Parasitology

Question 1

Trypanosoma brucei

Answer 1

• Life cycle: Tsetse fly injects into bloodstream, binary fission. Key point: extracellular
• Causes African Sleeping Sickness (African Trypanosomiasis) characterized by somnolence and demyelination
• Time scale to CNS system infection (stage 2): Gambiense (1-2 yrs); Rhodesiense (few weeks). Treat in stage 1 (lymphatics). *Waves of parasitemia

Question 2

Trypanocidal drugs

Answer 2

Stage 1:

• Pentamidine: does not penetrate CNS, IM delivery, mild toxicity
• Suramin: slow IV admin (not practical), loss of consciousness, nephrotoxic, etc. Don’t take unless have to.
• Nitroaromatics (Nifurtimox & Benznidazole): no BBB, but GI absorption. Pretty Toxic.

Stage 2:

• Arsenicals (Melarsoprol): The nasty one, extremely toxic; 5-10% encephalopathy and 1/2 of those die
• Eflornithine: trypanostatic, need long IV infusion. Not as bad toxicity as Melarsoprol. Need functional immune system. Inhibits ornithine decarboxylase

*Eflornithine + Nifurtimox is best option for late stage African trypanosomiasias.

Question 3

Trypanosoma cruzi

Answer 3

Endemic to Latin America or Mexico (kissing bug transmission). Causes Chagas’ disease. Intracellular and extracellular bloodstream stages.

Question 4

Chagas’ Disease

Answer 4

• Acute stage is mild, asymptomatic. Drugs effective
• Chronic stage (20-40%) can cause myocarditis. Can happen decades after initial infection. US transmission could occur through blood supply.

Question 5

Leishmania spp.

Answer 5

• Req. uptake by phagocytic cell
• Transmitted by sand fly
• Causes Leishmaniasis (skin lesions, splenomegaly, mucocutaneous leishmaniasis)

Question 6

Antileishmanial Drugs

Answer 6

Organic antimonials Sodium stibogluconate & Meglumine antimoniate

• interferes with glycolysis and fatty acid beta oxidation
• toxicity increases over time

Question 7

Toxoplasma gondii

Answer 7

• Ingest cysts, litterbox, cats usually pick it up by eating rats and birds, cats poop. Unwashed produce and animals that we eat that ingest cysts.
• Opportunistic: the T in TORCH infections.
• Causes toxoplamosis: often occurs in basal ganglia (tremors, chorea, hemiballism)

Question 8

Toxoplamosis

Answer 8

Caused by toxoplasma gondii.
-basal ganglia
-Ocular toxoplasmosis- headlight in the fog lesion in fund. exam
-Perinatal toxoplasmosis: prego dont change litter box. Abnormal head size and neuro deficits
*Pregnant women and immunocomprompised get drugs, most don’t
Treat with atovaquone and folate antagonist combo
-Spiramycin is macrolide used, need to obtain FDA if prego

Question 9

Naegleria fowleri

Answer 9

• Thermophilic freshwater amoeba
• Normally eats bacteria
• Rarely, can consume neural tissue and penetrate to CNS
• Penetrates via the olfactory epithelium if mucosal surface fails; into the olfactory bulbs and to the meninges

Question 10

What are the diagnostic hints of Primary Amebic Meningoencephalitis ?

Answer 10

Symptoms being about 5 days post-infection:
Initially: Headache, nausea, fever, vomiting
Later:
-Stiff neck
-Confusion
-Lack of attention to people and surroundings
-Loss of balance, seizures
-Hallucinations
Rapid disease progression, death usually occurs within about 5 days