Sunday, August 23, 2009

Case of the Week 82

The following thin Giemsa-stained blood smear is from a missionary who just returned from Tanzania. (CLICK ON IMAGES TO ENLARGE)

What are the identifying features of this case?

Saturday, August 22, 2009

Answer to Case 82

Answer: Plasmodium falciparum

The key identifying features are:
1. The infected RBCs are not enlarged (compared to the enlarged RBCs infected by P. ovale and P. vivax.
2. Parasite rings are small and delicate, occupying approximately 1/3 of RBC diameter.
3. Applique or Accole forms are present. These are rings that appear to be 'stuck' onto the edge of the RBC.
4. Presence of Maurer's clefts or dots. These are cytoplasmic structures derived from the malaria parasite. They have a similar appearance to the 'stippling' seen in infection with P. ovale and P. vivax, but the dots are fewer and larger. In order to see Maurer's clefts, it is essential to have your malaria buffer at the proper pH, that is, at 7.2.

Maurer's clefts and stippling are not seen in infection with P. malariae.

Monday, August 10, 2009

Case of the Week 81

The following worms were identified in this papanicolaou-stained sputum from a 70 year old man being treated with chemotherapy for disseminated lung cancer. They measure approximately 500 micrometers in length. What is the most probable diagnosis? (CLICK ON IMAGES TO ENLARGE)

Sunday, August 9, 2009

Answer to Case 81

Answer: Probable Strongyloides stercoralis filariform (L3) larvae.

Congratulations to everyone who wrote in with the correct answer! You all recognized that these are nematode (round worm) larvae. The clinical history and presence of larvae in the sputum are most suggestive of S. stercoralis, although it is difficult to make out specific features from these photographs to make a definitive diagnosis. The fact that they are relatively elongated suggests that they are the 3rd stage larvae (L3 or filariform) which is the typical stage that is seen in the lung during autoinfection.

Monday, August 3, 2009

Case of Week 80

The following insect is a vector of 2 important South American viruses. Identification?

Bonus: list the viruses

Answer to Case 80

Answer: Aedes aegypti mosquito
This is one of the most easily recognizable mosquitoes, due to its dark body and distinctive white markings. It closely resembles another human disease vector, A. albopictus (a.k.a. Asian Tiger mosquito), except that the latter has a single straight white stripe on its dorsal thorax instead of lateral curved stripes.

A. aegypti is the vector of Yellow Fever, Dengue, and Chikungunya virus. The former two viruses may be found in South America, and are the answer to the second question of this case.