Parasitology Notes PDF

INTRODUCTION TO 1-2 PARASITOLOGY PARASITOLOGY area of biology concerned with the phenomenon of dependence of one living organism on another medical parasitology deals with the parasites that cause human infections and the diseases they produce; broadly divided into two parts: protozoology and helmin...

INTRODUCTION TO 1-2 PARASITOLOGY PARASITOLOGY area of biology concerned with the phenomenon of dependence of one living organism on another medical parasitology deals with the parasites that cause human infections and the diseases they produce; broadly divided into two parts: protozoology and helminthology. 1. Medical Protozoology a branch of medical parasitology that deals with the study of protozoan, the animal-like” protists which are significant parasites of humans. 2. Medical Helminthology the field of medical parasitology that pertains to the study of helminths (worms) capable of causing diseases in humans. protozoa helminthes SYMBIOTIC RELATIONSHIPS 1. Commensalism One specie benefits from the relationship w/o harming or benefiting the other. Example: Entamoeba coli and Human 2. Mutualism Two organisms benefit from each other. Example: Termites and the flagellates inside their digestive system 3. Parasitism One organism lives in or on another for its survival at the expense of the host. Example: Ascaris lumbricoides and Human PARASITES vS HOSTS vS VECTORS 1. PARASITE A parasite is an organism that obtains nutrients and shelter from another living organism (the host), at the expense of the host's health 2. HOST A host is a living organism that harbors a parasite and provides it with nourishment and shelter 3. VECTOR A vector is a living organism that transmits infectious agents from one infected individual (human or animal) to another susceptible individual. PARASITES vS HOSTS vS VECTORS parasite are organisms that take part in Parasitic symbiosis or Parasitism. They are the organisms that live for its survival at the expense of the host. They are classified according to: 1. habitat 2. mode of living 3. duration of infection/infestation 4. pathogenicity. A. ACCORDING TO HABITAT ENDOPARASITE: A parasite, which lives within the body of the host. INFECTION is the term that denotes the presence of an endoparasite. EctOPARASITE: Those outside the body of the host those on body surfaces like skin, surface i.e. lice The presence of an ectoparasite will cause an INFESTATION. B. ACCORDING TO mode of living OBLIGATE Need a host to complete their development FACULTATIVE May exist in a free-living state. May become parasitic when the need arises. Parasite that established itself in a host where it ACCIDENTAL/INCIDENTAL does not ordinarily live. ERRATIC Parasite found in an organ w/c is not its usual habitat. ABERRANT Infect a host where they cannot develop further SPURIOUS Passes through the digestive tract w/o infecting the host PARTHENOGENETIC Female parasite capable of reproducing eggs without being fertilized by a male and whose eggs contain larva that immediately hatches COPROPHILIC Able to multiply in fecal matter outside human body HEMATOZOIC Those parasites that thrives inside red blood cells (e.g. Plasmodia, Babesia, Leishmania) CYTOZOIC Lives inside cells or tissues (e.g. Trichinella spiralis) COELOZOIC Lives in body cavities (Mansonella spp.) ENTEROZOIC Resides in intestines (Tapeworms, Entamoeba histolytica) C. ACCORDING TO DURATION 1. PERMANENT Remains on or in the body of the host for its entire life. 2. TEMPORARY Lives on the host only for a short period of time. D. ACCORDING TO pathogenicity 1. NON-PATHOGENIC aka Commensals, incapable of causing disease. 2. PATHOGENIC Disease causing parasites. host are organisms that harbor the parasites. The survival of the parasites depends on their hosts. Without a host, a parasite cannot live, grow and multiply. classification of host 1. DEFINITIVE/FINAL Parasite attains sexual maturity; host in which adult parasite lives. 2. PARATENIC One in which the parasite does not develop further to later stages. Parasite remains alive and is able to infect another host. 3. ACCIDENTAL Host in which the parasite is not usually found. 4. INTERMEDIATE Harbors the asexual/larval STAGE OF THE PARASITE 5. RESERVOIR Allows the parasite’s life cycle to continue and become additional sources of infection. VECTORS organisms that does not cause disease itself but which spreads infection by conveying pathogens from one host to another. classification of VECTORS 1. BIOLOGIC Transmits the parasite only after the latter has completed its development within the host. Example: Mosquito in Filariasis. 2. MECHANICAL/PHORETIC Those that are only capable of transporting the parasite. Example: Cockroaches in Ascariasis SOURCES OF INFECTION 1. SOIL MOST COMMON. Lack of sanitary toilets and the use of night soil or human excreta as fertilizer allow the eggs to come in contact with the soil and form the development of specific parasites. Examples: Hookworm Ascaris lumbricoides Trichuris trichiura Strongyloides stercoralis 2. arthropods Mosquitoes Malaria, Filarial worms Triatoma bugs Trypanosoma cruzi Phlebotomus sandflies Leishmania spp. 3. WATER Cysts of amebae or flagellates cercaria of schistosomes. 4. food Trematodes (Flukes) Cestodes (Tapeworms) 5. ANIMALS Cats – direct sources of Toxoplasma infectioN 6. ANOTHER INDIVIDUAL Asymptomatic carriers of Entamoeba histolytica working as food handlers. modes of transmission 1. ORAL (FECAL-ORAL) Most common method foodborne: Cestodes, Trematodes, Intestinal Protozoans 2. skin penetration Another important mode of transmission Hookworm and Strongyloides stercoralis enter upon exposure to soil Schistosoma spp. is acquired when cercariae in water penetrate the skin 3. arthropod Transmit parasites through their bites Malaria, Filariasis, Leishmaniasis, Trypanosomiasis, Babesiosis 4. CONGENITAL TRANSMISSION Toxoplasma gondii Trophozoites can cross the placental barrier during pregnancy 5. TRANSMAMMARY INFECTION Ancylostoma and Strongyloides May be transmitted through mother’s milk 6. INHALATION OF AIRBORNE EGGS Enterobius vermicularis 7. SEXUAL INTERCOURSE Trichomonas vaginalis 8. IATROGENIC TRANSMISSION Seen in case of transfusion malaria and toxoplasmosis after organ transplantation. OTHER IMPORTANT TERMINOLOGIES IN PARASITOLOGY 1. Epidemiology Study of patterns, distribution and occurrence of disease 2. incidence Number of new cases of infection in a given period of time 3. Prevalence (%) Number of individuals estimated to be infected w/ a particular parasite 4. Cumulative prevalence % of individuals in a population infected w/ at least 1 parasite 5. Intensity of infection Number of worms per infected person 6. Morbidity Clinical consequences of infections or diseases that affect an individual’s well-being 7. Deworming Use of anti-helminthic drugs in an individual 8. Cure rate (%) Number of previously positive subjects found to be egg- negative 9. Egg reduction rate % fall in egg counts after deworming 10. Selective treatment Number of worms per infected person 11. targeted treatment Group-level deworming 12. Universal treatment Population-level deworming 13. Coverage Proportion of the target population reached by an intervention 14. Efficacy Effect of a drug against an infective agent 15. effectiveness Measure of the effect of a drug against an infective agent 16. Information-education- communication A health education strategy that aims to encourage people to adapt and maintain healthy life practices 17. Environmental management Planning, organization, performance, and monitoring of activities for the modification and/or manipulation of environmental factors 18. Environmental sanitation Interventions to reduce environmental health risks 19. Sanitation Provision of access to adequate facilities for the safe disposal of human excreta 20. Eradication Permanent reduction to zero of the incidence of infection caused by a specific agent, as a result of deliberate efforts 21. Elimination Reduction to zero of the incidence of a specified disease in a defined geographic area as a result of deliberate efforts 22. Carrier Harbors pathogen and is asymptomatic 23. Pre-Patent Period/Biologic Incubation Period between infection and evidence of demonstration of infection 24. Clinical Incubation Period Period between infection to development of symptoms 25. Auto-reinfection Individual becomes infected by his/her own Nematodes: Capillaria philippinensis Enterobius vermicularis Strongyloides Cestodes: Taenia solium Hymenolepis nana Protozoan: Cryptosporidium hominis Cryptosporidium parvum 26. Superinfection/Hyperinfection Already infected individuals are further infected with same species (e.g. Strongyloides) specimen collection and transport Depending on its stage of development in the clinical specimen (adult, larvae, eggs, trophozoites, cysts, oocysts, spores), a particular parasite may not be able to survive outside the host. That’s why clinical specimens should be transported immediately to the laboratory to increase the likelihood of finding intact organisms. Two ordering/collection/processing/examination situations are considered STAT orders central nervous system (CNS) specimens to be examined for freeliving amoebae blood films in a potential malaria case. Among the possible specimens, the more common ones are: stool perianal swab tissue aspirate blood cerebrospinal fluid sputum tissue biopsy urine & urigenital specimens stool most commonly submitted sample. The most common procedure performed is the examination of a stool specimen for Ova and Parasites (O&P). routine stool examination: A. formed thumb-sized examined within 24 hrs semi-formed stool: within 1 hr B. watery 5-6 table spoons examined within 30mins stool consistency: formed cyst watery trophozoites soft cyst and trophozoites any consistency helminth eggs & larva stool processing: 3 specimens: one specimen collected every other day or a total of 3 collected in 10 days. SUITABLE CONTAINER: clean, wide mouthed container like a plastic container with a tight fitting lid, waxed cardboard box (1/2 pint), or matchbox. Toxic substances to intestinal protozoans: mineral oil bismuth antibiotics: delayed for 2wks antimalarial agents non- absorbable antidiarrheal preparations. barium: delayed for 5-10 days By gross examination, tapeworm proglottids and adult nematodes may be found on the stool sample. Temporary storage of fecal samples in a refrigerator (3-5°C) may be acceptable just up to 24 HOURS. stool preservatives Recommended fixative to specimen volume ratio is 3:1 For thorough fixation, preservative and the specimen must be mixed well The specimen must be fixed in the preservative for at least 30 minutes before processing begins. common stool preservatives A. FORMALIn All-purpose fixative; usually buffered with sodium phosphate to preserve morphological characteristics 5% concentration: recommended for protozoan cysts 10% concentration: recommended for helminth eggs and larvae Preserved stool can be concentrated using Formalin- Ether/Ethyl Acetate Concentration Technique (FECT/FEACT) b. SCHAUDINN’S SOLUTIOn Used to preserve fresh stool/fresh fecal specimen in preparation for staining the stool smears Provides excellent preservation of protozoan trophozoites and cysts For many years, considered as the ”gold standard” - Contains mercuric chloride which is highly toxic to humans C. SODIUM ACETATE-ACETIC ACID FORMALIN (SAF) Advantages: Does not contain mercuric chloride long shelf-life Disadvantage: Images are not as sharp after staining as compared with those fixed in PVA or Schaudinn’s solution D. MERTHIOLATE IODINE-FORMALIN (MIF) Components both fix and provide stain color Contains Merthiolate (Thimerosal) and Iodine that act as staining components Formalin acts as a preservative Useful for fixation of intestinal protozoans, helminth eggs, and larvae Disadvantages: Contains mercury compounds (thimerosal) Staining of preserved stools in MIF yields unsatisfactory results or not as good as Schaudinn’s fluid E. POLYVINYL ALCOHOL (PVA) Plastic resin that serves to adhere a stool sample onto a slide Normally incorporated into the Schaudinn’s solution Main advantage: preservation of protozoan cyst and trophozoites for permanent staining Stool preserved in PVA can be concentrated using FECT Disadvantage: use of mercuric chloride some replace this with cupric sulfate