Parasitology Lecture Notes PDF

Parasitology  Parasite Organism that lives in or on another organism (host) Typically, the parasite benefits from the interaction while causing harm to the host  Parasites Live in the body of another organism (the host) Gets nourishment from the hos...

Parasitology  Parasite Organism that lives in or on another organism (host) Typically, the parasite benefits from the interaction while causing harm to the host  Parasites Live in the body of another organism (the host) Gets nourishment from the host May cause damage to the host Responsible for many infections, infestations, and diseases Present challenges in terms of the determination of effective means of treatment  Parasitology The study of parasite-host relationships Medical parasitology focuses on the organisms that infect and live in humans  Disease Terminology Epidemiology: The study of the occurrence, distribution, and transmission of diseases in human populations. Endemic: A disease that is native to a local region. Epidemic: If the disease spreads to many individuals at the same time. Pandemics: Are epidemics that affect large geographic regions, perhaps spreading worldwide.  Disease Terminology cont’d Chronic: Disease that develops slowly and lasts for a long time (perhaps for life). Etiology: All the factors involved in causing a disease. Pathogenesis: Actual pattern of a disease's development. Idiopathic: Disease with undetermined cause(s). Communicable: Disease that can be transmitted from one person to another. Incubation: The latent stage of an infection.  Important Questions in Parasitology What effects do parasites have on the functioning of the internal systems of their hosts? What effects do parasites have on the tissues of their hosts? How is an organ’s structure and function altered by a parasite? How does the host's immune system respond to the presence of a parasite?  Challenges to the Control of Parasite Infections Resistance to antiparasiticals and antibiotics Emigration Vacation travel Construction in new habitats Climate change Diseases that create predisposition to infection Treatments/exposures that create predisposition to infection  Incidence Many parasites are causative agents of major public health problems of the world. Parasites are found throughout the world but common in tropical areas and other areas where poor sanitation is prevalent. 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 270 million Amebiasis 50 million Taeniad tapeworms 50 million Clonorchis 20 million Chagas’ Disease 15 million These parasites cause untold suffering and death in the world today.  Types of Parasites Obligatory Parasites – Unable to survive outside of their hosts Facultative/Opportunistic Parasites – Able to exist independent of their host  Types of Parasites Cont’d Endoparasite – Established inside the body, e.g., hookworms Ectoparasite – Established in or outside the surface of the body, e.g., some mites  Types of Parasitic Hosts Accidental/Incidental Host – Host that is not the normal host of the parasite Definitive Host – Adult and/or sexual phase of an adult occurs here  Types of Parasitic Hosts Cont’d Intermediate Host – Larval or asexual phase of a parasite occurs here Reservoir Host – Harbors parasites that are also infective to humans Carrier – Host that does not exhibit clinical symptoms of infection but is capable of infecting others Modes of Parasite Transmission to Hosts Arthropod vectors via bites (blood meals) – Primary mode of transmission Consumption of contaminated food or water, and hand-to-mouth transmission Direct transmission via parasite drilling through the skin (e.g. through bare feet)  Modes of Parasite Transmission Cont’d Sexual transmission via body fluids Mouth-to mouth contact via kissing Eye contact with contaminated swimming water  Factors that Contribute to Parasite Infestations Poor hygiene – Increased population density (e.g., prisons) Poor sanitation/lack of indoor plumbing Marginal/compromised water sources in developing countries Poor public health practices Environmental factors/changes that affect parasite life cycles and breeding  Additional Factors that Influence Parasite Infestation Global travel (increased rates of immigration and tourism) Immunocompromised individuals (e.g., children in daycare, AIDS patients)  Parasite-Host Relationships Symbiosis Commensalism Mutualism Parasitism  Parasite-Host Relationships Cont’d Symbiosis The association of organisms of different species Commensalism Mutualism Parasitism Association that is beneficial Association that is Association that is to one organism and is neither beneficial to both beneficial to one beneficial nor detrimental to organisms organism and the other detrimental to the other Parasite-Host Relationships Cont’d Some commensals are inaccurately characterized as parasites For example, Entamoeba coli, a protozoan of the intestinal flora Parasite-Host Relationships Parasite-Host Relationships Parasite-Host Relationships  Adaptations to Parasitism The result of preadaptation changes that allow these organisms to survive in harsh environments in the first place Most striking in organisms that are obligate parasites – such as the loss of locomotor structures Includes loss of metabolic activities which then makes the parasite dependent on the host for these products  Characteristics of Parasites Can adapt (morphologically) to their host environment Can protect themselves from the immune system of the host (by masking their antigenicity)  Adaptations to Parasitism Increased reproductive capacity, particularly at the infective [often larval] stages Mechanisms of host entry, e.g., enzymatic digestion, specialized burrowing structures Survival mechanisms once inside the host, e.g., encystation to evade the host’s immune system Effects of the Parasite on the Host Adverse effects on the host may arise in many ways: – Host enzyme systems may be compromised by secretions from the parasite – Tissue damage may arise in response to the parasites overpopulating an area – Obstruction of the intestines, vessels may arise in response to parasites overpopulating an area – Structures on the parasites (e.g., suckers, hooks) may damage/perforate host tissue – May deprive host of essential nutrients  Effects of the Host on the Parasite The genetic background of the host may influence the ability of the parasite to infect (e.g., sickle cell trait is linked to resistance to malaria) Nutritional status of the host also plays a role: high-protein diets are unfavorable for intestinal parasites; carbohydrate-rich diets are favorable to some tapeworms,  Acquired Immunity Is possible (e.g., with Leishmania) but much less common than for bacterial or viral infections No vaccines yet However, premunition (resistance to re- infection while the parasite is in the body) does confer protection against hyperinfection; of particular importance in endemic areas Parasites and the Compromised Host Nutrition influences infection Surgery, transfusion, intubation, and prolonged hospitalization may also may individuals more vulnerable to infection following exposure The potential benefits and harms must be weighed when considering treatments – aggressive treatment of leukemia may lead to toxoplasma; corticosteroid use may open the door to acute amebic colitis  Important Groups of Animal Parasites 1. Single-celled protozoa - flagellates, amebae, malarial organisms 2. Multicellular worms - parasitic worms such as the flukes, tapeworms, and roundworms 3. Arthropods - insects and arachnids that are ectoparasites and carriers of diseases  Main Targets of Parasitic Infestations Gastrointestinal and urogenital tracts Blood and tissue Liver, lung and other major organs Other locations (e.g., eyes) Symptoms of Parasitic Infestations – Diarrhea – Abdominal pain and cramping – Fever – Chills – Elephantiasis – Anemia – Bowel obstruction – Skin lesions – Blindness – Enlargement of major organs Prevention of Parasitic Infestations Designed to interrupt the transmission cycle – Education Insecticides Protective clothing Water treatment Personal hygiene Sanitation practices Safe food handling Safe sex practices Stages of the Parasitic Life Cycle Mode of transmission Infective stage Diagnostic stage Generic Parasitic Life Cycle  Typical Fecal-Oral Life Cycle excystation CYST TROPHOZOITE Feeding encystment Motile Replication w/in the Passed in feces Resistant wall large intestine Infective  Techniques Used in the Identification of Parasites Histological – Acid fast stain – Trichome stain – H and E stain – Skin tests Molecular – Polymerase chain reaction (PCR) – Deoxyribonucleic acid (DNA) hybridization – Antigen-antibody detection (e.g., enzyme immunoassay [EIA])  Summary Parasitic infections are widespread but the majority take place in tropical/developing countries It is becoming more challenging to treating and contain these infections Many different classes of organisms may play parasitic roles at some point in their life cycles