Introduction to Medical Parasitology PDF

Introduction to Medical Parasitology BIOLOGICAL RELATIONSHIP TERMINOLOGIES Symbiosis - the living together of unlike organisms. Different forms of Symbiosis: Parasitology -...

Introduction to Medical Parasitology BIOLOGICAL RELATIONSHIP TERMINOLOGIES Symbiosis - the living together of unlike organisms. Different forms of Symbiosis: Parasitology - the area of biology concerned with the phenomenon of dependence of one living organism on Commensalism - a symbiotic relationship in another which two species live together and one species benefits from the relationship without harming or benefiting the Medical Parasitology - concerned primarily with other. parasites of humans and their medical significance, as well as their importance in human communities Example: Entamoeba coli in the intestinal lumen: supplied with nourishment and protected from harm → it Tropical Medicine - a branch of medicine that deals with does not cause any damage to the tissues of its host. tropical diseases and other special medical problems of tropical regions Mutualism - a symbiosis in which two organisms mutually benefit from each other.  Example: termites Tropical disease - is an illness, which is indigenous to or and the flagellates in their digestive system → synthesize endemic in a tropical area but may also occur in sporadic cellulase to aid in the breakdown of ingested wood or epidemic proportions in areas that are not tropical Parasitism - a symbiotic relationship where one Anthroponotic - parasitic infection that affects humans organism benefits at the expense of the host.  Example: only. Entamoeba histolytica derives nutrition from the human Zoo-anthroponotic - parasitic infection mainly affecting host → amebic dysentery humans; animals are affected in the life cycle of the parasite like Taena saginata. Anthropozoonosis - parasitic infection mainly in animals, may accidentally acquired by human hosts like echinococcus granulosus. Medical Parasitology Branch of medical sciences dealing with Parasite - An organism that lives in or on another organisms (= parasites) which live temporarily or organism and benefits by deriving nutrients at the host’s permanently, on or within the human body expense Concerned primarily with parasites of humans CLASSIFICATION OF PARASITES and their medical significance, as well as their  According to habitat or mode of development: importance in human communities Endoparasite - a parasite living inside the body of a host. Classes of Medical Parasitology Infection is the presence of an endoparasite in a host. Medical Protozoology  Obligate parasites - they need a host at some - Deals with the study of medically important stage of their life cycle to complete their protozoa development and to propagate their species. Medical Helminthology  Example: Tapeworms - Deals with the study of helminthes (worms) that  Facultative parasite - may exist in a free-living affect man state or may become parasitic when the need arises. Medical Entomology  Accidental or incidental parasite - A parasite, which establishes itself in a host where it does not - Deals with the study of arthropods which cause or ordinarily live. transmit disease to man   Aberrant parasite – parasite which infect a  Example: Pigs or cattle serve as intermediate hosts of host where they cannot develop further; also known as Taenia spp. Snails are hosts of Schistosoma spp. wandering parasite Paratenic host - is one in which the parasite does not  Example: Toxocara canis (dog roundworm) develop further to later stages. infecting humans  Example: Paragonimus metacercaria in raw wild boar Ectoparasite - a parasite living outside the body of a meat can pass through the intestinal wall of humans and host. Infestation is the presence of an ectoparasite on a complete its development. The wild boar serves as a host. paratenic host transferring the infective stage to humans.  Examples: lice, Ticks and Mites  Reservoir hosts - allow the parasite’s life cycle to continue and become additional sources of human  Permanent parasite - remains on or in the infection. body of the host for its entire life.  Example: Pigs are reservoirs of Balantidium coli. Field  Temporary parasite – lives on the host only for rats of Paragonimus westermani. Cats of Brugia malayi a short period of time. Incidental/Accidental host – in which the parasite is not  Free-living parasite – refers to non-pathogenic usually found. stages of the active existence, which live independent of the host.  Example: Man is an accidental/incidental host for cystic echinococ  Spurious parasite - a free-living organism that passes through the digestive tract without infecting the Life Cycle of Parasites host. - Is the cycle of development beginning from  Example: cystic stage of Naegleria fowleri definitive host and back to the definitive host Direct Life Cycle when a parasite requires only single host to complete its development a parasite life cycle in which the parasite is transmitted directly from host to host without an intermediate Host - An organism that harbors a parasitic stage, Example: Entamoeba histolytica requires only providing nourishment and/or shelter to the parasite human host to complete its life cycle Definitive or final host - is one in which the parasite attains sexual maturity.  Example: In taeniasis, humans are considered the definitive host. Intermediate host - harbors the asexual or larval stage of the parasite. Indirect Life Cycle Self (Autoinfection) - the infected individual becomes its own source of infection when a parasite requires two or more species of host to complete its development Example: finger to mouth transmission: Capilaria philippinensis, Enterobius Example: Malarial parasite requires both human vermicularis, Hymenolepis nana, and host and mosquito to complete its life cycle. Strongyloides stercoralis MODES OF TRANSMISSION/INFECTION  Oral transmission  Most common method of transmission – ingestion of contaminated food, water, soiled fingers, or fomites  Skin transmission – entry through the skin: hook worm, schistosomiasis  Vector transmission – transmitted by insect bite: Anopheles mosquito, Culex mosquito  Direct transmission – transmitted by person-to-person contact: kissing (gingival amoeba) and by sexual intercourse (trichomoniasis)  Vertical transmission – mother to fetus transmission: malaria and toxoplasmosis  Iatrogenic transmission – in case of transfusion malaria and toxoplasmosis after organ transplantation Sources of infection  Inhalation transmission Contaminated soil and water Food Effects of parasites on the host Vector – an agent, usually arthropod that Lytic necrosis – enzymes produced by some parasite → transmits an infection from man to man or from lytic necrosis other animals to man Example: Entamoeba histolytica lyses intestinal cells Biologic vector transmits the parasite and produces amoebic ulcers only after completion of its development Trauma – attachment of hook worm on jejunal mucosa within the host; is therefore an essential leads to traumatic damage of villi and bleeding on the site part of the parasite’s life cycle. of attachment Example: Anopheles mosquito Allergic manifestations – clinical manifestations may be Mechanical or phoretic vector, only caused by host immune response to parasitic infection transports the parasite. Example: Eosinophilic pneumonia in Ascaris Example: Flies and cockroaches infection and anaphylactic shock in rupture of hydatid cyst Carrier – a person who is infected with parasite without clinical or subclinical disease. Physical obstruction – masses of roundworms can cause intestinal obstruction; Plasmodium falciparum malaria may produce blockage of brain capillaries in cerebral Prevention and Control malaria Reduction of the source of infection Inflammatory reaction – lymphadenitis in filariasis and Sanitary control of drinking water and food urinary bladder granuloma in Schistosomiasis haematobium infection Proper waste disposal Neoplasia – liver fluke, Clonorchis may induce bile duck Use of insecticides and other chemicals used to control the vector population carcinoma and S. haematobium may cause urinary bladder cancer Use protective clothing Space occupying lesions – some parasite may cause cystic Good personal hygiene lesions that may compress the surrounding tissue or organ Avoidance of unprotected sexual practices (Hydatid cyst) EXPOSURE AND INFECTION Effects of host to the parasite  Exposure - is the process of inoculating an infective Genetic makeup agent Example:  Infection - connotes the establishment of the infective In falciparum malaria, possession of sickle- agent in the host. cell trait confers some protection  Incubation period - is the period between infection and The presence of Duffy blood factor increases evidence of symptoms. the susceptibility of an individual to  Superinfection or hyper-infection - happens when the Plasmodium vivax infection already infected individual is further infected with the Nutritional status same species leading to massive infection with the parasite. Example:  Example: Strongyloides results in a large A diet rich in protein is not suitable for the increase in worm burden, which may lead to severe development of intestinal protozoans debilitation or even death due to an increase in the proportion of rhabditiform larvae that transform into Low-protein diet favors the appearance of filariform larvae while in the gut. symptoms of amebiasis and complications of the disease High carbohydrate diet favors the EPIDEMIOLOGIC MEASURES development of some tapeworms  Epidemiology - is the study of patterns, distribution, and Immune processes occurrence of disease. Example:  Incidence - is the number of new cases of infection appearing in a population in a given period of time. Absolute immunity to reinfection occurs rarely following protozoan infections  Prevalence - is the number (usually expressed as percentage) of individuals in a population estimated to be Acquired immunity may be very important in infected with a particular parasite species at a given time. modifying the severity of disease in endemic areas  Intensity of infection - refers to burden of infection which is related to the number of worms per infected person, measured directly (by counting expelled worms during treatment) or indirectly (by counting helminth eggs excreted in feces) and is also referred to as the worm ERADICATION VS ELIMINATION burden.  Disease eradication - is defined as a permanent  Morbidity - clinical consequences of infections or reduction to zero of the worldwide incidence of infection diseases that affect an individual’s well-being. caused by a specific agent → continued measures are no longer needed  Disease elimination - is a reduction to zero of the TREATMENT OF PARASITISM incidence of a specified disease in a defined geographic  Deworming - is the use of anti-helminthic drugs in an area → continued intervention or surveillance measures individual or a public health program. are still required  Cure rate - refers to the number (usually expressed as a percentage) of previously positive subjects found to be Classification of Medically Important Parasites egg negative on examination of a stool or urine sample using a standard procedure at a set time after deworming. Protozoa  Egg reduction rate (ERR) - is the percentage fall in egg Sarcodina (Amoebae) counts after deworming based on examination of a stool Entamoeba histolytica or urine sample using a standard procedure at a set time after the treatment. Endolimax nana  Efficacy - is the effect of a drug against an infective Iodameba butchlii agent. Dientamoeba fragilis  Drug resistance - is a genetically transmitted loss of susceptibility to a drug in a parasite population that was Mastigophora (Flagellates) previously sensitive to the appropriate therapeutic dose. Giardia lamblia PREVENTION AND CONTROL Trichomonas vaginalis  Morbidity control - is the avoidance of illness caused by Trypanosoma brucii infections, may be achieved by periodically deworming individuals or groups. Leishmania donovani  Information-education-communication (IEC) - is a Sporozoa health education strategy that aims to encourage people to Plasmodium falciparum adapt and maintain healthy life practices. Toxoplasma gondi  Environmental management - is the planning, organization and monitoring of activities for the Cryptosporidium parvum modification and/or manipulation of environmental Isospora beli factors to preventing or minimizing vector or intermediate host propagation and reducing contact between humans Ciliates and the infective agent. Balantidium coli  Environmental sanitation - safe disposal and hygienic Metazoa (Helminths) management of human and animal excreta, refuse, and waste water; control of vectors, intermediate hosts, and Platyhelminthes reservoirs of disease; safe drinking water and food safety; housing that is adequate in terms of location, quality of Trematodea shelter, and indoor living conditions; facilities for Schistosoma mansoni personal and domestic hygiene; as well as safe and healthy working conditions. Fasciola hepatica  Cestoda Examples: malaria (found inside the RBC), Bancroftian and Malayan filariasis (microfilariae Diphylobotrium latum found in the plasma) Taenia saginata Stool Echinococcus Examples: helminthic parasites, protozoan granulosus infections Hymenolepis nana Urine Nemathelminthes Examples: S. haematobium, W. bancrofti Intestinal Nematodes (Chyluria – microfilariae) Ascaris lumbricoides Sputum Somatic Nematodes Examples: Paragonimus westermani, Entamoeba histolytica Wucheraria bancrofti Biopsy materials Examples: Kala-azar, Cysticercosis, Classification of Arthropods Trichinelliasis and Chaga’s disease, Skin snip for Kingdom Animalia → Phylum Arthropoda → Onchocerciasis Class Urethral or vaginal discharge Crustacia: Scorpion Example: Trichomonas vaginalis Arachnida: Ticks Serological tests – where special antigens are Insecta: Mosquito available Chilopoda: Centipedes Cytological changes in the blood Pentastomida: tongue worms Example: eosinophilia, anemia, reduction of WBC Basic Concepts in Medical Parasitology Morphology Geographical distribution Mode of infection Life cycle Pathology and clinical manifestations Laboratory diagnosis Treatment Preventive/control measures Laboratory Diagnosis Blood (blood film) Summary Parasite is an organism, lives in/on the body of a host Host is that harbors the parasite Association between the parasite and the host: mutualism, commensalism, or parasitism → produce a variety of effects Structural and behavioral components of parasites assists classification: Protozoa, helminthes and anthropods  PROTOZOA Grouped according to the location in the body where they most frequently cause disease Meaning “first animal” Members of eukaryotic protista Distinguishing features: Ability to move at some stage of their life cycle Lack of cell wall They are within a mass of protoplasm → nucleus and cytoplasm INTESTINAL AMEBAE Nucleus contain clumped or dispersed chromatin and central nucleolus or karyosome Found in all moist habitats (sea, soil and fresh water) Size: ranging from 2 to more than 100ꭒՠ Multiply by asexual reproduction Transmission: cytoplasm of ameba is bounded by a membrane, Fecal-oral (contaminated food and water) differentiated into an outer ectoplasm and inner endoplasm Insect bite inoculum or rubbing infected insect feces in the site of bite Pseudopodia are formed by the ameba by thrusting out ectoplasm followed by endoplasm, Sexual intercourse for locomotion and engulfment of food by phagocytosis Pathogenesis: factors Cyst is quiescent, resistant, usually the infective Attachment to the host tissue followed by form replication to establish colonization Trophozoite is actively motile feeding stage Toxic product released Shifting of antigenic expression to evade immune response and inactivate host ENTAMOEBA HISTOLYTICA defenses Trophozoite irregular in shape and varies in size from Classification of Protozoa 12-60ꭒՠ; average of 20ꭒՠ Based on their morphology and locomotive Motility is rapid, progressive and system unidirectional (pseudopods) Amoeba – entamoeba histolytica Nucleus Flagellates – giardia lamblia, Characterized by evenly trichomonas vaginalis, trypanosoma arranged chromatin spp., leishmania spp. With small, compact centrally Ciliates – Balantidium coli located karyosome → giving a cartwheel appearance Coccidian – isospora belli, cryptosporidium parvum, toxoplasma Cytoplasm gondii, plasmodium species  finely granular with few ingested Amebiasis can present in different forms bacteria or debris in vacuoles and degree of severity, depending on the organ affected and the extent of damage RBC → may be visible → caused diagnostic Adherence: Amebic lectins (Gal/ Gal Ac lectin) mediates adherence to glycogen receptors of colonic mucosa Cytolysis: The metacystic trophozoites penetrate the columnar epithelial cells in the crypts of Lieberkühn in the Cyst colon. Size: 10 - 20 ꭒՠ Ameba pores are ionophore early cyst contains a single proteins of ameba capable of nucleus and two other structures: inserting ion channels into liposomes causing lysis of target a mass of glycogen and cell membrane of host cells 1-4 chromatid bodies or Mucosal penetration → produces bars, which are cigar- discrete ulcers with pinhead center and shaped refractile rods raised edges. the ameba penetrates to with rounded ends submucosal layer and multiplies rapidly, causing lytic necrosis and thus forming mature cyst is Quadri- an abscess → abscess breaks down to nucleated form an ulcer Amebic ulcer is the typical lesion → multiple and are confined to the colon, being most numerous in the cecum and next in the rectosigmoid region → flask- shaped in cross section, with mouth and neck being narrow and base large and Life cycle: rounded ingestion of mature quadri-nucleated Ameboma: Occasionally, a infective cyst from contaminated food granulomatous pseudo-tumoral growth and water or hand to mouth contact → may develop on the intestinal wall by stomach (cyst wall is resistant to gastric rapid invasion from a chronic ulcer → juice) most frequent at cecum and rectosigmoid junction Terminal ileum (alkaline ph) → excystation takes place → trophozoite Systemic manifestations of ameboma are rectal (being active) invade the tissue and lodge tenesmus, high fever, abdominal discomfort, in the submucous layer of the large bowel anorexia and nausea (colon) → grow and multiply by binary fission Intestinal amebiasis does not always result in dysentery, there may be only diarrhea or vague Invasion of blood vessels lead to abdominal symptoms popularly called secondary extra-intestinal lesions. "uncomfortable belly" or "growling abdomen''. Entamoeba hislolytica causes intestinal and extraintestinal amebiasis. Incubation period is highly variable (Average: ranges from 4 days to 4 months) PATHOGENESIS & CLINICAL FEATURES: EXTRAINTESTINAL AMOEBIASIS Hepatic involvement is the most common extraintestinal complication of amebiasis Hepatic amoebiasis: Develop an enlarged tender liver without detectable impairment of liver function or fever Due to repeated invasion by amebae from an active colonic infection or to toxic substances from the colon reaching the liver Amoebic Hepatic Abscess: Center of the abscess contains thick chocolate brown pus ( anchovy sauce pus) → liquefied necrotic liver tissue Cardinal signs of amebic liver abscess: painful hepatomegaly, Fever, Anorexia, Nausea, Weight loss and Fatigue may also be present, Jaundice develops only when lesions are multiple or when they press on the biliary tract have leukocytosis (>10,000/μL) increased serum transaminases  ameba → called as amebostomes → used for engulfing RBCs and white blood cells (WBCs) is the feeding, growing, and replicating form of the parasite, seen on the surface of vegetation, mud and water the invasive stage of the parasite and the infective form of the parasite Flagellate form: biflagellate form occurs when trophozoites are transferred to distilled PATHOGENIC FREE-LIVING AMEBAE: water NAEGLERIA FOWLERI transformation of trophozoites to Morphology: biflagellate pear-shaped form occurs the only species of genus Naegleria, within a minute which infects man flagellate can revert to the ameboid form occurs in three forms: → classified as ameboflagellate Cyst Life Cycle: Ameboid trophozoite form is a heat-loving (thermophilic) ameba that thrives in warm water at low oxygen Flagellate trophozoite form tension and is commonly found in warm freshwater (e.g. lakes, rivers, and springs) and soil infection occurs when people go swimming or diving in warm fresh water river or ponds and poorly maintained swimming pools or nasal irrigation using contaminated tap water completed in the external environment Cyst stage: ameboid form of trophozoite multiplies is spherical 7-10 μm in diameter and has by binary fission a smooth double wall it forms a cyst and which undergoes are the resting or the dormant form and excystation in favorable conditions can resist unfavorable conditions, such as Flagellate form of trophozoite helps in drying and chlorine up to 50 ppm the spread to new water bodies → revert can withstand moderate heat ( 45°C), but to ameboid forms to become infective to die at chlorine levels of 2 ppm and man salinity of 0.7% Ameboid form: is about 10-20 μm rounded pseudopodia (lobopodia), a spherical nucleus with big endosome and pulsating vacuoles vacuoles appear to be densely granular in contrast to highly vacuolated body of  Pathogenesis and Clinical Features: PATHOGENIC FREE-LIVING AMEBAE: ACANTHAMOEBA SPECIES water containing the amebae and usually follows swimming or diving in ponds → amebae invade the nasal mucosa and pass through the olfactory nerve branches in A. culbertsoni (formerly, HartmannelLa the cribriform plate into the meninges, culbertsoni) is the species most often responsible and brain to initiate an acute purulent for human infection but other species like A. meningitis and encephalitis called polyphagia, A. castellanii and A. astromyx have primary amebic meningoencephalitis also been reported (PAM) An opportunistic protozoan pathogen found incubation period varies from 2 days to 2 worldwide in the environment in water and soil weeks Morphology: patient experiences anosmia, fever, Trophozoite is large, 20-50 μm in size headache, vomiting, stiff neck, ataxia, and characterized by spine-like seizure and coma pseudopodia (acanthopodia) Cranial nerve palsies of the third, fourth Not having a flagellate stage and sixth nerves have also been documented forming cysts in tissues fatally within a week (average 5 days) Polygonal double-walled cysts are highly resistant Laboratory Diagnosis → present in all types of environment based on the finding of motile Naegleria trophozoites in wet mounts of freshly obtained CSF → cloudy to purulent, with prominent neutrophilic leukocytosis, elevated protein and low glucose, resembling pyogenic meningitis Wet film examination of CSF may show trophozoites Life Cycle: Cysts are not found in CSF or Both trophozoites and cysts are infective brain MOT: Culture: can be grown in several kinds of inhalation of cyst or trophozoite liquid axenic media or non-nutrient agar plates coated with Escherichia coli ingestion of cysts Both trophozoites and cysts through traumatized skin or eyes occur in culture After inhalation of aerosol or dust Treatment: containing trophozoites and cysts, the trophozoites reach the lungs and invade DOC: Amphotericin B intravenously the central nervous system through the Can also be instilled directly into bloodstream → producing the brain granulomatous encephalitis (GAE) Miconazole and Sulfadiazine has shown limited success only when administered early More than 9.5% cases of Primary Amoebic Meningoencephalitis (PAM) are fatal despite of treatment  Pathogenesis and Clinical Features: identification of ameba or cyst in corneal scraping by fluorescent microscopy Infection usually occurs in patients with using calcofluor white staining and IFA immunodeficiency, diabetes, Test (IFAT) procedure malignancies, malnutrition, systemic lupus erythematosus (SLE), or demonstration of trophozoites and cysts alcoholism in brain biopsy, culture and immunofluorescence microscopy using The parasite spreads hematogenous into monoclonal antibodies central nervous system → invasion of the connective tissue and induction of Cerebrospinal fluid shows proinflammatory responses lead to lymphocytic pleocytosis, neuronal damage → fatal within days slightly elevated protein levels, and normal or slightly decreased Acanthamoeba keratitis: infection of the eye glucose levels develops from the entry of the amebic cyst through abrasions on the cornea → majority Computed tomography scan of associated with the use of contact lenses brain provides inconclusive findings Unilateral photophobia, excessive tearing, redness and foreign body Treatment: sensation are the earliest signs and symptoms; disease is bilateral in some Topical administration of biguanide or contact lens users → keratitis and uveitis chlorhexidine with or without diamidine → result in permanent visual impairment agent or blindness No effective treatment is available Pathogenesis and Clinical Features: Multidrug combinations Granulomatous amebic encephalitis: including pentamidine, sulfadiazine, rifampicin and is a serious infection of the brain fluconazole are being used with and spinal cord that typically limited success occurs in persons with a compromised immune system is believed to follow inhalation of the dried cysts incubation period is long and the evolution of the illness is slow Clinical picture: intracranial space-occupying lesions with seizures, paresis and mental deterioration Disseminated infection: immunocompromised states like acquired immunodeficiency syndrome PATHOGENIC FREE-LIVING AMEBAE: (AIDS) → can affect skin, lungs, sinuses, BALAMUTHIA MANDRILLARIS and other organs Leptomyxid free-living ameba, is a newly Laboratory Diagnosis: identified species reported to cause granulomatous amebic encephalitis (GAE) demonstration of the cyst in corneal scrapings by wet mount, histology and Morphology: culture → from corneal scrapings exists in ameboid trophozoite stage inoculated on nutrient agar, overlaid with live or dead Escherichia coli and flagellate stage is absent incubated at 30°C  relatively large (12-60 μm), irregular in Diagnosis: demonstration of trophozoites and shape and actively motile by broad cyst in stool and also by serological tests and pseudopodia imaging techniques in hepatic amebiasis. usually spherical (6-20μm), surrounded Treatment: metronidazole or tinidazole along by a three-layered cyst wall: Outer with paramomycin, diloxanide furoate, or irregular ectocyst, middle mesocyst and chloroquine. inner endocyst round wall E. hartmanni, E. coli, E. gingivalis, E. nana, and transmitted through respiratory tract, skin Iodamoeba are commensals and nonpathogenic lesions, or eyes amebae. causes granulomatous amebic Naegleria and Acanthamoeba are pathogenic encephalitis in both healthy and free-living ameba. immunocompromised hosts particularly in children and elderly N. fowleri occurs in three forms: (1) cyst, (2) trophozoite and (3) flagellate. It causes identifying trophozoites in the CSF and PRIMARY AMOEBIC trophozoites and cysts in brain tissue and MENINGOENCEPHALITIS. polymerase chain reaction also gives reliable diagnosis Acanthamoeba species cause amebic keratitis and also GRANULOMATOUS AMOEBIC ENCEPHALITIS in immunocompromised subjects. SUMMARY E. histolytica is found in human colon and is mainly asymptomatic. Cyst contains glycogen mass and 1-4 chromatid bars. Stools: In amebic dysentery, stool is copious, foul-smelling brownish black often with blood- streaked mucus Amebic ulcers: Typical ulcers are discrete, flask- shaped, with ragged undermined margin, found in cecum and rectosigmoid region. Amebic granuloma or ameboma may develop from chronic ulcers. Extraintestinal complications: Amebic hepatitis and liver abscess are the most common. Abscesses in other organs such as lung, brain, spleen and genitourinary tract may result from hematogenous spread or by direct spread from hepatic lesion.