1. Protozoa of the digestive and urogenital system.pdf

# Introduction to parasitology and course organization This section provides an overview of the field of parasitology and details the organizational structure, student responsibilities, and requirements for this course. ### 1.1 Introduction to parasitology Parasitology is the study of parasitic organisms . The Department of General Biology and Parasitology is located at 5 Chałubińskiego Str., 02-004 Warsaw . The Head of the Educational Unit is Professor Daniel Młocicki, and the course coordinator and person responsible for the syllabus is Associate Professor Monika Dybicz, who can be contacted at [monika.dybicz@wum.edu.pl](mailto:monika.dybicz@wum.edu.pl) . Other teachers for the course include Aleksandra Sędzikowska and Julia Dąbrowska [1](#page=1). ### 1.2 Course organization and student responsibilities The organization of this course emphasizes active student participation and preparation. #### 1.2.1 Preparation and participation Students are required to prepare for each course session, and this preparation will be assessed through student answers or written tests . A key component of the laboratory work involves observing microscopic and macroscopic preparations of different developmental stages of parasites and documenting these observations through drawings [2](#page=2). #### 1.2.2 Safety and attendance Given the potential contact with invasive material during laboratory classes, strict adherence to hygiene instructions is mandatory . Attendance at all classes is obligatory, and students are expected to arrive on time . Absences due to illness must be made up with another group, requiring prior agreement with the person responsible for the subject [2](#page=2). #### 1.2.3 Course materials Students must possess the workbook titled "Parasitology - materials for 3rd year students of English Division Medicine," which is provided free of charge [2](#page=2). #### 1.2.4 Transfer of credit and subject recognition Individuals seeking to transfer the subject from previous years or from another university must submit an application to the Head of the Department of General Biology and Parasitology and obtain permission from the Faculty Dean [2](#page=2). > **Tip:** Always ensure you have reviewed the required materials before attending laboratory sessions to maximize your learning and be prepared for assessments. **Tip:** Familiarize yourself with the hygiene protocols in the laboratory setting to ensure a safe learning environment. * * * # Course objectives and learning outcomes This section outlines the primary goals of the course, focusing on equipping students with knowledge and skills in medical parasitology [3](#page=3). ### 1.1 Core knowledge acquisition The fundamental objective is to impart essential information regarding the biology, physiology, and morphology of medically significant parasites that affect human tissues, organs, and systems. This includes gaining knowledge about [3](#page=3): * **Current challenges in medical parasitology:** Understanding contemporary issues within the field [3](#page=3). * **Environmental influences on parasitism:** Recognizing how environmental factors contribute to parasite invasion and dispersion [3](#page=3). * **Opportunistic species:** Identifying parasites that cause disease in individuals with weakened immune systems [3](#page=3). * **Pathogenesis and disease progression:** Understanding how parasitic infections develop and manifest, particularly in states of immunosuppression or immunological defects [3](#page=3). * **Epidemiology of parasitic invasions:** Learning about the patterns and determinants of parasitic infections in populations [3](#page=3). ### 1.2 Awareness and practical skills development A key aim is to make future physicians aware of the dangers posed by parasites prevalent both in Poland and globally. Students will also learn [3](#page=3): * **Parasitological interview techniques:** The correct methods for conducting a patient interview to gather relevant parasitological history [3](#page=3). * **Modern laboratory diagnostics:** An introduction to contemporary methods used for diagnosing parasitic infections [3](#page=3). * **Interpretation of diagnostic results:** Developing the ability to accurately interpret the outcomes of diagnostic tests [3](#page=3). ### 1.3 Specific learning outcomes The course aims to achieve specific learning outcomes, denoted by C.W (knowledge) and C.U (understanding/skills): * **C.W13:** Understanding the epidemiology of parasitic infections, including their geographical distribution [4](#page=4). * **C.W16:** Identifying human invasive forms or developmental stages of selected parasitic fungi, protozoa, helminths, and arthropods, considering their geographical range [4](#page=4). * **C.W17:** Grasping the principle of the parasite-host system and recognizing the basic symptoms of diseases caused by parasites [4](#page=4). * **C.W19:** Understanding the fundamentals of parasitological diagnostics [4](#page=4). * **C.U6:** Evaluating environmental threats and utilizing basic methods to detect harmful biological and chemical factors in the biosphere, specifically within the field of parasitology [4](#page=4). * **C.U7:** Recognizing common human parasites based on their structure, life cycles, and the symptoms they cause [4](#page=4). * **C.U9:** Preparing microscopic preparations and identifying pathogens under a microscope in the context of parasitology [4](#page=4). > **Tip:** Pay close attention to the geographical distribution of parasites (C.W13, C.W16) as this is a recurring theme for both knowledge and understanding outcomes. > **Example:** Under C.U7, you should be able to identify \_Plasmodium species based on their characteristic ring forms, trophozoites, schizonts, and gametocytes seen in blood smears, and associate them with malaria symptoms. * * * # Parasite classification and interspecific relationships This topic explores the taxonomic classification of parasites and the various types of interactions between different biological species, focusing on how these relationships are defined and exemplified [7](#page=7) [8](#page=8) [9](#page=9). ### 3.1 Parasite classification Parasites are classified using a hierarchical taxonomic system, mirroring the classification of all living organisms, which includes units such as kingdom, subkingdom, phylum, subphylum, superclass, class, subclass, order, suborder, superfamily, family, genus, and species [7](#page=7). #### 3.1.1 Binomial nomenclature A fundamental aspect of parasite classification is binomial nomenclature, a system formalized by Linnaeus. This system assigns each parasite two distinct names: a genus name and a species name [7](#page=7). * **Naming conventions:** The names can be derived from various sources, including the names of their discoverers, Greek or Latin words related to their geographical origin, their habitat, or the hosts they inhabit. They can also reflect the parasite's size or shape [7](#page=7). * **Formatting:** In written form, the generic name always begins with an initial capital letter, while the species name starts with an initial lowercase letter. For example, \_Entamoeba histolytica [7](#page=7). ### 3.2 Interspecific relationships Interspecific relationships describe the interactions between individuals of different biological species. These associations can range from beneficial to antagonistic [8](#page=8) [9](#page=9). #### 3.2.1 Commensalism Commensalism is an association between two different species where one partner benefits from the relationship, while the other partner is neither harmed nor benefited [8](#page=8). * **Example:** Obligatory commensalic bacteria and protozoans found in the human intestine and on the skin are an example of this relationship [8](#page=8). #### 3.2.2 Parasitism Parasitism is an antagonistic interspecific relationship where one species, the parasite, harms its host and lives at the host's expense. This relationship can lead to parasitic infection or parasitic disease, also known as parasitosis [8](#page=8). > **Tip:** In parasitism, the parasite is the organism that benefits, while the host is the organism that is harmed. #### 3.2.3 Symbiosis Symbiosis refers to a close and often long-term interaction between two or more different biological species where different organisms live together and interact. In this association, one partner typically lives in or on the body of another [9](#page=9). * **Example:** The relationship between clownfish and sea anemones is a common illustration of symbiosis [9](#page=9). #### 3.2.4 Mutualism Mutualism is a form of symbiosis characterized by a permanent association between two different organisms where living apart is impossible. In mutualistic relationships, both partners benefit each other, and they are metabolically dependent, meaning neither can survive in the absence of the other [9](#page=9). * **Example:** The relationship between angulates (hoofed mammals) and the intestinal bacteria that aid in their digestion is an example of mutualism [9](#page=9). * * * # Types of parasites and transmission routes This section explores the classifications of parasites based on their host relationship and describes the various ways parasites can enter the human body and spread among hosts [10](#page=10) [11](#page=11) [12](#page=12) [13](#page=13) [14](#page=14). ### 4.1 Classification of parasites by host relationship Parasites can be categorized based on their dependence on a host and their location within or on the host [10](#page=10). #### 4.1.1 Location on or in the host * **Ectoparasite:** A parasite that lives on the exterior surface of the host [10](#page=10). * **Endoparasite:** A parasite that lives inside the body of its host [10](#page=10). #### 4.1.2 Dependence on the host * **Facultative parasite:** An organism that can complete its life cycle as a free-living organism but may live as a parasite under certain circumstances [10](#page=10). * **Obligatory parasite:** A parasite that cannot survive apart from its host [10](#page=10). #### 4.1.3 Host roles * **Accidental (incidental) host:** A host that is not the normal species for a parasite, leading to infection in an unusual host [10](#page=10). * **Definitive host:** The host in which a parasite reaches its adult stage and/or reproduces sexually [10](#page=10). * **Intermediate host:** The host in which a parasite undergoes its larval stage or asexual reproduction [10](#page=10). * **Reservoir host:** A species, typically an animal, that harbors a parasite also found in humans. These hosts can be involved in the parasite's development, act as a source of infection, and lead to human infection [11](#page=11). * **Opportunistic parasites:** These parasites can cause serious disease, particularly in individuals with compromised immune systems [11](#page=11). #### 4.1.4 Vectors and transmission * **Biological vector (carrier):** An organism that is an obligatory parasite and essential for the life cycle of a pathogenic organism, actively transmitting it [11](#page=11). * **Mechanical vector (carrier):** An organism that passively transmits a disease agent [11](#page=11). ### 4.2 Parasite distribution and terminology Parasites can be classified by their geographical prevalence and specific conditions they cause [11](#page=11) [12](#page=12). * **Cosmopolitan parasites/parasitosis:** Occur commonly in many countries or worldwide, such as \_Trichomonas vaginalis [12](#page=12). * **Endemic parasites/parasitosis:** Limited to specific geographical areas, with their distribution influenced by environmental and biological factors, such as malaria [12](#page=12). * **Parasitemia:** The presence of parasites in the blood, as seen in malaria [11](#page=11). * **Pathogenic:** Refers to the production of tissue changes or disease. Pathogenicity is the ability to produce these changes [11](#page=11). * **Zoonosis:** An infection in humans caused by parasites that are naturally found in wild and domestic animals [11](#page=11). ### 4.3 Routes of parasite transmission The infective route is the specific pathway through which a parasite enters the human body. Transmission modes describe how the parasite invades, for example, via active skin penetration by cercariae or ingestion of infective \_Ascarid eggs [12](#page=12). #### 4.3.1 Major transmission routes * **Congenital transmission:** Transmission from mother to infant, as seen in toxoplasmosis [13](#page=13). * **Contact transmission:** * **Direct contact:** Person-to-person transmission, such as with \_Trichomonas vaginalis [13](#page=13). * **Indirect contact:** Transmission through contaminated objects or environments, such as with \_Ascaris lumbricodes [13](#page=13). * **Food transmission:** Ingestion of food contaminated with the infectious stage of a parasite or consumption of undercooked meat from intermediate hosts containing infectious stages [13](#page=13). * **Water transmission:** Ingestion or contact with water contaminated with the infectious stage of a parasite [13](#page=13). * **Soil transmission:** Contamination of soil by feces containing specific parasite stages, which can then lead to infection [13](#page=13). * **Arthropod transmission:** Transmission facilitated by arthropods acting as vectors for parasitic diseases [13](#page=13). ### 4.4 Avenues of invasion into the human body The human body has several points of entry for parasitic infections [14](#page=14). * **Digestive tract:** This is the most common avenue for parasitic entry, often associated with food and water transmission [14](#page=14). * **Skin:** Invasive larvae can penetrate the skin, enter the body, and establish infection. This is common in soil and water transmission routes [14](#page=14). * **Blood:** Parasites can be injected directly into the bloodstream by bloodsucking insects during a bite, as seen in arthropod transmission of malaria [14](#page=14). * **Transfusion and transplantation:** In rare cases, parasites can be transmitted through blood transfusions or organ transplantation, such as with \_Trypanosoma or \_Toxoplasma [14](#page=14). * * * # Specific protozoan parasites and their diseases This section details specific protozoan parasites that infect humans, focusing on their morphology, life cycles, the diseases they cause, diagnostic methods, and prevention strategies [23](#page=23). ### 5.1 Giardia intestinalis * **Disease:** Giardiasis, also known as traveler's diarrhea. It is the most common intestinal parasite, frequently associated with traveler's diarrhea [24](#page=24) [25](#page=25). * **Morphology:** * **Trophozoite:** Bilaterally symmetrical, bi-nucleated, pear-shaped, measuring 12-15 µm. Features a ventral adhesive disc, four pairs of flagella, two axonemes, and two median bodies. Trophozoites are found in the feces, especially in chronic diarrhea [24](#page=24) [26](#page=26). * **Cyst:** Ovoid, 8-12 µm, highly resistant, and can remain viable for up to 3-4 months. It is bi- or four-nucleated, with nuclei at one end. The cytoplasm often retracts from the thick cyst wall. The cyst is the infective and diagnostic stage [24](#page=24) [26](#page=26). * **Life Cycle:** Trophozoites multiply by binary fission in the intestine. The resistant, infective cyst is passed in feces. Transmission occurs through the ingestion of cysts in contaminated water or food, or via feces, fingers, food, and flies. Excystation occurs in the small intestine [25](#page=25) [26](#page=26). * **Pathogenesis:** These protozoa are not tissue invaders; they cause mechanical irritation of the intestinal mucosa [25](#page=25). * **Diagnosis:** Recovery of trophozoites or cysts in feces is the primary method. Duodenal fluid or biopsy samples can also demonstrate trophozoites. Antigen detection and immunofluorescence are also used. The diagnostic stages are the cyst and sometimes the trophozoite [29](#page=29). * **Symptoms:** Abdominal pain, diarrhea, bloating, nausea, and vomiting [29](#page=29). * **Epidemiology:** Affects about 2% of adults and 8% of children in developed countries, and around 35% in developing countries. An infected person can excrete 1-10 million cysts daily, and as few as 10 cysts can cause disease. It is a zoonosis, with infection occurring in humans and animals [25](#page=25) [30](#page=30). * **Prevention:** High levels of personal and environmental hygiene, safe consumption of food and water, treatment of infected individuals, and protection of food from mechanical vectors [31](#page=31). * **Treatment:** Metronidazole and tinidazole are common treatments, acting by bioactivation to form cytotoxic products that damage DNA. Nitazoxanide interferes with anaerobic energy metabolism. Furazolidone (for children) and paromomycin (for pregnant women) are also used [81](#page=81). ### 5.2 Entamoeba histolytica * **Disease:** Amoebiasis, amoebic dysentery, and amoebic hepatitis if the liver is involved. It causes ulceration of the intestinal wall and bloody amoebic dysentery [32](#page=32) [34](#page=34). * **Morphology:** * **Trophozoite:** Amoeboid, 15-30 µm (up to 60 µm). Possesses one nucleus with a central karyosome and chromatin granules lining the nuclear membrane. Pseudopods are present, and food vacuoles may contain host erythrocytes [32](#page=32) [39](#page=39) [93](#page=93). * **Cyst:** Round or oval, 10-20 µm, with four nuclei having the same structure as in the trophozoite. Features an evident chromatoid bar. It can be invasive for one month and transmitted by insects [32](#page=32). * **Life Cycle:** Trophozoites multiply by binary fission in the large intestine. The resistant, infective cyst is passed in feces. Transmission occurs via ingestion of cysts in contaminated water or food, or through feces, fingers, contaminated food/water, and insects. Excystation occurs in the small intestine [35](#page=35). * **Pathogenesis:** Invades the intestinal wall and multiplies in the mucosal tissue, causing ulceration. Can spread via blood to other tissues, including the liver, lungs, skin, and brain, causing extraintestinal amebiasis [34](#page=34) [36](#page=36). * **Diagnosis:** Microscopic identification of cysts and trophozoites in stool is common. Stained preparations (wet mounts and permanent stains like Wheatley trichrome) are used. Trophozoites can also be identified in aspirates or biopsy samples. Diagnostic stages are the cyst and occasionally the trophozoite [36](#page=36) [38](#page=38) [82](#page=82). * **Symptoms:** May be asymptomatic or cause abdominal discomfort, bloody dysentery, diarrhea, and fever. Extraintestinal manifestations can include liver abscess, peritonitis, pleuropulmonary abscesses, and cutaneous/genital lesions [36](#page=36). * **Epidemiology:** Affects an estimated 500 million people, with 50 million having symptomatic amoebiasis. Annually, 40,000-50,000 deaths occur from complications. It is worldwide but most common in tropical areas with poor sanitation, institutions with poor sanitation, and among men who have sex with men [36](#page=36) [42](#page=42). * **Prevention:** Personal and environmental hygiene, consumption of fresh, clean food and boiled water, protection of food and water from vectors and contamination, and treatment of infected persons. Caution is advised with fountain drinks, ice cubes, unpeeled fruits/vegetables, unpasteurized dairy, and street vendor food/drinks when traveling [43](#page=43). * **Treatment:** Metronidazole, tinidazole, and ornidazole are used for amoebic colitis and extraintestinal amebiasis. Dehydroemetine is used for severe hepatic amebiasis [81](#page=81). ### 5.3 Nonpathogenic intestinal protozoa These protozoa are commonly found in the intestinal tract but are not associated with illness. They do not harm the body, even in immunocompromised individuals [44](#page=44). * **Examples:** * \_Entamoeba dispar (identical to \_E. histolytica) [44](#page=44). * \_Entamoeba hartmanni (identical to \_E. histolytica) [44](#page=44). * \_Entamoeba moshkovskii (identical to \_E. histolytica) [44](#page=44). * \_Entamoeba coli (colonizes the large intestine) [44](#page=44) [93](#page=93) [99](#page=99). * \_Endolimax nana (worldwide, resides in the large intestine) [44](#page=44) [99](#page=99). * \_Entamoeba polecki (usually in pigs and monkeys, rare in humans) [44](#page=44). * \_Iodamoeba butschlii (worldwide, less common than \_E. coli and \_E. nana) [44](#page=44). * \_Chilomastix mesnili (harmless commensal of cecum and colon) [44](#page=44). * \_Enteromonas hominis (rarely encountered in the large intestine, exists in trophozoite and cyst forms) [80](#page=80). ### 5.4 Balantidium coli * **Disease:** Balantidiasis [46](#page=46). * **Morphology:** * **Trophozoite:** Oval, 30-300 µm long and 30-100 µm broad. Covered by cilia for locomotion. Possesses an anterior groove leading to a mouth (cytostome) and a posterior broad end with an excretory opening (cytopyge). Has two nuclei: a large, kidney-shaped macronucleus and a small micronucleus. Two contractile vacuoles and many food vacuoles are present. The invasive form [46](#page=46). * **Cyst:** Round, 40-60 µm, surrounded by a thick, transparent cyst wall. Contains two nuclei and vacuoles; cilia are not observed. The infective form [46](#page=46) [48](#page=48). * **Life Cycle:** Completed in a single host, with pigs as the natural host and humans as accidental hosts. Excystation likely occurs in the small intestine, with multiplication in the large intestine. Trophozoites feed and multiply, either in the gut lumen or entering the submucosa. Both trophozoites and cysts are excreted in feces; cysts are resistant and infective [48](#page=48) [49](#page=49). * **Pathogenesis:** Trophozoites can enter the submucosa of the large intestine. Complications such as perforation of the large intestine, appendicitis, peritonitis, severe dehydration leading to renal failure can occur, especially in immunocompromised and malnourished individuals. Rare extraintestinal manifestations include liver abscess, pleuritis, and pneumonia [49](#page=49) [51](#page=51). * **Diagnosis:** Stool examination for cysts and trophozoites. Histopathological staining of biopsy tissue or ulcer scrapings can reveal trophozoites, cysts, and lymphocytic infiltration. Cultures can also be used [52](#page=52). * **Symptoms:** Majority are asymptomatic carriers. Chronic disease involves periods of increased bowel movements (mucous or rarely bloody) alternating with constipation. Acute disease resembles amoebic dysentery [51](#page=51). * **Epidemiology:** Worldwide distribution, particularly in tropical and subtropical countries with frequent pig-to-human contact. Infection is more common with decreased immunity. It is a zoonosis [52](#page=52). * **Prevention:** Treatment of carriers shedding cysts, hygienic rearing of pigs and prevention of pig-to-human contact, and preventing contamination of food and water with pig and human feces [53](#page=53). ### 5.5 Blastocystis hominis * **Disease:** Once considered a commensal, its pathogenic role is now recognized, causing symptoms like diarrhea, nausea, abdominal cramps, flatulence, excessive gas, and anal itching [54](#page=54). * **Morphology:** Exhibits significant morphological variation, appearing in four forms: * Vacuolar (5–40 µm, can be larger) [55](#page=55). * Granular [55](#page=55). * Amoeboid [55](#page=55). * Cystic (3–5 µm), postulated to be the infectious stage [55](#page=55). * **Epidemiology:** Found worldwide. Efforts are ongoing to characterize geographic and host distribution of its subtypes [54](#page=54). ### 5.6 Trichomonas species This group includes flagellates, primitive protozoa that parasitize the gastrointestinal, urogenital, or respiratory tracts of humans and animals [56](#page=56) [57](#page=57). #### 5.6.1 Pentatrichomonas hominis * **Parasite:** A digestive system parasite [56](#page=56). * **Morphology:** Teardrop trophozoite, 5x16µm, with 3-5 flagella, a undulating membrane, a large nucleus, and a long axostyle. Occurs only in the trophozoite stage [59](#page=59). * **Life Cycle:** Inhabits the small intestine, occasionally the reproductive organs [59](#page=59). * **Transmission:** Via contaminated food and drinks (water, milk) or contact with an infected person. More common in children [60](#page=60). * **Diagnosis:** Fecal trophozoites observed in stained preparations and cell cultures. The diagnostic stage is the trophozoite [61](#page=61). * **Symptoms:** Asymptomatic or correlated with intestinal location, causing diarrhea and intestinal ailments [61](#page=61). * **Epidemiology:** Worldwide distribution, more common in warm areas [61](#page=61). #### 5.6.2 Trichomonas vaginalis * **Disease:** Trichomoniasis of the urogenital system. A frequent infection (20%) of genitourinary organs [56](#page=56) [67](#page=67). * **Morphology:** Typical flagellate, larger than \_T. tenax. Occurs only as a trophozoite (no cyst formation). Trophozoite measures 8-30 µm, with flagella and a rippling membrane for vigorous movement [62](#page=62) [83](#page=83) [86](#page=86) [92](#page=92). * **Life Cycle:** Reproduces through longitudinal division [66](#page=66). * **Transmission:** Primarily transmitted in vaginal or urethral secretions during sexual intercourse. Has limited survival time outside the host (e.g., in bathtubs, towels). Infection can also occur through hygienic negligence, such as in hydrotherapy [66](#page=66) [67](#page=67). * **Pathogenesis:** Symptomatic in women, causing chronic vaginitis. Invasion often occurs alongside other venereal diseases [67](#page=67). * **Diagnosis:** Diagnosis can be difficult. Microscopic examination of vaginal secretions or urine sediment can reveal trophozoites. The diagnostic criteria include the absence of cysts, the presence of a trophozoite with one nucleus and flagella, and typical symptoms [67](#page=67). * **Symptoms:** In women, symptomatic with chronic vaginitis. Symptoms include whitish vaginal discharge, itching, and lower abdominal pain. An inflamed cervix with red, punctate lesions may be observed [67](#page=67). * **Epidemiology:** Men play a major role in spread as they are often asymptomatic [67](#page=67). * **Prevention:** Treatment is effective but requires repeated treatment and addressing co-infections (e.g., Candida) [67](#page=67). * **Treatment:** Metronidazole or tinidazole are used, acting by bioactivation to form cytotoxic products with nitro groups that damage DNA. Both partners should be treated [81](#page=81). #### 5.6.3 Trichomonas tenax * **Parasite:** An oral trichomonad, a cosmopolitan flagellate found in the mouth of humans [56](#page=56) [68](#page=68). * **Morphology:** Similar to \_T. vaginalis but smaller. Occurs only as a trophozoite [63](#page=63) [72](#page=72) [83](#page=83) [87](#page=87) [92](#page=92). * **Life Cycle:** Reproduces asexually by longitudinal division [74](#page=74). * **Pathogenesis:** Considered an oral commensal by many, but evidence suggests it can be pathogenic, exhibiting high proteolytic activity that damages mucous membranes and tissues. It is an etiological agent of oral trichomonosis. The presence of \_T. tenax is often associated with chronic inflammation of the oral mucosa, nasal sinuses, or tonsils [68](#page=68) [69](#page=69) [70](#page=70). * **Diagnosis:** Microscopic examination of direct preparations from oral mucosa scrapings, stained preparations (Giemsa), and cultivation methods. Modern techniques like PCR are also used [73](#page=73). * **Symptoms:** Predominant symptoms include dryness, burning, and taste disturbances. Less common are spontaneous or swallowing pains. Physical examination may reveal pathological pockets, tongue inflammation, and inflammatory foci in the oral mucosa [70](#page=70). * **Epidemiology:** Highest susceptibility observed in the 30-60 age group, with a tendency to increase with age. Common in individuals with gingivitis or poor oral hygiene. Not found in toothless individuals. Can be found in lymph nodes, salivary glands, tonsils, and even lung abscesses, pleural effusion, mammary glands, and liver ulcerations, particularly in individuals with reduced immunity [68](#page=68) [69](#page=69) [72](#page=72). * **Prevention:** Daily hygienic procedures and maintaining correct oral hygiene are important preventive measures [74](#page=74). * **Treatment:** Imidazole derivatives are effective [74](#page=74). * **Environmental Factors:** Trophozoites show reduced mobility or death in pool water, detergent, and at high temperatures (50°C). Salt and tap water have no significant effect, while metronidazole leads to death [76](#page=76). ### 5.7 Entamoeba gingivalis * **Parasite:** Found in the oral cavity (interdental spaces, gingival margins, tooth cavities, paranasal sinuses), throat, and bronchi [77](#page=77). * **Morphology:** Occurs only as a uninuclear trophozoite, 15-35 µm; cysts are not produced [78](#page=78) [93](#page=93) [94](#page=94) [96](#page=96). * **Pathogenesis:** Recognized as a commensal, it often occurs with gum inflammation. Infection may be asymptomatic or correlated with periodontal deterioration [77](#page=77) [78](#page=78). * **Life Cycle:** Simple; multiplies by binary fission in the oral cavity [78](#page=78). * **Transmission:** Transmitted directly from person to person (kissing, shared toothbrush and dishes) [78](#page=78). * **Diagnosis:** Recovery of trophozoites in swabs from gingiva, amorphous plaque, or dental pockets. The diagnostic stage is the trophozoite [79](#page=79). * **Symptoms:** Generally asymptomatic but may be connected to oral and dental diseases [79](#page=79). * **Epidemiology:** A cosmopolitan parasite [78](#page=78). * **Prevention:** High level of oral hygiene and using clean personal items like toothbrushes, cutlery, and dishes [79](#page=79). ### 5.8 Other Protozoa * **Dientamoeba fragilis:** A common commensal in the cecum and upper colon. Initially thought to be an amoeba, it's now classified as an amoeboflagellate. Cosmopolitan, with a higher incidence reported in children [80](#page=80). * **Enterocytozoon bieneusi:** A microsporidium that invades the small intestine; rarely causes nasal polyps or infections of the bile duct and bronchus [80](#page=80). ### 5.9 Diagnostic Preparations and Stains * **Giardia intestinalis:** Trophozoites in bile (Giemsa staining); cysts in stool (Lugol's fluid, J+K staining) [82](#page=82) [83](#page=83) [89](#page=89) [90](#page=90) [92](#page=92). * **Trichomonas vaginalis:** Trophozoites (Giemsa staining) [82](#page=82) [83](#page=83) [86](#page=86) [92](#page=92). * **Trichomonas tenax:** Trophozoites (Giemsa staining) [82](#page=82) [83](#page=83) [87](#page=87) [92](#page=92). * **Entamoeba gingivalis:** Trophozoites from oral swabs (Giemsa staining) [82](#page=82) [93](#page=93) [94](#page=94) [96](#page=96). * **Entamoeba coli:** Stool cysts (J + KJ staining) [82](#page=82) [93](#page=93) [99](#page=99). * **Entamoeba histolytica/E. dispar:** Faecal trophozoites and cysts (Wheatley trichrome staining) [82](#page=82) [93](#page=93). * **Charcot-Leyden crystals:** Composed of eosinophil phospholipase binding to galectin 10; detected in allergies and parasitoses [41](#page=41) [93](#page=93). * * * # Laboratory diagnosis and clinical cases This section details the methods used to diagnose parasitic infections and illustrates them through clinical case studies of patients presenting with parasitic diseases. ### 6.1 Diagnostic methods The laboratory diagnosis of parasitic infections relies on several key methods, including microscopic identification, antigen detection, and molecular techniques [38](#page=38). #### 6.1.1 Microscopic identification Microscopic identification is a common method for diagnosing parasitic infections, particularly by examining stool samples for cysts and trophozoites [38](#page=38). * **Stool examination:** * **Fresh stool:** Can be examined using wet mounts and permanently stained preparations [38](#page=38). * **Concentrates from fresh stool:** Wet mounts and permanently stained preparations can be used, but concentration procedures are not effective for demonstrating trophozoites [38](#page=38). * **Other sample types:** In addition to stool, trophozoites can be identified in aspirates or biopsy samples obtained during procedures like colonoscopy or surgery [38](#page=38). #### 6.1.2 Antigen detection and molecular techniques While not extensively detailed in the provided text for specific parasites, antigen detection and molecular techniques are mentioned as part of the diagnostic armamentarium. These methods can offer higher sensitivity and specificity compared to traditional microscopy and are valuable for identifying specific parasite genotypes [38](#page=38). ### 6.2 Clinical case studies The following case studies illustrate the application of diagnostic methods in identifying parasitic infections. #### 6.2.1 Case of Giardia intestinalis A 5-year-old boy presented with a constellation of symptoms including nausea, occasional vomiting, moderate diarrhea that subsequently resolved, malaise, poor appetite, headaches, and epigastric pain. The absence of fever and the appearance of an allergic rash were notable. Epidemiological data revealed the family were farmers living in the countryside who bred cattle and owned other animals such as poultry, dogs, and a cat. Sanitary conditions were reported as correct. Laboratory tests for bacterial, viral, and parasitic pathogens were ordered, with positive results only from parasitological studies . * **Diagnostic findings:** * Routine coproscopic examination of three consecutive stool samples showed: * Sample 1: Dry, formed feces with a few parasites (Photo A) . * Sample 2: Dry, formed feces with no parasites . * Sample 3: Loose feces with live and motile parasites (Photo B) . * Due to the positive results, all family members were tested. The mother's stool samples revealed the same parasites in one of three tests (Photo C). The mother reported no gastrointestinal complaints . * Molecular biology analysis of the parasites from both the boy and mother showed identical DNA sequences corresponding to genotype A, which is common in humans and animals, particularly dogs, cats, and young cattle . * **Diagnosis and Criteria:** \_Giardia intestinalis . * Oval cyst . * Trophozoite with 2 nuclei and flagella . * Typical symptoms . * Contact with animals suggesting zoonosis . #### 6.2.2 Case of Trichomonas vaginalis A 29-year-old female patient presented with a 15-day history of whitish vaginal discharge accompanied by itching and lower abdominal pain. A vaginal speculum examination revealed an inflamed cervix with red, punctate lesions. A Pap smear was collected and sent for Papanicolaou staining . * **Diagnostic findings:** * Microscopic examination (Figures A and B) using an oil immersion objective revealed objects measuring 10-15 micrometers in length . * **Diagnosis and Criteria:** \_Trichomonas vaginalis . * No cyst stage observed . * Trophozoite with 1 nucleus and flagella . * Typical symptoms of vaginitis . #### 6.2.3 Case of Entamoeba histolytica A 21-year-old exchange student from Nigeria presented to the university clinic with a 3-day history of diarrhea, mild abdominal pain, loss of appetite, and fatigue. Stool samples were collected in 10% formalin and Zn-PVA fecal preservatives for laboratory analysis . * **Diagnostic findings:** * Microscopic examination of a trichrome-stained slide from the Zn-PVA sample revealed organisms ranging in size from 12-26 micrometers (Figures A-C) . * **Diagnosis and Criteria:** \_Entamoeba histolytica . * Cyst with a chromatoidal body . * Trophozoite with a nucleus and ingested red blood cells (RBCs) . * Typical symptoms . #### 6.2.4 Case of Entamoeba coli A 35-year-old woman presented with complaints of abdominal pain, cramps, and diarrhea after a business trip to Mexico. Stool was collected in 10% formalin and polyvinyl alcohol (PVA) for routine ova-and-parasite (O&P) examination . * **Diagnostic findings:** * Microscopic examination at 1000x magnification on a trichrome-stained slide from the PVA-preserved stool revealed objects measuring on average 15-17 micrometers in diameter (Figures A-D) . * **Diagnosis and Criteria:** \_Entamoeba coli (considered non-pathogenic) . * Cyst size over 15 micrometers in diameter . * More than 4 nuclei per cyst . * * * ## Common mistakes to avoid * Review all topics thoroughly before exams * Pay attention to formulas and key definitions * Practice with examples provided in each section * Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Parasitology | The scientific study of parasitic organisms, their hosts, and their interrelationships. It focuses on understanding the biology, life cycles, pathology, diagnosis, and control of parasites that affect humans and animals. | | Medical parasitology | A specialized branch of parasitology concerned with the study of parasites that infect humans, including their role in causing disease, methods of diagnosis, treatment, and prevention strategies. | | Trophozoite | The actively feeding and motile stage of a protozoan parasite, typically found within the host's tissues or body fluids. This stage is often responsible for replication and causing pathological effects. | | Cyst | A resistant, dormant stage in the life cycle of some protozoan parasites, characterized by a protective outer wall. Cysts are crucial for survival in the external environment and for transmission between hosts. | | Binary fission | A form of asexual reproduction in unicellular organisms where a parent cell divides into two approximately equal daughter cells. This is a common method of multiplication for many protozoan parasites. | | Facultative parasite | An organism that can live independently as a free-living organism but can also act as a parasite under certain circumstances, often when a suitable host becomes available. | | Obligatory parasite | An organism that cannot survive independently and must live in or on a host to complete its life cycle. These parasites are entirely dependent on their host for survival and reproduction. | | Definitive host | The host in which a parasite undergoes sexual reproduction or reaches its adult, mature stage. This is where the parasite’s life cycle is completed. | | Intermediate host | A host that harbors the larval or asexual stages of a parasite's life cycle. Parasites often undergo development or multiplication in the intermediate host before reaching the definitive host. | | Zoonosis | An infectious disease that can be transmitted from animals to humans. Many parasitic infections are considered zoonoses, originating from either wild or domestic animals. | | Ectoparasite | A parasite that lives on the exterior surface of its host. Examples include fleas, lice, and ticks, which reside on the skin or in body hair. | | Endoparasite | A parasite that lives within the body of its host, such as in the gastrointestinal tract, blood, or internal organs. | | Pathogenicity | The ability of a pathogenic organism, such as a parasite, to cause disease in a host. This involves the mechanisms by which the parasite damages host tissues or disrupts physiological functions. | | Reservoir host | An animal species that harbors a parasite and serves as a source of infection for humans. These hosts are crucial for the continued existence of the parasite in the environment. | | Vector | An organism, often an arthropod like a mosquito or tick, that transmits a pathogenic microorganism or parasite from an infected individual or animal to another. | | Biological vector | A vector in whose body the pathogenic organism or parasite develops or multiplies before being transmitted to a new host. The organism is essential for the vector's life cycle. | | Mechanical vector | A vector that passively transmits pathogens or parasites without the pathogen undergoing any development or multiplication within the vector. It simply carries the infectious agent from one place to another. | | Giardiasis | An intestinal infection caused by the protozoan parasite Giardia intestinalis. Symptoms commonly include diarrhea, abdominal cramps, and bloating. | | Amoebiasis | An infection caused by the protozoan parasite Entamoeba histolytica. It can manifest as intestinal amoebiasis (dysentery) or invasive amoebiasis affecting organs like the liver. | | Trichomoniasis | An infection caused by protozoa of the genus Trichomonas. The most common form is urogenital trichomoniasis caused by Trichomonas vaginalis. | | Charcot-Leyden crystals | Crystalline structures found in the stools of individuals with parasitic infections, particularly those involving intestinal inflammation. They are composed of eosinophil granule proteins. |