Answer to Case 695

The following excellent answer to this week's case is by our guest author, Jacob Rattin (@eternalstudying), medical student and future pathologist. 

Answer to the Parasite Case of the Week 695: Strongyloides stercoralis hyperinfection. 

Many readers commented that this was Strongyloides stercoralis, with several Twitter and LinkedIn users correctly mentioning “hyperinfection.” Great job! Here is the DIGITAL SLIDE for your reference. 

While this case had a very sad outcome, it highlights important features of Strongyloides hyperinfection. Individuals who are elderly or immunocompromised (eg, solid organ transplant, malignancy, corticosteroid treatment) are more likely to experience hyperinfection and severe disease. Hyperinfection can be life-threatening, as it was in this case, with massive numbers of larvae invading the tissues and resulting in death. 

In this histologic section, the eggs and larvae are easily appreciated. These forms are part of the infective life cycle, which starts when a human is infected by filariform larvae penetrating the skin, entering dermal vessels, and journeying to the lungs. The larvae then migrate up the bronchial tree, are swallowed, and arrive to the intestinal tract. Here, they mature into the adult female worms and begin laying eggs. An autoinfective cycle is part of the normal life cycle, and allows for perpetuation of the infection for decades. In the intestinal tract, female Strongyloides stercoralis worms are parthenogenic and do not need a male worm to make or lay eggs (“Who needs men?!” – Quote from Strongyloides stercoralis females, probably). With immune compromise, the low level of autoinfection can turn into a dangerous level of hyperinfection, leading to intestinal and pulmonary hemorrhage (from migrating larvae), bacteremia and bacterial meningitis (from gut flora carried by the larvae), and extensive organ damage. We can appreciate the damage to in the intestinal tract in this case, with extensive denudation and sloughing of the epithelial cells. 

You may recall from previous blog posts that eggs usually do not appear in the stool since they hatch and release rhabditiform larvae in the intestine. This case shows intestinal eggs with appreciable maturation within the eggs. Larvae within blood vessels (on their way to other organs) can also be seen. The histopathologic appearance in this case is diagnostic for strongyloidiasis. The only other infection that has a similar appearance is intestinal capillariasis, but the eggs have a very different appearance. 

Bonus Question Answers:

1.  Are there any infectious concerns with handling the fresh autopsy specimens?

Yes! With Strongyloides stercoralis, it is possible for those handling the autopsy to be infected with the filariform larvae that penetrate human epidermis. As Florida Fan said, “As always when dealing with Strongyloides stercoralis, all precautions should be taken to avoid a percutaneous infection with filariform larvae possibly present in the raw specimen.”

2.  What parasite forms are seen in this image?

As mentioned above, the parasitic forms observed are egg, larvae (rhabditiform, and filariform), and even the rare adult female.