Summary from the authors: Contaminations contaminate common databases

Molecular barcoding of bird malaria and related parasites has unravelled a remarkable diversity of potentially cryptic species that may count in tens of thousands compared to the few hundred morphologically described species. The database MalAvi (Bensch et al., 2009) was initiated to structure the growing numbers of findings of these bird blood parasites. The polymerase chain reaction (PCR) is irrefutably a powerful method to detect and identify pathogens, however the high sensitivity of the method comes with a cost; any of the millions of artificial DNA copies generated by PCR can serve as a template in a following experiment. If such PCR-contaminations go undetected, it will result in erroneous findings of parasites and thus misrepresent their distribution.  We address this problem by re-analysing samples of surprising records in the MalAvi database, these being unusual host species or geographic locations for the parasites. Our analyses suggest that many of these are PCR contaminations, presumably originating from previous or parallel projects in the laboratory. The highlighted examples are from bird parasites, but the problem of contaminations, and the suggested actions to reduce such errors, should apply generally to all kinds of studies using PCR for identification.

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Fig 1. The database MalAvi ( presently contains >4,400 unique mitochondrial lineages of avian malaria parasites obtained from >2,000 species of birds.

References Bensch, S., Hellgren, O. & Pérez-Tris, J. MalAvi: 2009. A public database of malaria parasites and related haemosporidians in avian hosts based on mitochondrial cytochrome b lineages. Molecular Ecology Resources, 9: 1353-1358.

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