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Cell, Individual, and Community week 2/7 NTDs/Soil Transmitted Diseases

by: Claire Jacob

Cell, Individual, and Community week 2/7 NTDs/Soil Transmitted Diseases SPHU 1020

Marketplace > Tulane University > Public Health > SPHU 1020 > Cell Individual and Community week 2 7 NTDs Soil Transmitted Diseases
Claire Jacob
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These notes includes information on helminth infections both from class and the textbook
Cell, Individual & The Community
Dickey-Cropley, Lorelei
Class Notes
Public Health, The Microbial Challenge, helminths, NTDs




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This 12 page Class Notes was uploaded by Claire Jacob on Saturday February 13, 2016. The Class Notes belongs to SPHU 1020 at Tulane University taught by Dickey-Cropley, Lorelei in Summer 2015. Since its upload, it has received 32 views. For similar materials see Cell, Individual & The Community in Public Health at Tulane University.


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Date Created: 02/13/16
NTDs/ Soil Transmitted Diseases→ 2. 12. 16 Helminths: worms NTDs- neglected tropical diseases ● infectious diseases that principally impact world’s poorest people ● have been neglected for decades, initially as part of a general disregard for the developing world and more recently due to focus on HIV/AIDS and TB ● in tropical environments We use a web of causation when we talk about helminths ● poverty, social organizati on ● behaviour… Major neglected Tropical Diseases by causative organism ● diseases caused by helminths ● diseases caused by protozoa ● diseases caused by bacteria ● diseases caused by viruses … but today we’re focusing on worms... Helminth Diseases ● often transmitted by soil ● helminths: derived from greek for worm ○ evidence that mankind has been aware of these organisms throughout the centuries→ not usually microscopic ● AKA Multicellular eucaryotes classified as round or flat worms ● transmitted by food and water vectors or direct contact ● helminth infections are rarely fatal but they are debilitating in many instances Intestinal worms/ helminths ● Major public health problem in developing world. Why? ○ Place: helminths thrive in tropical areas ■ warm, moist soil provides an ideal environment for maintenance of helminth eggs and larvae ○ Poverty ■ occur predominantly in impoverished areas of sub -saharan africa, southeast asia, india, and parts of central and south america and the Caribbean ■ little market incentive in private industry to develop drugs or other biologicals to treat these diseases ● At least 1 billion people harbor 1 -3 major types of parasites. In some developing countries, as many as 90% of the population have at least one type of worm ; like normal fauna ● While most prevalent in tropical countries, presence in US and in other temperate of increasing concern because of immigration, travel, and AIDS Epidemiology and Risk Factors: Poverty ● greatest risk factor for infection with a soil -transmitted helminth ○ diseases of developing world: infection primarily in 2$ per day ○ global poorest of the poor usually live in areas with inadequate sanitation, scarce water supply and insufficient medical systems to treat How helminth infections and poverty are interrelated ● eggs passed out of humans through feces ○ lack of public health and sanitation infrastructure in many parts of the developing world supports continuous transmission of soil -transmitted helminths via a fecal- oral or fecal-skin route ● Short and long term health effects of soil -transmitted helminth infections lead to poverty - promoting disability in children and adults ○ in children, poor cognitive development because the worm is taking their nutrients which is le ading to anemia ○ in adults, reduced worker productivity ○ reduced cognitive abilities and productivity means that infected individuals may not be able to contribute to the growth and economy of their communities, thus contributing to the cycle of poverty ○ in addition, hookworm has an important impact on pregnancy outcomes, as anemia leads to low birth weight and increased risk of death for mother and child Age ● Significant risk factor ● school-aged at greatest risk ○ prevalence of infection sharply increases fr om birth and peaks between age of 5 and 10 ○ have highest intensity of infection (most # of worms) Long-term health impacts of chronic helminth infection ● chronic/ disabling conditions ● compromised nutritional status ● poor iron absorption/ anemia ○ intestinal blood loss is associated with decreased… Epidemiology and Risk Factors: Polyparasitism ● individuals often co-infected with 2 or more helminth infections ● linked to individual predisposition to helminth infections and environmental influences Transmission cycle: schematic life -cycle Clinical Disease: Ascariasis/ roundworm ● s/s (signs/symptoms) ○ asymptomatic ○ moderate to heavy infections may lead to malnutrition and nonspecific GI symptoms ○ adult worms in small intestine can cause intestinal obstructio n esp. in children ○ worm migration can cause peritonitis secondary to intestinal wall perforation and bile duct obstruction, pancreatitis and hepatitis ○ adult worms migration can be due to stressful conditions (eg fever, illness or anesthesia) and by some an tihelminthic drugs ○ larvae migrating to lungs before reaching intestine which can cause wheezing and coughing Clinical Disease: Trichuriasis/ whipworm ● disease proportional to intensity of infection ○ most infected children asymptomatic ○ adult worms cause inflammation in large intestine ○ children with heavy infection can experience a stunt in growth and cognitive development Clinical Disease: Hookworm ● heavy hookworm infection produce iron deficiency anemia and protein malnutrition ○ leading cause of iron deficiency (anemia) in children and women of reproductive age DX/TX ● DX: fecal exams to look for the presence of worm eggs ● TX: antihelminthic drugs (e.g. ivermectin) NTDs caused by other helminthes ● trichinosis ● draculiasis “guinea worm” - Jimmy Carter ● Lymphatic filariasis “elephantitis” ● Onchocerciasis “river blindness” Textbook notes: pg 316-333 Biology of Helminths ● The worms are divided into two morphological categories: roundworms (nematodes) and flatworms ● Possess circulatory, nervous, reproductive, excretory, and digestive systems ● Worms have complex reproductive systems ensuring the production of very large quantities of fertilized eggs and maximizing the continuance of the species. ○ dioecious→ the two sexes have different reproductive organs ○ hermaphroditic→ single animals produce both sperm and eggs Helminthic Diseases ● Infection with worms may result in death, but more frequently worm diseases are chronic and debilitating and may lower the quality of life in an entire community. ● Helminthic diseases are organized by their mode of transmission: Organism Classification Disease Transmission Principle Site(s) Foodborne and waterborne: -Ascaris Roundworm Ascariasis Food, water Intestinal tract, lungs -Trichuris Roundworm Whipworm Food, water Intestinal tract -Trichinella Roundworm Trichinellosis Pork consumption Intestinal tract -Dracunculus Roundworm Guinea worm Water Skin -Taenia saginata Flatworm Beef tapeworm Beef consumption Intestinal tract -Taenia solium Flatworm Pork tapeworm Pork consumption Intestinal tract Vectorborne: -Wuchereria Roundworm Filariasis Mosquitos Lymph vessels -Onchocerca Roundworm River Blindness Black Flies Skin, eyes Contact: -Ancylostoma/ Roundworm Hookworm Contact Intestinal tract, lungs, Necator lymph -Enterobius Roundworm Pinworm Contact Intestinal tract -Schistosoma Flatworm Schistosomiasis Water contact Skin, bladder, blood -Strongyloides Roundworm Strongyloidiasis Contact Small intestine, skin, bladder, small blood vessels Foodborne and Waterborne Diseases Ascariasis ● Caused by Ascaris lumbricoides→ large roundworms that resemble earthworms and live in the small intestine ● Life cycle: ○ infective eggs passed onto soil through infected feces ○ people become infected when they ingest food or water contaminated with the eggs ○ once in the intestine, the eggs hatch into larvae which penetrate the intestinal wall ○ enter blood vessels and are carried along by the blood flow into the heart and then into the capillaries of the lungs, migrate up the respiratory tree, and enter the back of the throat ○ swallowed and return to the small intestine ● s/s: in some people, damage to the lungs may occur as the worms journey through the lung tissue, causing a cough and the threat of secondary bacterial infection ○ rarely, adult worms may be coughed u p or block the pharynx, causing suffocation ○ malnutrition from a large number of worms feeding on intestinal contents ○ with high worm burden, intestinal obstruction and perforation of the intestinal tract may occur, leading to death ● Individuals practicing poor hygiene may suffer repeated bouts of infection Whipworm Infection ● Caused by Trichuris Trichiura which resembles a whip ● Life cycle: ○ eggs passed in fecal material onto moist, warm soil ○ eggs are ingested and hatch in the small intestine where they release larvae ○ larvae mature, migrate to the large intestine, and take up residence ○ life span is about four to seven years ● s/s: most cases produce no symptoms ○ abdominal pain, diarrhea, and recta l prolapse (particularly in small children) Trichinellosis ● Caused by: Trichinella Spiralis found in raw and undercooked pork ● Life cycle: this parasitic nematode has a direct life cycle, meaning that there is no intermediate host ○ pork or other meat that co ntains trichinella cysts is ingested ○ worms emerge in the small intestine ○ mating occurs and females lay eggs that develop into larvae ○ larvae migrate through the blood and lymph vessels and are transported to muscles, including the eye, tongue diaphragm, and chewing muscles, within which they form cysts ● s/s: ○ common: nausea, diarrhea, vomiting, fatigue and fever, followed by later symptoms of headaches, chills, aching muscles, and itchy skin ■ mild cases often go undiagnosed as they resemble flu -like symptoms ○ if the burden of worms is heavy: cardiac and respiratory problems Dracunculiasis ● Caused by: parasitic roundworm, Dracunculus medinensi s ● Present in poor countries ● Life cycle: ○ drinking water contaminated with dracunculus larvae→ small copepods (“water fleas”) feed on these larvae. Copepods are small crustaceans in the phylum Arthropoda. ○ when someone ingests water containing infected copepo ds, the copepods are digested but not the worm larvae, which penetrate the stomach and intestinal wall and enter the abdominal cavity ○ after appx 1 year, females migrate toward the skin surface, most commonly the foot or leg. A painful blister that eventually ruptures occurs at the site. ■ people sometimes immerse the blistered area in water in an attempt to relieve pain. the temp change causes the blister to open, exposing the adult worm. these worms are very skinny though, and in an induced event such as this, only part of the worm will escape and the rest will remain in the leg, leading to bacterial infection ■ after the natural rupture of the blister, the one -meter-long worm begins to enzymatically bore its way out through the skin→ causes excruciating and debilitating pain ● s/s: ○ fever ○ pain and swelling near the blister ○ difficulty in walking ○ loss of appetite ○ exhaustion ● Prevention: education about filtering drinking water and avoidance of entering water when worms are emerging, treating water sources with compounds to kill copepods, and the provision of clean water Tapeworms (Cysticercosis/Taeniosis) ● Taenia saginata (the beef tapeworm) and Taenia solium (the pork tapeworm) ● Life cycle: ○ initiated by ingestion of undercooked beef or pork containing encysted larvae (cysticerci) ○ larvae are digested, except the scolex (the head), which attaches to the intestinal wall by suckers ○ the scolex produces compartment-like segments known as proglottids, each of which is a reproductive bag containing both ovaries and testes ○ proglottids detach and move toward anus where they exit via feces ○ cattle and other herbivores graze on contaminated vegetation ○ larvae hatch from the eggs, penetrate through the intestinal wall, and become encysted as cysticerci in the muscle of the animal ● s/s ○ only mild abdominal symptoms ● A serious disease called cysticercosis can result from the ingestion of pork tapewo rm eggs ○ the tapeworm eggs hatch inside the stomach, penetrate the intestine and travel through the bloodstream; ultimately, they may cause cysticerci in the muscles, brain, or eyes ○ lumps may be present under the skin, and infection in the eyes may cause swelling or detachment of the retina ■ neurocysticercosis (cysticerci in the brain or spinal cord) is serious and may cause death. It is considered to be the most frequent preventable cause of epilepsy in developing countries Arthropodborne Diseases Lymphatic Filariasis (Elephantiasis) ● Caused by: filarial worms which block the lymphatic vessels and cause the accumulation of large amounts of lymphatic fluid in the limbs… blockage of these vessels results in a “backup” of lymph, causing swelling, partic ularly in the legs ● individuals with filariasis are prone to bacterial infections ● Life cycle: ○ initiated by the bite of mosquitos carrying filarial larvae ○ larvae migrate into the lymphatic vessels where, within about a year, they grow into adult worms with a lifespan of up to several years ○ the adult worms mate and the female release into the blood millions of microfilariae that may be ingested by mosquitoes taking a blood meal ● s/s ○ swelling of legs ○ chills, fever, and inflammation of lymph nodes and lymphatic v essels ○ some individuals remain asymptomatic and may never develop elephantiasis ○ the disease is not usually fatal, but still debilitating ■ WHO ranks filariasis as the second leading cause of permanent and lon- term disability worldwide Onchocerciasis (river blindness) ● world’s leading cause of blindness ● in many small villages nearly all villagers past the age of forty are blind, presenting a serious obstacle to socioeconomic development ● Caused by: Onchocerca volvulus, a parasitic worm ● Life cycle: ○ the disease vector, the black fly, bites a human and larval worms are deposited under the skin ○ they mature and produce millions of microfilariae (microscopic larvae) that migrate throughout the body, causing rashes, intense itching, depigmentation of the skin, and nodules that form around the adult worms. Some migrate into the eyes and invade the cornea, causing blindness ● s/s: ○ presence of nodules under the skin ○ severe itching ○ blindness or visual impairment Direct Contact Diseases Hookworm Disease ● Caused by: Ancylostoma duodenale (Old World hookworm) and Necator americanus (New World hookworm) ● The CDC estimates that about 20% of the world’s population is burdened by hookworms, particularly in tropical and subtropical climates where about one billion individuals carry hookworms ● Life cycle: ○ eggs hatch in warm, moist soil ○ penetrate the skin ○ carried to the lungs, where they are coughed up and swallowed, reaching the intestinal tract in about a week ○ in the small intestine the larvae mature where they live and mate whilst attached to the wall of the small intestine and produce thousands of eggs ○ eggs are passed out through the feces ● have biting plates→ mouth parts by which they attach and suck blood ● s/s: ○ anemia, protein deficiency, and fatigue ○ in children, severe cases can cause retarded growth and mental development as the direct result of blood loss ○ serious infection can be fatal in infants and causes children to be malnourished Strongyloidiasis ● Caused by: nematode Strongyloides stercoralis , sometimes called the threadworm because of its minute size ● females produce eggs by parthenogenesis, a process that does not require fertilization by males… tough luck, boys ● life cycle: ○ infective larvae in soil penetrate the skin and are sequentially transported by blood to the heart, lungs, and bronchial tree and into the pharynx, where they are coughed up and swallowed, finally reaching the small intestine ○ in the small intestine, the females mature and produce eggs ○ some eggs develop into larvae that penetrate the small intestine or the skin around the anus and repeat the cycle above ■ this repeated cycle results in internal autoinfection ● s/s: ○ nausea, vomiting, anemia, weight loss, and chro nic bloody diarrhea ○ in individuals who are immunocompromised, large numbers of invasive larvae can cause extensive damage, leading to death Enterobiasis (Pinworm Disease) ● most common helminthic disease in the US ● Caused by: Enterobius vermicularis ● Life cycle: ○ the adult male and female worms live and mate in the intestine ○ at night, while the infected person sleeps, egg -bearing females exit through the anus, deposit as many as 15,000 eggs around the skin in the anal area, and then die ○ the eggs are swallowed and hatch in the intestine, releasing larvae that mature into adults, and become established in the intestine ● self-infection is a common mode of transmission, particularly in children ● s/s: ○ anal itching, loss of appetite Schistosomiasis ● more than 207 million people have schistosomiasis in seventy -four countries of Africa, South America, the Caribbean, the Middle East, and the Far East ● Caused by: Schistosoma japonicum, haematobium, or mansoni→ frequently referred to as “blood flukes” ● Life cycle: ○ live in snails which release immature, free-swimming, microscopic forms, called cercariae ○ exposure to water containing cercariae allows penetration into the skin ○ migrate into blood vessels and enter into the liver ■ the adults coat themselves with antigens of the host to avoid detection by the host’s immune system ○ a male and female pair migrate into small blood venules (veins) of the intestinal tract or bladder ○ the worms feed on blood ○ eggs are discharged by defecation or urination into the water ○ the eggs hatch, penetrate the snails, and develop into cercariae ● s/s: ○ itchiness develops at the penetration site ○ fever, chills, cough, and muscle aches ○ damage caused to the liver, intestine, or bladder ○ more rarely, eggs may move to the brain or spinal cord , causing seizures, paralysis, or inflammation of the spinal cord ○ can also damage the spleen, liver, lungs, intestine, and bladder, causing the abdomen to become distended I’ve included a few public health valentines for your significant others on this f ine weekend… you’re welcome


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