The prevalence of S. stercoralis
among samples submitted to the Laboratory of Parasitology of the Muñiz Hospital has been approximately of 1% during the last 10 years. In our experience, it is more frequent than other roundworms (Ascaris lumbricoides
), although it should be noted that these data include all types of stool parasitological studies, such as controls after the therapy
Generally, patients referred from an outpatient clinic and different wards of the Muñiz Hospital are HIV positive, suffering from a syndrome of hyperinfection, and we observed in their stools a large number of rabditoid and filariform larvae of S. stercoralis
. Occasionally, in these patients whose parasitosis was found in the lungs, these stages of the parasite (preferably the former) are found in respiratory secretions obtained by sputum or bronchoalveolar lavage. Exceptionally, the microscopy of the respiratory secretions has revealed S stercoralis eggs in respiratory secretions of an AIDS patient
Even though the Muñiz Hospital is not located in an endemic region of this parasitosis, a lot of patients came from there and, as it is in the case herein described, they acquire the disease during the ealy ages of their lives, and they have clinical manifestations a lot of time later. The infection can remain in a latent state during several years, fulfilling cycles of self-reinfestation over a period that may exceed 30 years
The reported case is the first finding in our laboratory of S. stercoralis
adult females (together with eggs) in a clinical material, which has been prevoiusly mentioned by other authors, although in fecal samples
In the usual bilogical cycle of S. stercoralis
, adult forms evolve in the environment, where they develop a free life and cause the infectious forms of the parasite (filariform larvae) that infect humans through the skin. It is called endogenous self-reinfestation the mechanism by which the larvae of S. stercoralis
filariform, which are present in the patient's digestive tract, penetrate the intestinal mucosa and repeat the cycle, without going outside. This latter mechanism is probably the one that was present in the patient described herein, as well as in other situations in which the patient has a inmunoligical compromise
Regarding the strongyloidiasis diagnosis, in immunocompromised patients, this diagnosis is facilitated by the large number of parasites that are present in the materials, in which the large number of different microscopy parasitic forms is usually observed in the microscopy
. However, the use of a single sample may give a wrong diagnosis in more than half of these cases, which obliges, in case of a strong suspicion of parasitosis, to study several samples in order to improve the sensitivity of the method.
The concentration techniques of Baermann and the formalin-ethyl acetate, applied to fecal samples, improve the sensitivity of parasitological studies. The method of Harada-Mori (culture in filter paper) does not seem to be so successful, whereas the blood agar culture is preferred to the above-mentioned due to its high sensitivity and easy implementation in low complexity laboratories
. The duodenal sampling can be useful, although it is an invasive and less tolerable procedure.
The determination of antibodies is available and, even though it is sensitive, it has cross reactions with filarial infections or Ascaris lumbricoides. The sensitivity of these tests often decreases in HIV positive patients and in those with hematologic diseases.
A single serum sample is unable to differentiate current from past infections, although the persistence in the tissues of S. stercoralis
and the possibility that the antiparasitic treatment does not completely eradicate the parasite force to an empirical treatment due to a positive test accompanied by a compatible clinical history
In recent years, some techniques based on PCR and coproantigen detection has been developed for detection of intestinal parasites in feces
. Evaluation and standardization of such techniques are necessary to overcome the limitations of the current diagnostic methods. As regards the causes that favor the hyperinfection, the patient described herein had received, due to his underlying disease, prolonged courses of corticosteroids and methotrexate, referred to in the literature as such
. The presence of adult females of S. stercoralis
in respiratory secretions, as far the authors were able to investigate, has not been previously published, and it is possibly an exceptional finding.