Kato-Katz thick smears as a DNA source of soil-transmitted helminths.

Despite the reduction in the prevalence of soil-transmitted helminthiases in many regions of the world, morbidity rates remain high in some rural regions. The Kato-Katz technique is a simple, inexpensive and field-applicable tool commonly used for the diagnosis and worm-burden characterization of these infections. Molecular studies have revolutionized our understanding of the epidemiology and evolutionary genetics of parasites. In this study we recovered helminthic DNA from Kato-Katz slides (n = 93) prepared in 2011 in the Brazilian Amazon. We achieved DNA recovery by polymerase chain reaction (PCR) in 84% of cases for Ascaris sp. and 75% of cases for hookworms. The sequencing confirmed the specific species of the amplicons. The slides stored for a few years could be analysed using this methodology, allowing access to DNA from a large collection of samples. We must consider the Kato-Katz thick smears as a source of helminth DNA. This can significantly reduce logistical difficulties in the field in terms of obtaining, preserving, transporting and initial processing of samples.