Introduction To Medical Parasitology PDF

**INTRODUCTION TO MEDICAL PARASITOLOGY** Parasitology - An area of biology concerned with phenomenon of dependence of one living organism on another Medical Parasitology - Concerned primarily with parasites that affect humans and their medical significance Tropical Medicine - A b...

**INTRODUCTION TO MEDICAL PARASITOLOGY** Parasitology - An area of biology concerned with phenomenon of dependence of one living organism on another Medical Parasitology - Concerned primarily with parasites that affect humans and their medical significance Tropical Medicine - A branch of medicine that deals with tropical diseases and other special medical problems of tropical regions Tropical Disease - An illness, that is indigenous to or endemic in a tropical area but may also occur in sporadic or epidemic proportions in areas that are not tropical Epidemiology - is the study of how diseases spread, who they affect, and why they occur in specific populations. It helps identify patterns, causes, and ways to control or prevent diseases and other health-related issues. Populations at Risk for Contracting Parasites - Individuals in underdeveloped countries - Refugees - Immigrants - Visitors from foreign countries - Immunocompromised individuals - Individuals living in close quarters *PARASITE-HOST RELATIONSHIPS* Symbiosis -- living together; the association of two living organisms, each of a different species Forms of Symbiosis - Commensalism - Association of two different species of organisms that is beneficial to one and neutral to the other - Mutualism - Association of two different species of organisms that is beneficial to both - Parasitism - Association of two different species of organisms that is beneficial to one at the other's expense Pathogenic -- Parasite that has demonstrated the ability to cause disease Parasites - Often described according to their habitat or mode of development 1. Endoparasite -- a parasite that is established inside of a host 2. Ectoparasite -- a parasite that is established in or on the exterior surface of a host 3. Obligatory parasite -- a parasite that cannot survive outside of a host 4. Facultative parasite -- a parasite that is capable of existing independently of a host 5. Accidental or incidental parasite -- a parasite which establishes itself in a host where it does not ordinarily live 6. Permanent parasite -- a parasite that remains on or in the body of the host for its entire life 7. Temporary parasite -- a parasite that lives on the host only for a short period of time 8. Spurious parasite -- a free-living organism that passes through the digestive tract without infecting the host Host - Its main purpose is to carry on the parasite's life cycle 1. Accidental or incidental host -- host other than the normal one that is harboring a parasite 2. Definitive host -- host in which the adult sexual phase of parasite development occurs 3. Intermediate host -- host in which the larval asexual phase of parasite development occurs 4. Reservoir host -- host harboring parasites that are parasitic for humans and from which humans may become infected 5. Transport host -- host responsible for transferring a parasite from one location to another 6. Carrier -- parasite-harboring host that is not exhibiting any clinical symptoms but can infect others Vectors - Responsible for transmitting the parasite from one host to another 1. Biologic vector -- transmits the parasite only after the latter has completed its development within the host 2. Mechanical or phoretic vector -- only transports the parasite Exposure and Infection - Exposure -- a process of inoculating an infective agent - Infection -- connotes the establishment of the infective agent in the host - Incubation period -- the period between the infection and evidence of symptoms - Autoinfection -- results when an infected individual becomes his own direct source of infection - Superinfection or hyperinfection -- it happens when the already infected individual is further infected with the same species leading to massive infection with the parasite Source of Infection 1. Contaminated soil and water 2. Food 3. Arthropods 4. Infected individuals Modes of Transmission 1. Ingestion of contaminated food or drink 2. Hand-to-mouth transfer 3. Insect bite 4. Entry via drilling through the skin 5. Unprotected sexual relations 6. Mouth-to-mouth contact 7. Droplet contamination 8. Eye contact with infected swimming water **PARASITIC LIFE CYCLE** **Infective stage:** a morphologic form that invades humans **Diagnostic stage:** a form that can be detected via laboratory retrieval methods **Life Cyle:** refers to the development of a parasite in its earliest form and its survival and development in the outside environment and within the host +-----------------+-----------------+-----------------+-----------------+ | Group cycle | Parasite | Definitive host | Intermediate | | | involved | | host | +=================+=================+=================+=================+ | Those with | *Ascaris sp.* | Man/Pig | None | | definitive host | | | | | but does not | | | | | require | | | | | intermediate | | | | | host | | | | +-----------------+-----------------+-----------------+-----------------+ | Those with | *Echinococcus | Dog | Sheep, Goat, | | definitive host | granulosus* | | Swine, Cattle, | | with one | | | Horse, | | intermediate | | | Herbivores, | | host required | | | Human | +-----------------+-----------------+-----------------+-----------------+ | Those with | *Fasciola | Water | 1^st^ IH: Snail | | definitive host | hepatica* | buffalo/Man | | | and with two or | | | 2^nd^ IH: | | more | | | Aquatic plants | | intermediate | | | or vegetation | | host required | | | | +-----------------+-----------------+-----------------+-----------------+ **Epidemiologic Measures** Epidemiology - is the study of patterns, distribution and occurrence of disease Incidence - is the number of new cases of infection appearing in a population in a given period of time Prevalence - is the number of individuals in a population estimated to be infected with a particular parasite species at a given time Cumulative Prevalence - Is the percentage of individuals in a population infected with at least one parasite Intensity of infection - Refers to burden of infection that is related to the number of worms per infected person Morbidity - It refers to the clinical consequences of infections or diseases that affect an individual's well-being **Disease Processes and Symptoms** The major body areas associated with such processes are 1. Gastrointestinal (GI) and Urogenital (UG) tracts 2. Blood and tissues 3. Liver, lung and other major organs 4. Miscellaneous locations Symptoms associated with Parasitic Disease Processes - Diarrhea - Fever - Chills - Abdominal pain and cramping - Elephantiasis - Anemia - Vitamin Deficiency - Bowel obstruction - Edema - Enlargement of major organs - Skin lesions - Blindness **PATHOLOGY: SIGNS AND SYMPTOMS** **Effects of the Parasite on the Host** - Overt symptoms of infection with this parasite may depend on the number of worms present, the nutritional status of the host or both - Immune system of the host may also be affected - Mechanisms of parasitic infections: - *Fasciolopsis buski* (Giant intestinal fluke) - may produce severe local damage to the intestinal wall - *Entamoeba histolytica*: erodes the intestinal wall, destroying the tissues locally by means of proteolytic enzyme - *Plasmodium falciparum*: invade and multiply in red cells and may also attach to the walls of smaller blood vessels in the brain - *Ascaris lumbricoides*: may perforate the bowel wall that will cause intestinal obstruction if present in large numbers, and may invade the appendix, bile duct, or other organs - Human hookworms: suck blood deprive the host of more iron than is replaced by diet and therefore leading to a case of microcytic hypochromic anemia - *Dibothriocephalus latus*: selectively removes vitamin B12 from the alimentary tract, producing a megaloblastic anemia Effects of the Host on the Parasite - Genetic constitution of the host influences the host parasite relationship - Duffy null phenotype: demonstrates resistance to *Plasmodium vivax* infection - Sickle cell trait is associated with increased resistance to *Plasmodium falciparum* infection - Diet or nutritional status - High protein diet: unfavorable for the development of many intestinal protozoa - Low protein diet: favors the appearance of symptoms of amoebiasis - Rich-carbohydrate diet: favors the development of certain tapeworms Parasites and the Compromised Host +-----------------------------------+-----------------------------------+ | Risk Factor | Parasitic Infection | +===================================+===================================+ | Patient undergoing aggressive | Toxoplasmosis | | treatment for leukemia | | +-----------------------------------+-----------------------------------+ | Corticosteroids | Acute amoebic colitis | +-----------------------------------+-----------------------------------+ | State of malignancy: Reticulum | Primary gastric amoebiasis | | cell carcinoma | | +-----------------------------------+-----------------------------------+ | Immunologically compromised hosts | Strongyloidiasis and Trichonis | +-----------------------------------+-----------------------------------+ | Acquired Immunodeficiency | Toxoplasmosis | | Syndrome (AIDS) | | | | Cyclosporiasis | | | | | | Cryptosporidiosis | | | | | | Cystoisosporiasis | | | | | | Strongyloidiasis | +-----------------------------------+-----------------------------------+ **TREATMENT** **Parasite Treament Options** - Antiparasitic medications - Change in diet - Vitamins supplements - Fluid replacement - Blood transfusion - Bed rest Deworming - Is the use of antihelminthic drugs in an individual or a public health program *Cure rate*: the number of previously positive subjects found to be egg negative *Egg Reduction Rate (ERR)*: the percentage fall in egg counts after deworming Selective treatment - Involves individual-level deworming with selection for treatment based on a diagnosis of infection or assessment of the intensity of infection Targeted treatment - Is group-level deworming where the group to be treated may be defined by age, sex, or other social characteristics irrespective of infection status Universal treatment - Is population-level deworming in which the community is treated irrespective of age, sex, infection or other social characteristics Preventive Chemotherapy - It aims to reduce morbidity and transmission of selected helminth infections Coverage - It refers to the proportion of the target population reached by an intervention Efficacy - Is the effect of a drug against an infective agent in ideal experimental conditions Effectiveness - Is a measure of the effect of a drug against an infective agent in a particular host Drug resistance - Is a genetically transmitted loss of susceptibility to a drug in a parasite population that was previously sensitive to the appropriate therapeutic dose **PREVENTION AND CONTROL** **Parasite Prevention and Control Strategies** - Development and implementation of parasite awareness education programs - Use of insectides and other chemicals - Use of protective clothing - Use of protective netting - Proper water tre - Good personal hygiene - Proper sanitation practices - Proper handling, cooking, and protection of food - Avoidance of unprotected sexual relations Morbdity Control - Is the avoidance of illness caused by infections Information-education-communication (IEC) - Is a health education strategy that aims to encourage people to adapt and maintain healthy lifestyles Environmental management - Is the planning, organization, performance, and monitoring of activities for the modification or manipulation of environmental factors by preventing or minimizing vector or intermediate host propagation and reducing contact between humans and the infective agent Environmental sanitation - Involves interventions to reduce environmental health risks Sanitation - Is the provision of access to adequate facilities for the safe disposal of human excreta and combined witn access to safe drinking water Eradication vs. Elimination Disease Eradication - Is defined as a permanent reduction to zero of the worldwide incidence of infection caused by a specific agent - Once this is achieved, continued measures are no longer necessary Disease Elimination - Is a reduction to zero of the incidence of a specified disease in a define geographic area - Continued intervention or surveillance measures are still required  Parasite Nomenclature and Classification - Scientific names of parasites are written in italics and consist of two components: GENUS and SPECIE - When a parasite name first appears in a document, the entire parasite name is written out - Variations of scientific genus names are used to identify diseases and conditions associated with their presence - Suffix --iasis is often used to denote diseases or conditions Important Groups of Animal Parasites Protozoan - Exist as motile trophozoite stage and the non motile infective cyst - Locomotor apparatus serves as one of the bases of classification Phylum Sarcomastigophora - Sarcodina: amoebae: equipped with pseudopods ("false feet") - Mastigophora: flagellates: equipped with flagellum (a whip-like structure) Phylum Ciliophora - Ciliata: ciliates: equipped with ciliates (a hair-like structure) Phylum Apicomplexa - Parasites that are not equipped with definite locomotor apparatus - Schizogony: asexual cycle - Sporogony: sexual cycle - Contains of apical complex that is composed of the following: micronemes, subpellicular tubules, polar rings, conoids, rhoptries Metazoa Phylum Platyhelminthes - Flatworms; multicellular animals characterized by a flat, bilaterally symmetrical body - Most of them are hermaphroditic - Adult: may be less than 1 mm long or may reach a length of many meters 3 classes are: Class Turbellaria - Most existing free-living forms inhabiting terrestrial, freshwater and marine environment - Ciliated epithelium envelops the body of the adult worm - With or without suckers Class Trematoda: "flukes" - Leaf-shaped or elongate, slender organisms - Possess attachment organs in the form of suckers - Incomplete digestive tract is present - Inhabits the small intestine, liver, lungs, pancreas, and blood vessels Class Cestoda: "tapeworm" - Elongate, ribbon-like, segmented body that has a specialized attachment organ called scolex - A digestive tract is absent - Adult cestodes or tapeworms inhabit the small intestine - Cestode larvae require an IH for development Phylum Nemathelminthes: nematodes or roundworms - Elongate, cylindrical worms, frequently attenuated at both ends - Possess a stiff cuticle - Sexes are separate, the male frequently being smaller than the female and possess copulatory structures like spicule or bursa - Complete digestive tract is present - Intermediate hosts are necessary for the larval development of some forms - Inhabits intestine and tissues Arthropods Phylum Arthropoda - Arthropods are segmented and bilaterally symmetrical animals with a body enclosed in stiff, chitinous covering or exoskeleton and bearing paired, jointed appendages - Digestive system is well developed - Sexes are separate Classes: Class Crustacea - Primarily aquatic forms - Crabs, shrimps, crayfish, and copepods - Serve as intermediate hosts of human parasites - Freshwater crab: *Paragonimus westermani* - Copepods: *Dibothriocephalus latus* Class Chilopoda - Centipedes are characterized by the possession of one pair of legs on each body segment - First pair of appendages is modified as poison claws Class Arachnida - Spiderlike animals, possess a body divided into two parts: cephalothorax and the abdomen - Adults: 4 pair of legs - Scorpions, spiders, ticks, mites - Scorpions and spiders: produce venom - Ticks and mites may act as IH for certain parasitic infection Class Insecta - The most important of the arthropods - Three pairs of legs and body divided into three distinct parts: head, thorax, and abdomen Orders: Order Anoplura - Sucking lice - Wingless, dorsoventrally compressed insects - Human lice Order Hemiptera - True bugs, wingless bedbugs - Two pairs of wings - Cone-nosed bugs, or reduvids; vectors of *Trypanosoma cruzi* Order Coleoptera - Beetles - Two pairs of wings - Beetles are IH of tapeworms - Grain beetle: *Hymenolepis nana* - Flour beetle: *Hymenolepis diminuta* Order Hymenoptera - Ants, bees, wasps - Medically important source of venom - Ants serve as IH for flukes: *Fasciola lanceolata, Eurytrema pancreaticum* Order Siphonaptera - Fleas - Wingless and laterally compressed - Fleas act as IH of tapeworm: *Dypilidium caninum* Order Diptera - One pair of true wings - Mosquitoes, fleas and gnats - Some larval flies are parasitic in humans and animals - Acts as vectors of parasites