Medical parasitology Flashcards
What is a parasite
An organism that lives in or on another organism of a different species
Medical parasitology is the study of
Parasites that infect humans and the diseases they cause
Parasites may be
Endo parasites which live within a host
Ecto parasites which live on the surface of the host
Endo parasites of humans can be broadly divided into two groups
Parasitic protozoa and parasitic helminths
Routes by which a parasite can be transmitted
Sexually foodborne waterborne transmitted through direct and indirect contact transmitted by means of vectors
Parasitic protozoa can be divided into four groups based on their modes of locomotion and reproduction
Flagellates -which have at least one flagellum ciliates- which have rows or sections of cilia and two nuclei
Amoebae- which move using pseudopodia
sporozoa- which have complicated life cycles with alternating sexual and asexual reproductive phases
Parasitic helminths
Worms that parasite has humans
Two phyla of parasitic helminths
Nematodes (roundworms)
platyhelminthes (flatworms)
Nematodes
Very diverse group of worms that inhabit a broad range of environments they are long and tapered at both ends and in cross-section they are around there are many different species that parasitize humans such as hookworms pin worms and whipworms these worms typically live in the intestines of humans and a generally acquired through ingestion of the egg or larval stage
Platyhelminthes
Are flatworms there are dorsoventrally flattened in cross-section the pathological relevant flatworms belong to two classes the cestodes (tapeworm) and trematodes (flukes)
Cestodes
Are flat and are made up of a ribbon-like chain of segments the beef tapeworm taenia saginata and the pork tapeworm taenia solium infect millions of people worldwide taenia saginata can grow up to 20 m in length infection generally occurs when the cestode larvae are ingested these then mature into adult worms in the intestine of the host the symptoms of infection vary greatly between species
Parasites of humans include
Plasmodium spp causes malaria
Giardia spp causes giardiasis
Schistosoma spp which causes bilharzia
Taenia spp (tapeworm) infect the intestines
Distinguish between parasite and host
Parasite is an organism that lives on or in another organism of a different species (host)
Host is the organism a parasite infects
Distinguish between a pathogenic and commensal parasite
Pathogenic parasite
Commensal parasite
Give an example of a human parasite from each group of parasitic protozoa
Flagellates- Giardia lamblia
Amoebae- Entamoeba histolytica
Sporozoa- Cyclospora
Give an example of a human parasite from each group of parasitic protozoa
Ciliates- Balantidium coli
Flagellates- Giardia lamblia
Amoebae- Entamoeba histolytica
Sporozoa- Cyclospora
Example of each nematode, trematode and cestode that parasite humans
Nematode-
Trematode-
Cestode-
What the term reservoir and vector mean with regard to parasites
Reservoir-an animal, plant or environment in which a disease can persist for long periods of time
Vector- an organism that does not cause disease but can pass the disease to another organism
Plasmodium spp
Causes malaria
Sporozoan
Complex life cycle incorporating asexual and sexual life cycle that take place in separate hosts
Malaria is mosquito-borne
Infection by Anopheles mosquito biting a person and the sporozites of Plasmodium enter the blood stream
Symptoms are fever, headache, nausea and vomiting
4 main types of Plasmodium spp
Falciparum
Vivax
Malariae
Ovale
Life cycle of plasmodium
Has both sexual and asexual phases that take place in separate hosts
Asexual phase-in humans and further divided into exo-erythrocytic cycle (liver) and erythrocytic cycle (blood)
Sexual phase aka sporogonic cycle in female Anopheles mosquitoes
Pathogenesis and pathology of Plasmodium spp
Pathology varies from species to species and malaria differs in incubation time symptoms severity and response to chemotherapy
Symptoms and differences between the forms are likend to the differing life cycles of distinctive species. Some people have genetic traits that make them less susceptible to certain malaria forms
Incubation period is between 9- 30 days. Falciparum attacks both young and old RBC and so parasite levels may be very high and symptoms severe. Other Plasmodium species attack either young or old RBC but not both resulting in milder symptoms. Falciparum infections are more dangerous and more likely to be fatal.
Epidemiology of Plasmodium spp
Found in tropical regions of Sub-Saharan Africa, Asia and the America’s as this is the region in which the mosquito is able to live
Lab diagnosis of Plasmodium
Most reliable I’d Romanowsky-stained droplet of blood or urine under a microscope. Characteristics under a microscope
Treatment and prophylaxis of plasmodium
Several diff prophylactic drugs avail to prevent malaris. The choice of drug needs to take into account the traveller’s destination and other factors. Infection can be treated with a number of drugs although resistance to antimalarial medicines is a problem.
Control of plasmodium
Mosquito net., insect repellent insecticides and draining any standing water
At what points in the life cycle of Plasmodium are sporozoites, trophozoites and gametocytes present
Sporozites-mosquito stages sporogonic cycle
Trophozoites-human blood stages erythrocytic cycle
Gametocytes- human blood stages and erythrocytic stage
Giardia lamblia aka G intestinalis
Flagellate which lives in human small intestine and causes giardiasis. An infected person may be asymptomatic or develop severe diarrhea, cramps, nausea and dehydration
Life cycle of Giardia
Simple with only two stages: trophozoites and cysts. Cysts are resistant and can survive for months in cold water. Ingestion of even a small number of cysts can lead to infection
Epidemiology of giardia
Worldwide. Infection by ingesting fecally contaminated water or food containing Giardia cysts or by direct fecal contamination
Pathogenesis and pathology of giardia
Cysts may be found in the stool of an asymptomatic lerson
Diagnosis of giardia
Stool exam
EIA for antigens
Treatment and control of giardia
Metronidazole and quinacrine
Trichomonas vaginalis
Flagellate which lives primarily in vagina and causes genital infections. Transmitted sexually, most infections are mild or asymptomatic. In females symptoms include vagina dishlchargeblocal tenderness and burning. 10% male have thin white urethral discharge. Contaminated towels and other articles may result in infection. Babies may be infected during birth
Diagnosis of Trichomonas
Microscopic examination of discharge, urine or tissue scraping
Treatment of Trichomonas
Metronidazole
Pathology and pathogenesis of Trichomonas
Sexually transmitted, symptoms mold or asymptomatic. In women infection normally limited to vulva cervix and vagina, does not extend to uterus. Yellow cream discharge
Incubation period is 5-28 days
Schistosoma spp
Parasitic flatworms commonly known as blood-flukes. 2nd most important parasitic disease after malaria.
5 species of schistosoma
Mansoni Haematobium Japonicum Mekongi Intercalatum
Life cycle of schistosoma
Complex has several stages and requires two main hosts. Snails are intermediate host, humans and animals final host. Male is larger than female (dioecious). Adult Schistosoma worms live together in breeding pairs with the female worm tucked into a special groove in the male worm.
Pathogenesis and pathology of Schistosoma
Infection through active penetration of the skin by cercariae stage of the parasite. The cercariae then migrate through body to liver were they mature as adults. Eggs lodge in liver, urinary bladder, or urine or lumen of the inetstines
Diagnosis of Schistosoma
Stool exam for ova and parasites
Treatment
Praziquantel
