This week's case is a stool specimen from a 52-year-old Bolivian farmer. He complains of intermittent right upper quadrant pain, and an abdominal CT showed edema and dilation of the bile ducts.
A parasitologist's view of the world
The following microfilariae were seen on Giemsa-stained preparations of whole blood following the Knott's concentration procedure. They are between 180 to 200 microliters in length. No travel history was initially available. Identification?
Thanks to Heather Morris for these beautiful photos.
Answer to the Parasite Case of the Week 661: Mansonella perstans microfilariae.
As many of you noted, this filarial worm has very small, unsheathed microfilariae. Note that the microfilariae are more slender than the eosinophils - and even the RBCs! That is one of the most helpful features. They also have a blunt tail, and the nuclei extend to the tip of the tail.
Answer to the Parasite Case of the Week 660: Cysticercus; larval form of Taenia solium
As noted by Blaine, this is "ocular cysticercosis caused by T. solium, as indicated by a single protoscolex. Coenurosis caused by a zoonotic Taenia is also a possibility, but coenuri have multiple protoscoleces, as do hydatid cysts of Echinococcus. Sparganosis is another cestode infection that can manifest in the eyes, but they do not produce protoscoleces at all." Lots of great eye puns in the comments!
Here are some of the key diagnostic features:
This week's case features a digitally-scanned section of a subcutaneous nodule from the thigh of a man living in rural Senegal. The man presented with a several month history of severe itching in his lower extremities and abdomen, accompanied with a papular skin rash and focal loss of skin pigmentation.
Here is a low power view of the skin and underlying nodule:
Answer to the Parasite Case of the Week 659: Onchocerca volvulus adult worms and microfilarie.
If you didn't already see it, check out the whole slide scanned image HERE.
In this case, you can see a large subcutaneous nodule containing the adult worms (each female with a characteristic "double barrel" uterus) and microfilariae being released into the surrounding skin.
The microfilariae are the primary source of disease, as they crawl through the skin causing intense itching and inflammatory changes. They also go to the eye and cause irreversible blindness. The latter is the reason that infection is called "River Blindness". Infection is transmitted through the bite of infected black flies (Simulium sp.) which breed in fast flowing waters.
Answer to the Parasite Case of the Week 658: Trypanosoma brucei
Given the travel history and rapid onset of symptoms, T. b. rhodesiense is the most likely parasite present. This case shows very high parasitemia with numerous trypomastigotes seen on the patient's thick blood film. Here is the corresponding thin blood film, highlighting some of the key diagnostic features: