Parasite Types and Interactions PDF

1  1- Kinds of parasites Ectoparasite – a parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc. Endoparasites – parasites that live inside the body of their host, e.g. Entamoeba histolytica. Obligate Parasite – This parasite i...

1  1- Kinds of parasites Ectoparasite – a parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc. Endoparasites – parasites that live inside the body of their host, e.g. Entamoeba histolytica. Obligate Parasite – This parasite is completely dependent on the host during a segment or all of its life cycle, e.g. Plasmodium spp. Facultative parasite – an organism that exhibits both parasitic and non-parasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host. E.g. Naegleria fowleri Accidental parasite – when a parasite attacks an unnatural host and survives. E.g. Hymenolepis diminuta (rat tapeworm Erratic parasite - is one that wanders in to an organ in which it is not usually found. E.g. Entamoeba histolytica in the liver or lung of humans. 2  2- Kinds of hosts Definitive host – a host that harbors a parasite in the adult stage or where the parasite undergoes a sexual method of reproduction. Intermediate host – harbors the larval stages of the parasite or an asexual cycle of development takes place. In some cases, larval development is completed in two different intermediate hosts, referred to as first and second intermediate hosts. Paratenic host – a host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host, i.e. it is not necessary for the completion of the parasites life cycle. Reservoir host – a host that makes the parasite available for the transmission to another host and is usually not affected by the infection. Natural host – a host that is naturally infected with certain species of parasite. Accidental host – a host that is under normal circumstances not infected with the parasite. 3  :- These are mainly of five types Commensalism. The literal meaning of commensalisms is eating at same table, it is loose association, organism of different species live together. One animal may receive some benefit called commensal but the other neither get benefited nor harm from the other, it is not obligatory for their existence. Eg.- Pilot fish, Shark, Remora, many intestinal protozoa such aEntamoeba coli and Trichomonas sp. Parasitism. It is an intimate association between two specifically distinct organism in which one parterner usually smaller (Parasite) lives on or within the other usually larger organism (Host) in order to obtain nourishment and at the same time it causes harm to the host. One which is benefited is called parasite and other which is loser is called host. Mutualism. It is an intimate association or relationship of two animals or individuals in which both partners are benefited. However, this relationship is not permanent and obligatory. Either of the partners can break it without any loss to either of them. Eg.-Hermit crab and sea anemone. -Scorpion and Hydroids. -ruminal flora Symbiosis It comes from Greek word symbioum means to live together. It is an intimate or close association or relationship of two individuals in which both the partners are benefited like mutualism but in this, the participating species are dependent on each other for existence and are obligatory Eg. -Termites and their intestinal protozoa. -Zoochorella and Hydra Phoresis The term means ‘travelling together’ It is temporary association between two individuals or living beings in which 4 there is no metabolic dependence. Eg. Bacteria and amoebae on the leg of fly ,or fungal spores on the legs of the beetle. 5 Protozoa: unicellular organisms, e.g. Plasmodium (malaria) Metazoa: multicellular organisms, e.g. helminths (worms) and arthropods (ticks, lice) An endoparasite: “a parasite that lives within another living organism” e.g. malaria, Giardia An ectoparasite: “a parasite that lives on the external surface of another living organism” e.g. lice, ticks 6  Why study Parasitology?  Many of these parasites are causative agents of major public health problems of the world.  Recent estimates of prevalence of parasites in the world are: Ascaris 1.5 billion Hookworms 1.3 billion Whipworms 1 billion Filarial worms 657 million Malaria 500 million Schistosomes 210 million Amebiasis 50 million Taenia tapeworms 50 million Clonorchis 20 million Chagas’ Disease 15 million  These parasites cause varying morbidities and even mortalities 7 8 9  Examples of important intestinal nematodes  Ascaris (roundworm)  Trichuris (whipworm) A soil transmitted helminth Found world-wide in conditions prevalent in warm, humid conditions of poor hygiene, transmitted by Can cause diarrhoea, rectal prolapse and the faecal- oral route anaemia in heavily-infected people Adult worms lives in the small intestine  Ancylostoma and Necator (hookworms) Causes eosinophilia A major cause of anaemia in the tropics  Strongyloides  Enterobius (pinworm or inhabits the small bowel threadworm) prevalent in cold and temperate infection more severe in climates but rare in the tropics immunospressed people (e.g. found mainly in children HIV/AIDS, malnutrition, intercurrent disease) 10 Adult female A. lumbricoides. Unfertilized egg of A. lumbricoides Fertilized egg Trichinella larva in tongue muscle of a rat, Hookworm egg in an unstained wet mount stained with hematoxylin and eosin 11  Examples of important flatworms : cestodes Intestinal :(“tapeworms”) Systemic Taenia saginata  worldwide Echinococcus granulosus (dog  acquired by ingestion of tapeworm) and Echinicoccus contaminated, uncooked beef multilocularis (rodent tapeworm)  a common infection but causes minimal symptoms Hydatid disease occurs when the larval stages of these organisms Taenia solium are ingested  worldwide  acquired by ingestion of contaminated, uncooked pork The larvae may develop in the that contains cystercerci human host and cause space-  Less common, but causes cystercicosis – a systemic occupying lesions in several disease where cysticerci encyst organs, e.g. liver, brain in muscles and in the brain – may lead to epilepsy 12  Examples of important systemic nematodes  Toxocara Filaria worms including: A world-wide infection of  Onchocerca volvulus : dogs and cats Transmitted by the simulium black fly, Human infection occurs this microfilarial parasite can cause when embryonated eggs visual impairment, blindness and severe are ingested from dog or itching of the skin in those infected cat faeces It is common in children  Wuchereria bancrofti : and can cause visceral The major causative agent of lymphatic larva migrans (VLM) filariasis  Brugia malayi : Another microfilarial parasite that causes lymphatic filariasis Microfilaria of W. bancrofti in a thick blood 13 smear stained with Giemsa Protoscoleces in a hydatid cyst removed from lung tissue, stained with Taenia sp. egg in unstained wet mounts hematoxylin and eosin (H&E). Proglottid of T. saginata injected with India Ink 14  Examples of important trematodes (flukes) Intestinal  Fasciola hepatica (liver fluke)- a parasite of sheep, humans become  Fasciolopsis buski : A common parasite infected when ingest metacercariae that have encysted on watercress. of humans and pigs in South- east Asia. The adult trematode lives in the This parasite is one of the largest intra-hepatic bile ducts of the liver. trematodes to infect man (8cm in length) “Fascioliasis” can lead to severe anaemia in humans and lives in the upper intestine. Chronic infection leads to inflammation,  Clonorchis sinensis (liver fluke): ulceration and haemorrhage of the small Widespread in China, Japan, Korea intestine and Taiwan, this parasite is acquired by ingestion of infective metacercariae in raw or pickled fish Paragonimus westermani ( lung fluke)- Widespread in the Far East and South east  Schistosoma haematobium, S. Asia, the parasite is acquired by ingestion of infective metacercariae in raw or pickled mansoni and S. japonicum 15 crustaceans