This week's case is kindly donated by Dr. Vasundhara (Vasu) Rangaswamy, a primary care physician and laboratorian who spends most of her time doing rural community health work and building laboratory capacity in rural India. She and her team found the following object in a urine specimen from a middle-aged woman living in an impoverished community in rural central India. What is your identification?
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.
The following worm was found in a toadfish caught by Florida Fan in Blind Pass, Saint Petersburg, Florida. What is the likely identification?
Answer to the Parasite Case of the Week 818: Anisakid larva
As noted by Daniel Tanzola, Sarah Sapp, Antoine, Idzi Potters, HCLM fan, and others, the size and characteristic morphologic features of this worm - including the anterior perforant ("boring") tooth and slightly rounded caudal end with a small mucron - together with the fishy story, all point to this being an L3 anisakid larva.
Anisakiasis is a zoonotic infection caused by third-stage (L3) larvae of ascaridoid nematodes, most commonly species in the genera Anisakis, Pseudoterranova, and Contracaecum. Humans become accidental hosts when they consume raw or inadequately cooked fish or squid containing viable larvae. Since humans are not suitable definitive hosts, the larvae cannot mature to adulthood, but they may invade the gastric or intestinal mucosa and cause disease.
Anisakid larvae recovered from clinical specimens are typically several centimeters long (~20–35 mm) and can be provisionally identified by their gross and microscopic morphology. At the anterior end is a small, triangular boring tooth that the larva uses to penetrate host tissues. Note the developing lips; adult ascaridoids have 3 well-defined fleshy lips. An excretory pore is also present near the anterior end and its location can be useful for identification. The boring tooth may be difficult to appreciate and can be damaged or lost when the worm is extracted from the mucosa during upper endoscopy.
The posterior end provides another useful clue. Some anisakid L3 larvae possess a small terminal projection called a mucron, which is readily visible in a well-preserved specimen such as the one in this case. The presence or absence of a mucron, together with features of the digestive tract and the location of the excretory pore, can help distinguish among the major anisakid groups. A mucron is typically present in Pseudoterranova and Anisakis Type I larvae, whereas it is absent in Anisakis Type II larvae and Contracaecum.
Species-level identification based on larval morphology alone can be challenging, however, and molecular methods are generally required for definitive identification. Fortunately, for the purposes of this case, "anisakid larva" is a perfectly satisfying diagnosis - particularly since this particular worm ended up in formalin rather than in Florida Fan.
This week's case was generously donated by Dr. Ben Von Bredow. The following object was sent to the laboratory for identification after being passed by a patient from Michigan. No additional information is available. What is your identification?
