Answer to Case 634

 Answer to Parasite Case of the Week 634: Free-living mite, likely contaminant during specimen collection/preparation.

Note the 8 legs (consistent with a member of the arachnidae) and the long spines (setae). It is easier to appreciate all 8 legs by carefully watching the video in this case.

As noted by Marc Couturier, "I mite have to say this is a contamination of the preparation and not coming from stool."  I agree with this assessment! While this mite could have been ingested from a food source (e.g., mimolette cheese; see my previous post), I find it highly unlikely that the mite would still be alive and active after passing through the intestinal tract. I also find the presence of squamous epithelial cells nearby to be rather suspicious for environmental contamination. 

Thanks again to Dr. José Poloni for donating this interesting case, and to all of the readers who wrote in with their helpful commentary. 

Case of the Week 634

 This week's case was generously donated by Dr. José Poloni. The following was found in a stool specimen. Identification? Significance? 

(you may need to click twice on the video below to play)

 

Answer to Case 819

 Answer to the Parasite Case of the Week 819: Mite, not a human pathogen. 

Nice job to everyone who recognized it! As several of you noted, its presence in a urine specimen is almost certainly incidental and represents environmental contamination rather than a true infection. There are many different types of mites in the environment, and identification to genus or species can be quite challenging and generally requires examination of specific morphologic features by someone with expertise in acarology. Fortunately, we don't need to do that here. From a clinical laboratory perspective, the important thing is recognizing this as a mite and determining whether it could be medically significant.

Several readers correctly emphasized that this is not the scabies mite, Sarcoptes scabiei. Idzi nicely pointed out that S. scabiei has a much more rounded body with short, stubby legs. Compare our mite with the classic appearance of S. scabiei, and the difference is quite striking. The very long setae ("hairs") and long legs on our mite are also a useful clue that we are dealing with something else. As Florida Fan so aptly put it: “What so hairy! Yet so small…” — a mighty mite indeed! Florida Fan also noticed that we've encountered similar visitors before in Cases 548 and 634. Here is a nice image from Case 723:

While this is not a human parasite, it doesn't necessarily mean it is incapable of bothering humans. Some mites that normally parasitize birds, rodents, or other animals can opportunistically bite humans. Bird mites are a good example, particularly when their usual avian hosts disappear or abandon a nest. They do not establish a Sarcoptes-like infestation in humans, but their bites may cause pruritic papules and can be quite bothersome. Therefore, the clinical history is important. An incidental mite found in a specimen from an asymptomatic patient is quite different from mites repeatedly recovered in the setting of an ongoing unexplained dermatitis. In the latter situation, it may be worthwhile to have specimens formally identified by an entomologist or other appropriate expert and to investigate the home or workplace for a possible source. Pest-control professionals may also be helpful in identifying and eliminating an environmental infestation. 

So, what should the laboratory report? Something simple such as “Mite identified; not consistent with Sarcoptes scabiei” would be reasonable. Further identification is unnecessary unless there is a specific clinical or epidemiologic reason for doing so.

Thanks again to everyone for the excellent discussion! And many thanks to Dr. Vasundhara (Vasu) Rangaswamy for sharing this case with us. As I mentioned previously, Dr. Rangaswamy practices in rural India and has generously shared the following photographs of herself performing a slit-skin smear on a patient with leprosy. In one of the images, she is using a separate light source for microscopy, as reliable electricity is not always available in her rural setting.

Dr. Rangaswamy has kindly given me permission to share these photographs and hopes that they will help raise awareness of the realities of practicing medicine in rural, resource-limited settings. They are also a wonderful reminder of the ingenuity and dedication required to provide essential diagnostic services when many of the resources we routinely take for granted are not readily available.

Answer to Case 656

 Answer to the Parasite Case of the Week 656: mite, probable contaminant from the environment. Not likely of human medical significance.

As several readers noted, this mite is not one of the 2 human pathogenic mites, Sarcoptes scabei or Demodex. Instead, it is likely a mite from the environment, such as Dermatophagoides, the dust mite. The presence of many squamous epithelial cells in the background would support this idea:

You can read the following posts for more information for how to differentiate the various mites found in human specimens:

Case of the Week 634: Free-living mite found in stool

Case of the Week 196: Differentiating Sarcoptes scabei from other mites

Case of the Week 601: Key identifying features of Sarcoptes scabei