Introduction to Parasitology PDF

Introduction to Parasitology By Arcibel B. Bautista  PARASITOLOGY Parasitology- an area of biology that is concerned with the study of living organisms that depend on other living organisms for the purpose of procuring nourishment and securing protection.  MEDICAL PARASIT...

Introduction to Parasitology By Arcibel B. Bautista  PARASITOLOGY Parasitology- an area of biology that is concerned with the study of living organisms that depend on other living organisms for the purpose of procuring nourishment and securing protection.  MEDICAL PARASITOLOGY Medical Parasitology – concerned primarily with the animal parasites of man and their medical significance as well as their importance in human communities.  BIOLOGICAL RELATIONSHIP Parasitism – any reciprocal association in which a species depends upon another for its existence. Symbiosis – a permanent association of two organisms that cannot exist independently. Commensalism – one partner is benefited and the other is unaffected.  What is a Parasite Parasite is an organism that lives on or in other organisms from which it obtains nutrients to live and causes harm in the process. Its name comes from the Greek word para that means beside, and sitos, which means food.  CLASSIFICATION OF PARASITES I. According to Habitat a. Endoparasite – those that live within the body of the host. Example: protozoans and helminthic parasites b. Ectoparasite – those that live outside the body of the host. Example: lice, ticks and mites c. Free living parasites - refers to non- parasitic stages of active existence which live independent on the host. Example: Naegleria fowleri or known as “Brain eating amoeba” CLASSIFICATION OF PARASITES II. According to its Effects to Host Pathogenic – a parasite which causes injury to the host by its mechanical, traumatic or toxic activities. Non-pathogenic - a parasite derives benefits from the host without causing any considerable damage or harm. CLASSIFICATION OF ENDOPARASITES Cont. Accdg. to Mode of Living Facultative – capable of leading both a free and parasitic existing which can live as an opportunistic parasite. Example: Naegleria fowleri CLASSIFICATION OF ENDOPARASITES Temporary- a free-living during part of its existence and seeks its host intermittently to obtain nourishment. It visits the host for a short period. Permanent – remains in the body of the host from early life to maturity. Spurious or Coprozoic – a foreign species that has passed through the alimentary tract without infecting the host. CLASSIFICATION OF ENDOPARASITES Cont. Accdg. to Mode of Living Accidental or Incidental – one that establishes itself in a host in which it does not ordinarily lives. Example: Sheep liver flukes in dogs and cats CLASSFICATION OF ENDOPARASITES Cont. According to Mode of Living Aberrant Parasites – parasites which infect a host where they cannot develop further Example: Toxocara canis (dog roundworm) Types of Parasites  What is a Host? Host - an organism which harbors the parasite. TYPES OF HOST Final or Definitive Host – harbors the adult or sexual stages of the parasites. e.g. Man  TYPES OF HOST Intermediate Host – harbors part or all of the larval or sexual stages of the parasites e.g. snail in Schistosoma  TYPES OF HOST Reservoir Host – animals that harbors the same species of parasites as man. Such reservoir host ensures continuity of the parasite’s life cycle and act as additional sources of infection. e.g. rodents  TYPES OF HOST Paratenic Host - animal that harbors the parasite in an arrested state of development; however the parasite is capable of continuing its cycle in a subsequent suitable host. It serves as a means of transport so that the parasites may reach a suitable host. e.g. fresh water prawns  VECTORS VECTORS – host that transmit parasite to man Biologic vectors – essential in the life cycle Mechanical or Phoretic vectors – not essential in the life cycle.  PARASITE RESERVOIR A parasite reservoir (PR) is the biotope where the parasite lives. In general it is the Definitive Host, where lives the sexual stage of the parasite, producing large amounts of larvae or eggs, that serves as the PR. A PR can be: Human reservoir –Human is the sole host (schistosomiasis) –Human is an accidental host (leishmaniasis) Animal reservoir –1. domestic animals –2. wild animals Effects of Parasites to Man Parasites are responsible for many health problems because they secrete toxins and steal the vital nutrients from our bodies. Parasites can irritate or exaggerate other health problems you may be experiencing. Everyone is at risk and under their mercy during parasitic infections How do parasites survive inside an immunocompetent host? Ectoparasites Infestation leads to local lesions of minor to moderate importance. This leads only to: – allergic reactions (itching) – immunological reactions (without result) None of these reactions really harm the parasite, but do harm the host  How do parasites survive inside an immunocompetent host? Intracellular parasites These parasites try to escape any immunological reactions mounted by the host by hiding themselves inside the host cells where the immune system cannot reach them. Examples are: – Toxoplasma in lymphocytes, – Plasmodium in erythrocytes, – Leishmania, in macrophages, – T.cruzi in muscle cells. How do parasites survive inside an immunocompetent host? Extracellular parasites – Some parasites cover their cell surface with host serum proteins to avoid recognition by the immune system of the host Examples are: Schistosoma worms that cover themselves with host serum albumin Rodent trypanosomes that cover themselves with ablastin (IgE) – Antigenic variation in the African trypanosomes that live freely in the bloodstream and body fluids of the host is another effective mechanism of evasion. – Cyst formation by Entamoeba and other amoeboid parasites Harmful effects of the parasite on the host Such effects comprise: Wasting (cachexia, spoliatrices) African trypanosomiasis and leishmaniasis may lead to severe loss of weight in both animals and man. Superinfections In the case of (muco)cutaneous leishmaniasis ulcerations may lead to superinfections with bacteria Production of toxic compounds It is thought that the African trypanosome, when in the central nervous system, produces aromatic amino-acid analogues that may influence brain function. Harmful effects of the parasite on the host Immunodepression Malaria, bilharziasis, etc., lead to a certain degree of immune suppression which renders the infected host more susceptible to other diseases. Allergic reactions In the case of onchocerciasis (river blindness) the presence of the filarial worms under the skin may lead to depigmentation due to allergic reactions. Harmful effects of the parasite on the host Anaphylactic shock may be induced by the sudden release of large amounts of parasite internal antigens into the bloodstream. – In malaria this occurs when the merozoites are released in waves from infected erythrocytes. – In African trypanosomiasis or sleeping sickness this occurs when the immune response leads to the massive killing and lysis of the circulating parasites. – Also drug treatment leading to a massive killing of the parasites may result in anaphylactic shock. Harmful effects of the parasite on the host Mechanical damage – In the case of malaria the lysis of erythrocytes does lead to haemolysis and anaemia. – In the case of ascaris infection the presence of the worms in the small intestine may lead to intestinal occlusions Irritative reflexes (intestinal contractions: ascaris) Irritation of skin and tissues by ecto- and endoparasites Difference between Infection and Infestation Infection – the presence of endoparasite in a host Infestation – the presence of ectoparasite in a host 4 FACTORS OF PARASITIC INFECTION 1. The source of infection 2. Infective stage of the parasite 3. Portal of Entry 4. Presence of Susceptible Host SOURCES OF INFECTION OR INFESTATION 1. Soil- Transmitted Group These parasites require further development in soil before they become infective. Soil polluted with human excrete is commonly responsible for exposure to infection with: a. Ascaris lumbricoides b. Trichiuris trichiura c. Hookworms d. Strongyloides stercoralis SOURCES OF INFECTION OR INFESTATION 2. Snail-Transmitted Group This group requires further development within the body of snail host before they become infective. a. Trematodes (Flukes) b. Schistosomes  SOURCES OF INFECTION OR INFESTATION 3. Arthropod-Transmitted Group The numerous species of insects play an important role in the economic life of human beings. Some species are parasites of humans or act as vectors of parasitic diseases. a. Plasmodium b. Filarial worms c. Sand fly d. Leishmania (Sandfly) e. African Trypanosomiasis (Tsetse fly) f. American Trypanosomiasis (Reduvid bug)  SOURCES OF INFECTION OR INFESTATION 4. Food-Animal Transmitted Group This group requires further development in the flesh of some animals that man will consume. Eating raw meats. a. Trichinella spiralis (eating raw pork) b. Taenia solium (eating raw pork) c. Taenia saginata (eating raw beef) SOURCES OF INFECTION OR INFESTATION 5. Contact Transmitted Group Person-to-person transmission is directly responsible for a considerable amount of infection with pathogenic: a. Entamoeba histolytica b. Enterobius vermicularis c. Trichomonas vaginalis 6. One’s Self (Autoinfection)  PORTAL OF ENTRY 1. Mouth a. Ascaris lumbricoides b. Trichiuris trichiura c. Enterobius vermicularis d. Hymenolepis nana (dwarf tapeworm)  PORTAL OF ENTRY Intimate oral contact: a. Trichomonas tenax b. Entamoeba gingivalis 2. Skin Enter the body of the host from soil via the skin through the larval penetration a. Hookworm b. Strongyloides stercoralis c. Schistosoma (from fresh water)  PORTAL OF ENTRY Blood-sucking arthropods- puncture the skin to feed (biting) a. mosquito – Plasmodium & filaria b. black flies – Onchocerciasis or Riverblindness c. sand fly - Leishmaniasis d. Tse tse fly – sleeping sickness  PORTAL OF ENTRY 3. Sexual-intercourse a. Trichomonas vaginalis 4. Transplacental a. Toxoplasma gondii Occasionally: – Plasmodium – Trematodes  PORTAL OF ENTRY 5. Intranasal a. Acanthamoeba b. Naegleria 6. Inhalation a. Ascaris lumbricoides b. Enterobius vermicularis  DIAGNOSIS 1. Clinical Diagnosis based on the recognition of the characteristics signs and symptoms of certain parasitic disease. 2. Laboratory Diagnosis – final diagnosis and proper methods of treatment require the identification of the parasite in the laboratory.  TREATMENT The successful treatment of the infected patient includes medical and surgical measures, adequate nutrition to build up general resistance and specific chemotherapy.  PREVENTION Prevention of parasitic diseases depends upon the erection of barriers to the spread of parasites through the practical application of biologic and epidemiologic knowledge. The control of parasitic diseases includes the following procedures: 1. Reduction of the sources of infection in human beings by therapeutic measures.  PREVENTION 2. Education in personal prophylaxis to prevent dissemination of infection and to reduce opportunities for exposure. 3. Sanitary control of water, food, living and working conditions and waste disposal. 4. Destruction or control of reservoir hosts and vectors 5. Erection of biologic barriers to the transmission of parasites.  EPIDEMIOLOGY It is the body of knowledge that concerns disease in human populations or communities rather than in individuals. It may include the study of the manifestations of any diseases which happens to attack groups of individuals at any time. It is also concerned with the relationships of various factors and conditions which determine frequencies and distribution of an infectious process, a disease or a physiological state in a human community.  DISTRIBUTION OF DISEASE ENDEMIC – when a disease in human population maintain a relatively steady moderate level. HYPERENDEMIC – if the prevalence of a disease in a community is high. EPIDEMIC – if there is a sharp rise in the incidence or an outbreak of considerable intensity occurs. It typically results from introduction of an agent or a new strain into a community that is essentially non-immune. SPORADIC – if it appears only occasionally in one or at most few members of a community. PANDEMIC – the disease covers extensive areas of the world. ERADICATION vs. ELIMINATION Eradication – permanent reduction to zero of the worldwide incidence of infection caused by a specific agent. Elimination – reduction to zero of the incidence of a specified disease in a defined geographic area as a result of deliberate efforts.  LIFE CYCLE Many parasites have a fascinatingly complex development. Often different stages of the parasite live in and parasitize different hosts. To increase the odds of successful transmission from one host to the next parasites often increase their numbers massively at each step. This reproduction can occur sexually or asexually. The entirety of this development is often diagrammed as a life cycle. A number of terms are used to define the biological roles of various hosts within complex life cycles.