Background:
Storage of stool samples for molecular detection of soil-transmitted helminth (STH) species remains a challenge for the molecular diagnostic of STH infections. This study was designed to assess the capacity of whatman filter papers for the storage of stool samples for molecular detection of STH species.

Methods:
Stool samples from school-aged children with and without eggs of soil-transmitted helminths as results of Kato-Katz were used. From each sample, 10, 20, 40 and 80 mg of stool were spread on 6 types of filter paper that were stored at room temperature for one to ten weeks. DNA was extracted from stored stool using a cetyltrimethylammonium bromide-based method. The amount of stool and appropriate filter paper to use for the storage of stool sample was determined by amplifying specific DNA fragment of Ascaris lumbricoides. The capacity of filter paper for short and long-term storage of stool was assessed by amplifying specific DNA fragment of STH.

Results:
Amplification rates were significantly higher for 10 and 20 mg of stools compared to 40 and 80 mg. the whatman filter paper grade 2 yielded the highest amplification rate of 100%. For either A. lumbricoides or Trichuris trichiura or hookworm, the amplification rates of stored stools on this whatman filter paper were 100%. DNA fragments of A. lumbricoides and T. trichiura were detected in 5 (12.5%) and 9 (22.5 %) stools without soil-transmitted helminth egg. From the first to 8th weeks, the amplification rates of different soil-transmitted helminth species remained constant at 100%. It decreased to 86.7% after 10 weeks of storage.

Conclusions:
This study highlighted the capacity of whatman filter papers for long-term storage of stools for molecular diagnostic of STH. Storage of stool samples on filter paper is of great interest for the monitoring of STH control programs and for the post-elimination surveillance.