Intro to Parasitology PDF

Parasitology Medical Parasitology Introduction to Parasitology Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another. Man and other living things on earth live in an entangling relationship with each other. They don’t exist in an...

Parasitology Medical Parasitology Introduction to Parasitology Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another. Man and other living things on earth live in an entangling relationship with each other. They don’t exist in an isolated fashion. They are interdependent; each forms a strand in the web of life. Parasitology is the scientific discipline concerned with the study of the biology of parasites and parasitic diseases, including the distribution, biochemistry, physiology, molecular biology, ecology, evolution and clinical aspects of parasites, including the host response to these agents. Introduction to Parasitology…continuation… Parasite is a living organism, which takes its nourishment and other needs from a host. Host is an organism which supports the parasite. Zoonosis- an infectious disease that has jumped from a non- human animal to humans. Types of partnership between organisms Symbiosis- It is an association in which both are so dependent upon each other that one cannot live without the help of the other. None of the partner suffers any harm from the association. Commensalism- An association in which the parasite only is deriving benefit without causing injury to its host. A commensal is capable of leading an independent life. Parasitism- An association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury. A parasite has lost its power of independent life. Different 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. Different Kinds of Parasites…continuation…end… 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. Different 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. Different Kinds of Hosts…continuation…end… 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. Sources of Infection Contaminated soil and water Freshwater fishes- Diphyllobothrium latum and Clonorchis sinensis. Crab and crayfishes-Paragonimus wertermani. Raw or undercooked pork- Trichinella spiralis, T.solium. Raw or undercooked beef- T.saginata, Toxoplasma gondii. Watercress- Fasciola hepatica Blood sucking insects Housefly-Mechanical carrier- E.histolytica Dog- Echinococcus granulosus and Toxocara canis. Cat- T.gondii. Man- E.histolytica, Enterobius vermicularis and H.nana. Portal of Entry Into the Body Mouth- Commonest portal of entry of the parasites is oral through contaminated food, water, soiled fingers or fomites. Skin- Entry through skin is another important portal of entry of parasites. Infection with A. duodenale, N. americanus and S. stercoralis is acquired when filariform larvae of these nematodes penetrate the unbroken skin of an individual walking over fecally contaminated soil. Schistosomiasis caused by S. haematobium, S. mansoni and S. japonicum is acquired when the cercarial larvae, in water, penetrate the skin. Portal of Entry Into the Body…continuation… Sexual contact- Trichomonas vaginalis is transmitted by sexual contact. Congenital- Infection with T. gondii and Plasmodium spp. May be transmitted from mother to fetus transplacentally. Inhalation Iatrogenic infection- Malaria parasites may be transmitted by transfusion of blood from the donor with malaria containing asexual forms of erythrocytic schizogony. This is known as trophozoite induced malaria or transfusion malaria. Malaria parasites may also be transmitted by the use of contaminated syringes and needles. This may occur in drug addicts. Effect of Parasites on the Host The damage which pathogenic parasites produce in the tissues of the host may be described in the following two ways; (a) Direct effects of the parasite on the host (b) Indirect effects of the parasite on the host Effect of Parasites on the Host …continuation… (a)Direct effects of the parasite on the host Mechanical injury - may be inflicted by a parasite by means of pressure as it grows larger, e.g. Hydatid cyst causes blockage of ducts such as blood vessels producing infraction. Deleterious effect of toxic substances - in Plasmodium falciparum production of toxic substances may cause rigors and other symptoms. Deprivation of nutrients, fluids and metabolites -parasite may produce disease by competing with the host for nutrients. Effect of Parasites on the Host …continuation…end… (b) Indirect effects of the parasite on the host: Immunological reaction: Tissue damage may be caused by immunological response of the host, e.g. nephritic syndrome following Plasmodium infections. Excessive proliferation of certain tissues due to invasion by some parasites can also cause tissue damage in man, e.g. fibrosis of liver after deposition of the ova of Schistosoma. Nephritic syndrome is a clinical syndrome that presents as hematuria, elevated blood pressure, decreased urine output, and edema. The major underlying pathology is inflammation of the glomerulus that results in nephritic syndrome. Areas of Parasitology Medical Parasitology Agriculture, Aquaculture, and Veterinary Parasitology Wildlife and Fisheries Parasitology Ecological and Systematic Parasitology Biochemistry and Molecular Biology of Parasites Immunoparasitology Medical Parasitology Medical parasitology deals with the parasites which infect man, the diseases they produce, the response generated by them against them and various methods of diagnosis and prevention. Medical parasitology is the science that deals with organisms living in the human body (the host) and the medical significance of this host-parasite relationship. The parasites included in medical parasitology are protozoa, helminthes, and some arthropods. The hosts vary depending on whether they harbor the various stages in parasitic development. Medical Parasitology…continuation… Protozoan pathogens examples are Cryptosporidium, Giardia, and Entamoeba histolytica. Medical Parasitology…continuation… Helminths are worm-like parasites that survive by feeding on a living host to gain nourishment and protection, sometimes resulting in illness of the host. There are a variety of different helminths from the very large to the microscopic Medical Parasitology…continuation…end… Arthropod Parasites- Arthropods form a huge assemblage of small coelomate animals with “jointed limbs” (hence the name arthro-pods). They exhibit segmentation of their bodies (metamerism) which is often masked in adults because their 10- 25 body segments are combined into 2-3 functional groups (called tagmata). Most parasitic arthropods belong to 2 main classes: the 6-legged insects, and the 8-legged arachnids. Basic Concepts in Medical Parasitology In medical parasitology, each of the medically important parasites are discussed under the standard subheadings of morphology, geographical distribution, means of infection, life cycle, host/parasite relationship, pathology and clinical manifestations of infection, laboratory diagnosis, treatment and preventive/control measures of parasites. Basic Concepts in Medical Parasitology …continuation… Morphology - includes size, shape, color and position of different organelles in different parasites at various stages of their development. This is especially important in laboratory diagnosis which helps to identify the different stages of development and differentiate between pathogenic and commensal organisms. For example, Entamoeba histolytica and Entamoeba coli. Basic Concepts in Medical Parasitology …continuation… Geographical distribution - Even though revolutionary advances in transportation has made geographical isolation no longer a protection against many of the parasitic diseases, many of them are still found in abundance in the tropics. Distribution of parasites depends upon: a. The presence and food habits of a suitable host. b. Easy escape of the parasite from the host- the different developmental stages of a parasite which are released from the body along with feces and urine are widely distributed in many parts of the world as compared to those parasites which require a vector or direct body fluid contact for transmission. c. Environmental conditions favoring survival outside the body of the host, i.e. temperature, the presence of water, humidity etc. d. The presence of an appropriate vector or intermediate host – parasites that do not require an intermediate host (vector) for transmission are more widely distributed than those that do require vectors. Basic Concepts in Medical Parasitology …continuation… Life cycle of parasites - the route followed by a parasite from the time of entry to the host to exit, including the extracorporeal (outside the host) life. It can either be simple, when only one host is involved, or complex, involving one or more intermediate hosts. A parasite’s life cycle consists of two common phases one phase involves the route a parasite follows inside the body. This information provides an understanding of the symptomatology and pathology of the parasite. In addition the method of diagnosis and selection of appropriate medication may also be determined. The other phase, the route a parasite follows outside of the body, provides crucial information pertinent to epidemiology, prevention, and control. Basic Concepts in Medical Parasitology …continuation… Host parasite relationship - infection is the result of entry and development within the body of any injurious organism regardless of its size. Once the infecting organism is introduced into the body of the host, it reacts in different ways and this could result in: a. Carrier state - a perfect host parasite relationship where tissue destruction by a parasite is balanced with the host’s tissue repair. At this point the parasite and the host live harmoniously, i.e. they are at equilibrium. b. Disease state - this is due to an imperfect host parasite relationship where the parasite dominates the upper hand. It can result either from lower resistance of the host or a higher pathogenecity of the parasite. c. Parasite destruction – occurs when the host takes the upper hand. Basic Concepts in Medical Parasitology …continuation… Laboratory diagnosis – depending on the nature of the parasitic infections, the following specimens are selected for laboratory diagnosis:  a) Blood – in those parasitic infections where the parasite itself in any stage of its development circulates in the blood stream, examination of blood film forms one of the main procedures for specific diagnosis.  b) Stool – examination of the stool forms an important part in the diagnosis of intestinal parasitic infections and also for those helminthic parasites that localize in the biliary tract and discharge their eggs into the intestine.  d) Sputum – examination of the sputum is useful in the following: In cases where the habitat of the parasite is in the respiratory tract, as in Paragonimiasis, the eggs of Paragonimus westermani are found. In amoebic abscess of lung or in the case of amoebic liver abscess bursting into the lungs, the trophozoites of E. histolytica are detected in the sputum.  e) Biopsy material - varies with different parasitic infections. For example spleen punctures in cases of kala-azar, muscle biopsy in cases of Cysticercosis, Trichinelliasis, and Chagas’ disease, Skin snip for Onchocerciasis.  f) Urethral or vaginal discharge – for Trichomonas vaginalis Basic Concepts in Medical Parasitology …continuation… Indirect evidences – changes indicative of intestinal parasitic infections are: (a)Cytological changes in the blood – eosiniphilia often gives an indication of tissue invasion by helminthes, a reduction in white blood cell count is an indication of kala-azar, and anemia is a feature of hookworm infestation and malaria. (b) Serological tests – are carried out only in laboratories where special antigens are available. Basic Concepts in Medical Parasitology …continuation… Treatment – many parasitic infections can be cured by specific chemotherapy. The greatest advances have been made in the treatment of protozoal diseases. For the treatment of intestinal helminthiasis, drugs are given orally for direct action on the helminthes. To obtain maximum parasiticidal effect, it is desirable that the drugs administered should not be absorbed and the drugs should also have minimum toxic effect on the host. Basic Concepts in Medical Parasitology …continuation…end.. Prevention and control - measures may be taken against every parasite infectiving humans. Preventive measures designed to break the transmission cycle are crucial to successful parasitic eradication. Such measures include: Reduction of the source of infection- the parasite is attacked within the host, thereby preventing the dissemination of the infecting agent. Therefore, a prompt diagnosis and treatment of parasitic diseases is an important component in the prevention of dissemination. Sanitary control of drinking water and food. Proper waste disposal – through establishing safe sewage systems, use of screened latrines, and treatment of night soil. The use of insecticides and other chemicals used to control the vector population. Protective clothing that would prevent vectors from resting in the surface of the body and inoculate pathogens during their blood meal. Good personal hygiene. Avoidance of unprotected sexual practices. Classification of Medical Parasitology Parasites of medical importance come under the kingdom called protista and animalia. Protista includes the microscopic single-celled eukaroytes known as protozoa. In contrast, helminthes are macroscopic, multicellular worms possessing well differentiated tissues and complex organs belonging to the kingdom animalia. Classification of Medical Parasitology…continuation…end.. Medical Parasitology is generally classified into:  Medical Protozoology - Deals with the study of medically important protozoa. Medical Helminthology - Deals with the study of helminthes (worms) that affect man. Medical Entomology - Deals with the study of arthropods which cause or transmit disease to man.