Soil Transmitted Helminthiasis 1 PDF

SOIL TRANSMITTED HELMINTHIASIS 1 SOIL TRANSMITTED HELMINTHS Nematodes that complete their developmental stages to adult in human and need soil for their transmission from one host to another Ascaris lumbricoides Trichuris trichiura Hookworms (Necator americanus & A. duodenale)...

SOIL TRANSMITTED HELMINTHIASIS 1 SOIL TRANSMITTED HELMINTHS Nematodes that complete their developmental stages to adult in human and need soil for their transmission from one host to another Ascaris lumbricoides Trichuris trichiura Hookworms (Necator americanus & A. duodenale) Strongyloides stercoralis  General STH is one of the most common infections worldwide affecting the most deprived communities The STH are a group of parasitic nematode worms causing human infection through contact with parasite eggs or larvae that thrive in the warm and moist soil of the world's tropical and subtropical countries  A. lumbricoides infects over 1 billion people, T. trichiura 795 million, and hookworms (Ancylostoma duodenale and Necator americanus) 740 million. The greatest numbers of soil-transmitted helminth infections occur in sub-Saharan Africa, the Americas, China and east Asia. Infection is caused by ingestion of eggs from contaminated soil (A. lumbricoides and T. trichiura) or by active penetration of the skin by larvae in the soil (hookworms and strongyloides).  Epidemiology Climate is an important determinant of transmission of these infections, with adequate moisture and warm temperature essential for larval development in the soil. Equally important determinants are poverty and inadequate water supplies and sanitation. In such conditions, soil-transmitted helminth species are commonly co-endemic. Children most commonly affected PREVALENCE IN DIFFERENT TYPE OF COMMUNITIES (Schooling age 7 - 12) Urban slum - 68.7 % Urban flats - 35.1 % Semi rural - 32.8 % Rural/estate - 67.2 % Orang Asli - 77.8 %  Mode of Transmission People infected with STH have parasite eggs in their faeces. In areas where there are no latrine systems, the soil (and water) around the village or community becomes contaminated with faeces containing worm eggs. In the soil, the eggs mature – a process that takes between 2 and 4 weeks, depending on the type of worms: about 2 weeks for roundworms and hookworms; about 3 weeks for whipworms.  Route of Infection Oral transmission : – Ascaris lumbricoides and Trichuris trichiura -The eggs stick to vegetables grown in the area. If the vegetables are not carefully cooked, washed or peeled, the eggs are ingested and infect the person. -The eggs are ingested from water sources which have become contaminated. -Young children who play on the ground and often put their hands in their mouths without washing them, ingest the eggs and become infected.  Skin penetration – Hookworm & Strongyloides stercoralis – The eggs hatch into larvae which rest in the soil. – If a person walks on the contaminated soil, the larvae can penetrate the skin, usually between the toes. Hands penetration is also possible.  There is no direct person-to-person transmission or infection from fresh faeces because eggs passed in faeces need about 2-3 weeks in the soil before they can become infective.  Clinical Manifestation Generally only STH of moderate and high intensity in the gastrointestinal tract produce clinical manifestations, with the highest-intensity infections most common in children. The numerical threshold at which worms cause disease in children has not been established, because it depends on the underlying nutritional and immunological status of the host. Each of the major STH produces characteristic disease syndromes from general malaise and weakness, that may affect working and learning capacities and impair physical growth to a more serious complication.  Host-parasite interactions Despite their large size and ability to elicit potent immune responses, soil-transmitted helminths are refractory to host immunity, establishing chronic infections during the host's life, and, in the case of hookworm, intensity of infection actually rises with the age of the host. Able to subvert the host immune response to create niches that optimise successful residence, feeding, and reproduction  Control and preventive chemotherapy The strategy for soil-transmitted helminthiasis control is to treat once or twice per year : – preschool and school-age children; – women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) – and adults at high risk in certain occupations (e.g. tea-pickers, miners, etc.).  The World Development Report for 1993 entitled Investing in Health revealed that common soil-transmitted helmith infections caused the greatest burden of infectious diseases in children between 5 and 14 years in countries with developing economies.  This means that deworming school-aged children is probably the most economically efficient public health activity that can be implemented in any low-income country were soil-transmitted helminths are endemic. Apart from provision of safe water supply and proper sanitation, health education and personal hygiene  Ascaris lumbricoides Largest intestinal roundworm causing ascariasis Adult female (20-35cm), male (10-25cm) Fertilised egg is broadly oval (45-75 X 35- 50um) Thick shell, surrounded by brown bile stained mammilated outer covering (albumin layer)  Inside albuminous layer is vitelline layer When the mammilated outer covering is absent, the ovum is said to be decorticated. Infertile eggs are more elongated (80- 90um long), with prominent mammilations, showing disorganised globular internal contents  Life cycle Ingested embryonated ova containing second stage larvae hatch in the small intestine. Larvae penetrate intestinal wall and migrate to the liver, right heart, pulmonary vessels and lungs, eventually reaching the trachea and pharynx. Involves Lungs migration  The larvae then get swallowed and pass into the small intestine, where they mature and mate Habitat of adult worm = small intestine Fertilised ova passed in feces become infective in warm, moist soil, within 2 weeks. Females produce infertile eggs in the absence of males  Transmission & Pathogenesis Ascariasis occurs worldwide, transmitted by fecal oral route. Human becomes infected by ingesting embryonated eggs from contaminated soil Eggs passed in feces usually contain first stage larvae  Most infections are asymptomatic (5-10 worms) Heavy infection may cause nutritional deficiency, esp in children, abdominal pain, intestinal obstruction. During larval lung migration, the larvae may produce host sensitization resulting in allergic manifestation eg. Asthmatic attacks, eosinophilia (Loefflers syndrome)  Migrations of adult worm may cause blockage of bile ducts, gallbladder, liver, appendicitis (ectopic lesions) Lab Diagnosis – Identification of fertilised or unfertilised eggs in human feces (direct fecal smear, conc tech, Kato katz tech)  Pathology The intensity of host reaction is dependent on worm burden. 1. Lung migration of larvae → pulmonary signs. Loeffler’s syndrome. IgE antibodies responsible for bronchial asthma and urticaria. 2. Intestinal ascariasis: Preadult and adult Competition for food → malnutrition (PEM), anemia, fluid retention (edema). Intestinal obstruction. 3. Extraintestinal ascariasis → haemorrhagic infarction of intestine, perforation of appendix and small intestine, biliary or hepatic ascariasis, pancreatitis, peritonitis, asphyxia of upper respiratory tract. 3. Allergy to ascaris → hypersensitivity reactions in lung, skin, conjunctive and intestinal mucosa. Urticaria, facial edema.  Prevention and Treatment Antihelminthic drugs such as Mebendazole, Albendazole Personal hygiene, proper sanitation Avoid using feces as fertilizer  Trichuris trichura Also known as whipworm Long slender, threadlike anterior portion with thicker posterior portion which looks like a whip handle Adult worm 30-50mm, male with coiled tail having the spicule  The eggs are oval (barrel shaped) , bile- stained, with thick smooth shell and a clear prominent polar plug at each end Egg measures 45-55um X 20-23um  Life cycle Direct life cycle, after passage in feces, the eggs takes 2 weeks to mature in soil The eggs are ingested and development occur in large intestine its habitat. (no lung migration) The worm attaches by its anterior end to the intestinal mucosa and takes 3 months before the adult worm begins to lay eggs Whipworm occurs worldwide  Transmission & Pathogenesis Most infections are asymptomatic Heavy infection assoc with nausea, diarrhea, abd pain, weight loss Rarely anemia, dysentery or complication like rectal prolapse Diagnosis Identification of ova in feces Treatment & prevention as ascariasis Complication : Rectal Prolapse Adult worm in Caecum  Prevention and Treatment Antihelminthic drugs such as Mebendazole, Albendazole Personal hygiene, proper sanitation