Topic 5 - Introduction to Parasitology 2023 PDF

1 Microbiology: The Bad Bugs Part IV: The Parasites BIOL2700 Version 03 2 Microbiology Parasitology: What is it, and why study it? A parasite is a living organism, which takes its nourishment and other needs from a host; the host is an organism which supports the parasite. The parasites included in...

1 Microbiology: The Bad Bugs Part IV: The Parasites BIOL2700 Version 03 2 Microbiology Parasitology: What is it, and why study it? A parasite is a living organism, which takes its nourishment and other needs from a host; the host is an organism which supports the parasite. The parasites included in medical parasitology are protozoa (protists), helminthes, and some arthropods. Many of these parasites are causative agents of major public health problems of the world. Recent estimates of prevalence of parasites in the world are: Ascaris 1.5 billion Hookworms 1.3 billion Whipworms 1 billion Filarial worms 657 million Malaria 500 million Schistosomes 270 million Amebiasis 50 million tapeworms 50 million Clonorchis 20 million Chagas’ Disease 15 million Taenia The result is untold suffering and death. Mutualism - an association in which both partners are metabolically dependent upon each other and one cannot live without the help of the other; however, none of the partners suffers any harm from the association. Commensalism - an association in which the commensal takes the benefit without causing injury to the host. Microbiology Parasitology: Different Kinds of Parasites, Different Kinds of Hosts Parasites Ectoparasite – a parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc. We will be skipping these because they are not “Micro” enough. Endoparasites – parasites that live inside the body of their host, e.g. Entamoeba histolytica. Obligate Parasite - This parasite is completely dependent on the host during a segment or all of its life cycle, e.g. Plasmodium sp. Facultative parasite – an organism that exhibits both parasitic and non-parasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host. e.g. Naegleria fowleri Accidental parasite – when a parasite attacks an unnatural host and survives. e.g. Hymenolepis diminuta (rat tapeworm). Erratic parasite - is one that wanders in to an organ in which it is not usually found. e.g. Entamoeba histolytica in the liver or lung of humans Hosts Definitive host – a host that harbors a parasite in the adult stage or where the parasite undergoes a sexual method of reproduction. Intermediate host - harbors the larval stages of the parasite or an asexual cycle of development takes place. In some cases, larval development is completed in two different intermediate hosts, referred to as first and second intermediate hosts. Paratenic host – a host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host, i.e. it is not necessary for the completion of the parasites life cycle. Reservoir host – a host that makes the parasite available for the transmission to another host and is usually not affected by the infection. Natural host – a host that is naturally infected with certain species of parasite. Accidental host – a host that is under normal circumstances not infected with the parasite 3 Microbiology Parasitology: Effect of the Parasite on the Host Direct effects of the parasite on the host: Mechanical injury - may be inflicted by a parasite by means of direct destruction of tissues or pressure as it grows larger. Effect of toxic substances- parasites may produce toxic substances which may in turn cause rigors and other symptoms. Deprivation of nutrients, fluids and metabolites -parasite may produce disease by competing with the host for nutrients. Indirect effects of the parasite on the host: Immunological reaction: Tissue damage may be caused by immunological response of the host, e.g. nephritic syndrome following Plasmodium infections. Excessive proliferation (scarring) of certain tissues due to invasion by some parasites can also cause tissue damage in man, e.g. fibrosis of liver after deposition of the ova of Schistosoma. 4 5 Microbiology Parasitology: The “Landis” Classification Medically Important Parasites Fungi Cutaneous Systemic Opportunists Protozoa (Protists) Intestinal: Entameba histolytica Giardia lamblia Cryptosporidium sp. Balantidium coli Blood & Tissue: Plasmodium sp. Toxoplasma gondii Trypanosoma sp. Leishmania sp Naegleria fowleri Metazoa (Worms) Urogenital: Trichomonas vaginalis Platyhelminthes/ Flatworms Trematodes/Flukes Organ: Intestinal: Schistosoma sp Fasciolopsis sp. Clonorchis sp. Cestodes/Tapeworms Intestinal Taenia Sp. Systemic: Echinococcus sp Paragonimus sp. Fasciola sp.. Nemathelminthyes/ Roundworms Systemic: Onchocerca sp. Wuchereria sp. Brugia sp. Toxocara sp. Angiostrongylus sp. Intestinal: Trichuris (whipworm) Ancylostoma and Necator (hookworms) Enterobius (pinworm) 6 Microbiology Parasitology: The Life Cycle Parasite life cycles can take a variety of forms, all involving the exploitation of one or more hosts. Those that must infect more than one host species to complete their life cycles are said to have complex or indirect life cycles Those that infect a single species have direct life cycles. Important terms: Cyst: a resting stage similar to a spore with a thick wall and low level of metabolism Sporozoite: a motile sporelike stage in the life cycle of some parasitic sporozoans that is typically the infective agent introduced into a host. Trophozoite: stage in life cycle during which the microbe is feeding and growing. Direct Indirect Transmitted by the Fecal-Oral Route and Cause Diarrhea Microbiology Parasitology: Important Intestinal Protozoa/Protists Entamoeba histolytica: Epidemiology: Estimated to infect about 50 million people worldwide. Transmission: Cysts survive outside the host in water, in soils, and on foods, especially under moist conditions Clinical: Invades the colon and causes bloody diarrhea – amoebic dysentery. Also causes amoebic liver abscess. Trophozoites cannot survive gastric juice, storage at room temperature, cooking, and lyse in tap water. They divide by binary fission and feed on RBC, 7 Transmitted by the Fecal-Oral Route and Cause Diarrhea Microbiology Parasitology: Important Intestinal Protozoa/Protists Giardia lamblia Epidemiology: World-wide distribution; about 15% of cases of nondysenteric diarrhea in the United States Transmission: Present in contaminated wells and water systems, especially ponds (Beaver fever). Also occur in city reservoirs, and persist after water treatment, as the cysts are resistant to conventional water treatment methods. Fecal-oral transmission can also occur in day-care centers, where children may have poor hygiene practices. Clinical: Lives in the small intestine and results in a diarrheal syndrome with cramping, fatigue, vomiting, weight loss (malabsorption). NB: Not all Giardia infections are symptomatic, and many people can unknowingly serve as carriers of the parasite. 8 Transmitted by the Fecal-Oral Route and Cause Diarrhea Microbiology Parasitology: Important Intestinal Protozoa/Protists Cryptosporidium parvum/hominis: Epidemiology: Worldwide distribution, with many outbreaks in the United States associated with waterparks, community swimming pools, and day care centers. It sickened around 400,000 people in Milwaukee in 1993 when it got into the tap water. Cryptosporidia in this preparation are red, round and have faint halos. Transmission: Occurs through exposure to infected animals (mainly dogs & cats) or exposure to water contaminated by feces of infected animals. Clinical: Diarrheal syndrome Sporozoites along the microvilli of the intestine 9 10 Transmitted by the Fecal-Oral Route and Cause Diarrhea Microbiology Parasitology: Important Intestinal Protozoa/Protists Balantidium coli: Epidemiology: Worldwide distribution. Only ciliated protozoan known to infect humans. Transmission: Usually acquired by humans via the fecal-oral (contaminated water) route from the normal host, the pig, where it is asymptomatic. Clinical: Diarrheal syndrome that can lead to colonic ulceration Balantidium coli trophozoite. Trophozoite is pear shaped, has cilia, and a kidney shaped nucleus. It is a comparatively large parasite Microbiology Parasitology: Important Systemic Protozoa/Protists 11 Malaria Plasmodium: There are 4 species that infect humans: P. falciparum, P. vivax, P. ovale and P. malariae Epidemiology: Huge problem. 219 million cases, with >600k deaths (2010). Mainly in tropical & subtropical areas, with the Democratic Republic of the Congo, India and Nigeria accounting for 40% of cases. Transmission: Human to human via mosquito vector Clinical: Complex life cycle involving injection of Sporozoite by mosquito (vector), Hypozoites infect liver, Merozoites infect RBCs. Once in the RBCs, more Merozoites are formed, as well as Gametocytes, which are taken up by a mosquito. Malaria is characterized by anemia (obviously), and fever, malaise, headache, myalgias, jaundice and sometimes gastrointestinal symptoms of nausea, vomiting and diarrhea. trophozoites of the Plasmodium vivax parasite Microbiology Parasitology: Important Systemic Protozoa/Protists 12 Toxoplasmosis Toxoplasma gondii Epidemiology: Worldwide problem. Approximately 22% of US population has been infected Transmission: Most commonly transmitted by the ingestion of oocysts from cat feces or undercooked pork, lamb, or venison. Can cross the placenta. Clinical: Infection can range from a flulike syndrome, to ocular problems (retinochoroidal scarring), to brain lesions, and is also a cause of neonatal toxoplasmosis (stillbirth to CNS maldevelopment). toxoplasmosis ring enhancing lesions Microbiology Parasitology: Important Systemic Protozoa/Protists Leishmania sp.: Epidemiology: It is found in parts of the tropics, subtropics, and southern Europe. It currently affects 12 million people in 98 countries. There are ~ 2 million new cases each year. 21 species are known to cause disease in humans. Transmission: Sand fly is the vector Clinical: Begins as skin sores which erupt weeks to months after the person is bitten by infected sand flies. It is divided into the following types: Cutaneous leishmaniasis is the most common form, which causes an open sore at the bite sites, which heals in a few months to a year and half. Diffuse cutaneous leishmaniasis produces widespread skin lesions which resemble leprosy, and may not heal on its own. Mucocutaneous leishmaniasis causes both skin and mucosal ulcers with damage primarily of the nose and mouth. Visceral leishmaniasis or kal-azar is the most serious form, and is potentially fatal if untreated. 13 Leishmaniasis 14 Microbiology Parasitology: Important Systemic Protozoa/Protists Sleeping Sickness & Chagas Disease Trypanosoma sp.: Epidemiology: In Africa - Trypanosoma bruceisleeping sickness, and in South America Trypanosoma cruzi-Chagas disease. Millions of cases in Sub-Saharan Africa, with approximately 10k new cases per year. Only about 1 case/year in US. Transmission: Sleeping sickness is transmitted by the bite of the tsetse fly, and Chagas disease is transmitted by the bite of the Reduviid bug (an “assassin fly” ). Clinical: Through a process known as antigenic variation, some trypanosomes are able to evade the host's immune system by modifying their surface membrane antigens. Trypanosoma brucei is known for infiltrating the host's central nervous system. In its final stages, the disease may lead to extreme exhaustion and fatigue during the day (sleeping sickness), coma, and ultimately death. Trypanosoma cruzi may infect both blood or other body tissues. Left untreated, Chagas' disease may cause diverse effects such as dementia, megacolon, and myocarditis. Trypanosoma cruzi found in blood. Reduviid Tse Tse Transmitted by the Intra-Nasal Route and Cause PAM Microbiology Parasitology: Important Systemic Protozoa/Protists Naegleria fowleri: Epidemiology: Infections are rare. *. In the 10 years from 2006 to 2015, 37 infections were reported in the U.S. Of those cases, 33 people were infected by contaminated recreational water, 3 people were infected after performing nasal irrigation using contaminated tap water, and 1 person was infected by contaminated tap water used on a backyard slip-nslide. Transmission: You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose. Clinical: Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis. This diagram demonstrates the life cycle of N. fowleri and how it causes infection when it travels into the olfactory nerve 15 16 Microbiology Parasitology: The Helminths (aka Bad Worms) Sub kingdom Metazoa Phylum Nematodes Round worms; appear round in cross section, they have body cavities, a straight alimentary canal and an anus Platyhelminthes Flat worms; dorsoventrally flattened, no body cavity and, if present, the alimentary canal is blind ending Class Genus – examples Numerous… Ascaris (roundworm) Trichuris (whipworm) Ancylostoma (hookworm) Necator (hookworm) Enterobius (pinworm or threadworm) Amgiostrongylus (lungworm) Cestodes Taenia (tapeworm) Adult tapeworms are found in the intestine of their host They have a head (scolex) with sucking organs, a segmented body but no alimentary canal Each body segment is a hermaphrodite Trematodes Fasciolopsis (liver fluke) Non-segmented, usually leafshaped, with two suckers but no distinct head Schistosoma (not leaf shaped!) They have an alimentary canal and are usually hermaphrodite Schistosomes are thread-like, and have separate sexes Microbiology Parasitology: Important Metazoa – Intestinal Nematodes Trichuris (whipworm) – Fecal-oral transmission – Estimated 1 billion human infections. However, it is chiefly tropical, especially in Asia (“night soil”). – Prefers the large intestine. Can cause diarrhea, rectal prolapse and anemia in heavily-infected people Ancylostoma and Necator (hookworms) – A major cause of anemia in the tropics. Estimated that around 800 million people are infected with hook-worms worldwide, with 1.6 million suffering from anemia and 55,000 deaths annually – Primarily acquired transdermally (larvae secrete enzymes that break down skin) Enterobius (pinworm) – prevalent in cold and temperate climates but rare in the tropics – Fecal-oral transmission – found mainly in children, mild intestinal infections, pruritis ani Whipworm 17 Roundworms Ascaris (roundworm) – Found world-wide in conditions of poor hygiene, transmitted by the fecal-oral route – Affects as many as one billion people worldwide. – Adult worms live in the small intestine. Causes ascariasis, an enteritis. No symptoms in more than 85% of cases. – Symptoms increase with the number of worms present, and may include shortness of breath as they migrate to the lungs, and fever in the beginning of the disease. These may be followed by symptoms of abdominal swelling, abdominal pain and diarrhea. Hookworm Pinworm Heavy intestinal infections may occur with Ascaris. Adult worms can be several cms long. Microbiology Parasitology: Important Metazoa – Systemic Nematodes Onchocerca volvulus – Transmitted by the black fly, this microfilarial parasite can cause visual impairment, blindness and severe itching of the skin in those infected. It is the second most common cause of infectious blindness, after trachoma (Chlamydia) Wuchereria bancrofti – The major causative agent of lymphatic filariasis (lymphedema). Mosquito transmission. Brugia malayi – Another microfilarial parasite that causes lymphatic filariasis (lymphedema). Mosquito transmission. Lymphatic elephantiasis 18 Roundworms Toxocara sp. – Note that this begins as an intestinal infection, but spreads throughout body. Disease is Toxocariasis. – A world-wide infection of dogs (canis) and cats (cati) – Human infection occurs when eggs are ingested from dog or cat feces – It is common in children and can cause visceral larva migrans (VLM) – These nematodes can infect, but not mature, in humans. They will migrate (VLM) through the intestinal wall, travel with the blood stream to various organs where they cause inflammation and damage. Affected organs can include the liver, heart (causing myocarditis) and the CNS (causing dysfunction, seizures, and coma). A special variant is ocular larva migrans where usually T. canis larvae travel to the eye. Onchocerca Intestinal Toxocara Microbiology Parasitology: Important Metazoa – Systemic Nematodes 19 Roundworms Angiostrongylus cantonensis– Recent Increase in Cases in Hawaii: commonly resides in the pulmonary http://www.popsci.com/rat-lungworm-hawaii-prevention arteries of rats, giving it the common name rat lungworm. The most common cause of eosinophilic meningitis in Southeast Asia and the Pacific Basin Results from consumption of snails and slugs that act as intermediate hosts Rarely, unwashed fruits and vegetables, especially romaine lettuce, can be contaminated with snail and slug mucus or can result in accidental ingestion of these intermediate hosts The presence of the worms in the neural tissue of the human CNS will cause a parasitic encephalitis: – – – Direct mechanical damage to neural tissue from the worms' motion Toxic by-products such as nitrogenous waste Antigens released by dead and living parasites http://manoa.hawaii.edu/ctahr/farmfoodsafety/rat-lungworm/ 20 Microbiology Parasitology: Important Flatworms-Cestodes Intestinal Taenia saginata – Worldwide distribution – Causes Taeniasis, an intestinal infection – Acquired by ingestion of contaminated, uncooked beef – A common infection but causes minimal symptoms Taenia solium – Worldwide distribution – acquired by ingestion of contaminated, uncooked pork that contains cysticerci (encysted larval forms) – Less common, but causes taeniasis and cystercicosis – a systemic disease where cysticerci encyst in muscles (myositis) and in the brain – is actually an infectious cause of epilepsy Tapeworms c y s t e r c i c o s i s Systemic Echinococcus granulosus (dog tapeworm) and Echinicoccus multilocularis (rodent tapeworm) – Causes echinococcosis and hydatid disease. The latter occurs when the larval stages of these organisms are ingested – The larvae may develop in the human host and cause spaceoccupying lesions in several organs, e.g. liver, brain The most common form of brain tapeworm is the pork tapeworm -- Taenia solium. Echinococcus granulosus associated hydatid cyst. Microbiology Parasitology: Important Metazoa-Trematodes Intestinal Fasciolopsis buski (intestinal fluke)- A common parasite of humans and pigs in Southeast Asia. Causes faciolopsiasis, an intestinal infection.This parasite is one of the largest trematodes to infect man (8cm in length) and lives in the upper intestine. Chronic infection leads to inflammation, ulceration and hemorrhage of the small intestine Fasciola hepatica (liver fluke)- Primarily, a parasite of sheep, humans become infected when they ingest metacercariae that have encysted on watercress (salad parasites!). Causes fascioliasis. The adult trematode lives in the intrahepatic bile ducts of the liver. Fascioliasis can lead to severe anemia in humans A: Two Fasciolopsis covering the appendiceal orifice; B: Following removal of the parasites, the appendiceal orifice shows hyperemia and edema Hepatobiliary Fascioliasis 21 Flukes Microbiology Parasitology: Important Metazoa-Trematodes Clonorchis sinensis (liver fluke)- Widespread in China, Japan, Korea and Taiwan, this parasite is acquired by ingestion of infective immature forms in raw or pickled fish. It causes clonorchiasis, an infection of the liver. Paragonimus westermani ( lung fluke)- Widespread in the Far East and South east Asia, the parasite is acquired by ingestion of infective immature forms in raw or pickled crustaceans. Causes paragonimiasis, a lung infection. Schistosoma haematobium (bladder fluke), S. mansoni (blood fluke) and S. japonicum (blood fluke) – most commonly found in Asia, Africa, and South America, especially in areas where the water contains numerous freshwater snails, which may carry the parasite. Causes schistosomiasis. Although it has a low mortality rate, schistosomiasis often is a chronic illness that can damage internal organs and, in children, impair growth and cognitive development. 22 Flukes Clonorchis sinensis Paragonimus westermani Microbiology Parasitology: FYI-Treating Helminths 23 24 Microbiology Parasitology: Fungi Basic fungal biology: Eukaryotes Often dimorphic Yeast in body, mold in culture Classification of fungal diseases (mycoses) Superficial, cutaneous, subcutaneous Systemic and opportunistic Poisoning and allergies Treatment Azole drugs, amphotericin B, others Systemic Mycoses Generally acquired by inhalation of spores Fungal pneumonias, may spread beyond into other tissues Blastomyces sp.(blastomycosis) Coccidiodes sp.(coccidiomycosis) Histoplasma sp. (histoplasmosis) Most common in this area of country Many people exposed with asymptomatic cases Many test positive for exposure Cutaneous and subcutaneous Dermatophytes: various species, most frequently Trichophyton and Microsporum Cause skin and nail diseases Infections referred to as Tinea (worm) because of the ringlike appearance on skin. Cause ringworm, jock itch, athlete’s foot, etc. Limited to outer layer of skin Sporothrix schenckii Causes Sporotrichosis. Acquired from soil and plant material (rose handler's disease Infects deeper into skin, but not systemic Microbiology Parasitology: Fungal Opportunists Aspergillus sp. (aspergillosis: a fungal pneumonia) – Variety of species, very common in soil, plant materials – Serious infections in immunocompromized – Allergies to A. fumigatus – Poisoning from aflatoxin (a liver toxin) from A. flavus Candida sp.(candidiasis/thrush)- is a part of the normal microbiota – Cause of vaginal infections, diaper rash, oral lesions – Capable of infecting any part of the body – Dangerous in cancer patients, HIV infections, etc. Cryptococcus neoformans (fungal meningitis) – Inhalation of spores – Can infect many parts, but has predilection for CNS – Particularly serious in AIDS Pneumocystis carinii (fungal pneumonia) – Very protozoan like, but is a fungus – Most cases associated with AIDS – Very serious lung infection 25