Parasitology ch1.pdf

Parasitology INTRODUCTION TO PARASITOLOGY Symbiosis: A relationship between two different species living closely and for a long term. 2  Introduction to Parasitology Parasitism  A form of symbiosis in which on...

Parasitology INTRODUCTION TO PARASITOLOGY Symbiosis: A relationship between two different species living closely and for a long term. 2  Introduction to Parasitology Parasitism  A form of symbiosis in which one organism (parasite) benefits at the expense of another organism of different species (host).  A parasite is an organism that lives on or inside another organism the host  A parasite has different life stages that need more than one host (in most cases) 3  Human Parasites have various classifications, characteristics, and life cycles  Parasites that live on the surface of host are called Ectoparasites (lice & mite)  Parasites that live inside the host are called Endoparasites (Giardia lamblia & Ascaris lumbricoides)  Parasites usually require more than one host for completion of life cycle e.g. Plasmodium falciparum 4 There are three degrees of symbiosis : 1. Commensalism: ‫ﻋﻼﻗﺔ ﺗﻜﺎﻓﻠﯿﺔ‬  The host provides the habitat and food for its commensal (symbiont), which live without benefit or harm to it.  The symbionts are physiologically dependent on the host for its existence, while the host is not. (Certain protozoa in the alimentary canal of man) 5 2. Mutualism: ‫ﺗﺒﺎدل ﻣﻨﻔﻌﺔ‬ A relationship in which both the host and the symbiont are physiologically dependent upon each other and the relationship is mutually beneficial. (termites and their intestinal protozoa) 3. Parasitism: ‫ﺗﻄﻔﻞ‬ A relationship in which the symbiont is physiologically dependent on the host. The host provides the food and shelter for the parasite and the parasite always causes some degree of damage to the host. 6  TYPES OF PARASITES I. According to the location in the host: 1) Ectoparasites: live on the external surface of the body of the host or in cavities that open directly onto the surface. (Monogenetic trematodes & some insects) 2) Endoparasites: live in the internal organs of the hosts such as alimentary canal, lungs, liver, any tissues, cells or internal closed cavities. (Fasciola & Schistosoma) 7 II. According to the amount of time spent in or on the host: 1) Temporary parasites: visit the host only for feeding (Leeches & some insects). 2) Periodic parasites: spend part of their life cycle on/or in the host and then leave it to complete its life as nonparasitic.(boot flies & mermithid nematodes) 3) Permanent parasites: spend their entire life in hosts except while transferring from one host to another. (trematodes, cestodes & nematodes) 8 III. According to their physiological dependance on the host: 1) Obligate parasites: are unable to live without some degree of development on or in the host. (trematodes) are those organisms 2) Facultative parasites: that are normally free living, but are able to live as parasites in host under unfavorable environmental conditions. (Some nematodes) 3) Accidental parasites: are free-living organisms that can live as parasites when accidentally introduced into the bodies of other animals. (Some nematodes) 9 IV. According to host and site specificity: 1) Incidental parasites: occasionally appear in unusual hosts under natural conditions. 2) Erratic or aberrant parasites: may live in unusual places (sites) in their normal host. 10  TYPES OF HOSTS 1) Definitive host: The host in which the adult stages live or in which sexual reproduction takes place. 2) Intermediate host: The host in which the immature or larval stages of the parasite live or in which asexual reproduction occurs. 11 3) Reservoir host: The host may harbor a certain parasite and act as definitive host in the absence of its natural definitive host. It replaces the natural host and acts as a source of infection. 4) Vector: The host that mechanically or biologically transmits the parasites from one host to another. 12  Adaptation to Parasitism  The fact that parasites undergo some degree of modification to be able to live & develop successfully in the environment of the host, as well as the harsh climatic conditions of the outer environment. 13 There are many forms of modifications: 1- The development of some organs or organelles for attachment and penetration e.g. hooks, spines, teeth, suckers, adhesive organs, lips, glands, papillae,. …etc. 2- Shape of the body, small, spindle etc. 3- Large number of eggs. 4- Modifications in the digestive system. 5- Modifications in the reproductive system and life cycle pattern. 14 6- Locomotory organs or organelles. 7- Reduction of nervous system and sense organs. 8- Physiological adaptations. 9- Genetic adaptations. 15  TRANSMISSION OF PARASITES  Transmission of a parasite depends on the presence of: I- Susceptible hosts: ‫ﻋواﺋل ﻗﺎﺑﻠﺔ ﻟﻠﻌدوى‬  Parasites generally need a specific host (final or intermediate) to grow well and complete their life cycle.  The degree of host specificity varies with different parasitic species. 16 II- Sources of Infection: 1- Food: Food containing the infective stage may be a source of infection, whether eaten raw or improperly cooked or salted. a) Fish with encysted metacercariae of Heterophyes or Diphillobothrium. b) Meat with cysticerci of Taenia or infective stage of Trichinella. c) Vegetables with eggs of Ascaris and encysted metacercariae of Fasciola. 17 2- Water: contaminated water with cercariae of Schistosomes. 3- Soil: Contaminated soil with human excreta containing eggs of Ascaris and larvae of Ancylostoma. 4- Animals: Domestic animals may serve as direct sources of infection. Diseases transmitted from animal to man are known as zoonotic diseases, e.g. hydatid disease and visceral larva migrans transmitted by dogs. 18 5- Infected persons: e.g. Enterobius. 6- Blood sucking arthropods: e.g. Filaria by mosquitoes 7- Blood transfusion can accidentally transmit infection. 8- Congenital infection & transmammary transmission is of special importance in protozoan infection. 19 III- Mode of transmission : ‫طرﯾﻘﺔ اﻻﻧﺗﻘﺎل‬ The mode of parasite entry into the host through the following pathways: 1- Mouth: By ingesting the infective stages present in meat, fish, vegetable, water, contaminated hands (faeco-oral route). 2- Skin: Penetration of skin and mucous membranes by infective stages present in soil or water. The parasite may also be introduced into the skin through blood sucking arthropods. 3- Inhalation: Air born infection by inhalation of infective stages. 4- Congenital, transplacental & sexual transmission is of greater importance in protozoan parasites. 20 Parasites damage their hosts through different mechanisms: 1) Generalized: Anaemia caused by blood sucking parasites. 2) Mechanical: Obstruction of ducts by large numbers of parasites. 3) Traumatic: Compression & erosion of epithelial tissues resulting from parasites with spines, adhesive organs & cutting teeth. Chronic trauma may lead to ulceration & malignancy. 21 4) Toxic: Certain parasites introduce toxic products that circulate in the blood of the host and cause toxic reaction, e.g. excretory- secretory products, enzymes secreted by certain gland cells or metabolites. 5) Necrosis: Tissue erosion and enzymes elaborated by the parasite may cause cellular destruction and necrotic changes. 22 6) Allergic: Circulating metabolites and foreign proteins stimulate an allergic reaction in the form of urticaria, itching, bronchial asthma or anaphylactic shock in severe cases. 7) Foreign body reaction: Circulating metabolites and foreign proteins (antigens) stimulate cellular as well as humoral immune response provoking foreign body reaction in the form of inflammation, cellular infiltration and proliferation at the site of infection. 23 SYMPTOMS ‫اﻷﻋراض‬ Parasitic infection is accompanied by certain manifestations: 1- Leucocytosis with eosinophilia: occurs in early invasive and migratory phases especially in helminthes infection. 2- Monocytosis: results from stimulation of the reticulo-endothelial system and increased phagocytosis particularly in protozoan infection. 3- Abdominal pain: diarrhea or dysentery is usually present in symptomatic infection. 24 4- Anemia: Most frequently associated with blood dwelling and blood sucking parasites. 5- Asthma and bronchitis: Usually accompanying infestation of the respiratory tract in migrating parasites. 6- Fever: a Pattern of fever may be characteristic to a certain infection. Other symptoms include; appendicitis, abscess, ascites ‫اﻻﺳﺗﺳﻘﺎء‬, dermatitis, edema, lymphadenitis, ulceration. These symptoms and many others are specific to certain infections and vary with the severity and duration of infection. 25 CONTROL AND PREVENTIVE MEASURES Since a parasitic disease involves both individuals and the community in which they live, therefore control should involve both entities. The general techniques that should be followed to reduce the impact of parasitic diseases should include the following: 1- Treatment of infected individuals. 2- Reduce the population of reservoir hosts and vectors. 3- Improve the immunity of the potential hosts. 26 4- Reduce the probability of transmission by altering the environment. 5- Protect individuals from infection and avoid areas of high risk. 6- Biological control of the parasite. 7- Improve sanitation measures such as sewage disposal and supplying clean drinking water. 8- Educational programs. 9- Continuous epidemiological surveys. 10- Food inspection. 27 The main parasitic groups Parasitic protozoa (Unicellular) Parasitic helminthes (Multicellular) Protozoans are microscopic one-celled organisms that are categorized according to their method of movements 1- Ciliates: the only parasitic ciliate that causes disease in humans Balantidium coli 2- Flagellates: three of the most common and medically significant, include Giardia lamblia, Trypanosoma sp. and Trichomonas vaginalis 28 3- Sarcodines: Amoeba - use pseudopodia or protoplasmic flow to move, include the pathogenic amoeba Entamoeba and Endolimax which cause dysentery in humans 4- Sporozoa (Apicomplexa): undergo a complex life cycle, alternating sexual & asexual phases e.g. Plasmodium spp, Cryptosporidium spp. 29 Introduction to Parasitology HELMINTHS – Nematodes (roundworms) – Trematodes (flukes) – Cestodes (tapeworms)  Nematoda (roundworms)  Elongated , round and nonsegmented  Complete digestive system , highly developed separate-sexes 30  Eggs & larva are suited for external environment.  Most human infections through ingestion of eggs or penetration of larvae  Examples Ascaris lumbricoides, Ankylostoma duodenale, Enterobius vermiculoaris …. etc 31  Trematodes (flukes) Fasciola hepatica, Clonorchis sinensis, Schistosoma spp.  Cestodes (tapeworms) Taenia solium, Echinococcus granulossus Athropods  Host Parasites  Insects - Mosquitoes, lice, and fleas  Arachnids - Ticks and mites 32  LIFE CYCLE  Direct Life cycle  Only humans are hosts  Infective stage like ovum, cyst, larva passed out of body that infect healthy people Example E. histolytica, Giardia, Ascaris lumbricoides.  Indirect Life cycle  Multiple hosts & involvement of vectors  Definitive host, Intermediate host  Example Taenia saginata, Schistosoma spp.,.... etc 33  HOST PARASITE INTERACTION (Effect on Host)  Parasites utilize nutrition from host resulting in damage  Loss of nutrition e.g. Iron def. in hookworm infestation, Vit. B12 def in Diphyllobothrium latum Morbidity ‫اﻹﻣراض‬: due to tissue injury e.g. E. histolytica dysentery, severe itch due to Enterobius vermicularis  Mortality ‫اﻹﻣﺎﺗﺔ أو اﻟﻣوت‬: fulminant diarrhea ‫إﺳﮫﺎل ﺣﺎد‬ due to Cryptosporidium parvum infection & hyperinfection due to Strongyloides stercoralis in HIV. 34  Role of vector - Vector, a Latin word meaning "carrier"  Helps in transmission of parasites  No direct damage by vector  The Anopheles mosquito transmits Malaria, Filaria - Sandfly transmits Leishmania - Domestic cats - vector of Toxoplasma gondii 35  COMMON PARASITIC DISEASES  Amoebiasis: Entamoeba histolitica  Giardiasis: Giardia lamblia  Leishmaniasis: Leishmania spp.  Malaria: Plasmodium spp.  Hook worm: Ancylostoma duodenale  Round worm: Ascaris lumbricoides Echinococcosis: Echinococcus granulosus (tapeworm)  Pin worm: Enterobious vermicularis  Scabies: Sarcoptes scabiei