Introduction to Protozoa and Rhizopoda and Zoomastigophora PDF

Medical parasitology ▪ Parasitology is the area of biology concerned with studying phenomenon of dependence (parasitism) of one living organism on another, and biology of parasites (morphology, embryology, physiology, biochemistry and nutrition) and parasite- environment interaction....

Medical parasitology ▪ Parasitology is the area of biology concerned with studying phenomenon of dependence (parasitism) of one living organism on another, and biology of parasites (morphology, embryology, physiology, biochemistry and nutrition) and parasite- environment interaction. Parasitism: Parasite An association in which the parasite derives benefit Host and the host gets nothing in return and always suffers some injury. ▪ Parasite: A parasite is an organism that is entirely dependent on another organism, referred to as its host, for all or part of its life cycle by deriving nutrients at the host’s expense for survival. ▪ Host: It is an organism, which harbors the parasites and provides nourishment and shelter to them and is relatively larger than the parasites.  ▪ Medical parasitology It deals with the parasites, which cause infections and produces the diseases in human beings. It is broadly divided into 3 parts: - Medical Protozoology Protozoa Endoparasites -Medical Helminthology Helminths - Medical entomology Ectoparasites Arthropods - Non-pathogenic parasites: parasites which live in/on the body of the host and don’t cause disease. - Pathogenic parasites: parasites cause disease to the infected host. - Opportunistic parasites : parasites that don’t cause disease in healthy individual but do cause it in immunocomprimised individuals  Medical Parasitology deals the following points: Taxonomy classification - Taxonomy: Classification of Parasites Kingdom - Scientific (Latin) Names of Parasites - Common Names of parasites Subkingdom - Morphology of Parasites Phylum - Life cycle of parasites - Hosts and parasites interaction Subphylum - Habitats of Parasite Class - Pathogenesis of parasites Order - Diseases caused by Parasites - Diagnosis of parasites Family - Transmission of parasites Genus - Treatment - Prevention of diseases species  Host Is the organism harboring and providing the parasite shelter and nutrients for survival. Definitive host Intermediate host Paratenic host Reservoir host Accidental host Natural host - The host, in which - A host, in which A host, harbors The host, in The host that - The host, in naturally infect the larval larval stage of the the parasite which the which the adult with certain stage of the parasite remains without being parasite is parasite lives and species of parasite lives or viable without affected with the not usually undergoes sexual parasite. asexual further infection and acts found, e.g. man reproduction multiplication development as an important is an accidental takes place. source of host for cystic - It may be a infection to echinococcosis. - In some parasites, 2 Such host human or any other other living different intermediate transmits susceptible being hosts may be the infection Hosts. required, known as to another first and second host. intermediate hosts  Host-parasite Relationships A symbiosis is any type of a close and long-term biological interaction between two different biological organisms from different species, usually with benefits to one or both of the individuals involved. Host-parasite relationships are of following types : parasite parasite Host Host Host parasite Life cycle of a parasite: a period of time required by a parasite in a host organism for phases of growth, development, reproduction, and transmission. Life Cycle of Parasites Direct life cycle Indirect life cycle When a parasite requires only single host When a parasite requires 2 or more species of to complete its development. The parasite host to complete its development. Intermediate is transmitted directly from host to the host is necessary to transmit the parasite from next without intermediate host. host to another. e.g. Entamoeba histolytica requires only a e.g. Malarial parasite human host to complete its life cycle. requires both human host and mosquito to complete its life cycle. Domain: Eukarya (Eukaryote)  Protozoa Helminthes Morphology Single-celled eukaryotic microorganisms belonging Multicellular organism; a number of cells, that to kingdom protista have 3 germ layers, belong to the kingdom animalia. Physiology A single cell performs all the functions: reproduction, Each special cell performs a particular function digestion, respiration, excretion, etc. Multiplication Multiply in human body Don’t multiply in human body Pathogenicity - Most are nonpathogenic - Requires several infection to cause the disease, - Single infection causes a clinical disease, such as malaria, - Some larval stage cause serious disease leishmaniasis, and sleeping sickness. Structure and Trophozoite (mobile vegetative or proliferative ▪ Adult stage (worm): Life cycle satge) -have outer protective covering, (a cuticle ). stages -Mouth may be provided with teeth or cutting 1- Trilaminar unit membrane, supported by a sheet of plates. contractile fibrils enabling the cell to move and change in -May possess suckers or hooks for attachment to shape. host tissues. 2-Cytoplasm : -They do not possess organs of locomotion -Ectoplasm: outer part of cytoplasm, organ for locomotion -Locomotion by muscular contraction and and for engulfment of food, respiration and discharging relaxation. waste material. -The excretory system is better developed -Endoplasm: It is the inner granular portion of cytoplasm -Developed reproductive system that contains nucleus, the golgi bodies, endoplasmic reticulum, food vacuoles, and contractile ▪ Larva stage (multiplying stage) vacuoles. 3-Nucleus: It may be a single or multiple. The nucleus ▪ Egg stage contains one or more nucleoli or a central karyosome. - Survives the environment due to the presence ▪ Cyst (Immotile and dormant stage) of strong shell. - It is a dormant stage, survives the environment due to - -Responsible for reproduction the presence of thick wall. - Cysts don’t multiply Helminthes are either oviparous or larviparous. Life cycle stages of Protozoans Life cycle stages of Helminthes Cestode cycle Trematode cycle Nematode cycle egg-miracidium-sporocyst- egg - larvae (L1-L4) - adult egg - metacestode - adult redia-cercaria- (metacercaria)-adult egg larvae adult Endoparasite:  Sources of Infection Animals: Ingestion of Contaminated soil - Cow, e.g. T. saginata, contaminated - Pig, e.g. T. solium, and water food or vegetables - Dog, e.g. Echinococcus granulosus. (Schestosoma.spp, (E.histolytica, G.lamblia) A.doudenale) Insect vectors (true vectors) Autoinfection A vector is an agent, usually an Happens when affected person is a source of another infection for arthropod that transmits an infection himself by from man to man or from other animals - contaminated Finger to mouth to man. transmission, e.g. pinworm or - Biological vectors: they transmit the parasite -Internal reinfection, and assist in the transfer and development or e.g. Strongyloides. multiplication of parasites in their body as well. Persons ˆMosquito—Malaria, filariasis The infected or carrier person ˆSandflies—Kalaazar can transmit the parasitic ˆTsetse flies—Sleeping sickness infection to others. ˆReduviid bugs—Chagas’ disease - Mechanical vectors: assists in the transfer of e.g. vertical parasitic form between hosts but is not essential transmission of congenital in the life cycle of the parasite. (Housefly— infections (from mother to fetus) e.g. Toxoplasma amoebiasis )  Oral transmission (by Fecal oral transmission) It is the most common method in which many intestinal parasite enter the body by ingesting in contaminated food, water or fingers (Ameoba, Gardia) Skin transmission (by skin penetration) Parasite is transmitted by skin contact (such as scabies) or through skin penetration (such as Hookworm, Schistosomiasis ), when the larvae enter the skin of persons walking barefooted on contaminated soil. Vector-borne transmission (by bite or direct contact) Parasites are transmitted from one host to another by insect bite (malaria is Modes of transmitted by mosquitoes bite). It can be a biological or mechanical vector. Infection Direct transmission (by direct physical contact ) Parasitic infection occurs when there is physical contact between an infected person and a susceptible person, e.g. by kissing in the case of gingival amoebae and by sexual intercourse in trichomoniasis. Vertical transmission (mother to fetus ) Passage of parasite from mother to fetus during the period immediately before and after birth via Placenta or breast milk (may take place in malaria and toxoplasmosis) Iatrogenic transmission (medical procedure or treatment) Transmission through medical procedure or treatment, such as blood transfusion or organ transplantation (Malaria or Toxoplasmosis) ▪ Zoonosis refers to those diseases and infections, which are naturally transmitted from vertebrate animals to man. It is of following types: ▪ Protozoal zoonoses, e.g. toxoplasmosis, leishmaniasis, balantidiasis, and cryptosporodiasis ▪ Helminthic zoonoses, e.g. hydatid disease, taeniasis  Pathogenesis ▪ Parasitic infections may remain inapparent or give rise to clinical disease. such as E. histolytica may live as surface commensals, without invading the tissue. ▪ Clinical infection produced by parasite may take many forms—acute, subacute, chronic, latent, or recurrent. Lytic necrosis (destruction of tissue): Enzymes produced by some parasite can cause lytic necrosis. (E.histolytica produce amoebic ulcer) Trauma: Attachment of hookworms on jejunal mucosa leads to traumatic damage of villi and bleeding at the site of attachment Allergic manifestations: by host immune response to parasitic infection, e.g. Pathogenic eosinophilic pneumonia in Ascaris mechanisms infection and anaphylactic shock in rupture of hydatid cyst. Physical obstruction: Masses of roundworm cause intestinal obstruction. Plasmodium falciparum malaria may produce blockage of brain capillaries in cerebral malaria. Inflammatory reaction:caused by inflammatory changes and consequent fibrosis e.g. lymphadenitis in filariasis and urinary bladder granuloma in Schistosoma haematobium infection. Neoplasia: A few parasitic infection have been shown to lead to malignancy. The liver fluke may induce bile duct carcinoma, and S. haematobium may cause urinary bladder cancer.  Epidemiology ▪ Although parasitic infections occur globally ▪ The Majority occur in tropical regions, where there is poverty, poor sanitation and personal hygiene. ▪ Often entire communities may be infected with multiple, different organisms which remain untreated because diagnosis is lacking, and treatment is neither accessible nor affordable. ▪ Effective prevention and control of parasitic infection require mass intervention of strategies and intense community education. ▪ Examples include: -General improved sanitation: fresh water wells, piped water. -Vector control: insecticide impregnated bed nets, spraying of houses with residual insecticides, drainage. -Mass screening and drug administration programs which may need to be repeated at regular intervals  Laboratory Diagnosis Either microscopically or macroscopically - Blood analysis: blood film used in diagnosis for Plasmodium spp, Trypanosoma spp - Stool analysis: used mainly for the diagnosis of intestinal parasitic infections, and helminthic infection of biliary tract, such as (E.histolytica, G.lamblia, Ascaris lumbricoids) - Immunodiagnostic method: antigen and antibody detection method - Intradermal skin test: (immune reaction test) - Culture method: culturing of some parasites such as Acantamoeba parasites - Animal inoculation: insertion of parasite into animal for diagnosis of parasite, such as Toxoplasma. - X-ray, ultrasonography, computed tomography (CT) scan - Molecuar Diagnosis: PCR, DNA probe  Diagnostic and Infective stage Diagnostic stage: the stage during which the parasite can be detected using the naked eye or laboratory methods. The diagnostic stage typically coincides with the stage during which the parasite leaves the host (via stool, urine, or sputum) to proliferate. Infective stage: the stage during which the parasite assumes a form in which it can invade its host.  Treatment - Antiparasitic drugs: Albendazole, Mebendazole, Thiabendazole, Quinine, Chloroquine - Surgery : Cystic echinococcosis (hydatid disease) Prevention and control - ƒReduction of the source of infection - Sanitary control of drinking water and food. - Proper waste disposal – through establishing safe sewage systems - The use of insecticides and other chemicals used to control the vector population. - ƒProtective clothing that would prevent vectors from resting in the surface of the body and inoculate pathogens during their blood meal. - Good personal hygiene. - Avoidance of unprotected sexual practices.  Protozoa Four main groups of protozoa are recognized on the basis of their locomotion using specialized subcellular and cytoskeletal features: amoebae flagellates ciliates sporozoa motile motile motile non-motile spores ▪ Four main modes of transmission: faecal-oral vector-borne predator-prey Direct transmission Transmission Transmission transmission Trichomonas spp Entamoeba histolytica Trypanosoma brucei Toxoplasma gondii Intestinal Protozoa Urogenital Blood and tissue Oral Protozoa Neurological Protozoa Protozoa and ocular - Entamoeba gingivalis protozoa - Entamoeba histolytica - Trichomonas - Plasmodium spp - Toxoplasma gondii - Trichomonas tenax - Naegleria - Giardia lambilia vaginalis fowleri - Balantidium coli - Trypanosoma spp - Leishmania spp - Acantham - Trichomonas hominis oeba culbertsoni - Toxoplasm a gondii - Trypanoso ma spp Rhizopoda  Amoebae ▪ Amoeba species are composed of cytoplasm and a membrane differentiated into an outer ectoplasm and inner endoplasm. ▪ It has the ability to alter its shape and forms pseudopodia through thrusting out ectoplasm, followed by endoplasm. These are employed for locomotion and engulfment of food by phagocytosis. ▪ Reproduction occurs asexually by binary fission. ▪ Morphology: - Trophozoite: - It is a proliferative stage - It has an amoeboid appearance. - Trilaminar unit membrane – Cytoplasm (Endoplasm and Ectoplasm) - Nucleus (central karyosome) - Cyst: - It is dormant formed in unfavorable conditions - Usually the infective form that transfer the infection from one host to another. (e.g. Entamoeba histolytica).  Amoebae are classified as either free-living (tissue) or parasitic (intestinal) amoebae Parasitic amoebae (inhabitant intestine and tissue) Free-living amoebae (inhabitant tissue) - Entamoeba histolytica - Naegleria fowleri - Entamoeba coli - Acanthamoeba culbertsoni Note: All intestinal amoebae are nonpathogenic, Note: All free living amoebae are except Entamoeba histolytica opportunistic pathogens A few of the free-living amoebae occasionally act as human pathogens producing meningoencephalitis and other infections, e.g. Naegleria and Acanthamoeba. Most parasitic amoebae inhabit the alimentary canal.  Entamoeba Histolytica Latin name: Entamoeba histolytica It is worldwide in prevalence, being much more common in the tropics than elsewhere. It is the third leading parasitic cause of mortality, after malaria and schistosomiasis. Distribution: is related more to inadequate environmental sanitation and poor personal hygiene than to climate. Route of Infection: fecal-oral route Man acquires infection by swallowing food and water contaminated with cysts. cyst Trophozoite Habitat: Large intestine , colon Infective stage: Mature cyst Diagnostic stage: Trophozoite and Cyst Disease: Amoebiasis The majority of infected humans (80–99%) are asymptomatic. -  Morphology E. histolytica occurs in 2 forms: Trophozoite 1. Inconstant shape, trilaminar membrane and 20-30 µm, but range from 10-60 µm in size 2. Motile with blunt pseudopodia 3. Cytoplasm (Endoplasm and ectoplasm) 4. Spherical nucleus with central, dark karyosome 5. Food vacuoles present, may contain erythrocytes of host Cyst: 1- Round, measuring 10–15m. 2- Contain, 1, 2 or 4 nuclei with a central karyosome 3-Chromatoid bodies (aggregations of ribosomes) can be seen particularly in immature cysts. 4- Immature cysts (precyst) have single or 2 nuclei and Glycogen vacuoles. 5-Mature cyst has 4 nuclei (quadrinucleate cyst) 6- The cyst wall is highly resistant to gastric juice and unfavorable environmental conditions. Cyst is the infective form of the parasite  Life Cycle ▪ E. histolytica passes its entire life cycle only in one host (man). ▪ Infective form: Mature quadrinucleate cyst passed in feces of convalscents and carriers. The cysts can remain viable under moist conditions for about 10 days. ▪ Man acquires infection by swallowing food and water contaminated with cysts. ▪ Excystation: When the cyst reaches caecum or lower part of the ileum, due to the alkaline medium, the cyst wall is damaged by trypsin, leading to excystation to form metacystic trophozoite. ▪ Metacystic trophozoites invade the submucosal tissue of caecum and colon, where they lodge in the glandular crypts and grow by binary fission and cause amoebic dysentery (intestinal amoebiasis). ▪ Some metacystic trophozoites develop into cysts, which are passed in feces to repeat the cycle. This happens in unfavorable conditions. ▪ Trophozoites may get into the blood stream and be transported through blood stream or by direct extension to other sites in the body causing extraintestinal amoebiasis. ▪ In most of the cases, E. histolytica remains as a commensal in the large intestine without causing any ill effects. ▪ Such persons become carriers or asymptomatic cyst passers and are responsible for maintenance and spread of infection in the community.  Pathogenesis and Clinical Features ▪ E. histolytica causes intestinal and extraintestinal amoebiasis. ▪ Incubation period ranges from 4 days to 4 months. Intestinal Amoebiasis (Amoebic dysentery) ▪ E.histolytica parasites cause disease only when they invade the intestinal tissues. ▪ Acute: Frequent dysentery (diarrhea with blood), intestinal ulcers (produces flask- shaped ulcer) due to the enzymatic degradation of tissue by trophozoite and abdominal pain. ▪ Chronic: Recurrent episodes of dysentery with blood and mucus in feces. gastrointestinal disturbances and constipation. ▪ The disease occurs only in about 10% of cases of infection, the remaining 90% being asymptomatic. Extraintestinal amoebiasis Amoebiae may get into the blood stream and be transported through blood stream or by direct extension to other sites in the body causing further amoebic abscesses. - Hepatic Amoebiasis (Hepatic abscess) - Cutaneous Amoebiasis (Cutaneous abscess) - Pulmonary Amoebiasis (Pulmonary abscess) - Brain Amoebiasis (brain abscess)  Laboratory Diagnosis Diagnosis of Intestinal Amoebiasis Microscopic examination - it is a direct examination of fecal smear under microscope for finding the following diagnostic stages: 1- Trophozoites in - a fresh dysenteric faecal specimen - rectal scrape 2- Cysts in fresh faecal specimen Note : Amoebic dysentery (E. Histolytica infection) is distinguished from bacillary dysentery by: - Lack of high fever - absence polymorphonuclear leukocytosis Diagnosis of Extraintestinal Amoebiasis ▪ Microscopic examination for trophozoite in- pus aspirated from liver abscess and in liver biopsy specimen (case of hepatic amoebiasis or amoebic hepatitis) ▪ Serological tests: they are of value in the diagnosis of extraintestinal amoebiasis by detecting the antibody response after invasive infection. ▪ IHA (indirect hemagglutination test) ▪ ELISA (enzyme-linked immunosorbent assay)  Entamoeba Coli ▪ It is a nonpathogenic commensal intestinal amoeba ▪ It is worldwide in distribution ▪ Trophozoite is larger than E. histolytica about 20–50 µm with sluggish motility and contains ingested bacteria but no red cells. ▪ The nucleus is clearly visible in unstained films and has a large eccentric karyosome and thick nuclear membrane lined with coarse granules of chromatin. ▪ Cysts are larger than E. histolytica, 10–30 µm in size, with a prominent glycogen mass in the early stage. The mature cyst has 8 nuclei and chromatoid bodies. ▪ The life cycle is the same as in E.histolytica except that it remains a luminal commensal without tissue invasion and is nonpathogenic. ▪ It feeds on bacteria or any other cells Cysts  Prophylaxis ▪ Preventing faecal contamination of the environment and water supplies by using latrines. ▪ Hand washing after defaecation and before eating. ▪ Covering food and water to prevent contamination from flies which can act as cyst carriers. ▪ Not eating green salads or other uncooked foods which may contain cysts, usually as a result of fertilization with untreated human faeces. ▪ Boiling drinking water (E. histolytica cysts are killed at 55 °C) or using membrane filters. ▪ Health education, particularly of food handlers, and also in schools and community health centres.  Entamoeba gingivalis Latin name: Entamoeba gingivalis it is a type of commensal ameobae that inhabits the mouth inside the gingival pocket near the base of the teeth. It causes gum disease. It is found in 95% of people with gum disease (gingivitis) and rarely in people with healthy gums. Route of transmission is by direct contact from one person to another , through kissing or by sharing eating utensils. Morphology: - Trophozoite It has amoebic form and forms pseudopodia - No cyst  Giardia lamblia Distribution: Latin name: Giardia lamblia (intestinalis or duodenalis): It has a worldwide distribution and is particularly common in the tropics and subtropics. - Endemicity is very high in areas with low sanitation, especially tropics and subtropics. - In endemic areas, young children are more frequently infected than adults, Route of infection: G. lamblia is transmitted by the faecal-oral route. Habitat: Small intestine Trophozoite (duodenum and upper jejunum) Infective stage: Cyst Diagnostic stage: Trophozoite and Cyst Cyst Disease : Giardiasis  Morphology It exists in 2 forms: ▪ Trophozoite (or vegetative or proliferative form). It has a pear-shaped form. - It measures 15 µm x 9 µm wide and 4 µm thick. - Dorsally, it is convex and ventrally, it has a sucking disc, which helps in its attachment to the intestinal mucosa. - It is bilaterally symmetrical and possesses. - 1 pair of nuclei - 4 pairs of flagella - 1 pair of axostyles ▪ Cyst (or cystic form). -The cyst is small and oval, measuring 12 µm x 8 µm and is surrounded by a hyaline cyst wall. -2 pairs of nuclei. - 1 pair of Axostyle  Life Cycle ▪ Giardia passes its life cycle in one host. Infective form: Mature cyst. Mode of transmission: Fecal-oral route Man acquires infection by ingestion of cysts in contaminated water and food. ▪ Within half an hour of ingestion, the cyst hatches out into two trophozoites, which multiply successively by binary fission and colonize in the duodenum resulting in Gardiasis. ▪ During unfavorable conditions, encystment (formation of cyst) occurs usually in colon. ▪ Cysts are passed in stool and remain viable in soil and water for several weeks.  Clinical symptoms G. lamblia can cause abdominal pain, severe foul-smelling greasy diarrhoea, flatulence, vomiting, weight loss, malabsorption with lactose intolerance, and in children, impairment of growth. Laboratory Diagnosis - Microscopic examination and finding trophozoites and cyst in direct faecal smear or stained smear; ▪ G. lamblia trophozoites in fresh diarrhoeic faecal specimens. ▪ G. lamblia cysts in more formed faecal specimens.  Prophylaxis ▪ Preventing faecal contamination of the environment and water supplies by using latrines. ▪ Hand washing after defaecation and before eating. ▪ Covering food and water to prevent contamination from flies which can act as cyst carriers. ▪ Not eating green salads or other uncooked foods which may contain cysts, usually as a result of fertilization with untreated human faeces. ▪ Boiling drinking water (cysts are killed at 55 °C) or using membrane filters. ▪ Health education, particularly of food handlers, and also in schools and community health centres.  Genus : Trichomonas Genus Trichomonas has 3 species, which occur in humans; - T. vaginalis: - it is found in (vagina, urethra, seminal vesicles) -causes venereal disease and transmitted by direct contact (infective stage: Trophozoite). -T. hominis: is found in large intestine, harmless and transmitted by resistant stage (infective stage: Trophozoite). - T. tenax : in mouth, harmless and transmitted by direct contact (infective stage: Trophozoite). - No Cystic stage  Trichomonas Vaginalis Distribution: Prevalence of trichomoniasis varies from 5% patients at hospitals to 75% in sexual workers. Trichomonas exists only in trophozoite stage. Cystic stage is not seen. Trichomonas vaginalis is pathogenic in the genitourinary tract. Habitat of T. vaginalis : In females, it lives in vagina and cervix and may also be found urethra, and urinary bladder. In males, it occurs mainly in the anterior urethra, but may also be found in the Prostate, seminal vesicles. Route of infection: Sexual transmission (direct contact from person to person) Infective stage: Trophozoite Diagnostic stage: Trophozoite Disease: Trichomoniasis  Morphology Trophozoite form: - pear-shaped or ovoid and measures 15-18 µm in diameter -Single nucleus - 4 anterior flagella and a lateral flagellum attached by an undulating membrane. - Two axostyles are arranged asymmetrically. - It does not undergo encystation (no cyst) Life Cycle ▪ Life cycle of T. vaginalis is completed in a single host either male or female. ▪ It multiplies in genitourinary tract. Trophozoites divide by longitudinal binary fission The incubation period of trichomoniasis is 4 days to 4 weeks, roughly 10 days.  Clinical Features Infection is often asymptomatic. - In males, it may develop urethritis, epididymitis, and prostatitis. - In females, it may produce severe pruritic vaginitis , Cervical erosion. Laboratory Diagnosis Microscopic examination In females, microscopical identification of trophozoites in vaginal or urethral discharge. In males, trophozoites may be found in urine or prostatic secretions. Prophylaxis ▪ Avoidance of sexual contact with infected partners. ▪ Use of barrier method during intercourse. Trichomonas hominis (intestinali) Trophozoite - measures 8–12 μm - pyriform-shaped, - carries 5 anterior flagella - an undulating membrane that extends the full length of the body. ▪ It is a very harmless commensal of the caecum. ▪ Habitat : Large intestine (caecum). ▪ Transmission occurs in trophic form by fecal-oral route. ▪ Microscopic examination of stool will reveal motile trophozoite of T. hominis.  Trichomonas Tenax T. tenax, also known as T. buccalis, - It is smaller (5–10 μm) than T. vaginalis. - It is a harmless commensal which lives in mouth in the gum pockets, carious tooth cavities, and less often in tonsillar crypts. - It is transmitted by kissing, through salivary droplets, and fomites. - It may cause respiratory infections and thoracic abcesses. - Better oral hygiene rapidly eliminates the infection and no therapy is indicated. Trichomonas Tenax life cycle  Naegleria Fowleri It is the only species of genus Naegleria, which infects man. N. fowleri causes the disease primary amoebic meningoencephalitis (PAM), a brain infection that leads to destruction of brain tissue. Distribution ▪ It is worldwide in distribution. It grows best at high temperatures up to 115°F (46°C) ▪ N. fowleri is a heat-loving (thermophilic) amoeba that thrives in warm water at low oxygen tension and is commonly found in warm freshwater (e.g. lakes, rivers, and springs) and soil. It is commonly seen on the surface of vegetation, mud, and water. Morphology N.fowleri occurs in 3 forms: 1 – Cyst: Trophozoites encyst due to unfavorable conditions 2-Amoeboflagellate trophozoite - Amoeboid trophozoite form: - 10–20 µm, showing rounded pseudopodia (lobopodia) - spherical nucleus with big endosome, and pulsating vacuoles. - Flagellate trophozoite form: - it is a biflagellate pear-shaped form occurs within minute when trophozoites are transferred to distilled water.  Infection location in Brain human: Route of infection: Nasal-route Infective stage: Trophozoite Diagnostic stage: Flagellated trophozoite form Habitat: found warm, stagnant water such as freshwater lakes, ponds and rivers.  Pathogenecity and Clinical Features ▪ Human infection comes from water containing the amoebae and usually follows swimming or diving in ponds. ▪ The amoebae invade the nasal mucosa and pass through the olfactory nerve branches into the meninges, and brain to initiate an acute purulent meningitis and encephalitis, called as primary amoebic meningoencephalitis (PAM), which is usually fatal. ▪ Incubation period varies from 2 days to 2 weeks. The disease advances rapidly, causing severe fever, headache, vomiting, stiff neck, and coma. Finally results in death within 1-14 days. Laboratory Diagnosis The diagnosis of PAM is based on the finding of motile trophozoites in wet mounts of freshly- obtained CSF under microscope. - Wet film examination of CSF may show trophozoites. - Cysts are not found in CSF or brain  Acanthamoeba Species Acanthamoeba culbertsoni is the species most often responsible for human infection Distribution This is an opportiunistic protozoan pathogen found worldwide in the environment in water and soil. Morphology Acanthamoeba exists as - Active trophozoite form: it is large, 20–50 µm in size and characterized by spine-like pseudopodia (acanthopodia). - not having a flagellate stage - forming cysts in tissues - Resistant cystic form (Cyst): - The polygonal double-walled cysts are highly resistant. - The cysts are present in all types of environment.  Infection location: Brain, eye, skin Route of infection: Nasal-route, through the eye or ulcerated skin Infective stage: Trophozoite Diagnostic stage: Cyst and trophozoite form in the tissue Habitat: - Water and soil in the enviroment - brain, eye, skin in human body Disease: Acanthamoeba keratitis Granulomatous Amebic Encephalitis (GAE) Disseminated infection Skin lesions  Laboratory Diagnosis Diagnosis of amoebic keratitis Microscopic Examination: Finding cyst in corneal scrapings by wet mount, histology and culture. Diagnosis of GAE Microscpic examination : Finding trophozoites and cysts in brain biopsy immofluroscence microscopy Diagnosis of skin lesions cyst trophozoite Finding trophozoites and cysts in tissue