Intraspecific variation in parasites- what is a strain?

The use of molecular techniques in parasitology has revealed a startling degree of diversity within species of parasite. These discoveries have emphasized the need for parasitologists to define and describe accurately the organisms with which they work. Andrew Thompson and Alan Lymbery propose that parasite strains be described by a combination of genetic and biological characteristics since reliance on the genotype alone may confer significance on a feature of little biological relevance.