Semester 2 - Parasitic Infections Flashcards
What is the biological definition of parasites?
Parasites are eukaryotic organsisms which live on or in a host organism, and which utilize its resources for their own survival and propagation
What is the broad definition of a parasite?
Requires a host organism to survive/propagate
This includes viruses, bacteria, symbiotic organisms
What are the classifications of parasites?
Protozoa - unicellular
Metazoa - multicellular, include helminths (internal) and ectoparasites (external)
How do parasites replicate?
Extracellularly, some have intracellular stages
Where do parasites generally infect and how is it transmitted?
Largely infect the GI tract and blood
GI - fecal:oral route
Blood - animal vector
A number of parasitic infections are not communicable
Outline the life cycle of a parasite that uses two species.
Definitive host - sexual stage of reproduction is completed (primary host)
Intermediate host - non-sexual stages of reproduction are completed. May not reproduce at all, or may undergo differentiation
What are the characteristics of amoebas?
They obtain nutrients via phagocytosis and move with pseudopodia formation. These push cytoplasm to produce false feet and covert ectoplasm to endoplasm (and vice versa) to allow movement.
What are the characteristics of Entamoeba histolytica?
Endemic to tropical areas
Cyst stage is infective (4 nuclei)
Trophozoite stage is replicative (pathogenic, diagnostic)
Trophozoite stage ingests host cells to acquire nutrients
Phagocytosis of tissue = ulcer/abscess
Phagocytosis of erythrocytes indicates invasion
What are characteristics of an Entamoeva histolytica infection?
Intestinal amoebiasis, amoebic dysentery, extra-intestinal amoebiasis
Invasion of peripheral tissues: liver, lung, brain, skin
70-80% asymptomatic
Infective dose = 1 cyst
How is Entamoeba histolytica transmitted?
Fecal:oral - contaminated water and food
Cysts may survive for months in most conditions
Decontaminate food/water
What are the symptoms of intestinal ameobiasis?
Mild
Infection of the large intestine
Abdominal discomfort, colitis, diarrhea
What are the symptoms of amoebic dysentery?
Non-febrile
Frequent bloody and mucoid stool, severe fluid/electrolyte loss
Proteolytic enzymes causes intestinal abcess
Complications: amoeboma (amoebic granuloma), perianal fistula
What are the symptoms of extra-intestinal amoebiasis?
Invasive Systemic symptoms - fever, sepsis Liver most common - liver abscess, hepatitis Lung - abscess, pneumonia Brain - abscess, encephalitis
How is an entamoeba histolytica infection diagnosed?
Cyst detection in stool samples
Trophozoite detection in tissue
Serology (PCR)
What are the characteristics of flagellates?
They have a long flagella that whip to facilitate movement
Organisms may vear one or multiple flagella
Variety of cellular structures between flagellated protozoan parasites
What are the flagellate human pathogens?
Giardia lamblia (giardiasis)
Trichomonas vaginalis
Trypanosoma cruzi
What are some characteristics of giardia lamblia?
Beaver fever
Worldwide prevalence: acquired from contaminated still water
Highly contagious
Cyst is hearty and resistant to chlorination. Cyst is infective (4 nuclei, aflagellate) and the trophozoite is replicative (2 nuclei, flagellate)
What are the signs and symptoms of a Giardia lamblia infection?
Diarrhea, abdominal pain
Fluid/electrolyte loss, malabsorption of lipid and nutrients
Greasy, floating stool (no blood or mucus)
No extra-intestinal phase, no tissue invasion
Afebrile
How is Giardia lamblia transmitted?
Fecal:oral
How is a Giardia lamblia infection diagnosed?
Cyst detection in multiple stool samples Fecal immunoassays (ELISA etc.)
What are some characteristics of Trichomonas vaginalis?
Trophozoite is infective, replicative
No cyst stage
Anaerobic organisms
What are the signs and symptoms of a Trichomonas vaginalis infection?
50% women symptomatic, generally men asymptomatic in men
Persistent infection associated with long term complications; infection restricted to urogenital tract (infertility, cervical erosion, cervical cancer)
Vaginitis, vulvitis, urethritis, PID
Purulent foul smelling discharge, itching, burning
Colpitis macularis (strawberry cervix)
In men: urethritis, prostatitis, epydidymitis
How is Trichomonas vaginalis transmitted?
Mucosal (sexual)
How is Trichomonas vaginlais diagnosed?
Vaginal/urethral swab Microscopic examination (must be performed immediately after swab - why?)
What are some characteristics of Trypanosoma cruzi?
American trypanosomiasis, Chaga’s disease
Endemic to South and Central America, emerging in North America
Transmitted by Triatoma insects
Trypomastigote stage is infective
Replication occurs in insect vector
What are signs and symptoms of a Trypanosoma cruzi infection?
Acute inflammation near the point of infection
Fever, lymphadenopathy
Severe/chronic cases have cardiac manifestations - cardiomyopathy, arrhythmia, tachycardia
How is Trypanosoma cruzi transmitted?
Vector - also blood transfusion, placental
How is Trypanosoma cruzi diagnosed?
Blood smear
What are characteristics of ciliates?
Cilia provide motility, aid in feeding (phagocytosis)
Variety of feeding strategies, cellular structures
What are the human pathogens of ciliates?
Balantidum coli - the only human pathogen
What are some characteristics of Balantidum coli?
Endemic to tropical areas, common where pigs are raised (animal resevoir)
How is Balantidum coli transmitted?
Fecal:oral by contaminated food/water
What are the signs and symptoms associated with Balantidum coli?
GI infection: Diarrhea, abdominal pain, nausea, vomiting
How is Balantidum coli diagnosed?
Stool examination (microscopy)
What are some characteristics of sporozoa (Apicomplexa)?
Complex subcellular structure Apicoplast organelle - potential functions include fatty acid synthesis and heme synthesis Sporogony yields oocysts and sporozoites Merogony yields shizonts and merozoites Gametogony yields gamets and zygotes
What are human sporozoa (Apicomplexa) pathogens?
Cryptosporidium sp.
Toxoplasma gondii
Falciparum sp.
Babesia sp.
What are some characteristics of Cryptosporidium sp.?
Cryptosporidiosis, crypto
Widespread prevalence
Sporozoite is hearty - resistant to heat, desiccation, chlorination
All stages of reproduction occur in one host - can be communicated between individuals
What are the signs and symptoms of a Cryptosporidium sp. infection?
Generally asymptomatic, self-limiting, non-invasive
Watery, non-bloody diarrhea (1-2 weeks), afebrile
In immunocompromised individuals: severe chronic diarrhea and fluid loss, chronic infection, risk of dissemination
How is Cryptosporidium sp. transmitted?
Fecal-oral
How is a Cryptosporidium sp. infection diagnosed?
Stool sample analysis (multiple samples)
Immunoassay, PCR detection
What are some characteristics of Toxoplasma gondii?
Toxoplasmosis, associated with cat litter
What are the signs and symptoms of a Toxoplasma gondii infection?
Mild flu like illness in immunocompetent individuals
Risk of teratogenesis if acquired during pregnancy
In severe/immunocompromised individuals: Encephalitis (cognitive symptoms), Toxoplasma chorioretinitis (retinal inflammation/lesion, unilateral decreased visual acuity)
Tissue cysts lead to severe complications of infections: Myocardial, skeletal muscle, eye, brain
How is Toxoplasma gondii transmitted?
Fecal:oral
Ingestion of undercooked infected animals, handeling of infected feces/cat litter (cat reservoir)
How is a Toxoplasma gondii infection diagnosed?
Serology, immunoassays
Where is Malaria endemic and what is the name of the parasite?
Plasmodium sp.
Endemic in tropical/developing nations (Africa, South America, SE Asia, Central America)
Largest worldwide parasite epidemic
What are the signs and symptoms of a Plasmodium sp. infection?
Cyclical fever, fatigue, chills, nausea, myalgia,
Liver stage and blood stages of infection: Hepatomegaly, splenomegaly, jaundice, anemia, respiratory distress
Cerebral malaria in severe cases: cognitive impairment, confusion, lethargy, seizure
What are some characteristics of Plasmodium sp.?
Intracellular pathogen (hepatocytes and erythrocytes)
Asexual stages of reproduction occur in humans
Sexual stages occur in mosquitoes
How is Plasmodium sp. transmitted?
Vecotr borne (Anopheles mosquito) Malaria is NOT typically communicated between individuals
How is a Plasmodium sp. infection diagnosed?
Blood smear/film
Thick film: drop of blood on glass slide determines % of infected erythrocytes
Thin film: Drop of blood smeared across slide determines species of pathogen based on morphology
What are some characteristics of Babesia sp.?
Infects erythrocytes NOT hepatocytes
Life cycle similar to Plasmodium sp. and requires two hosts: asexual reproduction in humans and sexual in ticks.
Babesia microti most common
How is Babesia sp. transmitted?
Tick-borne parasite
What are the signs and symptoms of a Babesia sp. infection?
Mild malaria like illness: fever, chills, myalgia, nausea, fatigue.
No liver stage, not cyclical.
What are the complications of a Babesia sp. infection in immunocompromised individuals?
Hemolytic anemia, jaundice, DIC
How is Babesia sp. diagnosed?
Blood smear, molecular tests to distinguish from malarial parasites
What are characteristics of trematodes?
Flukes, flatworms
Dioecious or hermaphroditic
Require at least 1 intermediate host (mollusk)
Sexual stages in definitive host, asexual in intermediate hosts
Complex structure
What are the human pathogens of trematodes?
Schistosoma sp.
Paragonimus westermani
Fasciola hepatica
What are the characteristics of Schistosoma sp.?
Schistosomiasis aka bilharzia, snail fever
Endemic to Asia, Africa, South America, areas containing high levels of freshwater snails
Dioecius (female embedded in male adult)
Circarium infectious to humans, eggs secreted in urine or stool
What are the signs and symptoms of a Schistosoma sp. infection?
Swimmers itch - itch and rash
Acute infection: fever, chills, liver/spleen enlargement, lymphadenopathy, eosinophilia
Organ specific effects vary with species (Intestine, Urinary, kidney)
CNS invasion rare: transverse myelitis, flaccid paraplegia
What are the symptoms of a chronic Schistosoma infection?
Chronic infection: egg deposition, granuloma formation, fibrosis in affected tissue leading to long term complications
- portal hypertension
- bladder cancer
- hepatomegaly
- splenomegaly
- kidney failure
How is Schistosoma sp. transmitted?
Contaminated water, fecal/urine
Cercaria stage burrow into skin and migrate to liver to mature into adult stage
What are the signs and symptoms of the incubation period of Schistosoma sp.?
Many subclinical
Rash may appear days after exposure
Febrile illness may appear 1 - 2 months following infection
How is Schistosoma sp. diagnosed?
Serology (antibodies)
Urinalysis, stool sample analysis (eggs)
Tissue biopsy
What are some characteristics of cestodes?
Tapeworms
Segmented, hermaphroditic (each segment), macroscopic
Adult tapeworms lead to intestinal infections
Larval infections leads to extra-intestinal cyst depostion
What are the human cestodes pathogens?
Taenia solium (pork) Taenia saginata (beef) Diphyllobothrium latum (fish) Echinococcus sp. (dogs)
What is the scolex of a cestode?
The head. Responsible for attachment to the intestine, distinct structural anatomy
What is the proglottid of a cestode?
The body of the worm, each segment
Each segment is hermaphroditic. Proglottid secments can tear away and be shed in feces without consequence to the parasite.
What are the symptoms of an intestinal infection of a cestode?
Often asymptomatic
Abdominal pain, upset stomach, weight loss
E. granulosus - absorbs 80% of B12 ingested from food leading to anemia
What are the symptoms of an extra-intestinal infection of a cestode?
Taenia solis - Cysticercosis: deposition of cysts in muscle (generally asymptomatic) or brain (neurocystircercosis, seizure, confusion, difficulty with balance, hydrocephalus)
Echinococcus sp. Hydatid disease: humans are incidental dead end hosts. Occurs fecal/oral from dogs. Deposition of cysts in lung, alveoli, etc. Symptoms based on area of deposition. Cystic rupture leads to anaphylaxis
How is a cestode infection diagnosed?
Multiple stool sample
Tapeworm segments may be visible in stool
CT/MRI for suspected cystic echinococcosis followed by serology
What are nematodes?
Roundworms
Dioecious
Intestinal and extra intestinal pathogens
What are the human pathogens of nematodes?
Enterobias vermicularis (pinworm) Necator americanus (hookworm) Trichura trichiuris (whipworm) Ascaris lumbricoides (giant roundworm)
What are the signs and symptoms of a E. vermicularis infection (pinworm)?
Itchy anal region - larvae mature at perianal region
Vaginal itching - infection of vaginal canal
Restlessness, difficulty sleeping
How is E. vermicularis transmitted?
fecal-oral
Contact with contaminated surfaces, linens
May survive for weeks on inanimate surfaces
How is E. vermicularis diagnosed?
Tape test - clear adhesive tape in perianal region for 3 consecutive mornings
Stool, fingernail analysis for eggs
What are the signs and symptoms of an N. americanus (hookworm) infection?
mild/absent, children more commonly get symptoms
Intestinal inflammation, vomiting, abdominal pain, diarrhea
Anemia and protein deficiency (suck blood through intestine)
Ground-itch - local invasion of larvae in skin leads to lesions and itching
What are complications of an N. americanus (hookworm) infection?
Chronic anemia/protein deficiency in children may lead to growth retardation and delayed development
How is N. americanus transmitted?
soil transmitted helminth
Infects through the skin (walking barefoot on contaminated soil)
How is N. americanus diagnosed?
Stool analysis
What are signs and symptoms of a T. trichuris (whipworm) infection?
May be mild/absent
severe infections: painful passage of stool containing blood/mucus, rectal prolapse rare complication
Anemia, growth retardation and developmental delay in children
How is T. trichuris (whipworm) transmitted?
Fecal:oral
Contaminated soil, human fertilizer, contaminated fruits/vegetables
How is T. trichuris (whipworm) diagnosed?
Stool analysis
What are the signs and symptoms of an A. lumbrocoides (ascariasis) infection?
Most experience no symptoms
Intestinal primary infection: abdominal pain, vomiting, bloody stool
Lungs (invasive disease): migration of larvae lead to pneumonitis, similar to asthma attack. Wheezing, coughing, shortness of breath
How is A. lumbrocoides (ascariasis) transmitted?
Fecal-oral
Contaminated soil, human fertilizer, contaminated fruits/vegetables
How is a A. lubrocoides infection diagnosed?
Stool analysis
What are general characteristics of protozoa?
Unicellular eukaryotes causing a variety of parasitic infections in humans
Cyst stage generally infective to humans and is the result of the sexual reproductive phase of the parasite
Classified based on method of motility
What are general characteristics of helminths?
Multicellular eukaryotes causing a variety of parasitic infections in humans
Classified based on morphological features
Many dioecious or hermaphroditic
How can parasitic infections of the blood and GI tract distinguished?
Clinical features: Type of diarrhea Fever Extra-intestinal symptoms Paroxysmal features Dissemination of infection
