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?
Answer to the Parasite Case of the Week 817: Fish tape worm, Dibothriocephalus, Diphyllobothrium, or Adenocephalus species.
There are several characteristic morphologic features present in this case. First, we have a long portion of a tapeworm body (strobila) with proglottids that are broader than they are long. As noted by Florida Fan, the strobila is craspedote, meaning that the posterior margin of each proglottid overlaps the anterior portion of the following segment. Additionally, a dark, centrally located uterus is present in each mature proglottid. In well-cleared specimens, the uterus has a characteristic rosette-like appearance. Together, these features are characteristic of the fish tapeworms in the family Diphyllobothriidae.
Several readers wondered whether the very narrow portion of the worm represented the scolex (arrow below).
Had we been lucky enough to recover the scolex, we would expect it to have two longitudinal grooves called bothria, rather than the four muscular suckers seen in the more familiar cyclophyllidean tapeworms such as Taenia species.
Fish tapeworm infection is acquired by eating raw or inadequately cooked fish containing the infective plerocercoid larva. The life cycle involves a small aquatic crustacean (usually a copepod) as the first intermediate host and a fish as the second. Larger predatory fish may acquire plerocercoids by eating smaller infected fish, allowing the parasite to work its way up the food chain until, eventually, somebody decides that fish would be delicious raw or undercooked. I enjoyed HLCM fan's reminder that sushi and sashimi aren't the only potential exposures. Ceviche and inadequately processed fish are also possibilities, and smoking, salting, or pickling shouldn't automatically be assumed to kill the plerocercoids. Adequate cooking or appropriate freezing is needed to reliably dispatch these unwanted dinner guests.
So, could someone acquire a fish tapeworm from a fish caught in Michigan? Potentially, yes! Diphyllobothriid larvae have actually been documented in Michigan fish. A Michigan Department of Natural Resources review describes historical human infections with Dibothriocephalus latus (then Diphyllobothrium latum) associated with fish from Portage Lake in Michigan's Upper Peninsula. Unidentified Diphyllobothrium plerocercoids have also been reported from salmon collected from Michigan tributaries of Lakes Michigan, Superior, and Huron. Fish-eating mammals and birds can serve as definitive hosts and keep the cycle going quite nicely without us. Having said that, the extent of today's globally transported seafood means that the place where someone lives tells us surprisingly little about where their tapeworm had been living previously. A good dietary and travel history would be very helpful here.
Regarding the taxonomy, since several of you asked: the classic "broad fish tapeworm," Diphyllobothrium latum, is now Dibothriocephalus latus. Other important human pathogens include Dibothriocephalus nihonkaiense (formerly Diphyllobothrium nihonkaiense), particularly associated with Pacific salmon; Dibothriocephalus dendriticus; and Adenocephalus pacificus (formerly Diphyllobothrium pacificum), predominantly associated with the Pacific coast of South America. Several true Diphyllobothrium species can also infect humans.
Unfortunately, the proglottids and eggs generally don't allow us to reliably distinguish these species. Molecular testing is usually needed if species-level identification is desired. Thus, without molecular identification, "Dibothriocephalus, Diphyllobothrium, or Adenocephalus species" is a reasonable identification for this impressive specimen.
Many thanks again to Dr. Ben Von Bredow for sharing this spectacular specimen!
Answer to the Parasite Case of the Week 816: Trichuris trichiura adult.
Our readers presented an excellent differential diagnosis based on the appearance of the nematode and its location in the intestinal tract. Even if you don't have a lot of experience with histopathologic sections, you can narrow the differential based on a few key features:
First, the gross appearance is consistent with a small nematode (10mm long according to the measurements provided, but we can also approximate the size based on the diameter of the intestinal lumen). The small size helps us narrow the differential to a few potential nematodes: Enterobius vermicularis, hookworm, Trichuris trichiura (assuming that part of the worm broke off during removal), an anisakid larva, and an immature Ascaris lumbricoides. It's great that we have 2 sequential photos in this case, showing how the tail curled up on itself, leading me to think that it might be a male nematode:
This week's case was generously donated by Dr. Jacob Rattin, a pathology resident at Cleveland Clinic.
A traveler returning from a lengthy hiking exploration in South America presented with itching, pain, and lesions on the soles of their feet. A skin biopsy was performed with showed the following on hematoxylin and eosin (H&E):
H&E, 25x magnification
Answer to the Parasite Case of the Week 815: Tungiasis, caused by the flea Tunga penetrans
The following excellent description is written by Dr. Rattin:
Tungiasis is endemic in Latin America, sub-Saharan Africa, and the Caribbean. As is sadly all too common, it predominantly affects resource-poor communities. There is no standard treatment, but recommendations include surgical removal, wound disinfection, and dimeticone-based topical therapy (NYDA – a mixture of two low-viscosity dimeticones).
Tunga penetrans is the chigoe flea (with myriad other names). Gravid females lay eggs which are shed in the environment. Here, the eggs hatch into larvae, which have two stages prior to forming pupae. The pupae are in cocoons, from which the adults hatch and search for a warm-blooded host. The males and females can feed on the host, but only the females will burrow into the skin. This answers the question in the case whether this is a male or female – it is a female since it has burrowed and because of the numerous eggs that are visible. Only the posterior ends will be exposed to the environment, with their anterior end burrowed into epidermis. They can shed about 100 large eggs over a two-week period. They will then die and be sloughed off by the host’s skin. The damage to the skin can cause secondary bacterial infections, even possibly leading to sepsis. If the patient tries to remove the embedded female by themselves without sterile tools, tetanus is also a possible complication.
The hematoxylin and eosin (H&E) stained sections showed hyperkeratosis of the overlying host skin and important features diagnostic of tungiasis. Identifiable features are the sclerotized cuticle (yellow) and tracheal rings (Figure 1), digestive tract (Figure 2), and numerous large eggs (Figure 3). The eggs are actually visible to the naked eye! These features, along with the large size of the embedded flea and the position within the epidermis help differentiate Tunga penetrans from other arthropods such as scabies and ticks that may be seen embedded within skin.
Figure 1, H&E, 100x magnification:
Figure 3, H&E, arrows pointing to two of many eggs. 100x magnification
Thanks again to Dr. Rattin for donating this great case!
