Around the Rio Dulce area, the occurrence of tropical diseases is quite rare but isolated cases of intestinal problems, malaria and dengue fever will occasionally crop up. Some years ago there was a minor outbreak of cholera in the Fronteras area. The solution is simply this: 1) Under no circumstances should you drink the river water. 2) Don't bathe in the river near or downstream of heavily populated areas, ie. Fronteras.
Some have expressed a general interest in tropical diseases and have complained of the lack of information about such diseases. To satisfy this need the following general overview of tropical diseases worldwide is included here. Some of the diseases covered below do not occur in Central America but are included to satisfy the curious. Readers with a taste for the macabre may be especially interested in the news-clip about the Ebola virus.
Tropical diseases are illnesses that either occur uniquely in tropical and subtropical regions (which is rare) or, more commonly, are either more widespread in the tropics or more difficult to prevent or control. The tropics are more problematic for certain diseases for two reasons: 1) Tropical climates are more conducive to certain diseases. 2) Areas of poverty and primitive sanitation conditions are more common in the tropics. The agencies most concerned with improving health in tropical countries include the World Health Organization (WHO) and the Edna McConnell Clark Foundation.
Diseases Most Prevalent in the Tropics
The most important diseases in the tropical regions of Southeast Asia, Africa, and South America are malaria, schistosomiasis, leprosy, filariasis, trypanosomiasis, and leishmaniasis. Although effective chemotherapy and insecticides have reduced or eliminated malaria in most of the western hemisphere, these measures have been less successful in Asia. Both the infecting parasite and its mosquito carrier have become resistant to current drugs and 200 million persons are estimated to have malaria in tropical areas. In sub-Saharan Africa some 1 million children under five die of the disease each year.
Schistosomiasis has never been common in temperate climates, but it affects 125 million persons worldwide, of whom approximately 20 percent are at least partly disabled by the disease. Praziquantel, a highly effective new drug, is now available for treatment of schistosomiasis. Leprosy has also always been more common in tropical than in moderate climates, and about 11 million persons in the world have this illness. In endemic areas many severe cases of leprosy are now resistant to the drug first used against it, and newer, more expensive therapy must be employed. Filariasis is a common tropical debilitating illness caused by infection with roundworm larvae. Trypanosomiasis, which results from infection with a protozoan parasite, has caused 10 million cases of human sickness in Africa alone. A related protozoan in South America causes a less deadly form of trypanosomiasis called Chagas' disease. Leishmaniasis is also a result of worm infection, and in its Asian and African forms the disease can damage the internal organs.
Additional Health Problems
Although tuberculosis is largely under control in developed countries, it is still a considerable public health problem in much of the world and is responsible for about half a million deaths annually, 75 percent of them in Asia. Other diseases for which treatment is available but which are still common in developing countries include cholera, yellow fever, yaws, and amoebic dysentery (see Dysentery).
Two forms of cancer, Burkitt's lymphoma and liver cancer, are very common in Africa and Asia, respectively, although rare in temperate zones. Burkitt's lymphoma is thought to be due to a combination of massive infection with a virus early in life and malaria in adulthood. Liver cancer may be caused by infection with the hepatitis B virus.
As many as 25 million persons have become blind from preventable diseases in tropical countries. These diseases include xerophthalmia, due to lack of vitamin A in the diet; onchocerciasis, or river blindness, an infection of the skin by filarial larvae that may also affect the conjunctiva of the eye; and trachoma, a chronic conjunctival infection caused by the parasitic bacterium Chlamydia trachomatis, which is transmitted by flies or through close personal contact.
Finally, a number of severe virus-caused fevers that were identified during the 1970s are found predominantly in tropical regions. These diseases include Lassa, Ebola, Marburg, Bunya, and Chikungunya fevers, some of which cause death by hemorrhage (hemorrhagic fever). One member of this family, dengue virus (see Dengue Fever), was known for many years but has recently spread to the Caribbean and Mexico. All these diseases are rare.
Factors Which Aggravate Tropical Diseases
The severity of diseases in tropical areas is due to widespread poverty and poor sanitation as well as climatic influences. That is, because of low national incomes, most developing countries cannot afford to buy vaccines to prevent poliomyelitis, measles, and yellow fever. Only about 10 percent of the 80 million children in poor countries have been immunized against diphtheria, whooping cough, and tetanus, and such countries cannot afford to distribute drugs against tuberculosis or leprosy. Poverty is a condition that also leads to malnutrition, which makes people more susceptible to disease.
Poor sanitation is especially to blame for the spread of cholera, in which the infecting agent is transmitted through contaminated sewage; and schistosomiasis, in which the intermediate vector, a snail, lives in contaminated water.
Climate indirectly makes disease in tropical regions more severe by reducing agricultural production, which increases the risk of malnutrition. In a more direct way, hot weather and humid forests favor growth of the flies and mosquitoes that transmit malaria, yellow fever, dengue fever, trachoma, trypanosomiasis, and onchocerciasis.
Malaria, sometimes called "frios" (chills) in Guatemala, is a disease of animals, especially birds, monkeys and humans, caused by infection by protozoans of the genus Plasmodium and characterized by chills and intermittent fever. The causative organisms of human malaria are transmitted by the bite of about 60 species of mosquitoes in the genus Anopheles. The disease may occur in subtropical and tropical regions in almost all parts of the world as well as in other temperature areas. With the advent of control programs based on the use of residual insecticides, the distribution of malaria changed rapidly. Since 1950 malaria has been eliminated from almost all of Europe and from large areas in Central and South America. It remains a major problem in parts of Africa and in southeastern Asia. About 100 million cases of human malaria develop each year and about 1 million of those (1 percent) are fatal.
Malaria in Humans
Human malaria occurs in four forms, each caused by a different species of parasite. In each form, the symptoms usually are chills, fever and sweating. In untreated cases, these attacks recur periodically. The mildest form of malaria is benign tertian malaria, caused by Plasmodium vivax, in which the fever may occur about every second day after the initial attack (which may occur within two weeks after infection). Jungle fever, malignant tertian malaria, or estivo-autumnal malaria, caused by Plasmodium falciparum, is responsible for most of the deaths from malaria. The organisms in this form of the disease often block the blood vessels of the brain, producing coma, delirium, and finally death. Quartan malaria, caused by Plasmodium malariae, has a longer incubation period than either tertian malaria or jungle fever; the first attack does not appear until 18 to 40 days after infection. The attacks recur about every third day. The fourth and rarest form of the disease, caused by Plasmodium ovale, is similar to benign tertian malaria. In all forms of the disease, periodic fevers may be less regularly spaced in some people.
During the incubation period of malaria, the protozoan grows within cells in the liver; a few days before the first attack, the organisms invade the red blood cells, which they destroy in the course of their development, producing the typical febrile attack.
History of Malaria
Since 1638 malaria has been treated with an extract from the bark of the cinchona tree, known as quinine. Quinine, which is somewhat toxic, suppresses the growth of protozoans within the bloodstream. In 1930, German chemists synthesized Atabrine, which is more effective than quinine and less toxic. A new drug, chloroquine, that became available at the end of World War II in 1945, was found to be capable of preventing and curing jungle fever completely and to be much more effective in suppressing the other forms of malaria than Atabrine or quinine. It also had a much lower toxicity than any of the earlier drugs and was effective in less frequent doses.
Recently, strains of Plasmodium falciparum, the organism that causes jungle fever, have shown resistance to chloroquine and other synthetic antimalarial drugs. These strains are encountered most frequently in Vietnam, and also in the Malay Peninsula, Africa, and South America. Quinine is still the agent used against Plasmodium falciparum strains resistant to synthetics. In addition to the occurrence of strains of drug-resistant parasites, the fact that some vector mosquitoes (Anophelines) have become resistant to insecticides such as DDT has led to an upsurge of malaria in certain tropical countries. As a result, malaria has increased among American and Western European travelers to Asia and Central America and among refugees from these areas.
Currently, work is progressing on the development of a malaria vaccine. Several vaccine candidates are now undergoing clinical trials for safety and effectiveness in human volunteers, and scientists look forward to having a vaccine for general distribution.
Cholera is a severe infectious disease endemic in India and some other tropical countries and occasionally spreading to temperate climates. The symptoms of cholera are diarrhea and the loss of water and salts in the stool. In severe cholera, the patient develops violent diarrhea with characteristic "rice-water stools," vomiting, thirst, muscle cramps, and sometimes circulatory collapse. Death can occur as quickly as a few hours after the onset of symptoms. The mortality rate is more than 50 percent in untreated cases, but falls to less than 1 percent with proper treatment.
The causative agent of cholera is the bacterium Vibrio cholerae, which was discovered in 1883 by the German physician and bacteriologist Robert Koch. Virtually the only means by which a person can be infected is from food or water contaminated by bacteria from the stools of cholera patients. Prevention of the disease is therefore a matter of sanitation. Cholera epidemics swept through Europe and the United States in the 19th century but did not recur in those areas after improvement of the water supply.
Control of the disease is still a major medical problem in several Asian countries. The World Health Organization (WHO) estimates that 78 percent of the population in less developed countries is without clean water and 85 percent without adequate fecal waste disposal. Epidemics of cholera occurred in 1953 in Calcutta, India; between 1964 and 1967 in South Vietnam; among Bangladeshi refugees fleeing to India during the civil war of 1971; and in Peru in 1991. The 1971 outbreak killed about 6500 persons.
Treatment consists mainly of intravenous or oral replacement of fluids and salts. Packets for dilution containing the correct mixture of sodium, potassium, chloride, bicarbonate, and glucose have been made widely available by the WHO. Most patients recover in three to six days. Antibiotics such as tetracyclines, ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole can shorten the duration of the disease.
A vaccine made from killed bacteria is commercially available and offers partial protection for a period of three to six months after immunization. Experimental studies have shown that the cholera bacterium produces a toxin that causes the small intestine to secrete large amounts of fluid, which leads to the fluid loss characteristic of the disease. This has led to work on a vaccine containing inactivated toxin. Attempts are also being made to develop a vaccine containing live bacteria that have been altered so that they do not produce the toxin.
Dysentery is an acute or chronic disease of the large intestine of humans, characterized by frequent passage of small, watery stools, often containing blood and mucus, accompanied by severe abdominal cramps. Ulceration of the walls of the intestine may occur. Although many severe cases of diarrhea have been called dysentery, the word properly refers to a disease caused by either a specific amoeba, Entamoeba histolytica, or a bacillus that infects the colon.
Amoebic dysentery, caused by the parasite Entamoeba histolytica, is endemic in many tropical countries, but is attributable more to unsanitary conditions than to heat. It is the most common type of dysentery in the Philippine Islands, the Malay Archipelago, and the West Indies, but it also occurs in almost all temperate countries including the U.S.
Amoebic dysentery is most commonly spread by water or contaminated, uncooked food or from carriers. Flies may carry the cysts to spread the amoeba from the feces of infected persons to food.
Various drugs, including metronidazole, ementine, and iodine-containing preparations, have been useful in treating severe cases of the disease.
Bacillary dysentery is caused by certain nonmotile bacteria of the genus Shigella. This form of dysentery is also most prevalent in unhygienic areas of the Tropics, but, because it is easily spread, sporadic outbreaks are common in all parts of the world. This dysentery is usually self-limiting and rarely manifests the more severe organ involvements characteristic of amoebic dysentery. Bacillary dysentery is spread by contaminated water, milk, and food. Feces from active cases and those from healthy carriers as well contain immense numbers of the disease-producing bacteria. Flies carry the bacteria on their feet or in their saliva and feces and deposit them on food; ants are also believed to spread the disease.
In the treatment of bacillary dysentery, proper replacement of fluid is important. Sulfonamides, tetracycline, and streptomycin were effective in curing acute cases until drug-resistant strains emerged. Chloramphenicol is sometimes used to treat these strains. Quinolones such as norfloxacin and ciprofloxacin are also effective against Shigella infection.
The following is included courtesy of Dana Tucker, LPN, Resident Nurse at the Ak'Tenamit Clinic, Rio Dulce, Guatemala.
Diarrhea: The causes of diarrhea in the tropics are many and include viral or bacterial infections, amoebas, giardia, food poisoning and worm infestation (though worms rarely cause diarrhea). All may be prevented by careful selection of food and water sources. Eat foods that have been well cooked, not reheated. All raw foods, such as fruits and vegetables should be washed thoroughly and peeled. Only drink water that has been boiled and filtered or treated with iodine/chlorine compounds.
What should you do if you have diarrhea?
For most cases, no medicine is needed. The most important concept is to ensure adequate fluid replacement with broths, sweetened drinks or oral rehydration salts (a homemade version is 1/2 tsp. salt to 8 tsp. sugar in one liter of clean water). Start bland foods such as rice, crackers, bananas and potatos in small portions as soon as the patient is able to eat.
When is specific treatment indicated?
If diarrhea is bloody and/or associated with mucus, comes on slowly and is not associated with fevers, it may be caused by amoebas. Treatment with EXAMEB (2 grams in a single oral dose) or METRONIDAZOLE (35 to 50 mg per kilogram of body weight per day for 10 days).
If the diarrhea is yellow in color with bubbles of froth and associated with gas in the belly but no fever, it may be caused by giardia (a microscopic intestinal parasite). Treatment: EXAMEB as above or METRONIDAZOLE (15 mg per kilogram of body weight per day for 5 days).
When is it important to seek medical help?
1) When there is a rapid onset of bloody diarrhea associated with high fever.
2) "Rice water" stools in very large volumes may be a sign of cholera which requires antibiotics and aggressive rehydration.
3) Diarrhea associated with vomiting can be serious if the individual cannot hold down liquids; children are especially at risk for dehydration in this situation.
4) In any case, if the diarrhea lasts for more than 4 days and shows no signs of improvement or the patient appears significantly dehydrated (dry mouth, little or no urine, "loose" skin), seek medical help at once.
Roundworm and nematode are the common names for any of a phylum of unsegmented terrestrial, freshwater, or marine worms. Roundworms are almost worldwide in distribution and are abundant in the surface layers of soils. Many of them are economically and medically harmful, living as parasites in plants and animals, including humans. Roundworm infections are common and frequently go unnoticed, but several species cause serious diseases.
Roundworms are cylindrical, tapering animals with simple bodies consisting of an interior gut and a muscular outer wall, separated by a fluid-filled cavity called a pseudocoel. The outer wall secretes an elastic cuticle that is molted four times during the animal's lifetime. Species range in size from microscopic to about 10 cm (about 4 in) long. Most species have separate sexes, but a few are hermaphroditic; fertilization is internal. The young roundworms, which resemble the adults, develop without metamorphosis.
Classification of the approximately 12,000 known species of roundworms-many thousands of unknown species are suspected-is a subject of some controversy among zoologists. Many include the Gordian worms as a subclass, but others group them separately. Although numerous roundworms are free-living, the parasitic forms are of greatest economic interest. One important group, the ascaroid nematodes, includes the threadworms and the common worm of puppies. Another contains the eelworms, which produce root knot of cotton, and forms that produce earcockle of wheat. Other, medically significant forms of roundworm include the various genera known as hookworm; the filaria, which cause elephantiasis; the trichina worm, the cause of trichinosis; and the whipworm, which infests the human intestine.
Roundworms make up the phylum Nematoda. Threadworms belong to the genus Ascaris. The common worm of puppies is classified as Toxocara canis. Eelworms belong to the genus Heterodera, the forms that produce earcockle of wheat belong to the genus Tylenchus, and the trichina worm belongs to the genus Trichinella. The human whipworm is classified as Trichuris trichiura.
Flatworm is the common name for soft-bodied, usually parasitic animals, the simplest of animals possessing heads. They are bilaterally symmetrical and somewhat flattened, and most are elongated. Three main classes are included in the flatworm phylum: tapeworms, which in the adult stage are parasitic in the digestive tracts of animals; flukes, which are parasitic in various parts of different animals; and planarians, which are free-living and nonparasitic. Some authorities include a group of unsegmented marine worms. Other authorities consider them a separate phylum.
The ectoderm (outer surface) of the free-living flatworms is usually covered with cilia; in the parasitic forms the ectoderm usually secretes a hardened material called cuticle. A well-developed musculature, found directly under the epidermis (skin layer), allows the body to expand and contract, thus changing the body shape to a remarkable degree. Vivid pigmentation is sometimes present in the free-living forms, but the parasitic forms are usually unpigmented. Flatworms have no true body cavity; the spaces between the organs are filled with a compact connective tissue called parenchyma. Except in the simplest forms, one end of the body is more specialized for sensory perception, and locomotion takes place in the direction of specialization. The oral and genital openings are on the ventral (under) side. When present, the digestive tract is either saclike or branched and has only one opening. This opening may be equipped with a sucker, as in the flukes, or, as in most planarians, it may have a well-developed pharynx. The nervous system consists of a network with a large ganglion (brain) and various longitudinal nerve cords forming the principal parts. Sensory cilia and "eye spots" may be present in the free-living forms and in the larvae of the parasitic forms. The flatworm has no blood or vascular system. Specialized cells possessing cilia, called flame cells, lead from the interior to one or more openings in the exterior by means of a network of tubes. Together these structures form the excretory system. The reproductive system is highly complex and occupies a large portion of the interior of the animal. Although flatworms are almost all hermaphroditic (both male and female reproductive organs are present in each individual), the eggs and sperm are formed separately. These germ cells either leave the body by separate openings or enter a common chamber, called the genital atrium. Flatworms also are able to reproduce asexually both by binary fission-that is, by pinching themselves apart to become two-and by regeneration, producing an entire new worm from a piece that has been cut off.
Free-living flatworms are found in almost every kind of environment, on land and in fresh and salt water. These forms feed mainly on plankton. The parasitic flatworms often display a complicated life cycle, which may require development in four or five hosts before completion.
Flatworms constitute the phylum Platyhelminthes. Tapeworms constitute the class Cestoda. Flukes constitute the class Trematoda. Planarians constitute the class Turbellaria.
The following is courtesy of Dana Tucker, LPN, Resident Nurse at the Ak'Tenamit Clinic, Rio Dulce, Guatemala.
Intestinal worms are a fact of life for the indigenous populations of Central America and for travelers in the area. Prevention is once again the key. Many are passed through contaminated food and water; the cleanliness of these sources must be ensured. Others are acquired through poorly cooked meat or fish; eat only well cooked foods. Still others may pass through an individual's bare feet; wear shoes at all times.
Most cases of intestinal worms are not associated with specific signs or symptoms. Due to the prevalence of these parasites, we recommend treatment with MEBENDAZOLE (100 mg. orally twice a day for 3 days) every three months while in the region. Mebendazole is preferred over other agents widely available as it is the only one that will kill both the worm and egg stages.
Dengue fever, also called "breakbone fever", is an infectious tropical disease characterized by fever, extreme pain in the joints and muscles, and a skin eruption. The causative agent is a filterable virus transmitted from one person to another by AŽdes mosquitoes. Dengue is endemic in some parts of the tropics and has occurred in epidemic form in both tropical- and temperate-zone countries. It is seldom fatal and usually runs its course in 6 to 7 days, but convalescence is usually slow. No specific treatment for dengue is known.
Yellow fever is a noncontagious, infectious disease, caused by a virus, and characterized in severe cases by high fever and jaundice. Originally, yellow fever was believed to be exclusively a disease of humans, but research has revealed that it also affects monkeys and other animals. It is believed that diseased monkeys of Africa and tropical America are the primary source of infection and that carrier mosquitoes transmit the infection to humans. This type of the disease, which occurs only sporadically in human beings, is known as jungle yellow fever. If infected individuals move into a populated area, they may be bitten by a semidomestic species of mosquito, such as AŽdes aegypti, which lives close to human habitations. These feed on the blood of humans and are the chief transmitting agents in epidemics of urban yellow fever.
It is probable that the disease initially appeared in Africa and that it was brought to America at the time of the slave trade. The disease was first described in medical terms during the 17th century, when an outbreak was observed in the Yucatan Peninsula, Mexico. Ultimately yellow fever spread to the U.S., Spain, and other countries.
In 1881 the Cuban physician Carlos Finlay advanced the hypothesis that yellow fever is transmitted by mosquito bites. Finlay's theory was verified in 1901 by the work of several investigators, notably the American bacteriologist Walter Reed, who also proved the agent to be a virus. The disease was brought under control by advanced methods of sanitation, including drainage of mosquito breeding grounds and quarantine of ships arriving from infected areas.
The incubation period of yellow fever is three to six days. In severe cases the onset is sudden, with typical symptoms of headache, backache, and fever. The first stage is also characterized by nausea, vomiting, and presence of albumin in the urine. After the initial fever, the temperature usually returns to normal, but on the fourth or fifth day the temperature again rises. This second stage is marked by jaundice, hemorrhage from mucous membranes, vomiting of blood (the characteristic, so-called black vomit of yellow fever), and fatty degeneration of the liver, kidneys, and heart. The destruction of liver cells results in the accumulation of yellow bile pigments in the skin, giving the disease its name. Death usually occurs between the fourth and eighth day after the onset. In cases of spontaneous recovery, convalescence is rapid, although jaundice may persist for some time. The disease never recurs, one attack providing immunity for life.
No treatment is known for yellow fever. In 1939 the South African physician Max Theiler developed a vaccine that confers immunity to the disease. Vaccination is today required for all persons traveling between endemic regions and other parts of the world.
Schistosomiasis or Bilharziasis is a widespread disease caused by the infestation of the human body by flukes, commonly called blood flukes, of the genus Schistosoma. In many tropical and subtropical countries these flukes cause serious diseases; they rarely produce disease in temperate countries, even though they are widespread. It is estimated that 150 to 200 million persons throughout the world are afflicted with diseases caused by blood flukes. Blood flukes spend most of their life cycle in two hosts; the adult stage is spent in a mammal, usually humans, and the immature stages are spent in certain snails. Eggs discharged from the host hatch into larval forms in fresh water; from the water, the larvae, miracidia, invade the snail that acts as an intermediate host. The larval form of the parasite undergoes partial maturation in the snail, then escapes back into the water, as mature larvae called cercariae. At this stage they penetrate the skin of the host from the water and then migrate through the blood vessels to specific capillaries as maturation completes. There they remain and lay eggs.
Effects of Blood Flukes in Humans
Three species produce serious diseases. These are S. hematobium, S. mansoni, and S. japonicum, found in the Tropics and in the Orient. About eight other species are known to produce irritations of the skin, commonly called swimmer's itch, of bathers in the lakes of the north-central U.S., especially Michigan and Wisconsin, and of Canada, especially Manitoba. Only those species that produce serious disease are described here.
The Egyptian blood fluke, S. hematobium, was first described by the German physician Theodor Bilharz in 1851. The adult male is about 1.5 cm (about 0.6 in) long; the adult female is slightly longer and is much thinner than the male. The cercariae of the Egyptian blood fluke pierce the skin or mucous membranes when a human bathes in infested water. Eventually the flukes reach the venules and capillaries of the bladder. They mate and deposit eggs that, acting as foreign proteins, give rise to a severe inflammatory reaction in the walls of the bladder and find their way to the interior of the bladder; during their course, hemorrhages are produced, causing bloody urine and pain during urination. Eggs can be found in the urine on microscopic examination.
The rectal blood fluke, S. mansoni, and the Japanese blood fluke, S. japonicum, concentrate in the blood vessels of the large intestine and liver. Some are carried up the portal veins to the liver where they cause inflammation and scarring, with enlargement of liver and spleen. Because of obstruction to blood flow through the liver, enlargement of veins ensues, particularly in the esophagus (esophageal varices). These veins often rupture, causing serious hemorrhage.
Untreated schistosomiasis often results in death. The first line of attack is preventive, including proper sanitation and extermination of snails. Until 1982, none of the various drugs used to treat persons with the disease was completely effective and all had severe side effects. Then an unusual new drug, praziquantel (sold commercially as Boltricide in the U.S.), became widely available. Praziquantel taken orally, in a single dose or in several doses on the same day, is highly effective against S. mansoni, S. japonicum, and S. hematobium, without causing any serious side effects. Praziquantel increases the permeability of the worm's cell membranes to calcium ions, causing massive contraction and paralysis of its musculature, and then disintegration.
Leprosy or Hansen's Disease, chronic, infectious disease of human beings that primarily affects the skin, mucous membranes, and nerves. The disease is caused by a rod-shaped bacillus, Mycobacterium leprae, which is similar to the bacillus that causes tuberculosis. The leprosy bacillus was identified in 1874 by the Norwegian physician Gerhard Henrik Armauer Hansen.
In both the Old and New Testaments the name leprosy is given to a number of physical conditions unrelated to leprosy. These conditions were considered a punishment from God for sin. The victim was said to be in a state of tsara'ath, or defilement. This Hebrew term was later translated as lepros, from which came the word leprosy.
The disease spread from its probable area of origin in the Indus Valley in India to the Mediterranean and North African regions; all of Europe was affected. The disease is much less common now. It is estimated that less than 5 percent of the world population is susceptible. The disease is found more frequently in countries where nutrition is poor.
Scientists have not been successful in producing typical leprosy in experimental animals. The organism can be grown in armadillos, however, and several laboratories have reported cultivating leprosy in the test tube.
Approximately 5500 known cases of leprosy exist in the United States, and nearly 200 new cases are reported annually. In the western hemisphere, about 336,000 cases are registered; worldwide figures indicate about 5.25 million registered cases and about 10 million estimated sufferers.
Leprosy is classified, according to symptoms and histopathology (abnormalities of tissue cells affected by the disease), as lepromatous, a generalized form; tuberculoid, a localized form; or dimorphous (borderline), a form between tuberculoid and lepromatous. Strong resistance to the disease is shown by the development of the tuberculoid form. Lack of resistance to the organism results in the lepromatous form, in which the disease attacks not only the peripheral nerves but also the skin, the extremities, the mucous membranes, and the eyes.
The earliest symptom is often anesthesia (loss of sensation) in a patch of skin. In the lepromatous form, large areas of the skin may become infiltrated. The mucous membranes of the nose, mouth, and throat may be invaded by large numbers of the organism. Because of damage to the nerves, muscles may become paralyzed. The loss of sensation that accompanies the destruction of nerves may result in unnoticed injuries. These may result in secondary infections, the replacement of healthy tissue with scar tissue, and the destruction or absorption of bone. The classic disfigurements of leprosy, such as loss of extremities from bone damage or the so-called leonine facies, a lionlike appearance with thick nodulous skin, are signs of advanced disease, now preventable with early treatment.
The use of chaulmoogra oil was for many years the established treatment for leprosy. Present-day therapy includes use of drugs such as dapsone, rifampin, and clofazimine, and provision of adequate nutrition.
If too many bacilli are killed too quickly, a systemic reaction may occur. This reaction, called erythema nodosum leprosum, or ENL, may cause progressive impairment of the nerves. Corticosteroids control such reactions.
Leprosy is perhaps the least infectious of all the contagious diseases. At present, newly diagnosed patients are seldom isolated. In the continental United States, a patient may choose to go to the hospital at Carville, Louisiana, for complete diagnosis and therapy. Most patients, however, are treated on an outpatient basis. A leprosy vaccine is currently under development.
Filaria is the common name for a threadworm that is parasitic on vertebrates, including humans Many filariae cause diseases collectively known as filariasis.
The life cycle of filarial worms depends on two hosts, a vertebrate and an arthropod that is usually an insect. The adult worms are slender and transparent, the male usually measuring about half the length of the female. A simple alimentary canal opens near the anal end of the body; the female has two tubes, opening into an anterior vagina, that comprise the uterus. The eggs develop as they move forward in the uterus. By the time they are released, they contain microfilariae, or juvenile worms, about 0.008 cm (about 0.003 in) long, each enveloped by a membrane. On entering the peripheral bloodstream of the host, these microfilariae are taken up by a bloodsucking insect, usually some species of mosquito. The microfilariae shed their envelopes in the stomach of the insect and enter its thorax. After undergoing further development there, the young worms find their way to the proboscis of the insect. When the insect again feeds on the blood of a vertebrate, the microfilariae escape onto the skin of the second host, entering the bloodstream through the puncture made by the proboscis of the insect, or by burrowing into the subcutaneous tissues. Many microfilariae go no farther, but some find their way into surrounding capillaries and, by way of the circulatory system, eventually reach the lymphatics, lymph spaces, and glands, where they develop into adult worms.
Kinds of Filaria
The filaria endemic to parts of Africa, Spain, South America, East Asia, the Caribbean islands, various Pacific islands, and Charleston, South Carolina, reaches a maximum adult length of about 10 cm (about 4 in). Infection either manifests no clinical symptoms or may be indicated in various ways, the most medically important of which is the inflammation of the lymphatics, called lymphangitis, and elephantiasis. In all regions except Polynesia the microfilariae appear in the peripheral blood at night, coincident with the feeding time of mosquitoes and other insect carriers of the worms. Many theories have been developed to explain this nocturnal appearance, the most widely accepted being that the slowing down of heart action during the night helps retain microfilariae in the capillaries.
The eye worm, found in the connective tissues and in the conjunctiva, causes the inflammatory disease loaiasis, characterized by fugitive swellings called Calabar swellings. This worm, indigenous to the west coast of Africa, is transmitted by biting flies. The Guinea worm is a parasite found in Africa and Asia. This worm may grow to 3 m (10 ft) long and often causes painful tumors, blisters, and boils. The microfilariae are released into water and eaten by the tiny copepods. The disease is contracted by drinking water containing infected copepods.
Another filaria causes the disease called river blindness, or onchocerciasis, which is prevalent in regions of Africa and Central and South America. Onchocerciasis produces skin irritations and nodules and can cause blindness, apparently through the effect of metabolic by-products of the roundworm.
Filariae belong to the class Nematoda. The filaria endemic to parts of Africa, Spain, South America, East Asia, the Caribbean islands, various Pacific islands, and Charleston, South Carolina is classified as Wuchereria bancrofti. The eye worm is classified as Loa loa, the Guinea worm as Dracunculus medinensis, and the filaria that causes onchocerciasis as Onchocerca volvulus.
Trypanosomiasis or sleeping sickness is an endemic and sometimes epidemic, chronic disease caused by a protozoan blood parasite, genus Trypanosoma. In cattle and other animals, which serve as the reservoir for the protozoa, the disease is called nagana. Two variations of the disease occur in central and western Africa, both of them transmitted in the salivary glands of infected tsetse flies. The most common is caused by T. brucei gambiense, whereas a more local version is caused by T. brucei rhodesiense. In South America, another version of the protozoan, T. cruzi, is transmitted by the triatoma bug and is called Chagas' disease.
African sleeping sickness begins with a chancre at the site of the insect bite, an accelerated heartbeat, an enlargement of the spleen, and rash and fever. Over the next few months the nervous system is attacked, with accompanying mood changes, sleepiness, lack of appetite, eventual coma, and, frequently, death. Chagas' disease, which more frequently attacks children, also involves fever and damage to the spleen and nervous system, as well as to the liver and the heart muscles. It is also sometimes fatal. In early stages, African sleeping sickness can be alleviated by the administration of various antiparasitic drugs; treatment in later stages with arsenic-containing drugs is less likely to be effective.
Encephalitis is also sometimes called sleeping sickness.
Hepatitis or inflammation of the liver is usually due to acute viral infection, primarily of the liver, occurring in three or more forms. Lifelong immunity to the causative virus usually follows an attack, but since several distinct viruses cause the disease, immunity to one type does not confer immunity to the others.
Previously known as infectious hepatitis, this disease is transmitted by contaminated food or other objects taken into the mouth, or it can be contracted by injection with improperly sterilized hypodermic needles. Outbreaks often occur in army camps and in institutions where small children are crowded together.
Previously called serum hepatitis, this form has been recognized only since World War II. It is epidemic in parts of Asia and Africa. Hepatitis B is transmitted by injections transporting a virus-bearing serum, most often during blood transfusion and by contaminated needles and syringes. For a person who has been accidentally stuck by a needle contaminated with the virus, administration of gamma globulin containing antibodies to the virus greatly reduces the chance of developing the illness. The virus is also present in other body fluids and can be transmitted by sexual contact. In 1965 Baruch Blumberg, an American physician, identified a viral component called the Australia antigen that determines whether a sample of blood can transmit hepatitis B. All samples of blood intended for transfusion are now routinely tested for the antigen; this has greatly reduced post-transfusion hepatitis. In 1976 Blumberg received the Nobel Prize in physiology or medicine for this work.
In 1977 an Italian physician, Mario Rizzetto, identified a virus-now called the delta hepatitis virus-that cannot replicate on its own and requires the presence of the hepatitis B virus to be transmitted. The delta virus occurs worldwide and has caused major epidemics; this form of the disease, sometimes called hepatitis D, can also become chronic.
"Non-A, Non-B" Hepatitis
Two more types of hepatitis have also been identified. Hepatitis C, transmitted in blood or body fluids and caused by a virus which has now been cloned, is the most common cause of post-transfusion hepatitis. Hepatitis E is transmitted in contaminated drinking water and can cause an epidemic form of non-A, non-B hepatitis. At least three other distinct hepatitis viruses have been isolated from human blood samples, but the role that these viruses play in causing disease is as yet unknown.
Symptoms and Treatment
Symptoms of all forms begin with fever, usually followed by weakness, loss of appetite, digestive upsets, and muscle pains. The upper abdomen may be painful and tender. Jaundice appears gradually, reaching maximum intensity at two weeks. Convalescence may take up to six months. In about 5 percent of victims the disease goes on to a chronic form. The fatality rate from all types of hepatitis is about 1 percent but may be higher for hepatitis B.
An effective vaccine that prevents hepatitis B became generally available in 1982, but its use has remained limited because of its cost. A genetically engineered vaccine became available in 1986; it is recommended especially for health care workers and others who may be exposed to blood that may contain the virus. Recombinant alpha interferon, a naturally occurring antiviral substance now marketed as a genetically engineered drug, has been effective in treating many patients with chronic hepatitis C and some patients with chronic hepatitis B. No treatment is available for acute viral hepatitis.
Chlamydia is a genus of obligate intracellular bacteria with two species: Chlamydia trachomatis and C. psittaci, known to be pathogenic for humans. Infection with C. psittaci, which causes psittacosis, is relatively rare. C. trachomatis causes infection of the urogenital tract, known as lymphogranuloma venereum; in the early 1980s researchers determined it to be the most common of the venereal diseases in the U.S.
The effects of C. trachomatis infection are frequently masked by the similar but stronger symptoms (such as discharges and painful urination) of gonorrhea, which often accompanies it. Easily treated by antibiotics, it can be a serious infection if unchecked. It may cause severe pelvic inflammatory disease and extrauteral (ectopic) pregnancies in women and can even lead to sterility in both women and men. Children born to infected mothers may develop conjunctivitis and pneumonia. A strain of fly-borne C. trachomatis causes the very serious, sometimes blinding eye disease known as trachoma.