MOD1: Introduction To Parasitology PDF

MICROBIOLOGY 08/20/2024. MOD1: INTRODUCTION TO PARASITOLOGY...

MICROBIOLOGY 08/20/2024. MOD1: INTRODUCTION TO PARASITOLOGY Dr. Genevee Banta Trans Group/s: WH Univ I. MEDICAL PARASITOLOGY Do not penetrate the tissues. Study of parasites that infect humans, and its ability Serve as vectors for other microbes. to cause diseases. If a significant number of ectoparasites are present on Parasitic disease occurs universally, and affects the body surface of a host, it is known as infestation. people’s work productivity, economic statuses and children’s growth, and development. B. ENDOPARASITES People living in poverty are commonly affected. Penetrate the skin and tissues. Mainly live within the body of the host. A health condition due to the invasion of endoparasites RANKING OF HUMAN PARASITIC DISEASES BY is known as infection. DEATHS (2016) 1. OBLIGATE PARASITE Malaria 719,600 Needs a host in order for it to survive and live. Visceral 13,700 leishmaniasis 2. FACULTATIVE PARASITE Can either be attached on a host or be in a free living Schistosomiasis 10,100 state. Chagas disease 7,100 3. ACCIDENTAL PARASITE Ascariasis 4,900 Attach and cause infection to a host other than its usual host. Total for five leading 755,400 causes III. HOST-PARASITE RELATIONSHIP *Note: The deaths are not limited to the infections itself, but also the involvement of other organisms during the infection. A. COMMENSALISM The host and parasite benefit and do not cause any harm to each other. RANKING OF HUMAN PARASITIC DISEASES BY PREVALENCE/INCIDENT B. PARASITISM Ascariasis 800 million prevalent cases (1.3 The parasite is dependent and significantly benefits million DALYs) from its host, while the host is harmed. Hookworm 451 million prevalent cases (1.7 C. SYMBIOSIS million DALYs) The host and parasite need each other in order to live. Trichuriasis 435 million prevalent cases (0.3 IV. TYPES OF HOSTS million DALYs) The organisms from which the parasites are mainly dependent for survival and shelter. Malaria 213 million prevalent cases (56.2 million DALYs) A. DEFINITIVE HOST Where the sexual reproduction of the parasite occurs. Schistosomiasis 190 million prevalent cases (1.9 million DALYs) B. INTERMEDIATE HOST Where the asexual reproduction of the parasite are Total for five leading MORE THAN 2 billion mainly observed. causes prevalent or incident cases (61.4 million DALYs) C. RESERVOIR HOST Harbors the parasite, but do not get infected. Serve as a receptacle or source of the infection. II. TYPES OF PARASITES Parasites are organisms that live in or upon a host in D. PARATENIC HOST which the parasite depends on the host for its Serves as a means of transport for the parasite. nourishment and survival needs. Makes the parasite available for its definitive host. Described as “carrier hosts”. A. ECTOPARASITES The parasite does not undergo any changes or Reside on the body surface growth. Microbiology - Mod 1 Parasitology 1 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  G. lamblia, Cyclospora Small intestine V. MAJOR PARASITIC GROUPS E. histolytica Colon, liver A. PARASITIC PROTOZOA SEXUALLY TRANSMITTED PROTOZOA Under the kingdom Protista Unicellular eukaryotes T. vaginalis Vagina Grouped based on locomotory structures or mode of reproduction BLOOD AND TISSUE FLAGELLATES 1. CLASSIFICATION BASED ON LOCOMOTORY T. brucei Blood, lymph STRUCTURES AND MODE OF REPRODUCTION T. cruzi Intracellular, heart Leishmania species Skin, ulceration CLASSIFICATION BASED ON LOCOMOTORY Mucocutaneous STRUCTURES AND MODE OF REPRODUCTION (depending on the species) Have at least one (1) whip-like TISSUE AMOEBA flagella for movement Some have undulating Naegleria, Brain, spinal cord, eye membrane for movement Acanthamoeba, Free-living organism Balamuthia INTESTINAL AND GENITOURINARY BLOOD AND TISSUE PROTOZOA FLAGELLATES Giardia Plasmodium species Liver, intracellular in RBCs Trichomonas Babesia microti Intracellular in RBCs Toxoplasma gondii Intracellular in CNS BLOOD AND TISSUE FLAGELLATES Trypanosoma (have a flagella B. PARASITIC HELMINTHS: UNDER KINGDOM AND undulating membrane) ANIMALIA Leishmania Causes human infection. Amoeboid-shaped 1. PHYLUM NEMATODES (ROUNDWORMS) Pseudopodia for movement Round appearance in cross-section and Change of shape to unsegmented. capture/take-up food Elongated worms with tapering on each end of its Found in water length. AMOEBA Examples: Moves in whiplike manner using its longitudinal ○ Entamoeba muscles. ○ Naegleria Has a complete digestive system ○ Acanthamoeba Adult worm: diecious (bisexual) ○ Balamuthia Has ability to molt or shed its tough cuticles in order to change from larval stage into its adult form. Complex protozoa The eggs and larval stages have the ability to adapt Cilia for movement and nutrition and withstand the external environment. Appears in rows or patches Humans acquire the infection commonly through CILIATE Examples: ingestion of the egg or larval stage, skin ○ Balantidium coli: found in penetration, and insect vectors due to its presence in pigs; ONLY known ciliate to the environment. cause infection in humans ○ Specific mode of transmission vary depending on the nematode species. Has spore-like stage in their life Life cycle: 1 host (human) except filarial worms (e.g. cycle with alternating sexual and Wuchereria, Brugia, Loa loa, Onchocerca) because they asexual reproductive phases require definitive and intermediate hosts in the life cycle. Intracellular parasites ○ Humans are definitive hosts of filarial worms. Described based on its mode of ○ Mosquitoes are a common intermediate host of SPOROZOA reproduction filarial worms. Examples: ○ Plasmodium ○ Toxoplasma ○ Cryptosporidium ○ Cyclospora 2. SITE OF INFECTION OF DIFFERENT PARASITIC PROTOZOA PARASITE SITE OF INFECTION Nematode. INTESTINAL PROTOZOA Microbiology - Mod 1 Parasitology 2 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited. 2. PHYLUM PLATYHELMINTHES (FLATWORMS) Therefore, do not have a metacercariae Dorsoventrally flattened appearance in cross section. stage. Instead, it spreads through skin Hermaphrodites: they have both male and female penetration of cercariae. reproductive system in its adult stage ○ Diecious sexes Platyhelminthes. 2.1 CLASS TREMATODA “Flukes” Flat and leaf-shape 2 muscular suckers but NO hooklets Incomplete alimentary canal Bifurcated gut with circular and longitudinal muscle Syncytial epithelium (like nematodes) Most are hermaphrodite (except Schistosoma) ○ Schistosoma or blood flukes have a male and Life Cycle of Trematodes. female adult worms that are seen in union with each other within the small blood vessels. In general, trematodes have one (1) definitive host and two (2) intermediate hosts in its life cycle: ○ Definitive host: human ○ First intermediate host: freshwater snail or mollusk ○ Second intermediate host: aquatic plant, fish, or crab The cercarial stage develops within the first intermediate host. The metacercarial stage develops in the 2nd intermediate host. 2.2 CLASS CESTODA “Tapeworms” Flat and ribbon-like segments Mainly absorbs nutrients using its integument Does NOT have a mouth, gut, or alimentary canal. Anatomy of Trematodes. PARTS OF A CESTODE 2.1.1 LIFE CYCLE OF TREMATODA Located on anterior end Contains muscular suckers and Scolex hooks that aid in attachment to the LIFE CYCLE OF TREMATODA intestinal wall. 1 Eggs are released into freshwater via urine or Segment-containing reproductive feces. structures Proglottids Hundreds of segments with 2 In the environment, the miracidium will be released thousands of eggs per segment. & from the egg and will infect a snail, the first 3 intermediate host. 4 Within the intermediate host, the miracidium undergoes changes until it becomes a cercariae. 5 The cercariae is released from the snail and will enter the 2nd intermediate host (crustacean) and encyst into metacercariae. 6 Most human infections caused by flukes is through ingestion of 2nd intermediate host containing the metacercariae (except for Schistosoma species). Recall: Schistosoma species only have one (1) Parts of a Cestode. definitive host and one (1) intermediate host. Microbiology - Mod 1 Parasitology 3 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited. 2.2.1 DIFFERENT CLASSIFICATION OF CESTODE Fasciolopsis buski Small Intestine Heterophyes species ORDER FAMILY GENUS Metagonimus species Pseudophyllidea Diphyllobothriidae Diphyllobothrium Paragonimus Lungs westermani Cyclophyllidea Taeniidae Taenia Echinococcus Cestodes Diphyllobothrium Intestine Taenia species Hymenolepididae Hymenolepis Hymenolepis Dipylidium Dipylidiidae Dipylidium Cysticercus cellulosae Human (Taenia solium) muscles/organ 2.2.2 LIFE CYCLE OF CESTODE Echinococcus Most require one (1) definitive and one (1) intermediate host to complete its life cycle. ○ Intermediate host: egg > larvae Common denominator among the three is the intestine ○ Definitive host: larvae > adult as the common habitat for most parasites. ○ Cestodes such Taenia solium and Taenia saginata consider humans as their ONLY definitive host. 2.4 LIFE CYCLES Hymenolepis only need one host. Diphyllobothrium requires one definitive host and two intermediate hosts (crustacean and fish). DIRECT LIFE CYCLE INDIRECT LIFE CYCLE Simple life cycle “Complex” life cycle LIFE CYCLE OF CESTODES Requires a single Requires definitive host in the life cycle. and intermediate 1 Starts with excretion of parasitic egg via the feces, host. which will be ingested by the intermediate host. Trematodes and cestodes have 2 The larval stage will develop within the intermediate indirect or complete host. life cycles. 3 This larvae will be taken up by humans and will Some of the parasitic helminths may require three develop into adult worms in their intestines. hosts pertaining to one definitive host and two intermediate hosts. 3. HABITATS OF CESTODES, TREMATODES, AND NEMATODES PARASITES HABITAT Nematodes Ascaris lumbricoides Small intestine Ancylostoma duodenale Necator americanus Trichuris trichiura Large intestine Enterobius vermicularis Capillaria philippinensis Intestines Direct & Indirect Life Cycles. Wuchereria bancrofti Lymphatics Brugia malayi II. PATHOGENESIS OF PARASITIC DISEASE Brugia Timori After the parasite enters the body, it damages the organs through: Loa loa Eye and skin ○ Mechanical trauma Onchocerca ○ Inflammatory reactions ○ Allergic manifestation Trematodes S. haematobium Venous plexus ○ Form space-occupying lesions S. Mansoni, S. of bladder ○ Neoplasia Japonicum Portal venous plexus A. MECHANICAL TRAUMA Occur when trematode eggs deposit in the organ Fasciola hepatica Liver mucosa, causing irritation as the eggs accumulate. Fasciola gigantica Examples: ○ Schistosoma mansoni eggs into intestinal mucosa ○ Schistosoma hematobium eggs into the bladder Clonorchis species Bile duct ○ Paragonimus eggs into the lungs Opisthorchis species Microbiology - Mod 1 Parasitology 4 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  ○ Larvae of hookworms and ascaris reach the pulmonary capillaries, causing traumatic injury, PERIODICITY DEPENDING ON PARASITE triggering inflammation or allergic manifestations. Adult worms of hookworms, ascaris, and taenia Diurnal/Mid 10 AM to 2 PM Loa loa species may also cause mechanical trauma when they day adhere to the intestinal wall. ○ When these take advantage of the host Nocturnal/ After 8 PM (from Brugia environment to support its survival needs, it causes Night time 9 PM to 2 AM) Wuchereria bancrofti trauma to its host. Anytime of the Onchocerca Nonperiodic B. SPACE-OCCUPYING LESIONS day Mansonella Cystic lesions are formed as parasites embed into the tissue and compress the surrounding tissues 2. SPECIMEN May appear as a mass or tumor-like lesions in the organ Specimen of choice will depend on the site of infection of the parasite. C. NEOPLASIA History and presentation of the patient will be the guide Some parasites may all also cause neoplasia or in determining the possible parasitic infection and cancer. identifying the specimen of choice. Examples: ○ Schistosoma hematobium → bladder carcinoma SPECIMEN ○ Clonorchis and Opisthorchis → SITE OF OF SPECIES cholangiocarcinoma INFECTION CHOICE III. SUMMARY Red blood Plasmodium spp. Parasites are organisms that are dependent on the host Blood cells Babesia spp. for its survival The response of the host will depend on its relationship Giardia with the parasite Ascaris Parasitism: a relationship in which the parasite benefits Stool Intestine Entamoeba histolytica from the host and also causes harm to it Other soil-transmitted Parasites are divided into protozoa and helminths helminths ○ Protozoa: classified based on their means of locomotion Bladder Schistosoma ○ Helminths: divided into nematodes and Urine haematobium platyhelminthes Nematodes: elongated, cylindrical, and Not Genitourinary unsegmented Trichomonas vaginalis mentioned organ Platyhelminthes: classified into trematodes and cestodes Requested in ○ The types of helminths differ in their morphological patients with Acanthamoeba structure, developmental stages, and life cycle. CSF CNS Naegleria fowleri manifestations PART 2 I. LABORATORY DIAGNOSIS B. PARASITOLOGIC DIAGNOSTIC TESTS Macroscopic and microscopic examinations of A. SPECIMEN COLLECTION specimens are easily done in the laboratory. There are different tests for the diagnosis of different parasitic infections. 1. MACROSCOPIC EXAMINATION OF SPECIMEN History and physical examination should always be Observation done using the naked eye. considered when collecting the specimen. Examiner should observe for: The specimens should be collected and assessed ○ Consistency of the stool before initiating any treatment. ○ Detection of adult worms ○ Color of the stool 1. PERIODICITY ○ Presence of other materials in the stool There are parasites that follow a regular pattern or cyclic pattern for its easy detection in the blood. 1.1 CONSISTENCY OF THE STOOL It is the time when most of the microfilariae are Refers to a formed, soft, or liquid stool. detected in the blood. The consistency is necessary for the parasite to be May help determine the best time to collect the blood actively motile and in the detection of egg sample. concentration. Not always a concern since there is non-periodic Trophozoites of protozoa are actively motile in a liquid detection of parasites (Onchocerca and Mansonella). stool due to the presence of locomotory structure. ○ No specific periodicity Cryptosporidium eggs are also detected in liquid stool. T. vaginalis can be detected from urine samples or samples from a genital swab (WHO). 1.2 DETECTION OF ADULT WORMS Microfilaria is most likely detected microscopically The presence of adult stages of pinworms and Ascaris when the blood is collected in: lumbricoides should also be checked. Microbiology - Mod 1 Parasitology 5 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  2.5 BLOOD FILM EXAMINATION/COMPLETE BLOOD 1.3 COLOR COUNT Will determine if there is minimal bleeding or not. Helps in identifying parasites in the blood. Plasmodium and Babiesia species infect the red GI BLEEDING blood cells. Other parasites infect the white blood cells. Dark stool Upper GIT 2.6 SKIN MUSCLE/MASS BIOPSY Fresh/Bright red blood Lower GIT Done to individuals with nodules or mass-like lesions. The developmental stage that will be detected in the 1.4 PRESENCE OF OTHER MATERIALS biopsy may vary depending on the pathogen. Presence of other materials in the stool such as mucus should also be checked. C. CULTURE Soft or liquid stool with blood and mucus is suggestive of an infection caused by Entamoeba 1. XENIC histolytica, known as amoebiasis. Type of culture where the parasites are grown in the 2. MICROSCOPIC EXAMINATION OF SPECIMEN presence of an unknown microbiota. Observation of the characteristics of an organism using 2. AXENIC the microscope. Parasitic infection does not only demonstrate A pure culture in which no bacteria are present during eosinophilia but there are also other parasites that can the cultivation process. damage RBCs. The bacteria serves as the food for the parasites during the cultivation process. 2.1 DIRECT WET SMEAR/DIRECT WET MOUNT Done in the isolation of Leishmania species and Trypanosoma cruzi. Best used to observe the motile trophozoite stage of Few clinical laboratories offer the needed environment protozoa. for the cultivation of parasites (limitation), preventing its use as a routine diagnostic test. 2.2 FECAL CONCENTRATION TECHNIQUE More likely to detect helminth eggs, larvae, protozoan HARADA-MORI FILTER PAPER STRIP CULTURE cysts, and coccygeal cysts. E.g., Sedimentation and Flotation Detects light infections of Strongyloides stercoralis and ○ Mainly separate the protozoa and helminth eggs hookworm larval stages. and larva from the fecal debris through centrifugation. 1 A small amount of fresh stool is smeared into the filter paper and placed into a test tube. 2.3 KATO-KATZ METHOD 2 A small concentration of water is present in the The recommended method in estimating the parasitic tube where the filter paper has been placed. burden in a body of a human host. Helps quantify the soil-transmitted helminth eggs that are detected in the stool (e.g., Ascaris, 3 The fluid from the bottom of the tube is smeared hookworm, Schistosoma mansoni, and Trichuris and examined after a few days. species). 4 If the larvae of Strongyloides stercoralis or the hookworm are detected, this signifies that the stool specimen has the parasite and the patient has the parasitic infection. D. ANTIBODY DETECTION Can be requested if the standard diagnostic test is cost-effective or is not sufficient enough to confirm the diagnosis. Serum or CSF sample is the specimen of choices Kato-Katz method. depending on the patient’s presentation. In interpreting antibody test results, the examiner should 2.4 SCOTCH TAPE/CELLULOSE TAPE TEST also consider the location where the patient lives or if there is exposure to a pathogen. Most widely used in the detection of pinworm or A person with a positive test result does not always Enterobius vermicularis. mean that the patient has a recent infection. The best timing to collect the specimen for this test is ○ If a patient lives in an endemic area and has early in the morning before bathing or washing elevated antibodies against the pathogen, it because the female worm usually travels into the anus does NOT necessarily signify that they are having during the night and lays their eggs there. recent infection since a continuous exposure to the Commonly, children complain of intense itchiness at pathogen may have already activated his immune night due to the laying of eggs of these female system and have produced antibodies for some roundworms. time now. Microbiology - Mod 1 Parasitology 6 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  ○ If a patient who does not live in an endemic area has tested positive for a certain infectious disease, they can be diagnosed to have a recent infection. Their clinical presentation and positive antibody tests are clinically relevant due to their recent exposure. E. ANTIGEN DETECTION Used in identifying the presence of an antigen or antigenic components in the specimen. E.g., Immunochromatographic assay test, Enzyme-linked Immunosorbent Assay (ELISA) test. DISADVANTAGES: ○ Cannot differentiate if the patient is having active or inactive infection since it may still detect traces of dead parasites in the blood or antigenic components. ○ Sensitivity and specificity may vary, depending on the pathogen. ○ The use of antibody and antigen detection tests in diagnosing parasitic infections will also depend on its availability. 1. MOLECULAR TECHNIQUE Another test that may be requested. Commonly detects the presence of pathogens’ nucleic acid sequences and its amplification if a certain pathogen is present in the specimen. E.g., Polymerase Chain Reaction (PCR) II. SUMMARY Laboratory diagnosis is necessary in confirming a parasitic infection. The best timing to collect the specimen is before giving any medications. Macroscopic and microscopic examinations of the specimen, culture, antibody and antigen detection tests are all useful in the diagnosis of any parasitic infection. Microbiology - Mod 1 Parasitology 7 of 7 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.