Overcrowding is a significant factor contributing to endemic infection with Sarcoptes scabiei in human and animal populations. However, since scabies mites from different host species are indistinguishable morphologically, it is unclear whether people can be infected from scabies-infested animals. Molecular fingerprinting was done using three S. scabiei-specific single locus hypervariable microsatellite markers, with a combined total of 70 known alleles. Multilocus analysis of 712 scabies mites from human and dog hosts in Ohio, Panama and Aboriginal communities in northern Australia now shows that genotypes of dog-derived and human-derived scabies cluster by host species rather than by geographic location. Because of the apparent genetic separation between human scabies and dog scabies, control programs for human scabies in endemic areas do not require resources directed against zoonotic infection from dogs.

When scabies is endemic in humans and dogs in the same community, it is unclear whether humans and dogs are potential hosts in a single transmission cycle or whether there are two separate transmission cycles. Morphologic studies cannot distinguish mites from dogs (Sarcoptes scabiei var. canis) from those of human origin (var. hominis), and it is not known whether var. canis is capable of infecting and completing a life cycle in humans. 1–4 In Aboriginal communities in northern Australia, scabiesinfested dogs and people live in close proximity. Concerns have been raised about the allocation of health resources for dog scabies programs on the assumption that this will help control human scabies5. Additionally, if dogs are reservoirs of infection, an understanding of gene flow between mite populations is important for the development of rational policies to minimise the spread of any developing scabicide resistance. The genetic comparison of mites from different global locations is also important to understand whether a regional epidemiologic situation can be generalized to the remainder of the world, as well as to measure patterns of host specific differences, and investigate geographic variation among populations.