Presentation on theme: "Introduction to Parasitology & Lab Diagnosis of Parasitic Diseases"— Presentation transcript:
1 Introduction to Parasitology & Lab Diagnosis of Parasitic Diseases Dr. Sudheer Kher
2 Why study Parasitology? Many of these parasites are causative agents of major public health problems of the world.Recent estimates of prevalence of parasites in the world are:Ascaris billion Hookworms billion Whipworms billion Filarial worms million Malaria million Schistosomes million Amebiasis million Taenia tapeworms million Clonorchis million Chagas’ Disease million These parasites cause untold suffering and death in the world today.
3 The burden of some major parasitic infections ParasiteDiseasesNo. people infectedDeaths/yrPlasmodiummalaria273 million1.12 millionSoil transmitted helminths:Roundworm (Ascaris)Whipworm (Trichuris)Hookworm (Ancylostoma and Necator)Pnemonitis, intestinal obstructionBloody diarrhoea, rectal prolapseCoughing, wheezing, abdominal pain and anaemia2 billion200,000SchistosomaRenal tract and intestinal disease200 million15,000FilariaeLymphatic filariasis and elephantiasis120 millionNot fatal but 40 million disfigured or incapacitatedTrypanasoma cruziChagas disease (cardiovascular)13 million14,000African trypanosomesAfrican sleeping sickness0.3 – 0.5 million48,000LeishamaniaCutaneous, mucocutaneous and visceral leishmaniasis12 million; 2 million new cases/yr50,000
7 Key definitions: What is ….? Medical parasitology: “the study and medical implications of parasites that infect humans”A parasite: “a living organism that acquires some of its basic nutritional requirements through its intimate contact with another living organism”. Parasites may be simple unicellular protozoa or complex multicellular metazoaEukaryote: a cell with a well-defined chromosome in a membrane-bound nucleus. All parasitic organisms are eukaryotes
8 Key definitions: What is ….? Protozoa: unicellular organisms, e.g. Plasmodium (malaria)Metazoa: multicellular organisms, e.g. helminths (worms) and arthropods (ticks, lice)An endoparasite: “a parasite that lives within another living organism” – e.g. malaria, GiardiaAn ectoparasite: “a parasite that lives on the external surface of another living organism” – e.g. lice, ticks
9 Key definitions: What is ….? Host: “the organism in, or on, which the parasite lives and causes harm”Definitive host: “the organism in which the adult or sexually mature stage of the parasite lives”Intermediate host: “the organism in which the parasite lives during a period of its development only”Zoonosis: “a parasitic disease in which an animal is normally the host - but which also infects man”Vector: “a living carrier (e.g.an arthropod) that transports a pathogenic organism from an infected to a non-infected host”. A typical example is the female Anopheles mosquito that transmits malaria
10 Taxonomic classification of protozoa Sub kingdomPhylumSub-phylumGenus- examplesSpecies- examplesProtozoaSarcomastig-ophorafurther divided intoSarcodina-- - move by pseudopodiaEntamoebaE. histolyticaMastigophoramove by flagellaGiardiaG. lambliaApicomplexano organelle oflocomotionPlasmodiumP. falciparum,P. vivax,P. malariae,P. ovaleCiliophoramove by cilliaBalantidiumB. coliMicrosporaSpore-formingEnterocyto-zoaE. bienusi
11 Examples of important intestinal protozoa Transmitted by the faecal-oral route and cause diarrhoeaGiardia lamblia: world-wide distribution, lives in the small intestine and results in malabsorptionEntamoeba histolytica: may invade the colon and cause bloody diarrhoea – amoebic dysentery. Also causes ameobic liver abscess.Cryptosporidium parvum: more prevalent in the immunocompromisedCyclospora cyatenensis - parasitises the small intestinal mucosa and may cause diarrhoea for several weeksBalantidium coli: a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulcerationEnterocytozoon bienusi: a microsporidian that parasitises the small intestine. Also more common in the immunocompromised.
12 Examples of important systemic protozoa Detected in the bloodPlasmodium: the cause of malaria. There are 4 species that infect man: P. falciparum, P. vivax, P. ovale and P. malariaeToxoplasma gondi: transmitted by the ingestion of oocysts from cat faeces. Infection can lead to ocular problems and is also a cause of neonatal toxoplasmosisLeishmania: transmitted by sand flies, can lead to visceral, cutaneous and mucocutaneous leishmaniasisTrypanosoma: haemoflagellates which causeIn Africa - sleeping sickness (transmitted by the Tsetse fly)In South America - Chagas disease (transmitted by the Reduviid bug)Typical lesion of cutaneous leishmaniasisTsetse fly – the vector of African trypanosomiasis It has a painful bite!
13 Taxonomic classification of helminths Sub kingdomPhylumClassGenus – examplesMetazoaNematodesRound worms; appear round in cross section, they have body cavities, a straight alimentary canal and an anusAscaris (roundworm)Trichuris (whipworm)Ancylostoma (hookworm)Necator (hookworm)Enterobius (pinworm or threadworm)StrongyloidesPlatyhelminthesFlat worms; dorsoventrally flattened, no body cavity and, if present, the alimentary canal is blind endingCestodesAdult tapeworms are found in the intestine of their hostThey have a head (scolex) with sucking organs, a segmented body but no alimentary canalEach body segment is hermaphroditeTaenia (tapeworm)TrematodesNon-segmented, usually leaf-shaped, with two suckers but no distinct headThey have an alimentary canal and are usually hermaphrodite and leaf shapedSchistosomes are the exception. They are thread-like, and have separate sexesFasciolopsis (liver fluke)Schistosoma (not leaf shaped!)
14 Examples of important metazoa – intestinal nematodes Trichuris (whipworm)A soil transmitted helminthprevalent in warm, humid conditionsCan cause diarrhoea, rectal prolapse and anaemia in heavily-infected peopleAncylostoma and Necator (hookworms)A major cause of anaemia in the tropicsStrongyloidesinhabits the small bowelinfection more severe in immunospressed people (e.g. HIV/AIDS, malnutrition, intercurrent disease)Enterobius (pinworm or threadworm)prevalent in cold and temperate climates but rare in the tropicsfound mainly in childrenAscaris (roundworm)Found world-wide in conditions of poor hygiene, transmitted by the faecal- oral routeAdult worms lives in the small intestineCauses eosinophiliaHeavy intestinal infections may occur with Ascaris. Adult worms can be several cms long.
15 Examples of important metazoa –systemic nematodes Filaria including:Onchocerca volvulus – Transmitted by the simulium black fly, this microfilarial parasite can cause visual impairment, blindness and severe itching of the skin in those infectedWuchereria bancrofti – The major causative agent of lymphatic filariasisBrugia malayi – Another microfilarial parasite that causes lymphatic filariasisToxocaraA world-wide infection of dogs and catsHuman infection occurs when embryonated eggs are ingested from dog or cat faecesIt is common in children and can cause visceral larva migrans (VLM)
16 Examples of important flatworms - cestodes Intestinal - (“tapeworms”)Taenia saginataworldwideacquired by ingestion of contaminated, uncooked beefa common infection but causes minimal symptomsTaenia soliumacquired by ingestion of contaminated, uncooked pork that contains cystercerciLess common, but causes cystercicosis – a systemic disease where cysticerci encyst in muscles and in the brain – may lead to epilepsySystemicEchinococcus granulosus (dog tapeworm) and Echinicoccus multilocularis (rodent tapeworm)Hydatid disease occurs when the larval stages of these organisms are ingestedThe larvae may develop in the human host and cause space-occupying lesions in several organs, e.g. liver, brain
17 Examples of important metazoa –trematodes (flukes) IntestinalFasciolopsis buski - A common parasite of humans and pigs in South- east Asia. This parasite is one of the largest trematodes to infect man (8cm in length) and lives in the upper intestine. Chronic infection leads to inflammation, ulceration and haemorrhage of the small intestineFasciola hepatica (liver fluke)- Primarily, a parasite of sheep, humans become infected when they ingest metacercariae that have encysted on watercress. The adult trematode lives in the intra-hepatic bile ducts of the liver. “Fascioliasis” can lead to severe anaemia in humansClonorchis sinensis (liver fluke)- Widespread in China, Japan, Korea and Taiwan, this parasite is acquired by ingestion of infective metacercariae in raw or pickled fishParagonimus westermani ( lung fluke)- Widespread in the Far East and South east Asia, the parasite is acquired by ingestion of infective metacercariae in raw or pickled crustaceansSchistosoma haematobium, S. mansoni and S. japonicum – see below
19 Hookworm (1) Epidemiology >1200m infections each year of which 100m are symptomaticIt is due to 2 parasites both of which occur worldwide:Necator americanus - predominant species in sub-Saharan Africa, south Asia and the PacificAncylostoma duodenale –predominant in S. Europe, N. Africa, western Asia, northern China, Japan and the west coast of AmericaHookworm is a major cause of anaemia
20 Hookworm (2)Life cycleAdult worms live in the intestine and excrete eggs in the faecesIn the absence of latrines, eggs contaminate soil and develop in warm, damp conditionseggs hatch and infective filariform larvae develop in about one week and remain infective in soil for many weeksfilariform larvae penetrate the skin when a person walks barefoot in the soillarva migrate from the skin to the lungs via the lymphatic and blood systemslarvae penetrate the capillary wall to enter the alveolusLarvae are propelled up the respiratory tree to the epiglottis where they are swallowedDevelops to adult stage in upper intestine; adult worms are fully mature after about 5 weeksEggs are excreted in the faecesNote: eating soil (pica) is a common practice. Ingested filariform larvae of A. duodenale can pass directly to the gut mucosaEgg of A. duodenale in faecal smear (size µm by µm)Filariform larvae
21 Hookworm (3)PathologyHookworms move several times a day to different attachment sites in the upper intestinal mucosa to ingest bloodThey secrete an anticoagulant which causes the old attachment sites to continue to bleedHeavy hookworm infection results in chronic haemorrhage from the duodenal and jejunal mucosaThe combination of constant blood loss due to hookworm infection and poor iron intake in the diet results in iron deficiency anaemiaA. duodenale ingests 4-5 times more blood each day than N. americanusIn a child, the continued daily loss of 10ml of blood can lead to severe anaemiaAdult male and female worms of A. duodenale
22 Hookworm (4) Symptoms and signs Minor Often itchy papules are found at the site where the larva penetrated the skinThere may be cough and wheezing as the larva migrates through the lungsMajorHookworm anaemiaTiredness, aches and painsPallorBreathlessnessOedemaDiagnosisMicroscopic examination of faecal smears to demonstrate significant numbers of hook worm eggsMeasure Hb, serum ferritin, ironExclude other causes of anaemiaTreatmentMebendazole (cheap) – 100mg, twice daily for 3 daysMebendazole is contraindicated in pregnancy – use Bephenium hydroxynaphthoate “alcopar”For anaemia: ferrous sulphate mg three times a day for 3 months (adult regimen)Prevention and controlHealth education and improve sanitation facilities – install pit latrinesEncourage use of protective footwearDiscourage soil eating (pica)Mass drug treatment of communitiesIron supplementation in areas of low iron intake
23 Lymphatic filariasis (1) Epidemiology120m people infected in >80 countries in Africa, Asia, the Pacific islands and South and Central America40m of those infected are disfigured or severely incapacitated95% cases due to Wuchereria bancrofti, other species include Brugia malayi and Brugia timoriA female Anopheles mosquito taking a blood meal
24 Lymphatic filariasis (2) Life cycleWuchereria bancrofti is mainly transmitted byCulex mosquitoes in IndiaAnopheline mosquitoes in AfricaB. malayi and B. timori are transmitted mainly by Mansonia mosquitoesLarval forms of the parasite (microfilariae) are taken up by a female mosquito when it takes a blood meal from a human infected with adult wormsThe microfilariae develop inside the mosquitoWhen the mosquito takes another blood meal the infective filariform larvae enter the bite woundFilariform larvae migrate to the lymphatics and lymph glandsLarvae develop into sexually mature adult worms over 3-12 months depending on the species of filarial wormMicrofilaria of B. malayi in thick blood film (H&E stain; source: CDC)Adult worms of B. malayi in section in a lymph node (source: Univ South Carolina)
25 Lymphatic filariasis (3) PathologyAdult worms live in the afferent lymphatic vessels and cause severe disruption to the lymphatic systemScrotal damage and massive swelling may occur when adult Wuchereria bancrofti lodge in the lymphatics of the spermatic cordLate stage disease is typified by elephantiasis – painful and disfiguring swelling of the limbsTrauma and secondary bacterial infection of affected tissues is commonElephantiasis of the leg (source: WHO/TDR/Crump)
26 Lymphatic filariasis (4) Symptoms and signs – 3 stages1. Asymptomatic stageThere is internal damage to the lymphatics and kidneys2. Acute stage – Filarial lymphangitisCharacterised by bouts of feverheat, redness, pain, swelling and tenderness of the lymph nodes and ducts3. Chronic stageUsually results in elephantiasis as a result of chronic lymphoedemaThere is a massive overgrowth of tissue resulting in severe deformitiesThe legs are often affected and result in inability to walkThe scrotum is often affected in men and the breasts and vulva in womenElderly male with massive hydrocoele, and elephantiasis of the leg. Also has nodules in the groin due to onchocerciasis (source: WHO/TDR/Crump)
27 Lymphatic filariasis (5) DiagnosisMicroscopic examination of Giemsa stained thick blood films for the presence of microfilariaeW. bancrofti shows marked nocturnal periodicity, so it’s best to collect blood samples between 10pm and 1 amSerologyTreatmentDiethylcarbamazine (DEC) rapidly kills microfilariae and will kill adult worms if given in full dosage over 3 weeksRelease of antigens from dying microfilaria causes allergic-type reactions – add an antihistamine and aspirin to treatment regimenOther treatment options areivermectincombination of DEC and albendazolePrevention and controlRapid diagnosis and treatment of infected individualsMass drug administration to at risk communitiesVector control: eliminate mosquito breeding sites through improved sanitation and enviromental managementPersonal protection against mosquito bites by insecticides, bednets and repellants
28 Laboratory Diagnosis of Parasitic Infections Purpose –Confirmation of clinical suspicionIdentification of unsuspected infectionMethods same as used in Bacteriology & Virology but significance of different methods varies.Isolation least important, morphological identification very important.Serology relatively less important
30 Morphological identification Examination of BloodThin SmearThick smearWet mount for microfilariaStains used
31 Cultivation of parasites Culture methods –AmoebaLeishmania & TrypanosomaMalarial parasiteAnimal inoculation – Not practicalXenodiagnosis – Vectors infected experimentallyImmunological diagnosis
32 Immunological diagnosis Serology – All tests availableIHAELISACIEPIFCFTMore useful inAmoebiasisLeishmaniasisMalariaToxoplasmosisTrichinosisFilariasisEchinococcosisSkin Tests – Specificity low, cross reactions commonCasoni’s testLeishmanin test
33 Sources of information The Special Programme for Research and Training in Tropical Diseases (TDR UNICEF, UNDP, World Bank, WHO) website: ww.who.int/tdr/media/image.htmlUniversity of South Carolina School of Medicine:Lecture notes on Tropical Medicine, Dion R Bell,Fourth edition, 1996, Blackwell Science.Parasites and human disease, W. Crewe and D.R.W. Haddock, 1985, First edition, Edward Arnold