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FabulousSugilite5057

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Menoufia University

Dr. Mona Mohammed Saleh

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medical parasitology parasitology medical science biology

Summary

This lecture introduces medical parasitology, encompassing the science of parasites infecting and causing diseases in humans. It outlines parasites, hosts, and various transmission methods. The document further details different types of parasites, transmission methods, and diagnosis procedures vital to understanding the subject matter.

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Introduction of Medical Parasitology By Dr. Mona Mohammed Saleh lecturer of parasitology Faculty of medicine Menoufia university Introduction  Medical Parasitology: it is the science that deals with the study of the organis...

Introduction of Medical Parasitology By Dr. Mona Mohammed Saleh lecturer of parasitology Faculty of medicine Menoufia university Introduction  Medical Parasitology: it is the science that deals with the study of the organisms (parasites) that infect and produce diseases in human.  Parasite: is a living organism, which lives in or upon another organism (host) and derives nutrients directly from it, without giving any benefit to the host.  Host: it is a living organism that harbors the parasite  Types of hosts:  Definitive host: it is the host that harbors the mature stage of the parasite.  Intermediate host: it is the host that harbors the immature stage of the parasite.  Reservoir host: it is an animal that harbors the mature stage of the parasite.  Vector: an arthropod which carries the parasite from one host to another host. Medical parasitology is calssified into:  Helminthology: a) Class:Trematoda b) Class:Cestoda c) Class:Nematoda  Protozology  Arthropodology  Parasites may be classified as:  Ectoparasite: They inhabit the surface of the body of the host without penetrating into the tissues. The infection by these parasites is called infestation, e.g., fleas or ticks.  Endoparasite: They live within the body of the host (e.g., Leishmania). Invasion by the endoparasite is called infection.  Temporary parasite: visits the host to take its blood meal (mosquitoes).  Permanent parasite: lives in or on the host the whole of its life (Ascaris lumbricoides)  Facultative parasite: lives as parasite or free living (Strongyloides stercoralis).  Obligatory parasite: can"t live without it"s host )lice).  Specific parasite: affects one specific particular host (Entrobius vermicularis).  Nonspecific parasite: normally it inhabits and completes its life cycle in an animal host but can inhabits a human host without completing its life cycle (Avian schistosomes and Toxocara canis).  Opportunistic parasite: it can cause disease only in immunodeficient individuals, while no symptoms appear in immunocompetent individuals (e.g. Cryptosporidium).  Sources of Infection:  Man: Blood and human excreta (stool, urine, sputum) containing the infective stage of the parasite (e.g., toxoplasmosis, amoebiasis, enterobiasis, etc.).  Animal:  Raw or under cooked meat containing the infective stage of the parasite e.g Taenia saginata & Taenia solium.  Animal Stool containing different stages of the parasite.  The infection which is transmitted from infected animals to humans is called zoonosis.  Contaminated soil: Soil polluted with human or animal excreta containing eggs of the parasites can act as an important source of infection, e.g., Hookworm, Ascaris species, Strongyloides species and Trichuris species.  Contaminated water: with the infective stage of the parasite. e.g. E. histolytica or Giardia lamblia, can act as source of infection. Modes of Transmission  Ingestion: Infection is transmitted orally by ingestion of food, water or vegetables contaminated with feces containing the infective stages of the parasite. (e.g., cysts of E. histolytica, and ova of Ascaris lumbricoides)  Penetration of the skin and mucous membranes: Infection is transmitted by penetration of the skin by the larval forms of the parasite (e.g., filariform larva of Strongyloides stercoralis and hookworm)  Sexual contact: Trichomonas vaginalis is the most frequent parasite to be transmitted by sexual contact.  Vertical transmission: Mother to fetus transmission is important for some parasitic infections like Toxoplasma gondii, Plasmodium spp. and Trypanosoma cruzi.  Blood transfusion: Certain parasites like Plasmodium species, Babesia species, Toxoplasma species, Leishmania species and Trypanosoma species can be transmitted through transfusion of blood or blood products.  Autoinfection: some intestinal parasites may be transmitted to the same person by contaminated hand (external autoinfection) or by reverse peristalsis (internal autoinfection). e.g. Cryptosporidium parvum, Taenia solium, Enterobius vermicularis, Strongyloides stercoralis and Hymenolepis nana.  Inhalation: of dust carrying the infective stage of the parasite, e.g (Entrobius vermicularis.  Contact with infected patient e.g scabies.  Bite of vectors: Many parasitic diseases are transmitted by insect bite such as: malaria (female anopheles mosquito), filariasis (Culex), leishmaniasis (sandfly), Chagas’ disease (reduvid bug) and African sleeping sickness (tsetse fly) Diagnosis of parasitic diseases Several ways are important in establishing the specific diagnosis of various parasitic infections.  1-Clinical diagnosis: case history, symptoms and signs. Successful diagnosis depends upon:  II- Laboratory diagnosis: Direct: demonstrating the diagnostic stage of the parasite in the collected sample (stool, urine, sputum, blood). Parasitic diagnosis can be done either microscopically or macroscopically and detecting the different stages of the parasite by culture. Indirect: finding indicator for the presence of parasitic infection.  Intradermal skin tests  - Immunodiagnostic methods (antigen and antibody detection)  Molecular methods: DNA probes and polymerase chain reaction (PCR)  III-Imaging techniques: X-ray and ultrasonography  IV-Biopsy Medical parasitology is calssified into:  Helminthology: a) Class:Trematoda b) Class:Cestoda c) Class:Nematoda  Protozology  Arthropodology Trematodes (Fasciola and Heterophys) by Dr. Mona Mohamed Fahem Saleh Lecturer of medical parasitology Faculty of medicine Menoufia university Fasciola gigantica and Fasciola hepatica  Disease: Fascioliasis.  Geographical distribution: worldwide, especially in tropical and subtropical countries.  Habitat: Bile ducts of the liver and gall bladder.  Definitive host: Herbivorous animals most commonly, sheep, cattle, goats, camels, and buffalo. Man can be occasionally infected.  Intermediate host: Snails Lymnaea cailliaudi and Lymnaea truncatula. Morphology: Adult flukes: Size: 30 - 70 mm long by 8 - 15 mm wide. F. hepatica is smaller. Shape:  Adult flukes are flattened and leaf-like.  hermaphrodites (i.e., have both male and female sex organs), broader anteriorly, having an anterior cone and prominent shoulders.  The worm has 2 suckers, oral and ventral.  The tegument is armed with backwardly directed spines.  Egg: (Diagnostic stage) Size: 150 x 90 um. Shape: ovoid. Shell: thin, operculated. Color: bile stained (yellowish brown). Content: embryonic cells (immature). Encysted metacercaria (Infective stage):  Size: 0.25 mm diameter.  Shape: spherical with a thick white cyst wall.  Life Cycle:  In the definitive host, adult worms live in the bile ducts, lay eggs that are carried with bile to reach the intestinal lumen and passed with stool outside the body.  Eggs must reach water to complete the life cycle.  Immature eggs embryonate in fresh water and the miracidium develops and emerges from the egg to infect the snail intermediate host.  In the snail, the miracidium develops asexually sporocyst, redia and finally cercaria. The cercariae are shed out of the snail, lose their tail, and encyst on aquatic vegetation as encysted metacercaria  Definitive hosts acquire the infection by eating contaminated vegetation with metacercaria.  After ingestion, the cyst wall of metacercaria is destroyed during mastication and by the enzymatic activity of the intestinal environment.  The emerging juvenile flukes penetrate the intestine and migrate through the abdominal cavity and penetrate the Glisson’s capsule to reach the liver.  In the liver, it enters its final habitat, the bile ducts, and matures into adults.  Clinical picture:  The clinical course of human fascioliasis can be divided into two phases: acute and chronic.  Acute phase: patients may develop symptoms like prolonged febrile illness, anorexia, right upper quadrant abdominal pain, gastrointestinal disturbances, urticaria and weight loss. Ascites, hepatomegaly, splenomegaly, and anemia also occur.  Chronic phase:  patients may develop symptoms of biliary obstruction such as biliary colic, epigastric pain, jaundice, and right upper quadrant abdominal tenderness.  In severe cases, migrating parasites may erode into blood vessels, causing huge, life-threatening subcapsular liver hematomas.  Young children are especially susceptible to the disastrous long-term complications associated with malnutrition and anemia such as stunting and poor neurocognitive maturation  Ectopic Infection: is not frequent, but can occur in peritoneal cavity, intestinal wall, lungs, subcutaneous tissue.  Diagnosis: Clinical: history and clinical manifestations Laboratory: There is no gold standard test to diagnose fascioliasis. A. Stool examination: detecting parasitic eggs is confirmatory B. Serological tests: for antibody and antigen detection are of value during the migratory stage of the worms and ectopic infection. C. Eosinophilia. D. Ultrasound and CT. E. Molecular diagnosis: A nested-PCR was developed for detection of parasitic DNA in human stool and urine samples.  Treatment:  Biothionol: 30 -50 mg/kg on alternate days for 10 to 15 doses.  Triclabendazole: 10 mg/kg in two doses separated for 12 to 24 hours.  Nitazoxanide: is a good alternative in case of triclabendazole failure especially in the chronic stage of infection. It is given as 500 mg twice a day for 7 days in adults.  Metronidazole: 1.5 g/day for 3 weeks is an effective treatment for adults and can be applied for treatment of fascioliasis in children.  Prevention and control: Anthelmintic Therapy: Prophylactic anthelminthic therapy is given to the animal host. Mass drug administration to decrease the prevalence of fascioliasis in human especially in high burden countries  Health education.  Snail control. Intestinal Fluke Heterophyes heterophyes Geographical distribution:Fish-eating countries. Habitat: Small intestine. Definitive Host: Man- & fish-eating animals (dogs & cats). Intermediate Host: 1st intermediate host: Pirenella conica snail. 2nd intermediate host: boury & bolty fish. Infective stage: Encysted metacercaria Diagnostic stage: Egg Morphology: Adult worms: Pear-shaped, gray, and have a broadly rounded posterior end in addition to an oral and ventral sucker, contains a third sucker, the genital sucker, surrounding the genital pore. Egg: Size: 30 μm ×15 μm. Shape: oval. Shell: thick double walled with operculum & posterior knob. Color: brownish yellow. Content: miracidium (mature).  Cercaria:-  Formed of body and membranous tail (lophocercous cercaria).  Body contains oral and ventral suckers, primitive gut, 2dark eye spots and 7 pairs of penetrating glands Life cycle:  Adults live in between the intestinal villi (habitat) of the definitive host.  Mature eggs pass with stool.  In water eggs don’t hatch, they are ingested by 1st intermediate host (Pirenella conica).  Egg hatches inside the snail and the miracidium is liberated.  Miracidium changes into sporocyst → redia → cercaria.  Cercaria comes out of the snail.  Cercaria swims in water until they find the 2nd intermediate host (boury & bolty fish).  Cercaria penetrates the skin of fish leaving the tail outside and become encysted metacercaria under scales, gills, or inside fish muscles then it becomes infective after 2-3 weeks.  Man and fish-eating animals are infected by eating raw, undercooked, or under-salted fish (feseekh) for less than 10 days containing encysted metacercaria (the infective stage).  In the small intestine metacercaria is liberated and lodged in between villi and mature into adult in 3 weeks ⮚ Clinical Picture: Name of the Disease: Heterophyiasis. Clinical manifestations:  Most infections are asymptomatic or accompanied by mild intestinal discomfort, which may include mucous diarrhoea, colicky pains, intermittent neurasthenia, and lethargy.  Symptoms are more frequent in heavy infections, but they subside spontaneously after one month, although the flukes remain.  Upon further infection, symptoms may recur, giving rise to occasional episodes of diarrhoea in endemic areas. Diagnosis: Clinical: History of eating undercooked or under-salted fish. Symptoms and signs. Laboratory: Direct Microscopic examination: The diagnosis is suggested by detecting the characteristic eggs in the stool ⮚ Treatment: Praziquantel is the drug of choice. A single dose of 10–20 mg/kg is highly effective. Prevention and control:  Treatment of patients and infected animals.  Proper cooking of fish and salting not less than 10 days.  Snail control.  Health education: The life cycle could be disrupted by improved sanitary conditions and educational information about proper sewage disposal away from ponds or lakes where the intermediate hosts reside.

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