Parasitology Review - Lecture Summary that contains the significant information in things to remember PDF

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INTRODUCTION TO PARASITOLOGY PARASITOLOGY is the area of biology concerned with the phenomenon of dependence of one living organism on another is the science that deals with the study of living organism that depends on another organism for the purpose of procuring food and securing protection PARASI...

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INTRODUCTION TO PARASITOLOGY PARASITOLOGY - is the area of biology concerned with the phenomenon of dependence of one living organism on another - is the science that deals with the study of living organism that depends on another organism for the purpose of procuring food and securing protection PARASITE - organisms that obtain its food and shelter from another organism and derive all the benefits from the association - defined as n animal or plant, which lives in or upon another organism and draws its nutrient directly from it HOST -

the organism that provides physical protection an nourishment to the parasite organism which harbors the parasite and provide nourishment and shelter

BIOLOGICAL RELATIONSHIPS The relationship between the parasite and host which live together can be of the following types: Symbiosis It is the close association between the host and the parasite; both are so dependent on each other that one cannot live without the help of the other. Commensalism It is a symbiotic relationship in which two species live together and one species benefits from the relationship without harming or benefiting the other. Parasitism It is an association in which the parasite derives benefit from the host and always causes injury to the host. Mutualism It is an association that I beneficial to both the parasite and the host in which one can still survive even without the other CLASSIFICATION OF PARASITES 1. According to habitat a. Endoparasite – parasite living inside the body of a host, the presence of an endoparasite on a host is called infection. b. Ectoparasite – parasite living outside the body of a host, the presence of an ectoparasite on a host is called infestation  ERRATIC – when a parasite is found in an organ which is not its usual habitat 2. According to its effect to the host a. Pathogenic – cause injury by its mechanical, traumatic or toxic activities b. Non-pathogenic – derives benefits to the host without causing any damage 3. According to mode of living a. Obligate – they need a host at some stage of their life cycle to complete their development and to propagate their species

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b. Facultative – may exit in a free-living state or may become parasitic when the need arises or under favorable or appropriate circumstances c. Accidental or Incidental – a parasite which establishes itself in a host where it does not ordinarily live d. Temporary – free living during part of existence and seeks only its host intermittently to obtain nourishment e. Permanent – remains on or in the body of the host for its entire life f. Spurious or Coprozoic – free-living organism that passes through the digestive tract without infecting the host HOST It can be classified into various types based on their role in the life cycle of the parasite. Final or Definitive Host It harbors the adult or sexual stage of the parasite. It may be human or non-human living things Intermediate Host It harbors the asexual or larval stage of the parasite. Sometimes two different hosts may be require to complete different larval stages, these are:  First Intermediate Host – harbors the early larval stage of the parasite  Second Intermediate Host – harbors the infective larval stage of the parasite Reservoir Host They allow the parasite’s life cycle to continue and become additional sources of infection to other susceptible hosts Paratenic Host Is the one in which the parasite does not develop further to later stages. However, the parasite remains alive and is able to infect another susceptible host Natural Host The host which is naturally infected with certain species of the parasites Accidental Host The host in which the parasite is not usually found VECTOR They are responsible for transmitting the parasite from one host to another.  Biologic Vector – transmit the parasite after it has completed its development within the host, thus it is an essential part of the parasite’s life cycle  Mechanical or Phoretic Vector – it only transports the parasite EXPOSURE AND INFECTION Majority of animal parasites are pathogens which are harmful and which frequently cause mechanical injury to their hosts. A carrier harbors a particular pathogen without manifesting any signs and symptoms. Exposure is the process of inoculating an infective agent. The clinical incubation period is the time between exposure to the parasite and the appearance of the earliest signs and symptoms. The biological incubation period is the development of the parasite in a particular host and the demonstration of the parasite in the different specimens.

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Autoinfection results when an infected individual becomes his own source of infection. Superinfection or hyperinfection happens when the already infected individual is further infected with the same species leading to massive infection with the parasite. FACTORS AFFECTING TRANSMISSION OF PARASITES 1. Source of infection a. Man – source or reservoir for majority of parasitic infection. The condition in which the infection is transmitted from one infected man to another is called anthroponoses. b. Animal – in many of the parasitic diseases, it also acts as source of infection. The condition where infection is transmitted from animals to humans is called zoonoses c. Contaminated soil and water and foods – most common source of infection d. One’s self – in terms of autoinfection 2. Effective mode of transmission and portal of entry and exit 3. Presence of susceptible host 4. Successful entry of the infective stage of the parasite to the host SOURCE OF EXPOSURE TO INFECTION Based on the sources of exposure to infection, parasite maybe classified as follows: Soil Transmitted Group (STH – Soil Transmitted Helminths) These parasites require further development in the soil before they become infective Snail Transmitted Group These parasites require further development within the body of snails which serves as their intermediate host before they become infective Arthropod Transmitted Group The parasites are transmitted from one host to another by a vector Animal/Food Transmitted Group These parasites require further development in the flesh of some animals that man consume Contact Transmitted Group Person to person transmission, wherein the parasites require no further development and are readily infective MODES OF TRANSMISSION Transmission of infection from one host to another is caused by a certain form of the parasite known as the infective stage. The following are the modes of transmission of different parasites: Oral Route (Portal of entry = Mouth – most common) 1. Ingestion of contaminated food, water and vegetables 2. Ingestion of raw or undercooked meat, fish, crab, water plants, etc. 3. Ingestion of the infective stage 4. Intimate oral contact/kissing Penetration of the skin and mucous membrane 1. Active larval penetration/skin penetration 2. Bite of arthropod vector Others 1. Sexual contact 2. Transplacental

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3. Inhalation LIFE CYCLE Through adaptation to their hosts and external environment parasites have developed life cycles which maybe simple or complex/complicated.  

Simple Life Cycle – all the developmental stages of the parasites are completed in one single host. Change of host is only required to propagate the parasite in the community. Complex/Complicated Life Cycle – parasite requires two different hosts, one definitive host and another is intermediate host to complete their life cycle. Some parasites require two intermediate hosts aside from one definitive host

PATHOGENESIS AND PATHOLOGY Pathogenesis of parasitic disease is a dynamic process and depends on the complex interaction of a variety of host and parasitic factors. Host Factors 1. Nutritional status of the host, whether malnutrition or under nutrition 2. Immune status of the host 3. Immune response to parasitic infection 4. Presence or absence of co-existing disease or other physiological condition such as pregnancy 5. The age and the level of immunity at the time of infection Parasitic Factors 1. Site of attachment of the parasite 2. Size of the parasite 3. Number of invading parasites 4. Parasite strain, whether pathogenic or not 5. Growth, development and multiplication of parasites inside the human body and their metabolic products. The parasites can cause disease in human in various ways as follows: 1. Trauma 2. Invasion and destruction of host’s cell 3. Inflammatory reaction 4. Toxin 5. Allergic manifestation TREATMENT The use of antihelminthic drugs in an individual or a public health program is the most effective treatment for parasitic infections. Cure Rate Refers to the number of previously positive subjects found to be egg-negative on examination of stool or urine specimen using a standard procedure at a set time after deworming Egg Reduction Rate (ERR) It is the percentage fall in egg counts after deworming based on examination of a stool or urine specimen using a standard procedure at a set time after treatment Selective Treatment Involves individual-level deworming with selection for treatment based on a diagnosis of infection or based on presumptive grounds, it is used particularly in a defined risk group

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Targeted Treatment Group-level deworming where the risk group maybe defined by age, sex or other social characteristics irrespective of infection status Universal Treatment Population-level deworming in which the community is treated irrespective of age, sex, infection status or other social characteristics Coverage Refers to the proportion of the target population reached by an intervention DIAGNOSIS The diagnosis of parasitic infections depends upon: 1. Clinical Diagnosis – this method of diagnosis is based on the recognition of the characteristic signs and symptoms of the infection of disease. However, in some situations, it is hindered by the following: a. low prevalence of major clinical signs b. late development of clinical signs c. lack of specificities of clinical signs d. occurrence od asymptomatic carriers 2. Laboratory Diagnosis – this method is based on the identification of the parasite in different specimens. It depends upon: a. morphological recognition of the parasite in relevant specimen (parasitic diagnosis) b. immunological tests (immunodiagnosis) c. molecular diagnosis d. imaging methods PREVENTION AND CONTROL Morbidity Control It is the avoidance of illness caused by infections. It may be achieved by periodically deworming individuals or groups, known to be at risk of morbidity Information – Education – Communication (IEC) Is a health education strategy that aims to encourage people to adapt and maintain healthy life practices Environmental Management Is the planning, organizing, performance, and monitoring of activities for the modification and/or manipulation of environmental factors or their interaction with human beings with a view to preventing or minimizing vector or intermediate host propagation and reducing contact between humans and the infective agent Environmental Sanitation Involves intervention to reduce environmental health risks including the safe disposal and hygienic management of human and animal excreta, refuse and waste water. It also involves the control of vectors, intermediate hosts, and reservoirs of disease. It also covers the provision of safe drinking water and food safety; housing that is adequate in terms of location, quality of shelter, and indoor living condition; facilities for personal and domestic hygiene; as well as safe and healthy working conditions.

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GROUP OF PARASITE WITH MEDICAL AND PUBLIC HEALTH IMPORTANCE I. NEMATODES (Roundworms) 1. Intestinal Ascaris lumbricoides Trichuris trichiura Strongyloides stercoralis Hookworms - Ancylostoma duodenale - Necator americanus Enterobius vermicularis Capillaria philippinensis 2. Tissue Trichinella spiralis Visceral Larva Migrans (Toxocara canis or Toxocara cati) Cutaneous Larva Migrans (Ancylostoma braziliense or Ancylostoma caninum) Dracunculus medinensis Angiostrongylus cantonensis 3. Blood and Tissues Wuchereria bancrofti Brugia malayi, Brugia timori Loa loa Onchocerca volvulus Mansonella species II. CESTODES (Tapeworms) 1. Intestinal Diphyllobothrium latum Dipylidium caninum Hymenolepis nana Hymenolepis diminuta Taenia saginata Taenia solium 2. Tissue Echinococcus granulosus Echinococcus multilocularis Spirometria mansonoides III. TREMATODES (Flukes) 1. Intestinal Fasciolopsis buski Echinostoma ilocanum Heterophyes heterophyes Metagonimus yokogawai 2. Lung Paragonimus westermani 3. Liver Clonorchis sinensis Opistorchis felineus, Opistorchis viverrini

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Fasciola hepatica 4. Blood Schistosoma mansoni Schistosoma haematobium Schistosoma japonicum Schistosoma intercalatum Schistosoma mekongi IV. PROTOZOA 1. Amoeba (Intestinal) Entamoeba histolytica Entamoeba dispar Entamoeba hartmanni Entamoeba coli Entamoeba polecki Endolimax nana Iodamoeba butschlii Blastocystis hominis 2. Flagellates (Intestinal) Giradia lamblia Chilomastix mesnili Dientamoeba fragilis Trichomonas hominis 3. Ciliates Balantidium coli 4. Coccidia, Microsporidia (Intestinal) Cryptosporidium parvum Cyclospora cayetanensis Isospora belli Sarcocystis hominis, Sarcocystis suihominis 5. Sporozoa, Flagellates (Blood, Tissue) A. Sporozoa (Malaria and Babesiosis) Plasmodium vivax Plasmodium ovale Plasmodium malariae Plasmodium falciparum Plasmodium knowlesi Babesia microti B. Flagellates (Leishmania, Trypanosomes) Leishmania braziliensis Leishmania donovani Leishmania tropica Leishmania mexicana Leishmania peruviana Trypanosoma brucie gambiense Trypanosoma brucie rhodesiense Trypanosoma cruzi 6. Amoeba, Flagellates (Other body sites) A. Amoeba Naegleria fowleri Acanthamoeba species Hartmanella species Balamuthia mandrillaris

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Entamoeba gingivalis Flagellates Trichomonas vaginalis Trichomonas tenax 7. Coccidia, Sporozoa (Other body parts) A. Coccidia Toxoplasma gondii B. Sporozoa Pneumocystis carinii

PHYLUM NEMATODA (THE TRUE ROUNDWORMS) Morphology and general characteristics  The adult nematode is unsegmented, elongated, cylindrical worm.  The sexes are separate (dioecious). The male is smaller than female and the posterior portion of male is curved or coiled.  The supporting body wall consists of the following 1. an outer, hyaline, non-cellular cuticle with three main layers  cortical layer, which is the outermost layer composed of collagen and cuticulin  homogenous matrix, the middle layer  the fibrous layer 2. a subcuticular epithelium or hypodermis which is responsible for secretion of the cuticle 3. layer of muscle cell or somatic musculature, wherein there are two types of muscle cells (a) platymyarian muscle cells and (2) coelomyarian muscle cells  All of the viscera including the digestive system, excretory system and the reproductive system are suspended in a body cavity known as pseudocele or pseudocoelum.  The fluid of pseudocele known as hemolymph contains hemoglobin, glucose, proteins, salts and vitamins and fulfills the function of the blood. Digestive System  The adult worm has a complete digestive tract 1. Mouth - located at the anterior end; maybe equipped with hooks,teeth, plates and other structures for the purpose of abrasion, attachment and sensory response 2. Buccal cavity - tubular or funnel-shaped, which in some species is expanded for sucking purposes 3. Esophagus - a muscular tube that pumps food posteriorly into the intestine; characteristically varies in size, shape and structures which are useful for species identification

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Types of esophagus: Filariform - simple, long and slender; seen in Strongyloides 2 Rhabditiform - divided into distal corpus, an isthmus and and esophageal bulb; seen in 3 Enterobius Spiruroid - anterior portion muscular, posterior glandular; seen in Filarial worms Strongyliform - short, muscular with a waist, seen in Ancylostoma Stichosoma - long, thin, capillary-like lined with esophageal glands cells known as stichocytes or stichosomes seen in Trichuris, Capillaria and Trichinella

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4. Intestine/Midgut – a flattened tube with a wide lumen that follows a straight course from the esophagus to the rectum. This absorbs nutrients and probably plays a role in the excretion of nitrogenous waste products. 5. Rectum Nervous system  The most important commissure is the CIRCUM-ESOPHAGEAL RING COMMISSURE, which constitutes the nerve center.  PAPILLAE are minute inflations of the cuticle, which function as tactile receptors.  The paired minute chemoreceptor organs located in the cephalic or cervical region of all nematodes are known as AMPHIDS.  Pair of minute lateral post anal or caudal chemoreceptor organ present in some specie of nematodes without caudal glands is known as PHASMIDS. Reproductive system  The male reproductive organs are situated in the posterior third of the body as a single coiled or convoluted tube  Accessory copulatory apparatus consists of one or two unsheathed copulatory spicules which are sclerotizations of the cuticle arising from the dorsal wall of cloaca. This spicules maybe short or long and use for attachment of the male to the female during copulation.  In some species, a wing-like appendage or copulatory bursa/bursa copulatrix maybe present. Nematodes spermatozoa are stored in the seminal vesicle. 

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The female reproductive system may either be a single or bifurcated tube, differentiated into ovary, oviduct, seminal receptacle, uterus, ovijector, vagina and a vulva that opens to the exterior. The ovum passes from the ovary into the oviduct (fallopian tube) where it is fertilized. The female adult maybe classified into o oviparous, in which eggs are oviposited and the embryo develops outside the maternal body as in Ascaris, Trichuris o viviparous or larviparous, where the adult female gives birth to a larva as in Trichinella spiralis and Filarial worms o parthenogenetic where the female can produce viable eggs without being fertilized by the male worms as in Strongyloides stercoralis.

Ovum  The daily output of a gravid female may range from 20 to 200,000 eggs.  The egg consists of a multinucleated mass of protoplasm usually containing yolk granules. The egg shell may consist of three layers: o vitelline membrane - formed immediately after sperm penetration;waxy colorless and lipoidal in nature o chorionic or true shell - a secretory product of the egg; chitinous in nature and synthesized from glycogen and ovarian nitrogen o albuminous layer - outermost layer;has a tanning action

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CLASSIFICATION OF MEDICALLY SIGNIFICANT NEMATODES Phylum Nematoda A. Class Enoplea (Class Adenophorea; Class Aphasmidea) - without caudal chemoreceptor organ (phasmids) - provided with caudal glands 1. Species which parasitize the small intestine a. Trichinella spiralis b. Capillaria philippinensis 2. Species which parasitize the large intestine a. Trichuris trichiura B. Class Rhabditea (Class Secernentea; Class Phasmidea) - with caudal chemoreceptor organ (phasmids) - without caudal glands 1. Species which parasitize the small intestine a. Ascaris lumbricoides b. Necator americanus c. Ancylostoma duodenale d. Ancylostoma ceylanicum e. Strongyloides stercoralis 2. Species which parasitize the large intestine a. Enterobius vermicularis 3. Species which parasitize the tissue a. Wuchereria bancrofti b. Brugia malayi 4. Species which cause larva migrans in man a. Ancylostoma braziliense b. Ancylostoma caninum c. Angiostrongylus cantonensis

Ascaris lumbricoides • Most common and largest intestinal nematode of man • Common name: Giant Intestinal Roundworm • The distribution of the parasite is cosmopolitan • Primarily a parasite specific for man • There are two separate populations and reservations of the parasite: one consists of adult parasitizing man and the other of eggs/ova in the environment • Habitat: Small intestine • Infective stage: embryonated egg • Diagnostic stage: fertilized and unfertilized ova Morphology ADULT • Creamy-white or pinkish-yellow when freshly expelled • Female: bigger, tapered at both ends • Male: smaller, curved posteriorly • The anterior end is provided with 3 lips (trilobite) a...