Human Parasitic Worms - Essay Example

HUMAN PARASITIC WORMS The roundworms, the flukes, and the tapeworms are responsible for parasitic worm infestation in humans. The roundwormscause diseases such as enterobiasis, ascariasis, and necatoriasis; the flukes are responsible for schistosomiasis, while the tapeworms cause taeniasis. Parasitic worms are contacted by ingestion of their eggs/cysts, or by the penetration of exposed human skin on exposure by the larvae. In all worm infestations, complications usually arise from heavy presence of worms, and there are even research evidence (though not conclusive) to suggest that the presence of a minimal level of worms could play an important role in the treatment of some allergic and auto immune diseases. A holistic approach that involves preventive measures, drug therapy and non-drug measures is employed in tackling the menace of worm infestation. Introduction Human parasitic worms are a major health challenge in the developing world. To a far less degree, however, worm infestation in the developed countries is also a problem. Broadly speaking, three groups of worms cause parasitic worm infestation in man. These are the roundworms (also known as the nematodes), the flukes (also called the trematodes), and the tapeworms (the cestodes). The roundworms are responsible for the majority of parasitic worm infestations in the developing world. These roundworms are usually the large roundworms (Ascaris lumbricoides), the whipworm (Trichuris trichiura), and the hookworm (Acyclostoma duodenale). A few cases of infestation by these worms in the developed world are found in travelers and immigrants. On the other hand, threadworm (Enterobius vermicularis) is the roundworm that causes the most parasitic worm infestation in the United Kingdom. Other known roundworms include Strongyloides stercoralis that causes strongyloidiasis, and the Necator americanus (the new world hookworm) that causes necatoriasis. The flukes include all members of the Schistosoma species, and the cause schistosomiasis or bilharzia depending on the species that is contacted. The tapeworms are the Taenia species and their intermediate hosts are beef (Taenia saginata), pork (Taenia solium), or fish (Dipyllobothrium latum) from where they are passed to man (the definitive host). The dwarf tapeworm (Hymenolepsis nana) is passed from man to man.(Clark, 2006) Pathophysiology Threadworms are threadlike in structure and their infestation is commoner in children. They are passed from one person to another by the ingestion of their eggs. These eggs develop into larvae in the small intestine and are hatched to produce young worms. The worms mature in a couple of weeks and the adult females migrate to the anus where they lay numerous microscopic eggs. As a result of itching felt in the anus where these eggs are laid, the anus is scratched by the human and the eggs are reingested through the hand-to-mouth route. Infestation could also be through migration of hatched eggs up to the rectum (Clark, 2006). Strongyloides stercoralis is commoner in warm region, though its distribution is world wide. First infestation is through larvae deposited in soil that enter the skin and develop in the small intestine. Subsequent infestation is by larvae passed in stools of infected individuals which re-penetrate the skin of the same individual. A possible complication is the life threatening strongyloides hyper infestation syndrome(Clark, 2006). In infected individuals, the Schistosoma species lay eggs that are excreted in the human stool (Schistosoma japonicum and Schistosoma manson) or in the urine (Schistosoma haematobium) Larvae hatched from these eggs are called the miracidia, and they enter snails which are the intermediate hosts. Consequently, infective larvae called the cercariae are released from these snails and enter humans that wade in water in which they are present. These larvae migrate to the human intestine or the bladder where they mature, mate and produce eggs. Initial infestation may be asymptomatic, causing only a transient itching or fever, but long term infestation can lead to serious organ damage(Clark, 2006). Infective worms that are acquired through contact with contaminated soil are called soil transmitted helminthes, and they include the whipworm, hookworms and roundworms. Their fertilized eggs are laid in soil to mature. Poor hygiene is a predisposing factor to their prevalence. The hookworms are usually less than 2 cm in length at full maturity. Their larvae enter the skin through which they find their way to the lungs where they are coughed up and swallowed into the intestine. Here, they suck the host's blood and this on the long run lead to anaemia. Several eggs (up to 30,000) are produced per day and the cycle of infestation continues. Ancyclostoma brazilliense is a hookworm that affects cats and dogs, but humans could be infested accidentally(Clark, 2006). In roundworms, mature females are longer than the males and they have a longer lifespan. They lay up to 200,000 eggs everyday and these eggs are hatched in the human intestine. The larvae migrate to the lungs where, like hookworms they are coughed up and swallowed. In the intestine, they form adult worms. Complications arising from roundworm infestation are usually as a result of larvae migration in early infestation. Whipworms are slightly longer than the hookworms. The adult live in the large intestine where they burrow into the intestinal wall. They lay about 20,000 eggs everyday and their life span is 48 months. Complications may result from heavy infestation(Clark, 2006). Tapeworms possess segments known as proglottids. Each segment has a male and a female reproductive organ, hence tapeworms are said to be hermaphrotidic. They attach to the wall of the intestine of vertebrates with their head (scolex). They are more common in the developing world and Eastern Europe. Each segment breaks away and is excreted in the faeces. Eggs are released from it. These eggs hatch in the intestine of animals (intermediate hosts) that eat grass contaminated with infected faeces. The eggs then migrate through the wall of the intestine to the skeletal muscle of the animal and form cysts. Humans are infested by the ingestion of this meat that contains the cyst. The length of beef tapeworm could be up to 5 meters at full maturity. Infestation could be asymptomatic or symptomatic with anal itching. The dwarf tapeworm is smaller in length and is only acquired through auto-infestation, or from man-to-man(Clark, 2006). Diagnosis and Treatment Threadworm infestation is first noticed from the persistent, often nocturnal perianal pruritus. This sign may be absent at times, and confirmatory diagnosis is by sighting worms around the anus or in stool. To detect eggs if infestation in a suspected infestation, a type of adhesive tape is applied to the area around the anus first thing in the morning and then viewed under the microscope(Krumhardt, 2006). This is preferred to stool microscopy because in about 95% of cases, eggs are not seen in stool examination(Clark, 2006). Threadworm lives for 3-6 weeks, and a strict adherence to good hygiene standards within this period ensures elimination of already established infestation and at the same time prevents infestation with new worms. These hygiene practices include, but are not restricted to constant washing of the hand and underwears, wearing of close-fitting underwears at night, avoiding sharing of towels, keeping fingernails short, having constant, early morning baths, etc. For drug treatment, mebendazole is prescribed for adults and children over 2 years, and piperazine for adults and younger children less than 2 years old but older than 3 months. Every member of the household where there is an infestation should be treated with drugs and made to observe the prescribed hygiene standards(Clark, 2006). The diagnosis of strongyloidiasis is by the detection of larvae from patient's stool sample. Tiabendazole is the drug of choice, while alternative drugs are albendazole and ivermectin (Krumhardt, 2006). As a non-drug, preventive measure, going without foot wears should be avoided, especially in endemic areas(Clark, 2006). To diagnose schistosomiasis, a microscopic examination is done on the urine or stool sample of the patient. A positive report is given when eggs of schistosome are discovered. The drug of choice is praziquantel, and the dose of administration depends on the infective species(Clark, 2006; Krumhardt, 2006). A preventive measure is to avoid wading in fresh water. Swimming pools should also be chlorinated(Clark, 2006). Hookworm eggs are detected in microscopic examination of stool of infested individuals. Treatment is with mebendazole. There are also prospects of the development of a vaccine against hookworm. Cutaneous larva migrans, which is caused by the accidental infestation of humans by Ancyclostoma brazilliense, can be treated with tiabendazole, though albendazole and ivermectin are equally effective(Clark, 2006). Roundworm, which is diagnosed by the detection of egg in infected stool or excretion of mature worm, is treated with levamisole. Piperazine or mebendazole are alternatives to levamisole. Whipworm's eggs are detected in stool microscopy. The drug of choice is mebendazole(Clark, 2006). Tapeworm infestations are usually characterized by anal itching, but definitive diagnosis is through the detection of eggs in the faeces or perianal swab. Niclosamide is the drug used to treat taenia infestation, but praziquantel could be equally effective, with its dose adjusted according to the species causing infestation(Clark, 2006; Krumhardt, 2006). Future Research Prospects Recent research findings show that there might be the possibility of worm infestations playing a significant role in the treatment of some allergic and autoimmune diseases(Maizels & Yasdanbakhsh, 2003). In a randomized controlled trial, 43.3% of patients with ulcerative colitis treated with egg of Trichuris suis reported an improvement in symptom after 3 months, as against only 16.7% for placebo(Summers, Weinstock, Urban, Thompson, & Weinstock, 2005). Other studies also show that type 1 diabetes mellitus failed to develop in mice bred to develop the disease after they were infected with eggs of schistosome(Cambridge University Schistosome Research Group, 2006). There are therefore the prospects of employing worms at sub-infective doses in the treatment of conditions such as asthma, hay fever, Type 1 diabetes, and inflammatory bowel disease. Conclusion Human parasitic worms' infestations are largely as a result of poor hygiene practices, and are therefore commoner in poorer regions of the world. Three broad groups are recognized. Their presence in humans could be asymptomatic or symptomatic, and are usually diagnosed through microscopic examination of stool or urine of patients. Long-term infestation could lead to some far reaching complications. Treatment is by drug and non drug (mainly hygiene) means. There are prospects in the use of worms in the treatment of some allergic and auto immune diseases, but research is ongoing. 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