Medically Important Parasites Part II Flashcards
What is Giardia intestinalis?
A mild intestinal disease with global distribution
What is toxoplasma gondii?
A parasite that infects 30% of the world’s population and is the most successful parasite
What is the parasite with the highest rate of morbidity and mortality?
Malaria
What is the most diverse disease phenotype caused by a parasite?
Leishmania
What are the stages of giardiasis?
Trophozoite and cyst form
Where is giardiasis located?
It is distributed worldwide and is more prevalent in warm climates in water sources.
What ages does giardia commonly infect?
It is more common in children but can happen all over the world. It is highly capable of causing disease with only 10 cysts required for infection.
How is giardiasis diagnosed?
Faecal sample and biopsy can be done as well. String test Immunological tests (antigen immunoassays, immunofluorescence) Microscopic observation of cysts or trophozoites in faeces Symptoms
How is giardia transmitted?
Person to person (hand to mouth (children, siblings, etc and can be caused by some sexual practices) Contaminated food and water (Epidemic if water supply contaminated, unhygienic food handlers)
Why is giardiasis easily transmitted?
Infectious dose is very small The cysts are resistant to chlorine and other disinfectants They remain viable for weeks in cold water There are animal reservoirs of some genotypes
How can giardiasis be prevented?
Communal, group and personal hygiene Avoidance of potentially-contaminated water and food.
How is giardiasis treated?
Metronizadole (widely used and effective) Tinidazole Mepacrine Nitazoxanide Paromomycin Albendazole (similar to metronizadole with fewer side effects and simplified regimen)
How is giardiasis treated?
Metronizadole (widely used and effective) Tinidazole Mepacrine Nitazoxanide Paromomycin Albendazole (similar to metronizadole with fewer side effects and simplified regimen)
What does metronidazole act on?
DNA
What does tinidazole act on?
DNA like metronidazole but slightly more effective. (it is 5-nitrimidazole)
What does mepacrine do?
It is cell membrane active and related to mefloquine and causes psychosis.
What kind of reproduction takes place in the cat by toxoplasmosis?
Both sexual and asexual reproduction
Why is toxoplasmosis the most successful parasite ever (in Dr. Christopher’s opinion)?
- It has at least 5 mechanisms of transmission. 2. Despite it having only 1 definitive host it can infect every warm blooded animal and bird. 3. It can infect every nucleated cell 4. It can live inside you for your entire life and you would never know) 5. It does not kill it’s host (normally) 6. However, it does effect your brain to improve it’s chances of transmission 7. It is very hard to treat
What are the symptoms of toxoplasmosis?
Often asymptomatic (in 90% of people) Lymphadenopathy with/without fever Eye lesions Myocarditis
How is toxoplasmosis acquired?
Acquired from cysts in soil or pseudocysts in undercooked meat Transmission via faecal material in cat or other animals being touched after they have had cysts on them. Direct contact with animal faecal material Organ transplant + immunodeficiency Blood donation
What does toxoplasmosis do to foetal development?
Can result in abortion, still birth, hydrocephaly (mental retardation and eye lesions), acquired by vertical transmission across placenta.
What kind of disease does toxoplasmosis cause in immunodeficient people?
Reactivation of latent infection Fatal, acute fulminating disease: Necrotising encephalitis Pneumonitis Myocarditis
How does toxoplasmosis cause effects in foetuses?
It only has an effect when first contracted during pregnancy
What kind of infection can toxoplamsa gondii cause in immunocompetent?
Eye lesions: uveitis, retinochoiditis, choroiditis
How is toxoplasmosis commonly diagnosed via serology?
ELISA Fluorescent antibody Haemagglutination Complement fixation
What non-serological methods are there for toxoplasmosis diagnosis?
Biopsy or biopsy materials including bone marrow, spleen, CSF, lymph, brain Inoculation of suspect materials into lab animals such as mice, rabbits, or guinea pigs (Xenodiagnosis) PCR, especially in detecting congenital infections in utero
How can toxoplasmosis be prevented?
Adequate cooking of meat Proper disposal of cat faeces Protecting children’s play areas especially in household environment
How is toxoplasmosis treated?
No satisfactory treatment available. (Synergistic pyrimethamine is found to cause some improvement) Toxoplasmosis is not treated if person is asymptomatic but if the infectious titre is rising treatment is indicated especially when starting immunosuppressive therapy.
How are infants treated if they have a toxoplasmosis infection?
Infants are treated with transplacental treatment if the infectious titre is rising
What are the possible long term sequelae of toxoplasmosis?
Evidence indicates it being linked to schizophrenia (note that in this study only maternal antibody to genotype I was predictive of increased risk of psychosis in adult offspring) [contradictory results] Significant link to bipolar disorder but not to any unipolar mood disorders Brain cancer Manipulation hypothesis states that T.gondii manipulates host to act in ways that increase probability of transmission Reduces response time associated with car accidents
What kind of parasite causes malaria?
Oligate intracellular blood sporozoan found in tropical and sub-tropical climates.
Why is malaria limited to tropical and sub-tropical areas?
That’s where the vectors are located.
What are the causative pathogens of malaria?
5 species: P. falciparum P. vivax P. Malariae P. Ovale
Which species of malaria causes the most serious disease?
P. Falciparum
How are species of malaria differentiated?
Morphology and staining characteristics Number of merozoites in blood Appearance of infected blood cell Pathology
Which mosquito is implicated in transmission of malaria?
Female Anopheles Mosquitos
How do the malaria species differ morphologically?
What distinguishes P. falciparum from the others is the 2 banana shaped structures connecting 2 balls
How many cases of malaria are there every year?
350 - 500 million and more than 1 million deaths (mostly young children)
Where do most malaria cases occur?
90% of malaria cases in Africa
How does malaria do its damage?
Mosquito contains male and female gametophytes which combine sexually to form a sporozoite.
Sporozoite enters the blood stream and finds the liver and enters hepatocytes
Sporozoites reproduce asexually to form merozoites and shizont which eventually ruptures hepatocyte.
Merozoites enter the bloodstream and infect RBCs and form trophozoites which then also burst. The resulting trophozoite starts the cycle again.
New gametophytes form simultaneously to the merozoites and start the cycle again.
How does malaria kill people?
Haemorrhaging in internal organs (thousand of microhaemorrhages)
Anaemia
Raised intracranial pressure due to sequestered parasites
Hypoglycaemia and severe metabolic acidosis
Who does malaria typically affect?
Young children and people with immune deficincies.
What treatments are commonly used for malaria?
Quinine and related agents (choloroquine)
Amodiaquine (pyrimethamine)
Proguanil (sulfonamides, mefloquine, atovaquone)
Primaquine
Artemisin combination therapy
Halofantrine
Doxycycline
Clindamycin
Spiroindolones
Why is artemisinin combination therapy used?
To combat potential drug resistance
How can malaria be prevented?
Prophylaxis therapy
What are the types of life cycles that leishmania undergoes?
Digenetic life cycle, zoonosis
What are the types of Th responses to leishmania infection?
Cutaneous leishmaniasis creates a Th1 response
Mucosal leishmaniasis creates a Th1/Th2 response
Visceral leishmaniasis causes immune suppression
What species of leishmania cause cutaneous leishmaniasis?
L. major
L. tropica
What species of leishmania cause mucosal leishmaniasis?
L. braziliensis
What species of leishmania cause visceral leishmaniasis?
L. donovani
L.infantum
What does cutaneous leishmaniasis progress to?
Mucosal leishmaniasis
How is leishmaniasis typically diagnosed using parasitology?
Spleen palpation
Parastites found in aspirates of bone marrow, lymph nodes or spleen
Giemsa stain, culture in blood agar or hamster
How is leishmaniasis diagnosed using lab tests?
ELISA (Enzyme linked immunosorbent assay)
IFAT (indirect immunofluorescence test)
DAT (Direct agglutination test)
Formol Gel Test (aldehyde test)
Immunochromatographic dipstick test, specific antigen Kd39
Montenegro skin test - cannot differentiate between past and current infections
PCR (RFLP)
What happens if visceral leishmaniasis is coinfective with HIV?
They both potentiate each others effects and cause drop in CMI
How is visceral leishmaniasis diagnosed?
Hard palpable spleen, fever and wasting
How is leishmaniasis treated?
Pentavalent antimonials, amphotericin B, paromomycin, pentamidine isethionate, miltefosine and azoles.
Cytokine therapy is very expensive
All drugs for leishmaniasis are toxic
How can leishmaniasis infection be prevented?
Avoiding exposure, protective clothing, bed-nets (sandfly vector), repellents, vector control, and reservoirs control (treatment or elimination of infected dogs)
Do any vaccines exist for leishmaniasis?
Only in dogs
What is the problem with anti-leishmaniasis drugs?
They are toxic and are prone to resistance
What is the vector that is common in leishmaniasis?
Sandflies
What are the common symptoms of ascaris lumbricoides?
Often asymptomatic (85% of cases)
Worms can cause intestinal obstruction as well as inflammation due to presence in blood.
Ascaris metabolites can cause sensitizing phenomena like urticaraia and asthma.
It can move around the body and block narrow organs accidentally
How can ascaris lumbricoides be diagnosed?
Recovery of eggs from faeces or adult worms
How is ascaris infection treated?
Mebebdazole, albendazole (except in pregnancy), Levamisole, thiabendazole, Pyrantel, piperazine – worms can migrate away from gut to avoid drugs
How can ascaris infection be prevented?
Clean sanitary toilet and food preparation facilities.
Good personal hygiene.
What causes schistosomiasis?
3 separate species of trematodes:
Schistosoma (S. mansoni, S. japonicum (intestinal), and S. haemotobium (bladder))
How do schistosoma species get into people?
Schistosoma contaminate water and then burrow into skin.
Enter bloodstream
Migrate into lungs and cause eosinophilia (loefflers syndrome)
They go to mesenteric vessels or bladder vessels and they pair up near the organs and sexually reproduce to the outside of the body.
Fibrosis from the immunogenic eggs produced by these parasites cause damage.
What locations can granulomas be found in following schistosomiasis and what kind of symptoms do they produce?
Brain granulomas - epilepsy
Lungs - pulmonary hypertension
Heart - Cor pulmonale
Spinal cord - paraplegia
Liver - fibrosis
Spleen - Splenomegaly
Genitourinary tract - Bladder cancer
How can schistosomiasis be diagnosed?
Stool sample: Identify eggs (lateral spined, terminal spined, or small lateral knob)
Rectal snip: Proctoscopy: take 6 snips of mucosa, crush between glass slides and look on microscope
Serology: indicates past or present infection. CFT/ELISA. Useful for screening
Antigen detection: In research laboratories identifies living worms
How is schistosomiasis treated?
Praziquantel (single oral dose)
Metrifonate (can be used instead for SH 3 doses are given over several weeks)
Oxamniquine (for SM. 2 doses on 1 day. Less effective for children
How can schistosomiasis be prevented?
Educate public
Prevent urine and faeces from contaminating fresh water. Build latrines
Improve irrigation and agricultural systems to prevent snail build up.
Avoid skin contact with fresh water.
Provide cercariae-free water for drinking, washing
Identify infected persons and treat.
