Parasitology Study Notes PDF

* Ectoparasites: Organisms as flees, lice, ticks, bugs and leeches which live on the outside of their hosts, usually attached to the skin, feather, hairs, gills etc.... These parasites may be further divided into: a- Visiting ectoparasites: They visit their hosts for taking their blood...

* Ectoparasites: Organisms as flees, lice, ticks, bugs and leeches which live on the outside of their hosts, usually attached to the skin, feather, hairs, gills etc.... These parasites may be further divided into: a- Visiting ectoparasites: They visit their hosts for taking their blood meal and leave them immediately after feeding as flees, mosquitoes and blood sucking insects. b- Temporary ectoparasites: They remain attached to their hosts for sometimes suck blood and then drop off and do not need another meal for months as leeches. c- Permanent ectoparasites: They remain attached to their hosts all their lives as ticks and mites. *Endoparasites: Organisms that live within the bodies of their hosts in the gut, body cavities, lungs, body fluids or other tissues. The endoparasites may be subdivided according to their life pattern into: - a- Homoxenous or monoxenous parasites: These parasites have a simple, direct life cycles whereby the infective stage Homoxenous or monoxenous parasite is a parasite that uses only one host during its life cycle. b- Heteroxenous parasites: These parasites may have complicated indirect life cycles requiring one or more additional hosts, often belonging to different phylum to complete their development. Thus, heteroxenous parasite is a parasite that has two or more types of hosts in its life cycle. c- Heterogenic parasites: They have alternating parasitic and free-living generations in the life cycle. d- Heterogenetic parasites: These parasites have alternation of generations. They have two generations; one reproduces sexually and give rise to the other generation which reproduce asexually giving a new sexually generation and so on. * The host: There are several types of hosts as follows: 1- Definitive or primary host: is the host which harbors the adult stages of the parasites and where sexual activity of the parasite occur. 2- Intermediate host: is the host which harbors the larval or juvenile stage and develops into the infective stage. 3- Reservoir host: When a host harbors the adult stage of a parasite without any injury or disease and acts as a potential source of further infection to the definitive host. 4- Transport host: is a host that nearly caries the non-developing parasites to the next host. 5- Vectors: These hosts transmit infection from one host to another. They are essential intermediate hosts in which the parasite undergoes significant changes. * Factors affecting susceptibility of a given host to a parasite infection: - a. Factors belong to the host: 1- Age. 2- Physiological status. 3- Genetic factors. b. Factors belong to the parasite. 1- Dose of the infective Stage. 2- Viability of the infective stage. 3- Species of parasites and site of development. 4- Genetic factors. Entamoeba histolytica Mode of transmission: Feco-oral route (most common): By ingestion of contaminated food or water with mature quadrinucleated cysts Infective form: Mature quadrinucleated cyst is the infective form. Pathology and Symptomatology*: 1- Intestinal Amebiasis: It occurs when the trophozoites invade the wall of the large intestine. This causes ulcer, dysentery (amoebic dysentery), fever, colic, frequent motions and tenesmus in acute cases. These symptoms disappear in chronic cases. 2- Extraintestinal Amebiasis: It occurs when the trophozoites, invading the intestinal wall, are carried by blood to different organs such as: Hepatitis (amebic hepatitis) and liver abscess, Lung abscess, Brain abscess and other organs e.g. spleen, kidney, etc. 3- Cyst Passers: They are people who contain Entamoeba histolytica without showing any symptoms. The cysts pass with their stools without showing any signs of disease. These cyst-passers form a source of infection to community. Intestinal (Non-Pathogenic) Amebae: Entamoeba dispar, Endolimax nana, Entamoeba coli, Entamoeba hartmanni, Entamoeba polecki and Iodamoeba buetschlii. The zoomastigophorans (zooflagellates) that attack humans can be categorized according to their habitat in the human host into: 1- Intestinal flagellates. 2- Urogenital flagellates. 3- Hemoflagellates (blood flagellates). I- Intestinal Flagellates 1- Species living in the small intestine: e.g. Giardia lamblia (Giardia intestinalis).  2- Species living in the large intestine: A- Chilomastix mesnili. B- Retortamonas hominis (Embadomonas hominis). C- Enteromonas hominis. D- Trichomonas hominis. 3- Trichomonas tenax (Trichomonas buccalis). This species lives in buccal cavities. II- Urogenital Flagellates: This species is found in the genitourinary tract of male and female but mainly in vagina and male urethra e.g. Trichomonas vaginalis. III - Hemoflagellates (Blood Flagellates): They live in the blood and / or tissues of man. 1- Leishmania tropica. 2- Leishmania donovani. 3- Leishmania braziliense. 4- Trypanosoma gambiense. 5- Trypanosoma rhodesiense. 6- Trypanosoma cruzi. Trichomonas vaginalis I- Distribution: Worldwide. Higher prevalence among persons with multiple sexual partners or other venereal diseases. II- Disease: Trichomoniasis, vaginitis in females or urethritis & prostatitis in males.  1- Habitat: Vagina in female and urethra (sometimes prostate) of men. 2- Final Host: Man (male and female). 3- Infective stage: trophozoites. 4- Mode of infection: Through direct contact mainly during sexual intercourse. 5- Diagnosis: Finding the organism in stained smears of vaginal, prostatic or urethral discharge or sedimented urine. Leishmania species Infective Stage: The promastigote. Leishmania species cause three different diseases: I- Visceral leishmaniasis also known as kala-azar, black fever, and Dumdum fever is a life-threatening protozoal disease caused by Leishmania parasites L. donovani and L. infantum and it is the most severe form of leishmaniasis. This disease is the second-largest parasitic killer in the world (after malaria). The parasite affects several internal organs (usually spleen, liver, and bone marrow) and can be life threatening. The illness typically develops within months (sometimes as long as years) of the sand fly bite. Affected people usually have fever, weight loss, enlargement (swelling) of the spleen and liver, and low blood counts a low red blood cell count (anemia), a low white blood cell count (leukopenia), and a low platelet count (thrombocytopenia). II- Cutaneous leishmaniasis also known as oriental sore is the most common form of leishmaniasis caused by L. tropica in urban areas and L. major in dry desert areas. The incubation period is two to eight weeks, although longer periods have been noted. The disease begins as an erythematous papule at the site of the sandfly bite on exposed parts of the body. The papule increases in size and becomes a nodule. It eventually ulcerates and crusts over. The border is usually raised and distinct. III- Mucocutaneous leishmaniasis also known as espundia is an example of one of the less common forms of leishmaniasis and a chronic inflammatory process involving the nasal, pharyngeal, and laryngeal mucosa, which can lead to extensive tissue destruction caused by L. braziliensis. Balantidium coli Balantidium coli is the only species of the Ciliophora which parasitizes man. This organism also lives in the large intestine of pigs. It is nonpathogenic to pigs. 1- Disease: Balantidiasis or balantidial dysentery. 2- Mode of Infection: Man is infected with balantidial dysentery by ingestion of cysts. Control and Prevention: 1- Generalization of sanitary sewage disposal system [for disposal of feces]. 2- Prevention of use of untreated human feces as fertilizer. 3- Mass treatment (to eliminate the sources of infection). 4- Thorough (proper) washing of raw vegetables. 5- Purification of water supply. 6- Control of flies and other insects as cockroaches. 7- Personal hygiene. 8- Health education. Trypanosoma species There are two main types of trypanosomiases of man: A- African trypanosomiasis (sleeping sickness). B- American trypanosomiasis (Chagas’ disease). African trypanosomiasis (sleeping sickness) Salivarian trypanosomes (anterior station development): Trypanosomes in the gut of insect vector migrate anteriorly to the mouth and salivary glands, so the infection is transmitted through saliva (inoculative infection) such as T. brucei, causing African trypanosomiasis, also known as “sleeping sickness”. There are two sub-species T. brucei gambiense and T. brucei rhodesiense. How does a person get infected with sleeping sickness? During a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue. The parasites enter the lymphatic system and pass into the bloodstream. Inside the host, they transform into bloodstream trypomastigotes, are carried to other sites throughout the body, reach other body fluids (e.g., lymph, spinal fluid), and continue the replication by binary fission. The entire life cycle of African trypanosomes is represented by extracellular stages. The tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host. In the fly’s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission, leave the midgut, and transform into epimastigotes. The epimastigotes reach the fly’s salivary glands and continue multiplication by binary fission. The cycle in the fly takes approximately 3 weeks. Rarely, T. b. gambiense may be acquired congenitally if the mother is infected during pregnancy. Prevention and control: Control and Prevention (sleeping sickness): There is no vaccine or drug for prophylaxis against African trypanosomiasis. Preventive measures are aimed at minimizing contact with tsetse flies. Other helpful measures include: - Wear long-sleeved shirts and pants of medium-weight material in neutral colors that blend with the background environment. Tsetse flies are attracted to bright or dark colors, and they can bite through lightweight clothing. - Inspect vehicles before entering. The flies are attracted to the motion and dust from moving vehicles. - Avoid bushes. The tsetse fly is less active during the hottest part of the day but will bite if disturbed. - Use insect repellent. Permethrin-impregnated clothing and insect repellent have not been proved to be particularly effective against tsetse flies, but they will prevent other insect bites that can cause illness.