MLAB 1331 – Parasitology Lecture Guide I. Introduction to Parasitology: A. Diagnosis of parasitic infections requires knowledge of: 1. Types of patients at risk - travel, day care center attendance, refugee, etc. 2. Appropriate specimen - must be collected and processed correctly; Series of three specimens on alternate days 3. Accurate diagnosis - dependent on laboratory results utilizing appropriate procedures 4. Quality of results - dependent upon training B. North Americans do not suffer from a multitude of parasites: 1. high standards of education - better housing, higher standard of living 2. general good health - poor health = more susceptible to disease 3. nutrition - adequate diet 4. sanitation - sewers and septic systems keeps raw sewage out of streams 5. temperate climate - parasites do better in the warmth of the tropics 6. absence of certain appropriate vectors - intermediate hosts such as the tsetse fly, certain snails, etc. C. Parasitic infections in this country are generally due to: 1. increased travel - into areas of the world where parasitic disease is highly endemic 2. low level of understanding about parasitic infections - results in an increased likelihood of transmission D. Definitions 1. Parasite - one animal deriving its sustenance from another without making compensation. The uncompensated animal is the host. 2. Parasitology - the science or study of host-parasite relationships. 3. Medical parasitology - study of parasites which infect humans.4. Host - the partner providing food and/or protection. Some parasites require more than one host to complete their life cycle; or may not require a host during some stage(s). a. definitive host - the host in which sexual maturity and reproduction takes place. Man is usually a definitive host. b. intermediate host - the host in which the parasite undergoes essential development. More than one intermediate host may be required by some parasites. Man sometimes serves as an intermediate host (malaria). c. reservoir (carrier) host - the host harboring a parasite in nature, serving as a source of infection for other susceptible hosts. Reservoir hosts show no sign or symptom of disease. 5. Vector - “carrier” of a parasite from one host to another. Often an insect. 6. Symbiosis - “living together,” a close association between two organisms. a. mutualism - both organisms are benefited (bacteria in bowel) b. commensalism - “eating at the same table”; one organism is benefited, the other is unaffected. c. parasitism - one organism is benefited at the expense of another (host). 1) a parasite is successful - only when it is in delicate balance with the host. If the balance is upset, the host may destroy or expel the parasite; if the host is overly damaged, it may die - as will the parasite. 2) parasitology is important - because this balance is not always maintained E. Parasitic damage to host: 1. trauma - damage to tissues, intestine, liver, eye. 2. lytic action - activity of enzymes elaborated by organism. 3. tissue response - localized inflammation, eosinophilia. 4. blood loss - heavy infection with hookworm may cause anemia. 5. secondary infections - weakened host susceptible to bacterial infection, etc. F. Modes of infection 1. filth-borne or contaminative - serious where personal hygiene and community sanitation lacking. Cysts or eggs remain infective for long periods in contaminated soil. 2. soil or water-borne - difficult to control. Children eat dirt which can contain eggs, etc.; certain larvae can penetrate skin of bare feet or enter skin in infested water. Education & sanitary control of waste is best means of prevention. 3. food-borne - inadequately cooked beef, pork, fish, shell fish & some vegetables can be sources of infection.4. arthropod-borne - the most difficult of all to control; often produces diseases that are fatal. More commonly found in moist tropical areas of world. Mosquitoes transmit malaria, etc. II. Collection, Processing, & Examination of Diagnostic Specimens A. Overview: 1. Microscope - must be calibrated in order to insure accurate measurement of organisms 2. Centrifuges - Swinging bucket - the required type; should not use angle head centrifuges. Gravitational force (g-force) determined by revolutions per minute (RPM) and radius of the rotor. Use of flammable reagents hazard, prefer use of explosion proof centrifuge. 3. Types of specimens which can be examined for diagnosis of parasites - a. "Natural secretions" - feces, sputum, and urine are used to detect lumen dwelling parasites of GI, pulmonary and genitourinary tracts. b. Blood is usual specimen for detection of blood and tissue parasites, along with tissue biopsies, aspirates, etc. B. Intestinal Lumen Dwelling Parasites - Fecal Specimens 1. Patient preparation - must avoid the presence of substances which can interfere with stool examination. No antimicrobial medications should be taken during the 10 days prior to collection of specimens. Certain substances can interfere with visibility of organisms, reduce their numbers, and damage or destroy their morphology. a. Medications containing antimicrobial agents: 1) Bismuth 2) Barium 3) Mineral oil 4) Kaolin 5) Anti-diarrheal preparations 6) Laxatives b. Contaminant free specimens - no urine, water or dirt - these may destroy organisms, or could contain confusing free-living organisms. 2. Fecal (stool) specimens - the most commonly submitted specimen for parasitology examination. These specimens must be initially examined for consistency in order to determine which procedures are to be utilized. 3. Types of stool specimens submitted and forms of parasites which may be detected in each - a. Liquid specimens (loose & watery specimens) - trophozoite stages are more likely to be present. 1) Must be examined within 30 minutes of passage or placed intoan appropriate preservative - trophozoites begin to deteriorate rapidly, when this happens, morphology is adversely affected. 2) Freshly passed specimens are necessary in order to recover motile trophozoites. 3) Cyst formation will not occur once the organism is outside the body and trophozoites tend to disintegrate rapidly after passage. 4)