Microbiology - Parasitology Exam Notes PDF

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These are notes that were gathered from Sue's lectures on parisitology and cover most things needed for the exam. ...

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MICROBIOLGY – Sue V – Parasitology What are Parasitic Diseases? - Parasite o An organism that is deriving its sustenance from another without giving something in return - Symbiosis o ‘living together’ – a close association between two organisms o a) mutualism – both organisms are benefited (bacteria in bowel) o b) commensalism – one organism is benefited, the other is unaffected - Parasitology o The science or study of these host-parasite relationships - Vector o ‘carrier’ of a parasite from one host to another - The host o The organism that provides food and/or protection o a) definitive host – the host in which sexual maturity an reproduction takes place, e.g. humans o b) intermediate host – the host in which the parasite undergoes essential development. More than one intermediate host may be required by some parasites. Humans sometimes serve as an intermediate host, e.g. malaria o c) reservoir (carrier) host – the host harboring a parasite in nature – serving as a source of infection for other susceptible hosts. Reservoir hosts show no sign or symptom of disease o A number of parasites require more than one host to complete their life cycle

Major Types of Parasitic Diseases - Nematodes – intestinal helminths (worms)

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Cestodes – tapeworms Trematodes – Schistosomiasis, flukes, etc. Intestinal and Luminal Protozoa – Amebiasis, Giardiasis Blood Protozoa – Malaria, African sleeping sickness, etc. Arthropods & Ticks – Fleas, lice, ticks, etc.

Eradication, Elimination, and Control - Eradication o A permanent reduction to zero of the worldwide incidence of infection - Elimination (interruption of transmission) o Reduction to zero of the incidence of infection by a specific pathogen in a defined geographical area - Control o Reduction of disease incidence, prevalence, intensity, morbidity or mortality. o Continued intervention measured may be required - Endemic o Regularly found among particular people or in a certain area Main Strategy of the WHO roadmap - Provide coordinated guidance and technical assistance to governments and health programs to eradicate, eliminate, or control - Encourage coordination between pharmaceutical companies, health care agencies, philanthropists (e.g. Bill Gates), universities to overcome neglected tropical diseases (NTDs) - Outcome: a significate reduction in morbidity and transmission so that they are no longer a public health problem.

Nematodes – Intestinal Helminths (worms) - Nematodes are cylindrical worms, hence the name roundworm - The mode of transmission varies with the type of worm - May involve ingestion of eggs or larvae

MICROBIOLGY – Sue V – Parasitology - Penetration by larvae - Bite of vectors - Ingestion of stages in the meat of intermediate hosts - Worms are often long-lived - Morphology described as a tube within a tube – the outer tube contains musculature and inner tube contains the digestive tract - Soil-transmitted helminth (worm) infections – Neglected Tropical Disease o Ascaris lumbricoides (roundworm) (NTD) – infects >1 billion people o Trichuris trichiura (whipworm) (NTD) – infects 795 million o Ancylostoma duodenale and Necator americanes (hookworms) (NTD) – infects 740 million - Other examples of nematodes o Enterobius vermicularis (pinworm), o Trichinella spiralis (trichinosis), o Strongyloides stercoralis (Cochin-china diarrhea), o Dracunulus medinensis (fiery serpents) (NTD) WHO Action on Soil-Transmitted Helminths – Control Strategies - Morbidity to be controlled by delivering preventive chemotherapy - Elimination and eradication will not be achieved until affected populations have access to effective sanitation, and sewage treatment, and disposal - Treat once or twice a year – pre-school and school-age children - Adults at high risk in certain occupations (e.g. tea-pickers, miners..) - It is considered that ‘deworming school-age children is probably the most economically efficient public health activity that can be implemented in any low-income country where soil-transmitted helminthes are endemic’ - In 2010, 711 million people worldwide received preventive chemotherapy for at least one neglected tropical disease WHO’s challenges and goals for prevention of neglected tropical diseases - Preventive chemotherapy

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o The large-scale delivery of single-dose, quality-assured medicines, either alone or in combination, provided free of charge and at regular intervals to prevent selected diseases Innovative and intensified disease management o Controlling through case management the diseases that are difficult to diagnose and treat, and which in most cases trigger severe clinical manifestations and complications Vector control and pesticide management o The safe and judicious management of public-health pesticides to achieve vector control through integrated vector management Safe drinking-water, basic sanitation and hygiene services, and education o The prioritization of improved sanitation combined with the delivery of preventive chemotherapy and health education to sustain reductions in prevalence of many of these diseases Zoonotic disease management o The application of veterinary sciences and interventions to protect and improve human health (also referred to as veterinary public health)

Roadmap targets: WHO Action on Soil-Transmitted Helminths - 600 million tablets of albendazole or mebendazole - By 2015 o 50% of preschool children are regularly treated o 100% of countries have an action plan - By 2020 o 75% of preschool and school-aged children are regularly treated o 75% coverage of preschool and school-aged children in 100% countries affected

Ascaris lumbricoides (roundworm) - Background and epidemiology o A soil-transmitted helminth

MICROBIOLGY – Sue V – Parasitology o Estimated annual global morbidity – 1 billion o Estimated annual global mortality – 20,000 o Most prevalent in children aged 5-9 years, but can occur in all age groups o Worldwide distribution but incidence is highest in poor rural populations o Adults worms live in the small intestine o The worms measure 30cm x 5cm (male worm is smaller) - Life Cycle

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o Larvae are found in soil and are eaten due to contamination of food with soil/feces o Enter the small intestine

o Eggs hatch and larvae penetrate intestinal wall and enter the bloodstream o Stop at pulmonary arteries of the lungs for ~2 weeks – grow to 1.5cm o Break into the alveoli of the lungs and travel up to the throat where they are swallowed again o Adult worms attach to the small intestine to mate and survive on digested food o Female worms can release up to 200,000 eggs/day o Eggs require a period outside the host usually in soil in order to fertilize Symptoms o Abdominal pain, listlessness, weight loss, anorexia, distended abdomen, intermittent loose stool, occasional vomiting o Pulmonary stage – there may be a brief period of cough, wheezing o Complication include abdominal obstruction Diagnosis o Based on identification of eggs/worms in the stool Treatment o Mebendazole for 3 days is effective Prevention o Good hygiene is the best preventive measure o Good sanitation o Access to clean water

Ancylostoma duodenale and Necator americanes (hookworms) - Distribution o N. americanes

MICROBIOLGY – Sue V – Parasitology  The Americas, Central and Southern Africa, Southern Asia, Indonesia, Australia, and Pacific Islands o A. duodenale  Dominant species in the Mediterranean region and northern Asia - Morphology o Adult – 11mm long - Characteristics o Enter through the foot – ‘hookworm foot’ - Life Cycle -

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o A different strategy for entry into human o Eggs are released in the stool o Larvae hatch in soil 1-2 days called rhabditiform

o Undergo two moults in the soil over a period of 51 days and develop into infective filariform larvae ready to infect humans o Survive 3-4 weeks in this form o Humans become infected when infective flariform larvae penetrate skin, enter the bloodstream and move to the heart and lungs, penetrate the alveoli of the lungs ascend to the throat and are then swallowed o Develop into adults in the lumen of the small intestine and attach to the intestinal wall o Live for 1-2 years Symptoms o Major symptoms are from blood loss as the hookworms damage intestinal mucosa o Anemia is common o Loss of iron can retard growth and mental development Diagnosis and Treatment o Finding hookworm eggs in feces o Mebendazole for 3 days is effective Control o Sanitation is the chief method of control – avoid contact with infected fecal material o Avoid walking barefoot in hookworm-infected areas o Do not defecate in places other than latrines, toilets o Do not use human excrement or raw sewage as manure or fertilizer in agriculture

Dracunculus medinensis (Guinea worm) - History o Known as a parasite of humans since about 1530 BC

MICROBIOLGY – Sue V – Parasitology o Persian physicians removed D. medinensis from patient during 9th century - Hosts o Definitive: Humans o Intermediate: Copepod - Distribution o As of 2005, Guinea worm disease only occurs in Africa, and few remote villages in Rajasthan, India and Yemen. o Only 9 countries are endemic:  Sudan, Ghana, Nigeria, Mali, Togo, Burkina Faso, Ethiopia, Niger, and Ivory Coast o >50% of all cases of Guinea worm disease are reported from southern Sudan o 3.5 million cases in the 1980s - Morphology o The adult female guinea worms is a long, slender worm ranging from 30-120cm length x 0.09-0.17cm width o Three mature guinea worms (size)  Gravid (carrying eggs) female > mature female > mature male - Characteristics o Only helminthic parasite transmitted solely through water  But usually occurs during drought  Everyone is forced to drink from the same stagnant water supplies or pay for a well o Three conditions to be met before D. medinensis can complete its life cycle  The skin of an infected individual must come in contact with water  The water must contain the appropriate species of microcrustacean  The water must be used for drinking o Believed that parasites feed on blood due to the gut often being filled with dark brown gut material - Vector - Crustacean - Life Cycle

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o Humans become infected by drinking unfiltered water containing copepods (small crustaceans) which are infected with larvae of D. medinensis o Following ingestion, the copepods die and release the larvae, which penetrate the host stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space o The worm molts again 20 days and 43 days post infection o Females are fertilized by the third month o After maturation into adults and copulation, the male worm die and the females migrate into the subcutaneous tissues towards the surface of the skin o Approx. one year after infection, the female worm induces a blister on the skin, generally on the distal lower extremity, which ruptures o When this lesion comes into contact with water, which the patient seeks to relieve the local discomfort, the female worm emerges and releases larvae o The larvae are ingested by a copepod and after two weeks (and two molts) have developed into infected larvae Diagnosis

MICROBIOLGY – Sue V – Parasitology o Diagnosis is made from the local blister, worm, or larvae o The outline of the worm under the skin o Some people claim to be able to feel the worm moving towards the surface of the skin o Finding calcified worms - Pathology o Dracunculiasis may result in three major disease conditions  Emergent adult worms  Secondary bacterial infection  Non-emergent worms  When worms do not emerge, they degenerate and release antigens causing fluid abscesses or allergenic reactions  Calcified worms cause inflammation or arthritis if they remain in a joint  Can cause paraplegia if worms get into CNS o None until the female worms cause an allergic reaction by releasing metabolic wastes into the host o This occurs at the onset of migration to the skin  A rash accompanied by severe itching, Nausea, Vomiting, Diarrhea, Dizziness, Edema o Reddish papule-blister (local itching and intense burning). Blisters ruptures, become abscessed-very painful. Secondary bacterial infections of opening possible.  Retreating worm can draw bacteria under skin as well. o There may be later symptoms  Fibrosis of the skin, muscles, tendons and joints (may interfere with locomotion or use of limbs) - Treatment o Treatment includes the extraction of the adult guinea worm by rolling it a few centimeters per day  Usually takes weeks or months depending on how long the worm is o Exposing area to cold water helps remove worm faster. Preferably by multiple surgical incisions under local anesthesia

o Infection does not make a person immune Economic Impact o Seasonal pattern of worm emergence peaks at maximum agricultural labor demand o Significant decline in agricultural productivity and economic hardship - Control o Filter, boil, or treat water with chlorine to kill intermediate host  Finely-meshed cloth, or a filter made form a 0.15mm nylon mesh will be able to filter out the copepods from drinking water o Avoid bathing or wading in drinking water o Construction of copings around well heads or the installation of boreholes with hand pumps  Borehole is a deep and narrow well  Coping is a cap/cover over a well  Key is to prevent copepod growth by controlling sunlight  Light increases eh food source of the copepod - Eradication Efforts o Perhaps the only parasite that has potential to be eradicated in the near future o 98% decline in cases from 1986 to 2000 - Why has Dracunculiasis control been so successful? o Diagnosis is easy and unambigious (it relies on visual recognition of the emerging worm) o The intermediate host (copepod) is not airborne o Control is simple, cost effective, and easy to implement  Filtering of drinking water  Vector control – treating pods  Early detection and bandaging of infected individuals Blood & Tissue Helminths - Examples o Wuchereria bancrofti and W. (Brugia) malayi (elephantiasis) o Onchocerca volvulus (Blinding filariasis; river blindness) -

MICROBIOLGY – Sue V – Parasitology o Loa loa (eye worm) Wuchereria bancrofti (elephantiasis) - Human pathogen, distributed in tropical areas worldwide - 40 million people are estimated to be disfigured and incapacitated by this disease - Infected individuals are generally incapacitated - One of the major causes of disability worldwide - Insect vector required for transmission - by mosquitos – making control difficult - Adult Filarial worms are around 10cm long - The adult male and female worms reside in lymphatic where they mate and produce large numbers of larvae, called microfilariae - The microfilariae circulate in the blood stream where they can be picked up by a biting mosquito - Adult worms can live for many years, continuously producing microfilariae and contributing to ongoing transmission of the disease - Acquired by bite of a blackfly – insect-borne parasites are difficult to control - Symptoms o Parasites are lodged in the lymphatic system o Many people are asymptomatic and there is slow damage to the lymphatic system o Causes lymphedema – filarial worms obstruct the lymphatic system and cause swelling – usually in legs, arms, breasts, and genitalia o Can be associated with high fever every 8-10 weeks o Enlarged lymph nodes and inflammatory response to live and dead parasites - Diagnosis o Presence of microfilaria in blood samples collected at night - Treatment o DEC (Diethylcarbamazine) for 14 days kills the adult worms - Vector – mosquitos - Life Cycle

o L3 larve form called filariform larvae enter the human body during a mosquito bite o They enter through the bite wound and migrate lymphatic vessels and lymph nodes o Take ~1 year to mature o Adult females produce larvae called microfilaria (measuring ~250um) o Microfilaria move actively in the lymphatic and blood system o Mosquitos are infected during a blood meal o 10-14 days traverse mosquito and become infective for man in the mosquito

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The Global Program to Eliminate Lymphatic Filariasis (elephantiasis)

MICROBIOLGY – Sue V – Parasitology o In 2008, 496 million people were treated in a mass drug administration program o China and Republic of Korea no longer an endemic problem o There are 81 countries listed as endemic for lymphatic filariasis o 2.2 billion tablets of DEC have been donated to WHO by Eisai for 2013-2020 o The drugs are safe and are given to everyone in each area – this must be repeated for 4-6 years o WHO estimates if levels of drug therapy are maintained then elimination can occur in Pacific Islands (not Papua New Guinea) by 2015 o By 2017, the goal is to have 70% of 81 endemic countries to have stopped drug therapy and be in a surveillance stage o By 2020, 100% of all endemic countries will be certified free from disease

Onchocerca volvulus (Blinding filariasis; river blindness) - Caused by a Helminth worm

MICROBIOLGY – Sue V – Parasitology - The disease is called ‘river blindness’ because the blackfly that transmits the infection lives and breeds near fast flowing streams and rivers - Visual impairment or blindness - Skin disease, including nodules under the skin, or debilitating itching - Half a million people are blind or visually impaired due to Onchocerciasis - Causes ugly skin, de-pigmentation, and severe itching - Sub-Saharan Africa, Yemen, and Latin America - Insect vector – black fly - Life Cycle

o Infective L3 larvae are injected into the skin when blackfly takes a blood meal o Form nodules in subcutaneous tissue under the skin and mature into adults o Takes 8-10 months to mature and produce microfilaria o Adults can live for 15 years under the skin o There can be several adults in a single nodule

o Females measure 33-50 cm o Males measure 19-42 cm o Female can produce 1000 microfilaria – larvae are picked up during a blood meal o Larval stage of development occurs in the insect - Symptoms o 1000s of microfilariae are produced every day o Symptoms begin 10 months after infection o Move through the body and die, causing most of the symptoms o Blindness, skin lesions, intense itching o Larvae that die in the eye results initially in reversible lesions in the cornea o Without treatment progress to permanent clouding of the cornea, resulting in blindness o There can also be inflammation of the optic nerve resulting in vision loss, particularly peripheral vision, and eventually blindness - Treatment o Ivermectin is effective in killing the larvae o No treatment for the adult worm (although Jimmy Carter Foundation is reporting progress) o Pharmaceutical company Merck & Co provides unlimited supply Ivermectin free o 68.4 million people receiving regular treatment o Estimated 73% reduction in disease since the program began o Colombia and Ecuador, transmission appears to have been interrupted following mass drug administration with 85% population coverage o Vector control is also used to reduce transmission o By 2015, the aim is to have complete elimination from Latin America and Yemen o By 2020, the aim is to have global elimination Cestodes – Tapeworm - Morphology o Flattened ribbon-like body

MICROBIOLGY – Sue V – Parasitology o The scolex (head) contains sucksers and hooks o Proglottids form the ribbon-like body o Eggs are produced in each proglottid o Eggs are released when proglottids are broken down by digestive enzymes in the host o Each proglottid is 18x6cm o Eggs are 35x45 micrometers o Cestodes can have 3-3000 proglottids Tenia solium (Pork Tapeworm) & T.saginata (Beef Tapeworm) - Worldwide distribution – highest in developing countries - As high as 10% in the developing world - T. saginata are 4-6 meters long - T. solium are 0.5 meters long - Life Cycle

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o Transmission occurs with feces contaminated – with eggs that are eaten by cows or pigs

o Larval cyst called a cystercerci is ingested with poorly cooked infected meat o Larvae escape the cyst and pass to small...