Medical Parasitology M.Sc. Course/2024-2025 PDF

Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 Leishmaniases Leishmaniases cause considerable morbidity and mortality. In the genus Leishmania, there are four pathogenic “species complexes” with subspecies in each comp...

Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 Leishmaniases Leishmaniases cause considerable morbidity and mortality. In the genus Leishmania, there are four pathogenic “species complexes” with subspecies in each complex: L. tropica (Old World), L. mexicana, and L. braziliensis (New World), and L. donovani. Speciation has traditionally been based on clinical symptoms, geographic location, and case history. All Leishmania species are transmitted by the sandfly intermediate host, Phlebotomus spp. The bite of an infected sandfly initially results in a self- healing skin lesion at the bite site; the lesion may last up to 1 year and may be a wet or dry ulcer, depending on the species. Amastigote forms can be found multiplying intracellularly in local macrophages of the lesion. L. tropica and L. mexicana cause cutaneous, spontaneously healing ulcers, although some subspecies of L. mexicana spread to cause a disfiguring form. L. braziliensis affects the mucosa of the nasopharynx and mouth. In addition, L. braziliensis can flare up years later, resulting in subsequent erosion of cartilage in the nose and ears. Unlike the others, L. donovani does not stay localized in the skin lesion; the organisms spread to the viscera, multiplying in macrophages of all internal organs and eventually causing death if the patient is untreated. In tissue sections (e.g., liver, spleen), L. donovani can be seen as an intracellular multiplying amastigote form. All species of Leishmania that infect humans are zoonotic; the usual host is a vertebrate, such as a dog, fox, or rodent. Leishmania parasites have different extra- and intracellular environments. These organisms are digenetic parasites with two basic life cycle stages: one extracellular stage within an invertebrate host (phlebotomine sand fly) and one intracellular stage within a vertebrate host. 1 Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 Fig. (1): Leishmania pp Life Cycle. 2 Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 # The invertebrate hosts or vectors are small insects of the order Diptera ‫رتبة ثنائية االجنحة‬, belonging to the subfamily Phlebotominae. They are commonly called phlebotomine sand flies ‫ذباب الرمل‬. Like mosquitoes, the female needs a blood meal for egg development and only the female is haematophagous ‫دموية التغذية‬. # Leishmania are extremely successful parasites and natural infections are found in many different orders of mammals: rodents, canids ‫ الكالب‬, marsupials ‫ال ُجرابيات‬, and primates ‫الرئيسيات‬. All these mammals are considered as potential reservoirs of the disease. Humans are possible hosts of these parasites, but in the majority of cases they are considered to be accidental hosts. # The classification of Leishmania was initially based on ecobiological criteria such as vectors, geographical distribution, antigenic properties and clinical manifestation. However, biochemical and molecular analysis showed that pathological and geographical criteria were often inadequate and thus other criteria such as the patterns of polymorphism exhibited by kinetoplastic DNA (kDNA) markers, proteins or antigens came to be used to classify Leishmania. # Amastigotes are ovoid (2.5-5 mm diameter), nonmotile intracellular stages (Figure 2). They do not have a free flagellum and are located in the parasitophorous vacuoles ‫فجوة داخل الخلية تحوي على الطفيلي‬of the host’s macrophages. Fig. (2): Macrophage infected with Leishmania Amastigotes # Leishmania Genome: 1. Nuclear Genome: The determination of these Leishmania genome sequences will be a milestone ‫ نقطة مهمة‬for Leishmania researches 3 Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 2. Kinetoplast DNA: The kDNA is the mitochondrial DNA of the Kinetoplastida and constitutes 10–20% of the total DNA. It is a network of circular DNA. Kdna has mainly been used as a diagnostic tool to detect small amounts of parasite DNA in biological materials. Leishmania Species and Clinical Symptoms in Humans L. tropica: cutaneous or Old World leishmaniasis, Oriental boil, Baghdad or Delhi boil L. braziliensis: mucocutaneous or New World leishmaniasis, uta, espundia L. donovani: visceral leishmaniasis, kala-azar, Dumdum fever Major Pathology and Symptoms The type of illness results from immunopathology in specific tissue sites. L. tropica complex: Incubation period is several months (L. tropica) or as short as 2 weeks (L. major). One or more ulcerated, pus-filled lesions appear on the body. Lesions often are moist and shortterm in rural areas or dry and long-lasting in urban areas. L. mexicana: Symptoms are similar to L. tropica. L. braziliensis: Symptoms include a red, itchy ulcer; lesions may metastasize along lymphatics; lesion is self-healing. Disfigurement of nose and ears may occur years later from chronic mucosal ulceration. L. donovani: The incubation period is long. With the initial lesion, short- term, small papules are at the bite site. Malaria-like spiking chills and fever, along with sweating, diarrhea, dysentery, and weight loss. Splenomegaly and hepatomegaly develop after leishmania multiply in visceral reticuloendothelium. Death often occurs within 2 years if untreated (75% to 95% mortality). Order Trichomonadida Most species within this group are parasites or endosymbionts. The trophozoites are often ovoid or pear-like in shape: the anterior is usually rounded and the posterior pointed. The number of flagella varies between species but there are often between 4-6 emerging at their anterior apex. In addition, one flagellum usually curves backwards so that it runs along the cell membrane to form an undulating membrane – this flagellum is therefore said to be ‘recurrent’. Most species do not form cysts. 4 Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 Trichomonas vaginalis This is an extremely common parasite of humans and despite its name it is frequently found in men. T. vaginalis inhabits the vagina in the female and the urethra, epididymis, and prostate gland in the male. The parasite is ‘tear-drop’ shaped, with five flagella emerging at the anterior end: four of these flagella are free while the fifth curves back to form a short undulating membrane that extends just over half the length of the cell (Figure 3). Only one body shape is expressed, although the size can vary considerably. Fig. (3): Trichomonas spp. Humans are the only natural host for T. vaginalis. Apparently, the organisms feed on the mucosal surface of the vagina, where bacteria and leukocytes are found. Often, the organisms are recovered in the centrifuged urine sediment from both male and female patients. Life Cycle Typical of flagellates, T. vaginalis reproduces by longitudinal binary fission. The optimum pH range for the organism to reproduce is approximately 5 or 6. While the normal pH of the vagina is 4 to 4.5, when the level of acidity is disturbed, an environment is created in which T. vaginalis thrives. Normally, the pH of the vagina is maintained by the activity of a group of lactic acid-producing bacteria, but T. vaginalis can disrupt such bacteria, causing the pH to rise above 4.9. Symptomatology and Diagnosis 5 Medical Parasitology Prof. Dr. Malak M. Almusawi M.Sc. Course/ 2024-2025 Lec. 3 Trichomonas vaginalis produces deterioration ‫ تلف‬of the cells of the vaginal mucosa, resulting in inflammation and persistent vaginitis. The condition is characterized by a yellowish discharge accompanied ‫مصحوبة‬ by persistent itching and burning. In males, symptoms are much less noticeable, although there may be urethritis and swelling of the prostate gland. These symptoms are sometimes confused with gonorrhea ‫مرض السيالن‬. Diagnosis in females is confirmed by microscopical identification of motile trophozoites in vaginal discharge smears. Examination of the urine of both sexes, and examination of prostate secretions of the male following prostate massage are also helpful diagnostic procedures. In acute infections, vulvitis is seen and is due to copious leukorrhea ‫افرازات الدم الغزيرة‬. The discharge is frothy ‫ذو رغوة‬, yellow or green, and mucopurulent ‫ ;مخاطي متقيح‬however, only about 10 to 12% of women exhibit this frothy discharge. Small punctate ‫منقطة‬hemorrhagic spots can be seen on the vaginal and cervical mucosa; this has been called a “strawberry appearance” In general, symptoms include vaginal discharge (42%), odor (50%), and edema or erythema (22 to 37%). Other complaints include dysuria ‫عسر‬ ‫ البول‬and lower abdominal pain. Although millions of women are infected with Trichomonas vaginalis every year, in the majority of cases these are asymptomatic. Infection during pregnancy is often associated with poor outcomes ‫نتائج سيئة‬ such as premature delivery ‫ والدة مبكرة‬and below-average birth weight ‫قلة‬ ‫ وزن المولود‬for the baby, although whether the parasite actually induces these effects is uncertain. Chemotherapy Trichomoniasis can be treated effectively with metronidazole. It is recommended that sexual partners be treated simultaneously. 6