Parasitology 2025 PhD 221 PDF

Parasitology 2025 Reference: 1. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology / Larry S. Roberts, John Janovy, Jr. - 8th Ed.  Objectives Classifications of human and animal parasites  Morphology and life cycles  Paras...

Parasitology 2025 Reference: 1. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology / Larry S. Roberts, John Janovy, Jr. - 8th Ed.  Objectives Classifications of human and animal parasites  Morphology and life cycles  Parasite infectious to humans 3  Content Introduction and definitons of key terms ✓ Classification ✓ Protozoans - ✓ General characteristics & Morphology ✓ Various classifications & Specific examples of public health importance with their resulting diseases 4  Content Helminths – ✓ General characteristics & Morphology ✓ Various classifications & Specific examples of public health importance with their resulting diseases 5  Learning outcomes Describe the two main groups of organisms classified as human parasites ✓ State their general characteristics & know their perculiar morphologies ✓ State specific examples of parasites belonging to each classification ✓ Explain the life cycle of specific parasites of public health importance 6  Learning outcomes ✓ Know / predict how the transmission of these parasites can be prevented based on their life cycles ✓ Describe briefly, diseases caused by these parasites ✓ Appreciate the importance of knowing the life cycle of these parasites with regards to their treatment 7 Introduction What is parasitology? Study of parasites, their hosts and the association between them. 8  Key terms Parasites  A living organism which receives nourishment and shelter and is entirely dependent on another organism (host), for all or part of its life cycle and metabolic requirements.  May not necessarily cause disease.  The parasite derives all benefits from the association and the host may not be harmed or may suffer the consequences of this association, a parasitic disease. 9  Key terms  Host: an organism which harbors the parasite.  Vector: a living carrier that transports a pathogenic organism from an infected to a non-infected host. A typical example female Anopheles mosquito and Tsetse fly. Malaria Sleeping sickness 10  Key terms Temporary parasite: Visits its host for a short period. Permanent parasite: Leads a parasitic life throughout the whole period of its life. Facultative parasite: Lives a parasitic life when the opportunity arises. Obligatory parasite: Cannot exist without the parasitic life. Occasional or accidental parasite: Attacks an unusual host. Ecto-parasite (ectozoa): Lives outside on the surface of the body of the host. Eg. Endo-parasite (entozoa): Lives inside the body of the host, in the blood, tissues, body cavities, digestive tract and other organs. Eg. 11  Key terms Macroscopic parasites: eg. worms & arthropods. ✓ Large enough to be seen with naked eyes. ✓ They do not often multiply in or on a host. ✓ The level of infection depends on the initial number of organisms that entered the body. ✓ One infectious stage matures into one reproductive stage. ✓They occur in aggregated or clumped population NB: These have important clinical implications. 12  Key terms Microscopic parasites: Eg. bacteria, viruses, protozoa and fungi. ✓ Some are small enough to grow intracellularly. ✓ They replicate within the host to produce large numbers of progeny and hence cause overwhelming infection. 13  Key terms Intracellular parasites: ✓ Parasites within the cell (intracellular) protected from many of the host defense mechanisms. ✓ These parasites are difficult to treat because of the non-selective action of antibiotics. ✓ This is the case of the HIV virus which grows specifically within the lymphocytes. 14  Key terms Intracellular parasites: ✓ Plasmodium is an intracellular parasite of hepatocytes and erythrocytes ✓ Some of these intracellular parasites, such as viruses take over the host cellular machinery to reproduce themselves. ✓ Others meet their metabolic requirements directly from within the cell. 15  Key terms Extracellular parasites ✓ Extracellular parasites do not invade cells. They rather proliferate in the extracellular environment which is enriched with body fluids. Eg. Trypanosoma spp. ✓ Some of the extracellular bacteria even don’t penetrate body tissues (e.g. V. cholerae) but adhere to epithelial surfaces and cause disease by secreting potent toxins. 16  Classification Human parasites can be divided into two groups: Protozoans – microscopic, unicellular eukaryotes. Eg: Plasmodium spp, Leishmania spp, Entamoeba and Giardia spp. Helminths – macroscopic, multicellular worms ✓ Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa. Eg Schistosoma spp, Wuchereria bancrofti, Necator americanus (hookworm) and Taenia spp. (tapeworm). ✓ Group 17 them into cestode, trematode nematodes  Protozoa 18  Sub Phylum Genus- examples Species- examples Major diseases kingdom Protozoa Sarcomastig- Entamoeba E. Histolytica Amoebiasis ophora further divided Trypanosoma T. Brucei Sleeping sickness into sarcodina T. cruzi Chagas disease A and mastigophora Trichomonas T. vaginalis Vaginitis n Leishmania L. donovani infantum Visceral, cutaneous i Have organelles L. donovani chagasi and mucocutaneous for locomotion. Giardia G. Lamblia Giardiasis m Apicomplexa Plasmodium P. falciparum, Malaria a Divided into P. vivax, l sporozoa, P. malariae, coccidia and P. Ovale i haematozoa P. knowlesi No organelle of a Locomotion. Toxoplasma T. Gondii Toxoplasmosis Isospora Isospora belli Isosporiasis Ciliophora Balantidium B. coli Dysentry move by cillia Microspora Enterocyto-zoa E. bienusi Diarhoea 19 Spore-forming  Protozoa  On the basis of their microscopic morphology, the protozoa are currently classified into six phyla.  Most species causing human disease are members of the phyla Sacromastigophora and Apicomplexa.  Most protozoan infections are acquired through ingestion of contaminated water / food or via insect vectors 20  Protozoa  Protozoans are eukaryotic, mostly unicellular microorganisms ranging from 2 to 100 nm.  Many protozoa are free-living motile organisms that occur in water and soil  Some are parasites of plants and animals, including humans. 21  Protozoans  Protozoans may be intracellular parasites (in cells of the brain, RBC, muscle etc. ) and  extracellular parasite (in the blood, intestines and genitouriniary system).  Of all the protozoan parasites, malaria presents the biggest and most severe global problem and kills >400000??? people per annum. 22  Protozoa - morphology Unicellular A single cell performs all the functions of reproduction, digestion, respiration, excretion etc. Morphology The protozoal cell is composed of: 1. Cytoplasmic body 2. Nucleus 23  Protozoa - morphology Cytoplasm: Cytoplasm consist of two portions Ectoplasm: This is the external hyaline portion; its function are sensory, protective and locomotive. Endoplasm: the internal granular portion; its function is nutritive and reproductive. 24  Protozoa - morphology The protozoal parasites may exist in two stages: trophozoite and cyst. The protozoal parasite possesses the property of being transformed from an active trophozoite (feeds, grows and reproduces) to an inactive stage, losing its power of motility and enclosing itself within a tough wall (encystment). 25  Protozoa - morphology  At cyst stage, the parasite loses its power of growth and multiplication.  The cyst is the resistant stage of the parasite and is also infective to its human host.  In order to reach a new host, it must be transferred mechanically, either by a carrier or by some intermediaries (insect-house flies) or 27  Protozoa-transmission Through food and drink which become contaminated with the cysts of protozoa. A protozoal parasite may multiply vigorously by asexual method and by a change of process have recourse to sexual reproduction. 28  Protozoa The sexual method of reproduction often occurs in a different host other than the one utilized for asexual multiplication; ✓ this process is known as alternation of generation ✓ This has been observed in the plasmodium and Trypanosoma spp 29  Protozoa - Life cycle A protozoal parasite may pass its life cycle in one or two hosts. Primary host and Secondary host required: Egs. are Trypanosoma, Leishmania and Plasmodia. In Trypanosoma, Leishmania and Plasmodia all require two hosts ie definitive and intermediate hosts 30  Protozoa - Life cycle Second host not required: Egs. rhizopodea, intestinal flagellates, ciliates, amoeba. ✓ This group adapts themselves for passive transfer from one host to another by encystment. ✓ They multiply asexually in trophic stage and in circumstances unfavorable for existence, secretes a gastric juice resistant cyst membrane/wall, transforming themselves into a cyst for protection. 31  What are the features of protozoa ?  Sarcodina 33  Sub Phylum Genus- examples Species- examples Major diseases kingdom Protozoa Sarcomastig- Entamoeba E. Histolytica Amoebiasis ophora further divided Trypanosoma T. Brucei Sleeping sickness into sarcodina T. cruzi Chagas disease A and mastigophora Trichomonas T. vaginalis Vaginitis n Leishmania L. donovani infantum Visceral, cutaneous i Have organelles L. donovani chagasi and mucocutaneous for locomotion. Giardia G. Lamblia Giardiasis m Apicomplexa Plasmodium P. falciparum, Malaria a Divided into P. vivax, l sporozoa, P. malariae, coccidia and P. Ovale i haematozoa P. knowlesi No organelle of a Locomotion. Toxoplasma T. Gondii Toxoplasmosis Isospora Isospora belli Isosporiasis Ciliophora Balantidium B. coli Dysentry move by cillia Microspora Enterocyto-zoa E. bienusi Diarhoea 34 Spore-forming  1a. Sarcodina Sarcodines include the genus Amoeba Sarcodines have cells that are either spherical or irregular in shape and form. The pellicles, or envelopes, of their cells are generally soft, transparent and flexible.  Some Sarcodines have external shells or skeletons; have cytoplasm made up of ectoplasm & endoplasm, May have multiple nuclei. 35  1a. Sarcodina These organisms obtain energy by consuming food particles and organic matter. Sarcodines generally eat by trapping food particles and substances with their pseudopods then carrying out digestion in the food vacuoles. They move by pushing out the ectoplasm to form pseudopodia. 36  1a. Sarcodina Sarcodines reproduce sexually by syngamy (fusion of two gametes) and asexually by division or budding This group includes Entamoeba, Endolimax, Iodamoeba, Naegleria, Acanthamoeba* etc. 37  Amoebiasis 38  Amoebiasis Amoebiasis is commonly caused by Entamoeba histolytica.  Other amoebae infecting humans include Dientamoeba fragilis, which causes dientamoebiasis.  The symptoms of amebiasis include loose stool, abdominal cramping, and stomach pain.  However, most people with amebiasis won’t experience significant symptoms. 39  Amoebiasis  Infection occurs usually ✓ in the large intestines ✓ and causes internal inflammation as its ✓ name ‘histolytica’ suggests (tissue - destroying). ✓ 50 million people are infected worldwide, mostly in tropical countries in areas of poor 40 sanitation.  Amoebiasis ✓ In industrialized countries, most of the infected patients are immigrants, institutionalized people and those who have recently visited developing countries. 41  Amoebiasis  Inside humans, Entamoeba histolytica lives and multiplies as a trophozoite.  Trophozoites are oblong and about 15-20 µm in length.  To infect other humans, the trophozoites encyst & leave the body.  Mature cysts are passed in the faeces of an infected human.  Another human can get infected by ingesting faecally contaminated water, food or hands.  If the cysts survive the acidic stomach, they transform back into trophozoites in the small intestine.  Trophozoites migrate to the large intestine where they live and multiply by binary fission.  The life cycle of Entamoeba histolytica does not require any intermediate host. 42  Amoebiasis  NB: Both cysts and trophozoites are sometimes present in the faeces.  Cysts are usually found in firm stools, whereas trophozoites are found in loose stools.  Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans.  If trophozoites are ingested, they are killed by the gastric acid of the stomach. 43  Mastigophora 44  Sub Phylum Genus- Species- examples Major diseases kingdom examples Protozoa Sarcomastig- Entamoeba E. Histolytica Amoebiasis ophora further divided Trypanoso T. Brucei Sleeping sickness into sarcodina ma T. cruzi Chagas disease and mastigophora Trichomona T. vaginalis Vaginitis s Have organelles for locomotion. Leishmania L. donovani infantum Visceral, cutaneous and L. donovani chagasi mucocutaneous Giardia G. Lamblia Giardiasis Apicomplexa Plasmodiu P. falciparum, Malaria Divided into m P. vivax, sporozoa, P. malariae, coccidia and P. ovale haematozoa No organelle of Toxoplasma T. Gondii Toxoplasmosis Locomotion. Isospora Isospora belli Isosporiasis Ciliophora Balantidium B. coli Dysentry 45 move by cillia Microspora Enterocyto- E. bienusi Diarhoea  1a. Mastigophora These are flagellates They have one or more whip like flagella for locomotion at some stage of their life cycle. Eg Trypanosoma* The mastigophora includes ✓ the intestinal and genitourinary flagellates ✓ and the blood and tissue flagellates.  The intestinal and genitourinary flagellates are Giardia, Trichomonas etc.  The blood and tissue flagellates are Trypanosoma, Leishmania etc. 46  Trypanosomiasis 47  Trypanosoma  Caused by two varieties of Trypanosoma brucei gambiense & Trypanosoma brucei rhodesiense.  Trypanosoma brucei is transmitted by the tsetse fly.  Less than 1 % of tsetse flies carry the parasite.  Trypanosoma brucei rhodesiense causes East African trypanosomiasis.  T. b. rhodesiense causes 1000 new infections annually. 48  Trypanosoma - Sleeping Sickness  Trypanosoma brucei gambiense causes West African trypanosomiasis (Gambian sleeping sickness).  More than 12 x103 new infections are reported to the WHO annually.  The two subspecies do not overlap in geographic distribution.  A third member of the complex, T. b. brucei, does not infect humans under normal conditions. 49  Trypanosoma  Humans are the main reservoir for Trypanosoma brucei gambiense, but this species can also be found in animals.  Wild game animals are the main reservoir of T. b. rhodesiense. 50  Trypanosoma  T.b. rhodesiense found in eastern and southeastern Africa.  Over 95 % of the T. b. rhodesiense infections occur in Malawi, Tanzania, Uganda, and Zambia. 51  Trypanosoma  T. b. gambiense is found predominately in Central Africa and in some areas of West Africa.  Over 95 % of the T.b. gambiense infections occur in Angola, Central African Republic, Chad, northern Uganda, Sudan, Republic of the Congo and Democratic Republic of the Congo. 52  Trypanosoma  Trypanosoma brucei evades the immune system because it has a variant surface glycoprotein (VSG) coating.  The coating makes its cell membrane very thick and hard to recognize.  In the first stage of the disease, there are fevers, headaches, itching and joint pains.  Weeks to months later, the second stage begins with confusion, poor coordination, numbness and trouble sleeping. 53 Life cycle of trypanosoma  54  Trypanosoma  During a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue.  The parasites enter the lymphatic system and passes into the bloodstream.  Inside the host, they transform into bloodstream trypomastigotes, which are carried throughout the body to other sites and body fluids (e.g., lymph, spinal fluid) and they continue replication by binary fission. 56  Trypanosomaiasis  The entire life cycle of African Trypanosomes is represented by extracellular stages.  The tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood mea from an infected mammalian host.  In the fly’s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission, leave the midgut, and transform into epimastigotes. 57  Trypanosoma  The epimastigotes reach the salivary glands of the fly and continue multiplication by binary fission.  The cycle in the fly takes approximately 3 weeks.  Infective metacyclic trypomastigotes are deposited on human skin when the tsetse fly takes a blood meal. Trypomastigotes invade cells, where they reproduce asexually as amastigotes. Amastigotes are released when the cell dies. 58  Trypanosoma  Some will infect other cells and continue the amastigote reproductive cycle, while others will circulate in the blood, where they develop into nondividing trypomastigotes. 59  Food for thaught  What are the causative organisms for trypanosomiasis?  What are the symptoms of trypanosomiasis?  Can trypanosomiasis be prevented? Why? 60  Trichomoniasis 61  Trichomonas vaginalis  Trichomonas vaginalis is an anaerobic, flagellated protozoan parasite and causes genitourinary infection - trichomoniasis.  Trichomonas vaginalis is the most common pathogenic protozoan infection of humans in industrialized countries.  Infection rates between men and women are similar, with women being symptomatic. 62  Trichomonas vaginalis  Trichomoniasis, is a sexually transmitted infection of the urogenital tract.  Is a common cause of vaginitis in women, while men with this infection can display symptoms of urethritis.  Frothy, greenish vaginal discharge with a 'musty' malodorous smell is a characteristic of this infection. 63  Trichomonas vaginalis  Transmission usually occurs via direct, skin-to-skin contact with an infected individual, most often through vaginal intercourse.  The WHO has estimated that 160 million infections are acquired annually worldwide 64 65  Apicomplexa 66  Sub Phylum Genus- Species- examples Major diseases kingdom examples Protozoa Sarcomastig- Entamoeba E. Histolytica Amoebiasis ophora further divided Trypanoso T. Brucei Sleeping sickness into sarcodina ma T. cruzi Chagas disease and mastigophora Trichomona T. vaginalis Vaginitis s Have organelles for locomotion. Leishmania L. donovani infantum Visceral, cutaneous and L. donovani chagasi mucocutaneous Giardia G. Lamblia Giardiasis Apicomplexa Plasmodiu P. falciparum, Malaria Divided into m P. vivax, sporozoa, P. malariae, coccidia and P. ovale haematozoa No organelle of Toxoplasma T. Gondii Toxoplasmosis Locomotion. Isospora Isospora belli Isosporiasis Ciliophora Balantidium B. coli Dysentry 67 move by cillia Microspora Enterocyto- E. bienusi Diarhoea  3. Apicomplexa  They are a large group of parasites with most possessing a unique form of organelle that comprises  A type of plastid called an apicoplast, and an apical complex structure. 68  3. Apicomplexa The apicoplast organelle is an adaptation that the organism applies in penetration of a host cell. All apicomplexans are intracellular parasites at some stage in their life cycle 69  3. Apicomplexa Members of this super-class exhibit complex life cycles with alternating sexual and asexual reproductive phases in two different hosts. Class Coccidia includes Isospora and Toxoplasma. Class Haematozoa includes the malarial parasites- Plasmodium. 70  3. Apicomplexa  Isospora is responsible for the condition isosporiasis, which causes acute, non-bloody diarrhoea in immunocompromised individuals.  Toxoplasmosis is caused by Toxoplasma gondii. ✓ It causes symptoms similar to those of the flu, including: general body aches, headache, fever and fatigue. ✓ The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid (cat) family. 71  Plasmodia 72  Plasmodium falciparum - Malaria  Plasmodium falciparum is the Plasmodium species responsible for 85 % of the malaria cases.  The three less common and less dangerous Plasmodium species are: P. ovale, P. malariae and P. vivax. 73  Plasmodium falciparum - Malaria  Malaria infects over 200 million people annually, mostly in poor tropical and subtropical countries of Africa. It is the deadliest parasitic disease killing over one million people each year.  90 % of the deaths occur south of the Sahara desert and most are under five-year-old. 74  Plasmodium falciparum - Malaria  In addition to Africa, malaria occurs in South and Southeast Asia, Central and South America, the Caribbean and the Middle East.  Even within tropical and subtropical areas, malaria does not usually occur at high altitudes (over 1500 meters), during colder seasons, in countries of successful malaria programs or in deserts. 75  Plasmodium falciparum - Malaria  The vector of the parasite is the female Anopheles mosquito.  Of the over 400 Anopheles species, only 30–40 can transmit malaria.  The infection starts, when a female mosquito injects sporozoites in her saliva into human skin while taking a blood meal. 76  Plasmodium falciparum - Malaria  A sporozoite travels in the bloodstream and invades the liver cells.  It matures into a schizont (mother cell) which produces merozoites within six days.  The merozoites are released into blood stream  Merozoites invade red blood cells, transform into ring stage, trophozoite and then schizont that burst to release more merozoites that invade new erythrocytes. 77  Plasmodium falciparum - Malaria  P. falciparum can prevent an infected red cell from going to the spleen by forming adhesive proteins to the cell membrane of the red cell.  The proteins make the infected RBC to adhere (stick) to the walls of small blood vessel ie. cytoadhesion.  The cytoadhesion leading to parasite sequestration RBC might microvessel, especially in the brain to create a more serious problem. 78  Plasmodium falciparum - Malaria  Some merozoites develop into gametocytes, which is infective to a mosquito.  They are ingested by a mosquito, when it takes a blood meal.  Inside the mosquito's midgut, microgamete (male) and macrogamete (female) fuse into zygotes which then develop into ookinetes. 79  Plasmodium falciparum - Malaria  The motile ookinetes penetrate the midgut wall and develop into oocysts.  The cysts eventually release sporozoites, which migrate into the salivary glands to be injected into a vertebrate host (humans).  The development inside a mosquito takes about two weeks and only after that time can the mosquito transmit the disease.  P. falciparum cannot complete its life cycle at temperatures below 20 °C. 80  81  4. Ciliophora These are the complex protozoa bearing cilia distributed in rows or patches by which they move. They have two kinds of nuclei (macronucleus and micronucleus) and a large contractile vacoule.  The most prominent example of the group is Balantidium coli*, a giant intestinal ciliate of humans and82pigs. 4. Ciliophora  These parasites can be transmitted via the fecal-oral route by contaminated food and water.  Balantidium coli infection is mostly asymptomatic,  but people with other serious illnesses can experience persistent diarrhea, abdominal pain, and sometimes a perforated colon. 4. Ciliophora  Helminths 85  Helminths A term used for all parasitc worms. Many helminths live in the intestines while others live in deeper tissues. Almost all organs can be parasitized. Majority of helminths do not replicate within the host. Thou certain tapeworms can reproduce asexually within the host.  In most worms, sexual reproduction results in the production of eggs which are released from the host in faecal matter 86 or urine.  Helminths Infection can occur mainly through Ingestion of larvae and infective eggs via faeco- oral transmission. Swallowing infective larvae from the tissue of a host Active penetration of the skin Bite of infected blood sucking vector 87 Classification of Parasitic Helminths Sub Phylum Class Genus – examples kingdom Metazoa A. Nematodes (round Ascaris (roundworm) worms) Trichuris (whipworm) These worms appear round Ancylostoma (hookworm) in cross section, they have Necator (hookworm) body cavities, a straight alimentary canal and an Enterobius (pinworm or anus. threadworm) Strongyloides (roundworm) B. Platyhelminthes (Flat worms) Cestodes (Tape worm) Taenia (tapeworm) These worms are have Adult tapeworms are found in the Taenia solium flattened dorsoventrally intestine of their host Taenia saginata flattened, no body cavity They have a head (scolex) with and, if present, the sucking organs, a segmented body alimentary canal is blind but no alimentary canal ending Each body segment is hermaphrodite Trematodes (Flukes) Non-segmented, usually leaf-shaped, with two suckers but no distinct head Fasciolopsis (liver fluke) They have an alimentary canal and Schistosoma are usually hermaphrodite and leaf shaped Schistosomes are the exception. They 88 are thread-like, and have separate sexes  Nematodes 89  Nemathelminthes (round worms)  Their body is elongated, cylindrical and unsegmented.  Sexes are separate (diecious).  They also lack hooks and suckers.  They possess a complete Ascaris lumbricoides - giant roundworm. alimentary canal and body cavity. 90  Ascaris lumbricoides 91 Ascaris lumbricoides - giant roundworm  Is the largest and most common parasitic worm in humans.  Infection occurs when a person ingests ascaris eggs which may have contaminated soil from faeces.  It is estimated that about 25 % of humans are infected with ascariasis.  Ascariasis occurs worldwide, mostly in tropical and subtropical countries. 92 Ascaris lumbricoides - giant roundworm  It has highest prevalence in areas of poor sanitation and where human faeces are used as fertilizer.  The life cycle of Ascaris lumbricoides takes about 3 months.  Ascariasis starts, when Ascaris lumbricoides eggs are accidentally swallowed from fingers, water or food that has been contaminated with faeces of an infected human. 93  Ascaris lumbricoides - giant roundworm  Larvae hatch from the eggs, penetrate the intestinal wall and enter the bloodstream.  They stop at pulmonary arteries and stay in the lungs for two weeks.  They break into the alveoli and travel up the respiratory system to the throat to be swallowed again. This migration is needed for the larvae to develop into adults.  Adult worms attach themselves to the intestinal wall ready to 94mate.  Ascaris lumbricoides - giant roundworm  Adults survive by eating food digested by the host and can live up to 2 years.  A female produces about 2×105 eggs per day that are passed out through the faeces.  Fertile eggs embryonate and become infective after 18 days to several weeks, depending on favorable environmental conditions.  Unfertilized eggs are not infective. 95  Ascaris lumbricoides - giant roundworm  The eggs are very resistant to chemicals, extreme temperatures and other rough conditions and can survive for months.  Adult females are 20-35 cm long and 3–6 mm in diameter.  Male worms are a little smaller reaching 15–30 cm in length and 2–4 mm in width.  This cycle takes between 2-3 months. 96 97 Nemathelminthes PINWORMS (Threadworms) They look like small threads of white cotton. The adults are white and ½ inch long. Number 1 parasite in the North America and Europe. They cause an itchy anus, digestive problems, irritability and insomnia.  Most readily seen of all of the species of parasites because they live in the colon and they come out at night to lay their eggs in the anus and on bedclothes. The eggs can become airborne and are able to live without host for 2 days. They are also transmitted by the anus – hand – mouth route.  School age children and preschoolers have the highest infestation 98 rates. Eg. Enterobius vermicularis*, Stongyloides stercolaris.  Nemathelminthes WHIPWORMS Human whipworm -Trichuris trichiura* Adult whipworm is 2-3 inches (50 to 76 mm) long. It is threadlike for the most part, but is thicker at one end (whiplike). They attach themselves to the intestinal wall where they inject their digestive fluid into the tissue which then digests into liquid and is sucked up. This causes anaemia, bloody stools, lower abdominal pain, weight loss and nausea. When the eggs are passed out through the faeces, they are 99able to live for three weeks without a host.  Nemathelminthes HOOKWORM  Ancylostoma duodenale are the most common canine intestinal parasite in the United States, infecting nearly 20% of all dogs.  Hookworm infection is transmitted by ingesting the infective larvae (which usually live in soil) or by the larvae attaching to and burrowing through the dog's skin.  Once inside the dog's body, larvae travel to the small intestine, mature, mate and lay eggs.  The eggs pass into the soil through the dog's feces.  Since hookworms can penetrate skin tissue, it is possible for people to pick up the larvae when walking barefoot on infected soil. 100  Nemathelminthes HOOKWORM  Hookworm can also be transmitted through breast feeding  Symptoms of hookworm infection include the following: ✓ Anaemia (severe cases) ✓ Diarrhoea ✓ Diminished strength and vitality 101  Round worm infections 1. Intestinal infections i. Small intestines only: Ascaris lumbricoides, Ancylostoma duodenale, Necator americanus, Strongyloides stercolaris ii. Caecum and vermiform appendix: Enterobius vermicularis, Trichuris trichuria. 102  Round worm infections 2. Somatic infections (inside the tissues and organs) i. Lymphatic system: Wuchereria bancrofti, Brugia malayi ii. Subcutaneous tissue: Onchocerca volvulus, Dracunculus medinensis* iii. Lungs: Ancylostoma duodenale, Necator americanus, Ascaris lumbricoides iv. Conjunctiva: Loa loa 103  Life cycle of Strongyloides stercoralis 104  Strongyloides stercoralis  A pin worm with a unique and complex life cycle.  It has both free-living and parasitic cycles and has the potential to cause autoinfection and multiply within the host (a characteristic other nematodes do not possess).  Free living cycle: From the large intestine, rhabditiform larvae are excreted in the stool.  They develop into free living adult males and females which mate and produce eggs from which larvae hatch. The larvae will become infective. 105  Strongyloides stercoralis Parasitic cycle:  The larvae penetrate the host’s skin and migrate to the intestines to lay eggs which then hatch to yield larvae  The rhabditiform larvae can either be passed in the stool to undergo the “Free-living cycle” or can cause autoinfection.  In autoinfection, the rhabditiform larvae become infective filariform larvae, which may penetrate the intestinal mucosa, the skin etc.  They travel just under the skin until they grow too big.  They then settle in the small intestine where they mature and reproduce and the cycle starts all over again. 106 Strongyloides stercoralis 107  Life cycle of filarial worms 108  Filarial worms  Filariasis is a parasitic disease that is caused by thread- like roundworms belonging to the Filarioidea type.  These are spread by blood-feeding black flies and mosquitoes.  Eight known filarial nematodes use humans as their definitive hosts.  These are divided into three groups according to the niche they occupy within the body (lymphatic, subcutaneous and serous cavity). 109  Filarial worms  Lymphatic filariasis is caused by the worms Wuchereria bancrofti, Brugia malayi and Brugia timori. These worms occupy the lymphatic system, including the lymph nodes, notably those draining the legs and genital area, where the adult worms induce allergic reactions in the sensitized tissues.  In chronic cases, these worms lead to the disease elephantiasis. 110  Filarial worms  Subcutaneous filariasis is caused by Loa loa (the eye worm), Mansonella streptocerca and Onchocerca volvulus. These worms occupy the subcutaneous layer of the skin, in the fat layer. Loa loa causes Loa loa filariasis, while O. volvulus causes river blindness. 111  Filarial worms  Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi, which occupy the serous cavity of the abdomen. 112  Filarial worms  In the human body the female nematode gives birth to microfilariae.  The microfilariae worms migrate through the peripheral blood and skin, from which they are taken up by blood- sucking insects.  Within the insect carrier, the microfilariae grow into motile, infective larvae.  At the insect’s next blood meal, these are introduced into the113human host, where they reach maturity in about a year.  114  Filarial worms  The term filariasis is commonly used to designate bancroftian filariasis, caused by Wuchereria bancrofti.  These organisms are widely distributed in tropical and subtropical regions of the world and are transmitted to man by mosquitoes, usually Culex fatigans.  Repeated mosquito bites during several months are usually needed to develop lymphatic filariasis.  Wuchereria bancrofti infection is usually asymptomatic. 115  Filarial worms  Some develop lymphedema (swelling), which is prevalent in the legs, but sometimes also in the arms, genitalia and breasts.  The swelling and decreased flow of the lymph fluid exposes the body to skin and lymph system infections.  This may occur within six months.  Over time the disease causes thickening & hardening of the skin called elephantiasis which can be fatal. 116  Filarial worms  Filarial infection might also cause pulmonary tropical eosinophilia syndrome, which is mostly found in patients living in Asia which causes cough, shortness of breath, and wheezing. 117  Life cycle of the hookworm 118  Hookworm The two main species of hookworm infecting humans are Ancylostoma duodenale and Necator americanus. Infection is directly by the ingestion of larvae in contaminated food and water. Hookworms from dogs and cats can penetrate human skin causing skin problems, rashes, itches and edema at the site of penetration. They then travel to the small intestines to reproduce by laying 119 eggs.  Hookworm In the intestines, they hook themselves into the intestinal walls where each one sucks blood. The eggs hatch in the intestines, then migrate to the lungs through the bloodstream where they are coughed up and swallowed. These eggs get into the soil or water when infected human faeces is left on the ground. 120  Hookworm Tiny larvae will hatch out. If the soil is wet the larvae will develop to a stage where they can infect people. Larva can survive in wet soil for several weeks. Hookworms also cause asthma, pneumonia, eye pain, insomnia, dry skin and hair. While a light infection may cause no symptoms, heavy infection can cause anaemia, abdominal pain, diarrhoea, loss of appetite, and weight loss. Heavy, chronic infections can cause stunted growth and mental retardation. 121 122  Platyhelminthes 123 Classification of Parasitic Helminths Sub Phylum Class Genus – examples kingdom Metazoa A. Nematodes (round Ascaris (roundworm) worms) Trichuris (whipworm) These worms appear round Ancylostoma (hookworm) in cross section, they have Necator (hookworm) body cavities, a straight alimentary canal and an Enterobius (pinworm or anus. threadworm) Strongyloides (roundworm) B. Platyhelminthes (Flat Cestodes (Tape worm) Taenia (tapeworm) worms) Adult tapeworms are found in the Taenia solium These worms are have intestine of their host Taenia saginata flattened dorsoventrally They have a head (scolex) with flattened, no body cavity sucking organs, a segmented body and, if present, the but no alimentary canal alimentary canal is blind Each body segment is hermaphrodite ending Trematodes (Flukes) Fasciolopsis (liver fluke) Non-segmented, usually leaf-shaped, Schistosoma with two suckers but no distinct head They have an alimentary canal and are usually hermaphrodite and leaf shaped Schistosomes are the exception. They are thread-like, and have separate 124 sexes  http://1.bp.blogspot.com/-m_mluUvV0kM/TkOPkZnbRiI/AAAAAAAAAJQ/GAcjKt_GxWM/s1600/cestode.jpg Platyhelminthes Cestodes (Tapeworms): These are tape-like, segmented hermaphrodites organisms. Adult worms are found in the intestinal canal of man, and animal. 125  Platyhelminthes Cestodes: There are three regions in an adult worm: 1. a head (scolex) 2. a neck and 3. a strobila (a body or trunk) consisting of a series of segments (proglottides). 126  Platyhelminthes Cestodes: http://1.bp.blogspot.com/-m_mluUvV0kM/TkOPkZnbRiI/AAAAAAAAAJQ/GAcjKt_GxWM/s1600/cestode.jpg The suckers or hooks in their head is used to attach themselves to the host. Alimentary canal and body cavity are absent. There is no mouth or digestive system. Examples are Diphyllobothrium, Taenia, Echinococcus, Hymenolepsis etc. 127  Platyhelminthes Newly formed proglottids are small and immature. Mature proglottids contain fully developed reproductive organs (several testes, ovary and a uterus). Fertilization takes place between the segments; it may be a self fertilization or a cross-fertilization. Excretory and nervous systems are present. 128  Life cycle of the Tapeworm 129  Taenia Saginata - Beef Tapeworm Taenia saginata is a large tapeworm that causes an infection called taeniasis. It uses cattle as the intermediate hosts. Humans are the only definitive hosts. Taeniasis occurs worldwide and is relatively common in Africa, Eastern Europe, Latin America and the Philippines. Eggs are passed in the faeces of an infected human. 130  Taenia saginata (beef tapeworm)  Eggs are found in a proglottid or a tapeworm segment. They can survive a few months out in the environment. If a cow feeds on contaminated vegetation, it ingests mature eggs or gravid proglottids. In the small intestines, larvae hatch, penetrate the intestinal wall, enter the bloodstream and migrate to muscle tissue where they encyst into cysticerci. 131  Taenia saginata (beef tapeworm) The cysticerci can survive for years and still be infective when humans eat the meat. If the beef is not cooked properly, cysticerci excyst in the small intestine and develop into adults within two months. Adults attach to the intestinal wall with their scolex using suckers. 132  Taenia saginata (beef tapeworm) The proglottids mature and absorb nutrients through their membranes and produce up to 100 000 eggs per day. Proglottids break off from the tail and move with the stool out of the human body. The eggs usually stay inside the proglottids until they are out in the environment. When the proglottid dries up, it ruptures and releases the eggs. 133  Taenia saginata (beef tapeworm) If the faeces land on grazing ground, a cow might accidentally ingest proglottids or eggs. Taenia saginata can live up to 25 years and grow up to 5 meters but in some cases can reach lengths of over 10 meters (coiled in the intestinal tract). 134  135  Taenia solium - Pork Tapeworm  Taenia solium infection is not as common as Teania saginata.  Unhygienic disposal of human faeces is the primary means of dissemination.  Eggs can survive outside for several weeks.  Cysticercus is killed at 45-50 oC.  Often, pigs and cows which act as intermediate hosts ingest the gravid proglottids in human faeces.  Gastric secretions dissolve and the oncosphere hatches in the duodenum. 136  Taenia solium - Pork Tapeworm  Oncospheres penetrates the intestinal wall into the venous capillaries and mesenteric lymph vessels.  Embryos are carried by the circulation until they reach voluntary muscles where they hook their embyronic hooks and develope into cysticercus larvae.  In pigs, cysts are found in heart muscles, diaphragm, tongue, liver, kidneys, brain and eyes.  Human infection with cysticerci can result from ingestion of eggs from infected meat. 137  Trematodes 138  Platyhelminthes Trematodes: Commonly known as flukes. They are leaf-like unsegmented organisms. These organisms are haemphroditic except in the schistosomes which are diecious. They do not have hooks and suckers in their head. Alimentary canal is present but is not complete (anus absent). 139  Platyhelminthes Trematodes: The body cavity is absent. Excretory and nervous systems are present. Excretory system consists of “flame cells” and collecting tubules which opens posteriorly, into an excretory pore. Examples are Schistosoma, Gastrodiscoides, Fasciolopsis, Fasciola, Clonorchis, Heterophyes etc. 140  Schistosoma spp-Life cycle 141  Schistosoma spp Causes SCHISTOSOMIASIS sometimes referred to as bilharzias or snail fever.  Caused by blood flukes (trematodes) of the genus Schistosoma. Infection comes from penetration of the skin by cercariae larvae in contaminated fresh water. Days after infection, itchy skin or a rash develops. After 1-2 months, fever, chills, cough and muscle aches set in. . 142  Schistosoma spp The eggs can be found in the brain and spinal cord, and can cause seizures, spinal cord inflammation and paralysis. The parasite can damage the liver, intestines, lungs and bladder. The body reacts to the eggs produced by the worms only  After malaria and intestinal helminthiasis, schistosomiasis is the third most devastating tropical disease in the world, being a major source of morbidity and mortality for developing countries in Africa, South America, the Caribbean, the Middle East, and Asia.143  144 Inferior and/or Veins of the vesical plexus superior around the bladder and mesenteric along the ureters veins around the walls of the large bowel, small intestine or rectum Urine/ faeces 145  Arthropods 146  Arthropods  An arthropod is an invertebrate having an exoskeleton, a segmented body, and jointed appendages.  They include insects (mosquitoes), arachnids (flea) etc.  These cause diseases directly by their feeding or indirectly by transmitting infections.  Those of importance in human diseases are those that feed on human tissue fluids and blood (insects, ticks, mites) 147  Arthropods  and those that transmit infections through viruses, bacteria, worms and protozoa.  Anopheles mosquito - Malaria,  Aedes mosquito - Yellow fever and Dengue fever,  Flea - Bubonic plague  Body louse - Epidemic typhus 148  Parasitic infections 149 150  Objectives ✓ Classifications of human and animal parasites ✓ Morphology and life cycles ✓ Parasite infections of humans 151 152