Abstract
Strongyloidiasis is prevalent in Thailand, yet its prevalence in the south is lower than in other parts of the country. This might be due to the long rainy season in the south resulting in stool submersion in water inhibiting worm development. In this study, the effect of water submersion of fecal samples on development of Strongyloides stercoralis was investigated. Ten ml of a 1∶5 fecal suspension were placed in 15-ml tubes, 35-mm dishes, and 90-mm dishes producing the depths of 80 mm, 11 mm and 2 mm-suspensions, respectively. The worm development was followed at 1/6, 4, 6, 8, 10, 12, 14, 16, 24, and 36 h, by determining the number of filariform larva (FL) generated from agar-plate cultures (APC). Fecal suspensions kept in tubes and 35-mm dishes showed a decline in FL yield relative to incubation time and reached zero production 14 h after incubation. In contrast, the number of FL generated from the suspension kept in 90-mm dishes remained stable up to 36 h. Cumulatively, all tubes and 35-mm dishes became negative in APC after 14 h while 90-mm dishes remained APC-positive up to 36 h. Adding more water or stool suspension to dishes resulted in a decreased number of FL. Mechanical aeration of the suspensions in tubes restored an almost normal FL yield. It appears that the atmospheric air plays a significant role in growth and development of S. stercoralis in the environment and may be one of factors which contribute to a lower prevalence of human strongyloidiasis in the south of Thailand.
Highlights
Strongyloidiasis, a harmful infectious disease for immunosuppressed patients caused by Strongyloides stercoralis, is estimated to occur in 30-100 million people worldwide [1]
A preliminary experiment showed that mixing S. stercoralispositive stool with distilled water or saline at 1:5 and left standing for 6 hours was detrimental to survival of rhabditiform larva (RhL) as reflected by negative agar plate cultures
The samples were selected according to the following criteria (a) agar plate culture generated a large number of filariform larva (FL), (b) a simple direct stool smear showed at least 1 motile RhL, and (c) the RhL count by the modified formalin-ether concentration technique [11] revealed 50–200 RhL per gram of stool, (d) other parasites were not detected in stool, and (e) all patients had not been treated with any anthelmintic drugs prior to stool collection
Summary
Strongyloidiasis, a harmful infectious disease for immunosuppressed patients caused by Strongyloides stercoralis, is estimated to occur in 30-100 million people worldwide [1]. May be one of the factors as rainy season was longer in the south These differences raise questions that environmental factors which affect transmission of the worm may be different among regions. Areas continuously covered with surface water for some period may be adverse to worm growth and development. In accordance with this postulation, unexpected findings in a previous study revealed that the number of rhabditiform larva (RhL) per gram of stool was decreased when specimens were left in saline for up to 6 hours [11]. A preliminary experiment showed that mixing S. stercoralispositive stool with distilled water or saline at 1:5 and left standing for 6 hours was detrimental to survival of RhL as reflected by negative agar plate cultures
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