Amebiasis PDF

Amebiasis By Dr. Ameer kadhim Hussein. M.B.Ch.B. FICMS (Community Medicine).  OBJECTIVES Describe and discuss the epidemiology and mode of transmission amoebiasis. Describe and discuss preventive and control measures to control amoebiasis.  IDENTI...

Amebiasis By Dr. Ameer kadhim Hussein. M.B.Ch.B. FICMS (Community Medicine).  OBJECTIVES Describe and discuss the epidemiology and mode of transmission amoebiasis. Describe and discuss preventive and control measures to control amoebiasis.  IDENTIFICATION The term "amoebiasis" has been defined by WHO as the condition of harbouring the protozoan parasite Entamoeba histolytica with or without clinical manifestations. The symptomatic disease occurs in less than 10 percent of infected individuals. The symptomatic group has been further subdivided into intestinal and extraintestinal amoebiasis. Only a small percentage of those having intestinal infection will develop invasive amoebiasis.  IDENTIFICATION The intestinal disease varies from mild abdominal discomfort and diarrhoea to acute fulminating dysentery. Extraintestinal amoebiasis includes involvement of liver (liver abscess), lungs, brain, spleen, skin, etc. Amoebiasis is a potentially lethal disease. It carries substantial morbidity and mortality.  IDENTIFICATION Infection with Entamoeba histolytica is a leading parasitic cause of death in developing nations and is an important health risk to travelers. Amebiasis is transmitted by parasite cysts via fecal- oral contamination from infected individuals or from contaminated food or water. E. histolytica infections may be noninvasive and asymptomatic or may cause varying degrees of symptoms through tissue invasion.  INFECTIOUS AGENT Amoebiasis is caused by potentially pathogenic strains of E. histolytica. E. histolytica exists in two forms vegetative (trophozoite) and cystic forms. Trophozoites dwell in the colon where they multiply and encyst. The cysts are excreted in stool. Ingested cysts release trophozoites which colonize the large intestine. Some trophozoites invade the bowel and cause ulceration, mainly in the caecum and ascending colon; then in the rectum and sigmoid. Some may enter a vein and reach the liver and other organs.  INFECTIOUS AGENT The trophozoites are short-lived outside the human body; they are not important in the transmission of the disease. In contrast the cysts are infective to man and remain viable and infective for several days in faeces, water, sewage and soil in the presence of moisture and low temperature. The cysts are not affected by chlorine in the amounts normally used in water purification, but they are readily killed if dried, heated (to about 55 deg C) or frozen. INFECTIOUS AGENT  RESERVOIR Man is the only reservoir of infection. The immediate source of infection is the faces containing the cysts. Most individuals infected with E. histolytica remain symptom free and are healthy carriers of the parasite. The greatest risk is associated with carriers engaged in the preparation and handling of food.  PERIOD OF COMMUNICABILITY As long as cysts are excreted; the period may be several years, if cases are unrecognized and untreated. INCUBATION PERIOD Variable from few days to several months or years, commonly 2 to 4 weeks or longer  MODES OF TRANSMISSION Water polluted with sewage may cause an epidemic, the feco oral route being the predominant mode of entry. Food handlers, if they are convalescent or healthy carriers, play an important role. Flies and cockroaches can harbour cysts and contaminate food. Farm vegetables contaminated by sewage may infect man.  MODES OF TRANSMISSION Sexual transmission as a result of oro anal contact, especially among male homosexuals, has been increasingly reported during recent years. Poverty, ignorance and poor sanitation are favorable to the spread of disease in developing countries. Hot, dry climate is inimical to the cysts. MODES OF TRANSMISSION  HOST FACTORS Amoebiasis may occur at any age. There is no sex or racial difference in the occurrence of the disease. Amoebiasis is frequently a household infection. When an individual in a family is infected, others in the family may also be affected. Specific anti- amoebic antibodies are produced when tissue invasion takes place. There is strong evidence that cell mediated immunity plays an important part in controlling the recurrence of invasive amoebiasis.  ENVIRONMENTAL FACTORS Amoebiasis is more closely related to poor sanitation and socio-economic status than to climate. In countries with marked wet-dry seasons, infection rates are higher during rains, presumably since cysts may survive longer and the potential for transmission is there by increased. Epidemic outbreaks are usually associated with sewage seepage into the water supply.  EPIDEMIOLOGY Amoebiasis is a common infection of the human gastro-intestinal tract. It has a worldwide distribution. It is a major health problem in the whole of China, South East and West Asia and Latin America, especially Mexico. Globally it is estimated that 500 million people carry E. histolytica in their intestinal tract and approximately one-tenth of infected people suffer from invasive amoebiasis. It is probable that invasive amoebiasis, accounted for about 100,000 deaths in the world.  EPIDEMIOLOGY Prevalence rates vary from as low as 2 per cent to 60 per cent or more in areas devoid of sanitation. In areas of high prevalence, amoebiasis occurs in endemic forms as a result of high levels of transmission and constant reinfection. Epidemic water-borne infections can occur if there is heavy contamination of drinking water supply.  EPIDEMIOLOGY Amebiasis has a worldwide distribution but is most common in the developing world. In underdeveloped areas where drinking water is obtained from fecally contaminated water sources and contaminated water or sewage is used to grow or freshen vegetables, amebiasis has high incidence.  EPIDEMIOLOGY Worldwide, approximately 50 million cases of invasive E histolytica disease occur each year, resulting in as many as 100,000 deaths. This represents the tip of the iceberg because only 10%-20% of infected individuals become symptomatic. The incidence of amebiasis is higher in developing countries. Amebiasis is the second leading cause of death due to parasitic diseases, killing about 40,000-100,000 people per year globally.  EPIDEMIOLOGY The prevalence of Entamoeba infection is as high as 50% in areas of Central and South America, Africa, and Asia. E histolytica seroprevalence studies in Mexico revealed that more than 8% of the population were positive. In endemic areas, as many as 25% of patients may be carrying antibodies to E histolytica as a result of prior infections, which may be largely asymptomatic. The prevalence of asymptomatic E histolytica infections seems to be region-dependent; in Brazil, for example, it may be as high as 11%.  EPIDEMIOLOGY In Egypt, 38% of individuals presenting with acute diarrhea to an outpatient clinic were found to have amebic colitis. A study in Bangladesh indicated that preschool children experienced 0.09 episodes of E histolytica -associated diarrhea and 0.03 episodes of amebic dysentery each year. In Hue City, Vietnam, the annual incidence of amebic liver abscess was reported to be 21 cases per 100,000 inhabitants. An epidemiologic study in Mexico City reported that 9% of the population was infected with E histolytica in the 5-year to 10- year period preceding the study.  EPIDEMIOLOGY Various factors, such as poor education, poverty, overcrowding, contaminated water supply, and unsanitary conditions, contributed to fecal-oral transmission. Several studies have evaluated the association of amebiasis with AIDS. The impact of the AIDS pandemic on the prevalence of invasive amebiasis remains controversial. Some reports suggest that invasive amebiasis is not increased among patients with HIV infection, however, others suggest that amebic liver abscess is an emerging parasite infection in individuals with HIV infection in disease-endemic areas, as well as in non–disease- endemic areas.  EPIDEMIOLOGY Of 31 patients with amebic liver abscess at Seoul National University Hospital from 1990 to 2005, 10 (32%) were HIV- positive. Symptomatic intestinal amebiasis occurs in all age groups. Liver abscesses due to amebiasis are 10 times more frequent in adults than in children. Very young children seem to be predisposed to fulminant colitis. Amebic colitis affects both sexes equally. However, invasive amebiasis is much more common in adult males than in females.  EPIDEMIOLOGY E. histolytica is a common diarrheal pathogen in returned travelers. Long-term travelers (duration >6 months) are much more likely than short-term travelers (duration