Midterm III (Leiel) Flashcards
Define accidental intermediate host, examples
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- accidental host: a host in which the parasite cannot complete its life cycle.
- IH: parasites either do not reproduce or do so asexually, but the parasite always develops to a new stage in this type of host.
- e.g: humans in echinococcus granulosus, echinococcus multilocularis
Species causing filariasis
- Wuchereria bancrofti
- Brugia malayi
Which protozoon cannot form cysts
Trichomona vaginalis - no cysts, only trophozoite form
Life cycle and disease of taenia solium
Life cycle:
- In the muscle “cysticercus” (“bladder worm”) of the infected animal (pig) →
- human infected by eating the meat (4) →
- small intestine larva maturation →
- mature worm →
- proglottids break off →
- pass out with feces →
- pig eats vegetation contaminated by eggs or gravid proglottids →
- oncospheres hatch, penetrate intestinal wall, and circulate to musculature →
- “cysticercus”
Disease:
Taeniasis due to T. solium is usually characterized by mild and non-specific signs and symptoms; 6-8 weeks after ingestion of the cysticerci, abdominal pain, nausea, diarrhoea or constipation might arise and last until the tapeworm dies following treatment (otherwise it may live many years).
Diagnosis of schistosomes
Identification of eggs in urinary sediment
Viable eggs contain a motile miracidium (a free-swimming ciliated larval stage in which a parasitic fluke passes from the egg to its first host, typically a snail)
Eggs can occasionally be found in feces
ELISA, IF, RIA
What causes hydratidosis
Caused by the larval stage of Echinococcus granulosus
Define proglottid, scolex
Proglottid:
- The body is composed of successive segments called proglottids. The sum of the proglottids is called a strobila, which is thin, and resembles a strip of tape.
- Besides the scolex, the rest of the body forms the strobila and consists of a chain of flattened proglottids
- Gravid proglottids are lost from the end of the worm and are replaced by other that have matured as they pass down the strobila.
- Each proglottid possesses a complete set of hermaphroditic sex organs and marginal genital openings
- Eggs accumulate in the uterus of gravid proglottids and only enter the fecal stream when the proglottids are disrupted
Scolex:
- The anterior end of a tapeworm, bearing suckers and hooks for attachment
- The tapeworms maintain anchorage to the host small-gut mucosa by means of the scolex.
- The structure is bearing a circlet of 4 suckers and usually a central rostellum with one or more circlets of minute hooks.
Host of D. latum and disease
2 intermediate hosts: freshwater crustaceans and freshwater fish
Most of D. latum infections are asymptomatic. Occasionally, people complain of epigastric pain, abdominal cramping, nausea, vomiting, and weight loss.
Low serum level of vitamin B12 because of the competition the worm and the host for dietary vitamin B12.
Protozoon transmitted by snail
Schistosoma
Fasciola hepatica
Paragonimus westermani*
Life cycle of malaria
- Plasmodia undergoes sexual divisions in the anopheles mosquito
In the human body:
- The mosquito releases a motile, spindle-shaped sporozoites into the blood stream
- It invades the liver and starts the pre-erythrocyte cycle
- The sporozoite forms a ball → trophozoite
- Trophozoite undergoes nuclear division → 1000s of new nuclei are formed → a big mass of them is called schizont
- Formation of membrane around the nuclei → merozoites → burst into the liver and blood stream → some will infect other liver cells (as the sporozoites did initially)→ a new cycle is starting → exo-erythrocyte cycle
- Those merozoites that enter the blood stream, enter the RBC → starting the erythrocyte cycle
- The merozoites form trophozoites- a ring-like shape where the nuclear material looks like a “diamond on the ring”
- Nuclear division occurs again, forming schizont →merozoite → lysis of the RBC and release of the merozoites to the circulation
- The last step initiate immune response- resulting in fever, chills and sweats
- The merozoites continue the cycle
- Some of them will change to female and male gametocytes → these are taken back by the mosquito
- Plasmodium vivax & plasmodium ovale produce dormant form in the liver, called hypnozoites→ grows years after the first infection
In the mosquito:
- The sexual cycle = sporogony
- The gametocytes are sucked into the stomach → female and male gametocytes fuse
- The DNA is mixed → oocyte is formed
- Oocyte divides to spindle-shaped sporozoites →disseminate to the blood stream → reach the salivary glands → injected into humans, starting the human cycle
Diagnosis of fungal disease
Staining properties:
- False Gram positive
- Can be stained by
- methenamine-silver
- periodic acid-Schiff stain (PAS)
- methylene blue
Specimens:
- Scrapings from the skin and the nails
- Hairs plucked from involved areas
- Microsporum-infected hairs fluorescent under Wood’s light (365nm) in a darkened room
Microscopy:
- Wet mount
- Simple staining (e.g. methylene blue)
- Before native examination- 30% KOH for keratolysis (for keratinized tissues)
Biochemical reactions:
- Sugar fermentation
- Sugar assimilation test
- Nitrate assimilation test
Serology: ELISA, latex agglutionation
Trichomonas vaginalis spreading and treatment
Transmitted by vaginal sexual contact; can survive for many hours at room temperature if kept damp, so the theoretical possibility of non-venereal transmission exists
Occurs in female vagina and male urethra
Treatment: metronidazole, tinidazole
Fasciola hepatica – intermediate and final host and disease
Intermediate host - snail
Final host - cattle, sheep
Symptoms vary depending on if the disease is chronic or acute.
- During the acute phase the immature worms begin penetrating the gut, causing symptoms of fever, nausea, swollen liver, skin rashes and extreme abdominal pain.
- The chronic phase occurs when the worms mature in the bile duct, and can cause symptoms of intermittent pain, jaundice and anemia.
The disease is called fascioloasis.
Toxocara canis
Life cycle:
- Final host: cat, dog → gravid female vacates the eggs in the gut → with feces, the eggs get into the soil → maturation in the soil → larvae in humans → granulomatous infection (liver, brain)
- The infection is acquired from ingestion of embryonated eggs released in the soil
- After ingestion, the larvae begin somatic migration to the lungs, liver, eye, CNS
Disease:
- The clinical presentation depends on the number of larvae ingested and the degree of allergic response
- 2 major syndromes have been identified:
- Visceral Larva Migrans (VLM)- characterized by fever, malaise, leukocytosis with hypereosinophilia, hepatomegaly, cough, myalgias, high titers of isohaemagglutinins. Other manifestations: myocarditis, encephalitis and pneumonia
- Ocular Larva Migrans (OLM)- characterized by retinal granulomas and uveitis → blindness
Diagnosis:
- Western-blot analysis
- Detection of antibodies by ELISA
Therapy: tiabendazole
Subcutaneous mycosis
- Infections involving the dermis, subcutaneous tissues, muscle and fascia
- Present in soil or on vegetation
- Traumatic inoculation by contaminated material
- In rare cases, they become systemic and produce life-threatening disease
Sporothrix schenckii:
- A thermally dimorphic fungus that lives on vegetation: grass, trees, moss, rose bushes, and other horticultural plants
- Initial lesion is usually on the extremities
- Initial lesion develops as a granulomatous nodule that may progress to form necrotic lesion
- Dissemination: bones, eyes, lungs
- Treatment: local treatment- potassium iodide, itraconazole, fluconazole, amphotericin B
Chromoblastomycosis:
- Chronic, localized infection of the skin and subcutaneous tissue of the limbs
- Characterized by raised, crusted lesions
- Slow development
- Fungi are introduced to the skin by trauma
- Over months, the primary lesion becomes verrucous and wart-like
- Cauliflower-like nodules cover the area
- Rarely elephantiasis may result from secondary infection and fibrosis of lymph channels
Maduromycosis:
- Mycetoma: local swelling and interconnecting. Containing granules which are microcolonies
- Eumycetoma: mycetoma caused by a fungus, develop after traumatic inoculation with soil
- Suppuration, abscess formation, granulomas
- May spread to muscle and bone
- Treatment: ketoconazole, itraconazole
