Introduction to Parasites and Parasitic Infections PDF

Introduction to Parasites and Parasitic Infections  The “Parasites” Characteristics as a group: Eukaryotic Distinct from Fungi No chlorophyll Mixed group of organisms from protozoa to helminths – Single celled to multicellular – Microscopic to macroscopic ...

Introduction to Parasites and Parasitic Infections  The “Parasites” Characteristics as a group: Eukaryotic Distinct from Fungi No chlorophyll Mixed group of organisms from protozoa to helminths – Single celled to multicellular – Microscopic to macroscopic  Types of parasites Protozoa – Single celled, Organized cellular structure – May ingest solid particles – Require aquatic environment – Reproduce by binary fission at some point in life cycle Helminths (worms) – Multicellular, Organized internal structure; includes Platyhelminths (flatworms) Nematoda (roundworms) Ectoparasites – Insects and arachnida found on the skin.  Classification, disease and detection of parasites Protozoa (based on means of locomotion) – Amoebae Form cytoplasmic protrusions (pseudopodia). Occur as trophozoites (active, growing) and cyst (environmentally protected) forms.  Entamoeba histolytica An enteric amoeba Disease - Ranges from: asymptomatic, diarrhea to dysentery and liver disease. Transmission - Fecal-oral - contaminated water/food, (especially in the tropics). – Poor living conditions. There is a morphologically identical non- pathogenic species called Entamoeba dispar. It is distinguished on the basis of clinical history / findings. Entamoeba histolytica in colonic infection  Commons.Wikimedia.org Environmental amoebae Found in natural surface water – Can reach high numbers in hot springs Can cause corneal infections in contact lens wearers – Chronic ulcers unresponsive to treatment – May require transplant Cause of rare conditions: amebic meningoencephalitis – Lifethreatening CNS infection Amoebae can also cause corneal infection in contact lens wearers Cultivated amoebae from contact lens related infection  Flagellates Propelled by flagella. May occur in two forms: – trophozoites which are active and multiply – cyst which is a dormant environmentally protected form. Have shape because of rigid outer wall. May cause infection in the gut (enteric), or widespread in the body  Giardia lamblia an enteric flagellate Disease - Ranges from asymptomatic to acute or chronic diarrhea Giardia cyst Transmission - Fecal-oral, – waterborne, – world wide, including Canada Diagnosis: microscopy of stool sample or antigen detected in stool using EIA Giardia trophozoite  Trichomonas trophozoite Trichomoniasis (flagellate infection) Trichomonas vaginalis – Disease - Vaginitis. (usually no symptoms in males, but carriage) – Transmission - Sexual. – Detection - Microscopy of discharge (wet mount of discharge for live organisms, or gram stained for nonviable organisms) , culture (large or research centres only). – Non pathogenic trichomonas spp are found in the oral cavity and gut Trypanosomiasis Africa – Systemic flagellate infection – Sleeping sickness Fever, encephalitis Transmission - Tse-Tse fly – Detection - Parasites stained on blood smears, serology. Tse-tse Fly T. brucei gambiense/rhodesiense  Trypanosomiasis South America Chagas Disease Cardiac complications (Chagas Disease). Transmitted by Reduvid Bug – Detection - Parasites stained on blood smears, serology. Trypanosoma cruzi Reduvid bug Leishmaniasis – Systemic flagellate infection – Cutaneous ulcers or visceral infiltration Hepatosplenomegaly (enlarged liver and spleen)  Apicomplexa Mature forms are non motile. Complex life cycles. Malaria Pathogens - Plasmodium spp. Cause malaria. Disease - Episodic fevers, anaemia - life threatening! Transmission - Mosquito bites. Detection: - Parasites stained on blood film.  Cryptosporidium spp an enteric apicomplexa 1993: Caused an outbreak in Milwaukee affecting 403,000 people Disease: - watery diarrhea (chronic in immunosuppressed, e.g. AIDS) Transmission: - fecal-oral, water borne, animals (zoonosis), world wide distribution Detection: - microscopy of stool using acid fast stain, or detection of antigen in stool using EIA.  Cyclospora Disease - Watery diarrhea, similar to Cryptosporidium Transmission - Fecal - oral, especially in tropics, outbreaks have occurred in North America. Detection – Microscopy of stool as for Cryptosporidium.  Toxoplasma gondii apicomplexa causing systemic disease – Disease - Mostly asymptomatic infection, but new infection in pregnancy causes fetal malformations; also can cause infection in immuno-suppressed. Oocyst from – Transmission - By poorly cooked meat, cat from cat stool, rarely water. – Detection - By serology. Toxoplasma eye infection Lifecycle of Toxoplasma  Helminths Platyheminths (flatworms) Cestodes – “tapeworms” – Ribbon like, segmented Largest is ~10M long Scolex – Hermaphrodite. – No digestive system, – Adult attached to gut wall by scolex (hooks or suckers for attachment to gut wall), – larval forms in tissues (cysts).  Life cycle of Cestodes Definitive Host gut contains adult worm; produces ova passes into… Environment: where the ova are consumed by… Intermediate Host: in whose tissues the larval stage develops… When the intermediate host is eaten by the definitive host, the adult worm develops in the gut from the larval form, and later produces ova....  Example of a »E x cestode lifecycle a m p l e o f a  Taenia saginata (beef tapeworm),Taenia solium (pork tapeworm) Principle Cestode Pathogens Taenia solium scolex Disease: - Abdominal discomfort (man is definitive host {i.e. has adult}). Transmission: - Larval forms ingested in food. Detection: - Identification of ova or adult segments in stool. – Some cestodes infect humans by the adult form in the gut, some infect by larval forms in tissues, and some infect in both forms. Taenia saginata Cysticercosis (T. solium larvae) – Disease -Cysts throughout the body tissues. – Transmission - Ova are ingested; – Detection - Serology, also x-ray, ultrasound, and other methods to detect mass lesions.  Trematodes: "Flukes". – Leaf shaped, Hermaphrodite, Primitive gut, Suckers for attachment. – Life cycle: Definitive Host (contains adult worm produces ova) – Ova (Environment) consumed by 1st Intermediate Host, ova becomes larva – then 1st Intermediate Host consumed by 2nd Intermediate Host and larva develops a new stage in it, – 2nd Intermediate Host eaten by the definitive host, larva develops into an adult, which produces more ova…  Snail host Schistosomiasis (blood flukes) Pathogens - Schistosoma spp. Disease - Effects of inflammation, hematuria (blood in urine). Transmission - Penetration of skin in fresh water (by larval form {cercaria}). Detection - Ova in stool/urine depending on species of schistosome. Chronic Schistosomiasis Cercaria  Nematodes - “Round worms” Big enough to be seen Separate sexes, GI tract, entrance and exit. – Pathogens: e.g. Ascaris lumbricoides Some are adapted to attach to gut wall, e.g. Hookworms. Ascaris Nematodes (roundworms) – Disease - Abdominal pain/discomfort (most found in the gut). – Transmission - Fecal-oral via ova in stool. – Detection Recognition of ova using stool microscopy. Identification of adult worms. Enterobius Vermicularis infection ova  Hookworms Disease - Chronic blood loss. Transmission - Larvae penetrate skin. Detection - Identification of ova or larvae in stool. Hookworms attached to the bowel mucosa Hookworms: Means of Attachment.  Cutaneous Larva Migrans -Cat/dog hookworm infection -Larva wanders in tissue looking for cat/dog tissue receptor - Immune repose gives rash and itch for weeks -A risk of travel to the Caribbean: walking barefoot on beaches shared with cats and dogs.  Filariasis nematode in tissues – Filaria block lymph channels – Disease - Fevers, elephantiasis, swelling and deformity of limbs, genitalia. – Transmission - Mosquito borne. – Detection – parasite larvae (microfilaria) stained on blood film.  Ectoparasites Colonize the body vs. Micropredators that bite only. – Insects - ( 6 legs) - fleas, head-, body- and pubic lice (singular – Louse), bedbugs – Arachnida - ( 8 legs, but can have 6 in immature form) - ticks, mites Their importance is as vectors of disease and to a lesser extent cosmetic. Scabies Body/Head Louse Nit (louse egg) Pubic Louse Bedbug Tick Flea Ecto- parasites mite