Intestinal Schistosomiasis And Its Possible Prevention And Control
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Schistosomiasis is a neglected tropical disease that ranks second only to malaria in terms of human suffering in the tropics and subtropics. Five species are known to infect man and there are currently over 240 million people infected worldwide. The cornerstone of control to date has been mass drug administration with 40 mg/kg of praziquantel but there are problems with this approach. Human and bovine vaccines are in various stages of development. Integrated control, targeting the life cycle, is the only approach that will lead to sustainability and future elimination.
1.1 DESCRIPTION OF SCHISTOMIASIS
, also known as bilharzia, snail fever, and Katayama fever, is a disease caused by parasitic flatworms of the schistosomatype. The urinary tract or the intestines may be infected. Signs and symptoms may include abdominal pain, diarrhea,(Akpinar, 2012). Bloody stool, or blood in the urine. In those who have been infected a long time, liver damage, kidney failure, infertility, or bladder cancer may occur. In children, it may cause poor growth and learning difficulty (Antounet al., 2005).
The disease is spread by contact with fresh water contaminated with the parasites. These parasites are released from infected freshwater snails. The disease is especially common among children in developing countries as they are more likely to play in contaminated water(Akpinar, 2012). Other high risk groups include farmers, fishermen, and people using unclean water during daily living. It belongs to the group of helminth infections. Diagnosis is by finding eggs of the parasite in a person’s urine or stool. It can also be confirmed by finding antibodies against the disease in the blood (Duke, 2002).
Methods to prevent the disease include improving access to clean water and reducing the number of snails.(Duke,.2002) In areas where the disease is common, the medication praziquantel may be given once a year to the entire group. This is done to decrease the number of people infected and, consequently, the spread of the disease. Praziquantel is also the treatment recommended by the World Health Organization(WHO) for those who are known to be infected (Akpinar, 2012)..
(Antounet al., 2005) Schistosomiasis affected almost 210 million people worldwide as of 2012. An estimated 12,000 to 200,000 people die from it each year. The disease is most commonly found in Africa, as well as Asia and South America. Around 700 million people, in more than 70 countries, live in areas where the disease is common. In tropical countries, schistosomiasis is second only to malaria among parasitic diseases with the greatest economic impact. Schistosomiasis is listed as a neglected tropical disease(Akpinar, 2012).
Schistosomiasis is caused by infectious trematode worms of the genus Schistosoma. There are five schistosome species known to infect humans: S. haematobium (identified in 1852), S. japonicum (1904), S. mansoni (1907), S. intercalatum (1934), and S. mekongi (1978). In 2011, an estimated 243 million people in 78 countries were living in areas of high risk for the disease. The African region is the most affected, with 42 countries endemic for the infection, followed by the Eastern Mediterranean region with 16 countries affected. Schistosomiasis was also endemic in 10 countries in the region of the Americas, six in the Western Pacific regions, and three in the Southeast Asian region and in Turkey, the only country affected in the European region.
The disability-adjusted life years (DALYs) lost as a result of schistosomiasis was estimated to be 1.7 million.3,4 However, in estimating the DALYs, the case definition used for schistosomiasis was limited to infection and associated mortality from schistosomiasis, and excludes mortality from bladder cancer, cirrhosis, or colon cancer that may be related to the infection. Hence, only an average of 0.006 disability weights was used in the estimation.3 King re-estimated the DALYs associated with Schistosoma infection using the assumption that all past and present Schistosoma infections are part of the ongoing disease burden of schistosomiasis. Using a disability weight of 2%, the new DALYs estimate was 24–29 million, which was almost 20 times higher than the previous estimate. Elimation and control of schistosomiasis has been successful in a number of countries including Japan, Tunisia, Puerto Rico, Iran, Mauritius, Venezuela, Morocco, and most of the Caribbean, but it remains a major public health challenge in many other countries. In this current perspective, we discuss the current burden of disease, the life cycle, morbidity, treatment, integrated control, and disease prevention.
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1.1 Definition of Terms
a. Ascites: an abnormal pooling of fluid in the abdominal cavity; the fluid contains large amounts of protein and other cells. Ascites is usually noticed when more than 1pint (500 ml) of fluid has collected
b. Bacteriuria :the presence of bacteria in the urine. More than 100,000 bacteria per ml of urine usually mean urinary tract infection is present.
c. Dermatitis, an inflammation of the skin marked by redness, pain, or itching. The condition may be long-term or sudden
d. Dysuria, painful urination, usually the result of a bacterial infection or blockage in theurinary tract. Dysuria is a symptom of such conditions as inflammation of the urinary bladder (cystitis), swelling of the urethra (urethritis), swelling of the prostate (prostatitis), urinary tract tumors, and some gynecological disorders
e. Hematuria, abnormal presence of blood in the urine. Many kidney diseases anddisorders of the genital and urinary systems can cause hematuria
f. Pyuria, white blood cells in the urine. It is a sign of infection of the urinary tract. Pyuriaoccurs in inflammation of the bladder, kidney, or urethra, and tuberculosis of the kidney. Pyuria may be caused by an infection from viruses. Miliary pyuria causes blood, pus, and tissue cells, as well as bacteria, in the urine.
g. Miracidium, the larval stages of aquatic invertebrates (e.g. Flukes) that lead sedentary,or attached, lives in the adult stage are typically motile and free-swimming. Such larvae are found in sponges, sessile mollusks, and many rotifers and worms. These larvae serve to increase the distribution of the adults
h. Fistula, an abnormal passage from an internal organ to the body surface or betweentwo internal organs. Fistulas may occur in many sites from the mouth to the anus and may be made for treatment follow the course of a disease
1.3 Life cycle
Schistosoma eggs are excreted from the human host into a fresh water environment through urine or feces. Once an egg comes in contact with fresh water, it hatches and releases a miracidium, a free-living and ciliated form, which remains infective for 6–12 hours. The miracidium swims by ciliary movement toward the snail intermediate host and penetrates its soft tissue. The Schistosoma species are transmitted by different fresh water snails that serve as their intermediate hosts: Biomphalaria, Bulinus, and Oncomelania for S. mansoni, S. haematobium, and S. japonicum, respectively.
The miracidium that penetrated the snail loses its cilia and develops into a mother sporocyst, which multiplies asexually to produce daughter sporocysts. These migrate to and develop in the hepatic and gonadal tissue of the snail. Within 2–4 weeks, these daughter sporocysts metamorphose into cercariae.Under the stimulation of light, hundreds of free-swimming, fork-tailed cercariae leave the snail intermediate host. They swim through the water until they come into contact with human skin or the skin of other mammalian hosts, in the case of S. japonicum. S. japonicum can infect more than 40 mammals that can serve as reservoir hosts.8 The cercariae penetrate the skin by mechanical activity and via proteolytic enzymes. Upon skin penetration, the cercariae lose their tail and become schistosomules which pass through the epidermis and dermis before exiting via the blood or lymphatic vessels.There seems to be a difference in the way different schistosome species migrate through the skin. Within 2 hours of exposure, more than half of the S. japonicum schistosomula are found in the dermis, and as early as this, some are
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