Pathogenesis of human strongyloidiasis: autopsy and quantitative parasitological analysis

The distribution of pathologic lesions and the parasite burden of major organs were studied in seven patients with disseminated strongyloidiasis who were autopsied at the University of Texas Medical Branch (Galveston, TX). All patients were immunosuppressed and had additional bacterial, viral, and fungal infections; six patients had received cortisone therapy and one patient had AIDS. High Strongyloides burdens were noted in untreated patients or in those with a short period of treatment. The proximal small intestine and the lungs showed the heaviest parasite burden, with large numbers of filariform larvae found in both locations. The lungs showed persistence of larvae in all patients, in the absence of intestinal or extraintestinal infection; this suggests that the respiratory cycle may be more resistant to therapy than the intestinal cycle. In the intestines, filariform larvae were seen at all levels, but higher burdens were seen in the upper as compared to lower small intestine, and larvae were more concentrated in the proximal jejunum than in the duodenum. Autoinfection (i.e., filariform larval penetration) occurred more prominently in the distal small and proximal large intestine than in the distal colon. Most filariform larvae were found in the intestinal lymphatics and were highly concentrated in mesenteric and retroperitoneal lymph nodes; conversely, larvae were not found in the spleen and were found in very low density in the liver. These findings, in concert, suggest that during autoinfection in humans, the Stronglyloides larvae transverse lymphatics to the thoracic duct, then pursue a lymphohematogenous dissemination to the lungs where they penetrate the air spaces and ascend through the airways to reach the gut.