Amebiasis was first described as a disease by a Russian physician, F. Losch, in 1875 (Anderson, 3).
Deepa Dahal
1 December 1998
Biology Extra Credit
Amebiasis
Amebiasis was first described as a disease by a Russian physician, F. Losch, in 1875 (Anderson, 3). The history of amebiasis has centered on the relationship of amebas found in the intestinal tract of mammals and the role they play in causing disease (4). During the first half of this century, the study of amebiasis has evolved from a disease thought to be purely tropical and one that didn't necessarily require concern to one that is "practically cosmopolitan in its distribution" worldwide and easily treatable (Anderson, 6-8).
Amebiasis indicates presence of Endamoeba histolytica, a protozoan in the class Rhizopoda, and it implies that certain invasion of the intestinal tract, especially the colon and liver, has occurred (MDE, 1). Endamoeba histolytica is a pathogen that is capable of invading and destroying the host's tissue without the aid of pathogenic bacteria (Anderson, 8). It is a typically single-celled parasite whose body consists of cytoplasm, nucleus or nuclei, ingested materials, and vacuoles (Craig, 13).
Endamoeba histolytica has four stages in its life cycle: the trophozoite or motile stage, the precystic stage, the cystic stage, and the metacystic stage (Anderson, 39). The trophic ameba is especially adapted for life in the tissues of its host. The ameba passes out of the body of the human host in the feces into the external environment in its precystic form (39). The cystic form of the Endamoeba histolytica is the resistant form of the pathogen, and it exists free in nature (40). The metacystic stage is basically the reproductive stage, where each nuclei divides into two daughter nuclei. These small amebas develop into the trophozoite form within a few hours (40). It is this rapid multiplication of the ameba in the host which causes various forms of amebiasis in man.
The appearance of amebiasis is world-wide, although it is more frequently observed in tropical climates (Anderson, 12). The disease appears in endemic form in Central and South America, the Indies, Southeast Asia, Africa, Siberia, and the Mediterranean countries (12). In the United States, incidence of the disease generally ranges from five to ten percent (Anderson, 12). It has varied during the last few decades, however, from about .05 percent in a Philadelphia hospital to about 55.5 percent in a New Orleans orphanage (12).
The protozoan is transmitted from human to human, requiring no intermediate hosts (Anderson, ...
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The appearance of amebiasis is world-wide, although it is more frequently observed in tropical climates (Anderson, 12). The disease appears in endemic form in Central and South America, the Indies, Southeast Asia, Africa, Siberia, and the Mediterranean countries (12). In the United States, incidence of the disease generally ranges from five to ten percent (Anderson, 12). It has varied during the last few decades, however, from about .05 percent in a Philadelphia hospital to about 55.5 percent in a New Orleans orphanage (12).
The protozoan is transmitted from human to human, requiring no intermediate hosts (Anderson, 12). There are several ways infection is transmitted. Water is a suitable agent for the transfer of pathogen, since they are able to remain viable in it for three to five days (305). When the water supply in any community becomes contaminated with sewage, lacking proper disposal and treatment, the risk of being infected with amebiasis increases greatly. High incidence of amebiasis also occurs if fruits and vegetables have been irrigated with sewage water or fertilized with human feces, and are eaten raw. Infected persons who handle food and are not careful about hygiene also play an important role in transmitting the disease (306). Finally, flies and other insects contaminate food and drinks if they carry the microscopic Endamoeba histolytica parasite (MDE, 2). The risk of infection increases in areas of crowded and unsanitary living conditions. Traveling to another country also increases the risk. Those who practice the combination of anal-oral sex increase their risk of being infected with amebiasis (MDE, 2).
Throughout the United States and the world, all cases of amebiasis are not being diagnosed properly. Anderson states the reason for this is that the incidence of significant symptoms and signs of amebiasis is significantly low and interpreting symptoms is difficult (32). Symptoms include constipation in early stages, followed by intermittent diarrhea. Other symptoms may be gas and abdominal bloating, or abdominal cramps and tenderness. Fever may accompany the disease. Sometimes, mucus and blood is found in the stool of the infected person. A person may find himself or herself incessantly fatigued, with aching muscles. If the amebiasis attacks the liver, symptoms may include tenderness over the liver and right side of the abdomen as well as jaundice. (MDE, 1). Loss of weight and impaired appetite may be some symptoms (Anderson, 199). Symptoms of amebiasis can appear anywhere from a few weeks to a few years (CDC, 1). Sometimes, however, no symptoms are present. Since all the symptoms of the disease may not necessarily occur, diagnosis of the disease is fairly difficult.
According to Anderson, a correct diagnosis of amebiasis requires an exact, systematic procedure by a completely competent personnel. Definitive diagnosis depends upon microscopic examination and proper recognition of Endamoeba histolytica in stools and tissues (226). Importance of the laboratory is emphasized in any diagnosis procedure (225). Because of the difficulty associated with recognizing amebiasis, Anderson and other researchers recommend using fresh samples of stools and tissues and doing both macroscopic and microscopic examination (227-8). Modern diagnostic measures include x-rays of lower bowel and sigmoidoscopy (use of the sigmoidoscope - a tubular examination speculum - to inspect the sigmoid colon) (MDE, 2).
Every known case of amebiasis should be treated, both in the interest of the individual and of the public. According to Craig, proper treatment of amebiasis varies considerably between patients, due to the fact that they may not have similar symptoms (Craig, 268). If untreated, the prognosis of amebiasis is favorable so far as mortality is concerned; according to health statistics, relatively few people have died from amebiasis infections (253). However, as long as people are carriers of Endamoeba histolytica, it is uncertain that they will continue in good health (254).
In the past, several drugs were used to treat amebiasis. Among these were ipecacuanha, emetine, acetarsone, treparsol, carbarson, and chiniofon. Ipecacuanha was used as early as the 1600's in India (Craig, 269). It has proven most effective in causing disappearance of symptoms in certain types of amebic dysentery, although its use has declined, giving way to more modern medicines (270). Emetine has amebicidal properties that serve in the treatment of amebiasis. However, this drug is very toxic, and can have some nasty side-effects, such as failure or sudden paralysis of the heart muscle and weakening of other muscles (271). Acetarsone, treparsol, and carbarson were three other drugs which produced excellent results in eliminating amebic infection. However, through development of better medicine, use of these drugs has been abandoned (279-81). Chiniofon, a drug also sold under the name of yatren or anayodin, is a very efficient amebicide if administered properly, with virtually no toxicity. Craig said that chiniofon should be preferred to any of the other chemical because it is less toxic and can be used in mass treatment safely and effectively (284).
Modern treatments of amebiasis include drugs such as metronidazole, tetracycline, or emetine hydrochloride (Thomas, 67). Antibiotics are probably the most common treatments today (CDC, 2). Repeated treatment at intervals of up to three months is recommended to ensure elimination of all protozoan.
Preventing infection of amebiasis is relatively easy, requiring only careful hygienic practices. Washing hands before eating and after using the toilet; boiling water that could be contaminated; avoiding raw, unpeeled fruits and vegetables are all ways to prevent amebiasis. Being extra careful when eating out and traveling and practicing safe sex also decreases the risk of infection.
Early detection of amebiasis infection and adequate treatment keep the infection from spreading to other people. Ultimately, prevention of amebiasis is related directly to proper disposal and treatment of human excrement (Craig, 311). Therefore, prohibiting use of human feces as fertilizer; keeping insects out of food supplies; keeping water supply free of pollutants; and finally, disposing sewage safely all ensures the prevention of transmission of amebiasis.
References
Anderson, Hamilton H. 1953. Amebiasis: Pathology, Diagnosis, and Chemotherapy.
Charles C Thomas, Illinois.
Center for Disease Control and Prevention. 1998. Amebiasis Infection.
http://www.cdc.gov/ncidod/dpd/amebias.htm
Craig, Charles F. 1934. Amebiasis and Amebic Dysentery. Charles C Thomas, Illinois.
Medical Data Exchange. 1998. Amebiasis. http://www.thriveonline.com/health/Library/
illsymp/illness10.html
Thomas, Clayton L. 1985. Taber's Cyclopedic Medical Dictionary. F.A. Davis
Company, Philadelphia.
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