6/22: Protozoans III: Toxoplasmosis and Malaria Flashcards
Humans are ___ hosts of Toxoplasma gondii?
Humans are intermediate hosts of Toxoplasma gondii
Cats are the ___ hosts of Toxoplasma gondii?
Cats are the definitive hosts of Toxoplasma gondii; the actual life stages occurs in those hosts
Life cycle of T. gondii in cats?
- Infected by carnivorism of tissue cysts (containing dormant bradyzoite) ingested by the cat
- Viable organisms are released and trophozoites/tachyzoites invade epithelial cells of small intestine
- Undergo sexual cycle and produce oocysts which are excreted
So the three forms are:
- Trophozoite/tachyzoite (invade tissues)
- Dormant bradyozoite (in tissue cysts)
- Oocyte (excreted by cats)
How can humans be infected with T. gondii?
- Ingestion of undercooked infected meat containing Toxoplasma cysts
- Ingestion of oocyst from fecally contaminated hands or food
- Organ transplantation or blood transfusion
- Transplacental
What is this? Which end is front?
Tachyzoites (of T. gondii)
- Tapered anterior end
- Blunt posterior end and large nucleus
Found in various sites throughout body of host
What is this? Found where?
Tissue cysts of T. gondii
- Most commonly in skeletal muscle, myocardium, and brain
- May remain throughout life of the host
- Typ spherical in the brain but more elongated in cardiac/skeletal muscle
Where in the world is T. gondii normally found?
High prevalence in France (related to eating raw/undercooked meat)
- up to 90% by age 30-40
US:
- 5-45% of population is seropositive
Congenital infection
- 0.1% of pregnancies
Acute infection of T. gondii presents how? Sx last how long?
- Often asymptomatic in immunocompetent persons
- Cervical lymphadenopathy and/or mononucleosis-like illness (10-20%)
- Clinical course typ benign and self-limited with symptoms resolving within a few months to a yr
- Ocular Toxoplasma: retinochoroiditis (from congenital infxn or infxn after birth)
Characteristics (of spread) of congenital Toxo?
- Results from acute primary infection acquired by mother during pregnancy
- Chance of infection is greater with advancing gestational age at the time of maternal linfxn (but severity worse if earlier infection?)
- Treatment of mom may reduce incidence of congenital infection and reduce sequelae in infant
Symptoms of congenital Toxo?
Fetal infection may lead to:
- Intracranial lesions
- Disseminated infxn in early infancy
- Serious neurological impariment
- Retinochoroiditis
Ocular Toxoplasma (from congenital infxn or infxn after birth)
- Causes retinochoroiditis
- Pt often asymptomatic until 20s/30s when lesions develop in the eye
Reactivation infection of Toxoplasmosis is possible in what hosts?
- AIDS
- Transplant patients
Usually caused by reactivation of chronic infection
Primary symptoms of reactivation infection of Toxo?
- Encephalitis or CNS mass lesion (picture)
- Rarely chorioretinitis or pneumonitis
What is this?
Ocular Toxoplasma (from congenital infxn or infxn after birth)
- Causes retinochoroiditis
- Pt often asymptomatic until 20s/30s when lesions develop in the eye
How do you diagnose Toxoplasmosis?
Serologic testing is the routine method of diagnosis
Also:
- Observation of parasites in pt specimens (e.g. BAL material or LN biopsy)
- Isolation of parasites from blood or other body fluids, by intraperitoneal inoculation into mice or tissue culture
- Detection of parasitic genetic material by PCR, esp in detecting congenital infxns through amniocentesis
Who needs to be treated for Toxoplasmosis?
- Not need for healthy non-pregnant person (Sx will usually go away within few weeks)
- Do need to treat compromised pts, pregnant women, and newborns
Treatment of Toxo: AIDS?
AIDS: 4-6 wks of primethamine and sulfadiazine
Alternatively: cinda/pyrimethamine
- Followed by suppressive therapy
Treatment of Toxo: Congenital?
1 yr of pyrimethamine and sulfonamide
Treatment of Toxo: Women in 1st TM? After 1st TM?
1st TM: Spiramycin
> 1st TM without transmission to fetus: Spiramycin
> 1st TM with transmission in utero: Pyrimethamine and Sulfadiazine
Characteristics of Spiramycin for treatment of Toxoplasmosis?
- Class
- Delivery
- Method
- Adverse side effects
- Macrolide
- Oral
- Inhibits growth of susceptible organisms (mech unknown)
- Side effects: GI, prolonged QT
Characteristics of Pyrimethamine for treatment of Toxoplasmosis?
- Dihydrofolate reductase inhibitor (folic acid antagonist)
- Long-acting
- Most effective agent for Toxoplasmosis
Toxicity:
- Dose related suppression of bone marrow; decreased by giving folinic acid (Ca leucovorin)
- GI distress, rash, headache, bad taste in mouth
- Potential teratogen; only use after 1st TM!!
Characteristics of Sulfadiazine for treatment of Toxoplasmosis?
- Sulfonamide
- Intermediate-acting
- Acts synergistically with pyrimethamine
Toxicity:
- Skin rashes (sometimes life-threatening)
- Crystal induced nephrotoxicity
- Hallucinations, new onset of psychiatric symptoms
What is the treatment of choice for Toxo?
Combo of Pyrimethamine and Sulfadiazine
- Response rates 68-95%
- Limited by toxicity (but used ubiquitously in AIDS pts) ((Single most efficient agent is Pyrimethamine)
How to treat someone with Toxo who’s allergic to sulfa drugs?
Pyrimethamine and Clindamycin
Characteristics of Clindamycin for treating Toxoplasmosis?
- Acts by targeting transplantation in the apicoplast of T. gondii
- Acts synergistically with pyrimethamine
Toxicity:
- Rashes
- Nausea/vomiting (if oral; not with IV)
- Diarrhea; may be associated with C. difficile infection
(Also limited to toxicity)
Alternative Toxo Treatments? When to use? Characteristics?
Trimethoprim/Sulfamethoxazole (Bactrim)
- Not 1st line, but used for prophylaxis for toxo and pneumocystis
- Used in treatment of Isospora and Cyclospora infxns
- Toxicity: bone marrow suppression, rash, elevated liver enzymes, interstitial nephritis, nausea/vomiting
Pyrimethamine & Folinic Acid and one of:
- Atovoquone - Clarithromycin - Azithromycin - Dapsone
- These have been used in clinical studies with few pts and have response rates lower than the standard regimens
What is the #1 cause of parasitic death?
Malaria