Medical parasitology

Medical parasitology

Parasitology is the science dealing with parasites.Parasites can be classified into:Helminthes.Protozoa.Arthropods.

Medical terms you should knowParasite: is a living organism that lives at the expense of its host.Host: the living organism at which the parasite lives on his expense.Parasitism: relationship between two living organisms one gets the benefit (parasite) and the other looses (host).As regard to the hostDefinitive (final host): The host that harbors the adult or sexual stages of the parasite.Intermediate host: The host that harbors the larval or asexual stages of the parasite.Vector: an arthropod the carries the infective stage of the parasite and can transmit it by active biological sharing in life cycle.Reservoir hosts: other hosts that harbor the parasite and thus ensure continuity of the parasite's life cycle and act as additional sources of human infection.

As regard to parasiteObligate parasite is termed when the parasite can live only in a host. Facultative parasite when it can live both in a host as well as in free form. Endoparasites parasites that live inside the body.Ecto-parasites parasites that exist on the body surface.

ProtozoaGeneral characters of protozoaUnicellular organisms that are capable of performing whole life functions.Eukaryotic.Complex life cycle involving various stages or formsReproduction : sexual and asexualMotility : flagella, cilia, amoeboid movementThese ways of motility are used to divide them into taxonomic groups

Asexual reproduction:Binary fission: longitudinal or transverse.Schizogony : Nucleus undergoes multiple divisions before the cell divides.

Sexual reproduction1. Gametogony: process often involves production and fusion of gametes.2. Conjugation and exchange of genetic material between different mating types in Ciliophora (Balantidium coli).

Cyst formationEncystment of some protozoa is essential for survival outside the body and during the transmision from host to host.

Intestinal protozoaIntestinal protozoa significant to human health includeEntamoeba histolytica (Amebae). Balantidium coli (Ciliates). Giardia lamblia (Flagellates). Cryptosporidium parvum and Isospora belli (Sporozoa).

Entamoeba histolytica

DiseasesAmebic dysentery and liver abscess.Morphology: it has two form stagesTrophozoite: With the ameboid appearance due to presence of pseudopodia. Cyst: cysts are spherical with a cyst wall.1 to 4 nuclei which are similar to trophozoite.Life cycleThere are: no intermediate or reservoir hosts. infective stage: mature cysts. Mode of infection: feco-orally through contaminated food or hands.Clinical Findings# Dysentery. # Amebic abscess Laboratory diagnosisFinding cysts in the stool. TreatmentMetronidazole (Flagyl)

A:Entamoeba histolytica trophozoite with one ingested red blood cell and one nucleus (circle with inner dotted line represents a red blood cell). B:E. histolytica cyst with four nuclei

Gardia lambliaDiseasesGardiasis= Lambliasis.MorphologyTrophozoite: half pear-shaped organism with 8 flagella and 2 axostyles arranged in a bilateral symmetry. There are two anteriorly located large suction discs. The cytoplasm contains two nuclei and two parabasal bodies.Cyst:The cytoplasm contains four nuclei with smooth well-defined wall. Life cycle Definitive host: Man.Infective stage: cystMode of infection: ingestion of cysts Clinical findingsteatorrhiaLaboratory diagnosisCysts (constipation) and trophs ( diarrhea) in the stool.TreatmentMetronidazole

Balantidium coli

Disease: Balantidiasis.This is a parasite primarily of cows, pigs and horses (zoonotic protozoan). MorphologyPresence of cilia on the cell surface. Macro- and a micro-nucleus. Cytostome.Life cycle:Infective stage: cyst.Mode of infection: ingestion of cysts in fecal material of farm animals.Symptoms and pathogenesis of balantidiasis are similar to those seen in entamebiasis. However, extra intestinal abscesses are not seen.Diagnosis:Finding cysts in stool.Treatment:Metronidazole

Urogenital protozoaTrichomonas vaginalis (a flagellate)Disease: TrichomoniasisMorphologyTrophoziote is the active and infective form, no cyst stage.Life cycleInfective stage: trophozoitesInfection occurs primarily via sexual contact.SymptomsIn Females withheavy infection: copious foul-smelling yellowish, frothy discharge.TreatmentMetronidazole Vinegar douche may be useful.

Blood & Tissue ProtozoaPlasmodiumDiseaseMalaria is caused by four plasmodia: Plasmodium vivax.Plasmodium ovale. Plasmodium malariae.Plasmodium falciparum. malaria is one of the most common infectious diseases and a leading cause of death.Life cycleThere are two phases in the life cycle:the sexual cycle in mosquitoes, the final host.asexual cycle schizogony, occurs in humans, the intermediate hosts.Infective stage: sporozoitesMode of infection:Mosquito bites. Across the placenta. Blood transfusions. Intravenous drug abuse.PathogenesisMost of the pathologic findings of malaria result from the destruction of red blood cells.

Malaria presents with abrupt onset of fever and chills.The timing of the fever cycle is 72 hours for P. malariae (quartan malaria) and 48 hours for the other plasmodia (tertian malaria). Malaria caused by P. falciparum is more severe than that caused by other plasmodia because:It is characterized by infection of more red cells. Occlusion of the capillaries with aggregates of parasitized red cells leading to: Cerebral malaria. Hemoglobinuria "black water fever.Laboratory DiagnosisBlood films for finding the parasite inside RBcs

Toxoplasma

DiseaseToxoplasma gondii causes toxoplasmosis.Life cycleInfective stageOocysts in animal stools.True cysts in meat.Tachyzoites in blood or transplacentally.Mode of transmissionIngestion of cysts in uncooked meat or cat feces.Transplacental transmission: congenital infection of the fetus occurs only when the mother is infected during pregnancy for the 1st time. Clinical FindingsAsymptomatic in immunocompetent adults.Immunosupressed patients (e.g., AIDS patients), life-threatening disseminated disease.Congenital infection.Laboratory DiagnosisImmunofluorescence assay for IgM antibody is used. IgM is used to diagnose congenital infection, because IgG can be maternal in origin.

TrypanosomaThe genus Trypanosoma includes three major pathogens:Trypanosoma cruziDiseaseT. cruzi is the cause of Chagas' disease (American trypanosomiasis).Life cycleVector: reduviid bug (cone-nose or kissing bug).Infective stage: metacyclic trypomastigotes Mode of transmission: contamination of bite wound with bugs feces leads to infection.

Clinical FindingsFacial edema and a nodule (chagoma) near the bite. Fever, lymphadenopathy, and hepatosplenomegaly. Some patients progress to the chronic form with myocarditis and megacolon.Laboratory DiagnosisAcute disease :presence of trypomastigotes in films of the patient's blood. Because the trypomastigotes are not numerous in the blood, other diagnostic methods may be required(1) a stained preparation of a bone marrow aspirate. (2) culture of the organism on special medium.

Trypanosoma gambiense & Trypanosoma rhodesiense

DiseaseThese organisms cause sleeping sickness (African trypanosomiasis). Life cycleVector for both is the tsetse fly.Infective stage: metacyclic trypomastigotes.Mode of transmission: injection of organisms in the saliva of the insect during biting.Clinical FindingsThe initial lesion is an indurated skin ulcer ("trypanosomal chancre") at the site of the fly bite.Enlargement of the posterior cervical lymph nodes (Winterbottom's sign).The encephalitis is characterized initially by headache, insomnia and finally coma.Laboratory DiagnosisMicroscopic examination of the blood reveals trypomastigotes.

LeishmaniaDiseaseL. donovani is the cause of kala-azar (visceral leishmaniasis).The life cycle Vector: sandfly.Infective stage: metacyclic promastigotes.Mode of infection: bite of sand fly.

Visceral leishmaniasisClinical FindingsSymptoms begin with intermittent fever, weakness, and weight loss. The disease affect reticuloendothelial system leading to enlargement of the spleen. Hyperpigmentation of the skin is seen in light-skinned patients (kala-azar means black sickness).Post kalazar dermal lishmaniod.

Cutaneous leishmaniasis

Old world cutaneous leihmaniasis oriental sore: charecterized by uler at the site of bite faceor exposed parts of the bodythe lesion heals spontaneously in 1-2 years leaving disfiguring scar.New word cutaneous leishmaniasisMucocutaneous leishmaniasis: skin lesions which metastasize to oropharynx after months or years leading to destruction of cartilage.Checleros ulcer: single lesions affecting ears

Laboratory DiagnosisDiagnosis is usually made by detecting amastigotes in a bone marrow, spleen, or lymph node biopsy or "touch" preparation. TreatmentPentavalent antimonial drugs.PreventionTreatment of cases.Vector control.Active immunization with living organism from an active ulcer results in life long protection.

Helminthes3 main classes of medically important helminthes1. The Nematodes 2. The Trematodes 3. The Cestodes

TrematodaCestodaNematodaFlattened, leaf-like, Bilaterally symmetrical, not segmentedFlattened, ribbon -shaped & segmentedElongated. cylindrical, round in cross section & not segmentedShapeSimple blind tube(no anus)AbsentSimple straight tube with anusDigestive systemAbsentAbsentPresentBody cavityHermaphrodite (except schistosoma)HermaphroditeseparateGender(Sex)TrematodesTrematoda (Flukes)Hepatic flukes: - Fasciola gigantica. - Fasciola hepatica.Intestinal flukes: - Heterophyes heterophyes.Blood flukes: - Schistosoma haematobium. - Schistosoma mansoni. Lung fluke: - ParagonimusFasciola giganticaDisease: Fascioliasis, liver rot.MorphologyThe adult is a large fleshy worm.The adult worms live in the bile ducts of herbivorous animals & man. Fasciola haptica differs from Fasciola gigantica: - Smaller in size (3 x 1.3 cm). - Intermediate host: Lymnaea trancatula.Life cycleFinal host: herbivorous animals and human.Intermediate host: Lymnaea cailliaudi snailInfective stage: encysted metacercaria.Mode of infection: ingestion of encysted metacercaria in aquatic vegetables (usually leafy plants e.g. lettuce) or in water.

Clinical finding:FeverEnlarged tender liverBiliary colic. Jaundice.Laboratory diagnosis:Detection of eggs in feces or duodenal aspirate.Treatment:Antiparasitic drugs e.g. Bithional.

Heterophyes heterophyesMorphology: Very small, intestinal flukes.Disease: Heterophyiasis.Life cycle:Final host: Man & fish eating animals. Two intermediate hosts: Pirenella conica snail .Bolty & boury fishes.Infective stage: encycted metacercaria.Mode of infection: eating raw, undercooked or freshly salted fish containing encysted metacercaria. Clinical findingsColicky pain and diarrhea.Egg emboliLaboratory diagnosisDetection of the eggs in faeces. TreatmentAntiparasitic drugs, Praziquantel

SchistosomaDisease: Schistosomiasis (Bilharziasis). It differs from other trematodes in :Separate sexes.Eggs with spine.Cercaria is the infective stage.3 known schistosomes infect humans:S. haematobiumS. mansoni:S. japonicumS.mansoni : mesenteric venules of bowel &, rectum. It causes intestinal schistosomiasis and eggs pass in stool.S. haematobium: venous plexus of the bladder, ureter & kidneys. It causes urinary schistosomiasis and eggs pass in urine.

Life cycleIntermediate host is a snail S. heamatobium (Bulinus trancatus) S. mansoni (Biomphalaria alexandrina).Infective stage: is the cercariaMode of infection: Penetration of the cercaria (which is attracted to man by the body temperature) to skin when water begins to dry.

Clinical featuresUrinary bilhariziasis: terminal haematuria.Intestinal bilhariziasis: dysentery.Laboratory diagnosis:Detection of eggs in stools or urine.Treatment:Praziquantel.

CestodaTaenia saginata (beef tapeworm)Disease: taeniasis saginata.Morphology:Has a scolex.Segmented from 1000-2000 segments. Immature segments. Mature segments. Gravid segments.Life cycle:Definitive host: human.Intermediate host: cattle (beef).Infective stage: Cysticercus bovis. Mode of infection: ingestion of raw or improperly cooked beef containing the cysticercus bovis.Ingestion of eggs is not infective to human.Clinical finding #Intestinal obstruction#Loss of weight as the parasite consumes much of patients food.DiagnosisDetection of the eggs or gravid segments in stool.T. solium is the same as T. saginata but.Intermediate host is the PorkEggs could be infective to human leading to cysticercosis.

Diphyllbothrium latum (fish tapeworm)Disease: DiphyllobothriasisMorphologyFormed of scolex & 3000-4000 immature & mature segments (no gravid segments).Life cycleDefinitive hosts: man, dogs, cats and other fish-eating animals.1st intermediate host: Cyclops2nd intermediate host: Fresh water fishes e.g. salmon. Infective stage is Plerocercoid in infected fish muscles ( the 2nd intermediate host).Mode of infection: by eating infected fishes either raw or improperly cooked (smoked or pickled).Clinical featuresIntestinal symptomsMacrocytic hyperchromic anemiaDiagnosis: Detection of eggs in feces.Treatment: Antiparasitic drugs.

Hymenolepis nana (Dwarf tapeworm)Disease: hymenolepiasis nana Life cycle: Adult worms live in the small intestineDefinitive hosts are human, rats & mice More common in children.Infective stage: egg.Mode of infection:Ingestion of eggs through; Contaminated food. Autoinfection either internal or external.Clinical pictureIn heavy infection: Intestinal irritation, enteritis Nervous manifestationsDiagnosis: Detection of eggs in stool. Peranal swab is more diagnostic.Treatment: Antiparasitic drugs, praziquantel.

Echinococcus granulosa (Dog tapeworm)Disease: hydatid cyst diseaseMorphology:scolex and only three proglottids, making it one of the smallest tapeworms.Humans are almost always dead-end intermediate hosts.Clinical featuresThe cyst acts as a space-occupying lesion, putting pressure on adjacent tissue.The cyst fluid contains parasite antigens, if the cyst ruptures spontaneously or during trauma or surgical removal, life-threatening anaphylaxis can occur. DiagnosisIndirect hemagglutination test.Surgical removal and microscopic examination of cyst contents.TreatmentTreatment Albendazole with or without surgical removal of the cyst.

NematodesEnterobius vermicularis (pinworm)Disease: pinworm infection (enterobiasis).Life cycle:Infective stage: Egg.Mode of infection: ingesting of the worm eggs.At night, the female migrates from the anus and releases thousands of fertilized eggs on the perianal skin and into the environment.Clinical FindingsPerianal pruritus is the most prominent symptom.DiagnosisThe eggs are recovered from perianal skin by using the Scotch tape technique and can be observed microscopically (Figure 563).Unlike those of other intestinal nematodes, these eggs are not found in the stools. TreatmentMebendazole . Whole family must take the treatment as it is highly infectious.

Trichuris trichiura (whipworm) Disease: whip worm infection or trichuriasisLife cycle:Infective stage is emberyonated egg.Mode of infection: ingesting worm emberyonated eggs in food or water contaminated with human feces.Clinical FindingsTrichuris may cause rectal prolapse in children with heavy infection. Prolapse results from increased peristalsis that occurs in an effort to expel the worms. Laboratory DiagnosisDiagnosis is based on finding the typical eggs, i.e., barrel-shaped with a plug at each end, in the stool TreatmentMebendazole is the drug of choice.

Ascaris lumbricoides Disease: ascariasisLife cycle:Infective stage: egg.Mode of infection: ingesting eggs in food or water contaminated with human feces Clinical FindingsMost infections are asymptomaticMalnutrition and intestinal obstruction in a heavy worm burden patient.Laboratory DiagnosisMicroscopically by detecting eggs in the stools. TreatmentBoth mebendazole and pyrantel pamoate are effective.

Ancylostoma duodenale (hookworm) Disease: Ancylostomiasis.Life cycle:Infective stage: filariform larvae.Mode of infection: penetration of the skin by the filariform larvae on walking with bared foot on moist soil.Clinical Findingsloss of blood at the site of attachment in the small intestine will lead to microcytic aneamia.Laboratory DiagnosisMicroscopically by finding eggs in the stools.TreatmentBoth mebendazole and pyrantel pamoate are effective.

WuchereriaDisease: W. bancrofti leads to elephantiasis.Vector: female mosquito (especially Anopheles and Culex species).Infective stage: infective larvae. Mode of infection: Humans are infected when the female mosquito deposits infective larvae on the skin while biting.Clinical FindingsAdult worms in the lymph nodes cause inflammation that eventually obstructs the lymphatic vessels, causing edema. Massive edema of the legs is called elephantiasis.Laboratory DiagnosisThick blood smears taken from the patient at night reveal the microfilariae.TreatmentDiethylcarbamazine is effective only against microfilariae; no drug therapy for adult worms is available.