disease when broken skin or mucous membranes contact the infected urine or water, soil, or vegetation. The bacteria survive best in warm water (72 degrees F) that is stagnant; most cases have been reported from swimming, wading, or splashing in pools, streams, or puddles that were contaminated with animal urine.

In addition to urban dwellers, leptospirosis is an occupational disease of farmers, sewer workers, or others whose job requires contact with animals (especially rats). Most victims are male teenagers and young adults. Leptospirosis is not usually transmitted from person to person.

Symptoms Leptospirosis has two phases. After an incubation period of up to three weeks, the first phase begins with an acute ill ness of sudden headache, fever and chills, severe muscle aches, and skin rash appears. Up to 10 percent of infected patients develop a serious systemic form of the illness, called Weil's syndrome. This phase starts a few days after the fever drops; fever will return and bacteria may spread to the brain, causing MENINGITIS. Other serious symptoms include jaundice, confusion, depression, or decreased urine. The kidneys are often affected, and liver damage is common. People infected with this potentially fatal form of leptospirosis are usually very ill and are often hospitalized.

Leptospirosis is often mistaken for viral meningitis or HEPATITIS, but its two distinct phases separate it from those infections.

Diagnosis The disease is diagnosed using specific blood, urine, or fluid tests available through state public health laboratories. If positive, they are sent to the Centers for Disease Control and Prevention lab for confirmation. However, it takes up to a month to get a final determination. A physician must request such testing; it is not routinely done, and local labs do not ordinarily perform these tests. However, researchers have developed an experimental test that can detect within 24 hours tiny amounts of the bacterium's genetic material. The test has not yet been validated.

Treatment Tetracycline and erythromycin are effective, and in about one third of cases patients improve rapidly. Fluid replacement is essential if jaundice or other signs of severe illness occur. Kidney dialysis may be needed in some cases.

Complications Untreated patients may develop Weil's syndrome, a severe form of leptospirosis that can cause permanent kidney and liver damage; most patients recover, but sometimes the disease is fatal.

Prevention The disease can be prevented by good sanitation practices, including using boots and gloves in hazardous places and practicing rodent control. It is common practice to immunize livestock and dogs against the disease, but even vaccinated animals can shed the bacteria in urine for a long time and infect humans.

lice Small wingless insects about the size of a sesame seed, with six legs and claws for grasping the hair; they feed on human blood. Lice are crawling insects that cannot jump or fly. Lice are divided into three species: Pedicu-lus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Phthirius pubis (the crab, or pubic louse). All three have flat bodies that measure up to 3 mm across.

Head lice live on and suck blood from the scalp, leaving red spots that itch intensely and can lead to skin inflammation (dermatitis) and skin infection (impetigo). The females lay a daily batch of pale eggs, called "nits" that attach to hairs close to the scalp; the nits hatch in about a week, and the adults can live for several weeks.

Head lice are not simply a plague of the poor, but are found among people of all walks of life. About 6 million cases of head lice occur each year among U.S. schoolchildren between ages 3 and 12, even among those who shampoo daily. Children are most often affected by contracting the lice through direct contact, usually at school by sharing hats, brushes, combs, or headrests. Pets cannot get head lice.

Because lice move so quickly, it is usually the nits that will be seen on the hair shaft. Nits are the tiny eggs of a louse that are yellow when newly laid, turning to white once they hatch. Nits are small, oval-shaped eggs that are "glued" at an angle to the side of the hair shaft. They hatch within eight days, and the empty eggshells are carried outward as the hair grows. Both head and pubic lice lay eggs at the base of hairs growing on the head or pubic area. Nits can be seen anywhere on the hair, especially behind the ears and at the back of the neck.

Nits should not be confused with hair debris, such as fat plugs or hair casts. Fat plugs are bright white irregularly shaped clumps of fat cells stuck to the hair shaft. Hair casts are thin, long cylinder-shaped segments of dandruff encircling the hair shaft; they are easily dislodged.

Lice infestations are diagnosed by the presence of nits; by calculating the distance from the base of the hair to the farthest nits, it's possible to estimate the duration of the infestation.

All nits must be removed, according to the National Pediculosis Association. Since no lice pesticide kills all nits, any nits left on the hair can be confusing; thorough nit removal will reduce or eliminate the need for more treatments.

Nits can be removed with a special nit removal comb, with baby safety scissors, or with the fingernails.

Head lice and their nits can also be found on eyebrows and eyelashes. If one person in a family has head lice, all family members should be checked. However, only those who are infested should be treated with lice pesticide.

Body lice live and lay eggs on clothing next to the skin, visiting the body only to feed. Body lice affect people who rarely change their clothes.

Crab lice live in pubic hair or (rarely) armpits and beards. Pubic lice are commonly known as "CRABS" because they resemble a crab under the microscope. Crab lice cause incessant itching, are visible to the naked eye, and are easily transmitted during sex. It's also possible to pick them up from sheets or towels. They can live away from the host's body for up to one day, and the eggs can survive for several days. Affected patients who don't wash underwear, sheets, and towels in hot enough water are likely to be reinfected.

Treatment For head lice, lotions containing malathion or carbaryl kill lice quickly; the lotion should be washed off 12 hours after application, followed by combing the hair with a fine-toothed comb to remove dead lice and nits. Shampoos containing malathion or carbaryl are also effective if used repeatedly

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