Ixodes holocyclus (Acarina: Ixodidae) and Ixodes cornuatus (Acarina: Ixodidae) 
are two tick species found in the more densely populated areas of Australia and 
are known to be the cause of the neurotoxic disease tick paralysis in humans and 
mammals. Borreliosis otherwise known as Lyme disease is an emerging infectious 
disease in humans in Australia. Borrelia burgdorferi sensu stricto 
(Spirochaetales: Spirochaetaceae) and sensu lato are closely related spirochetal 
species that are the causative agents of Lyme disease in humans. Clinical 
transmission of this tick-borne disease can be identified in several but not all 
cases by a characteristic rash known as erythema migrans. However, there has 
been no study of the tick vectors of this infection in Australia. We used 
morphological and molecular techniques to identify unequivocally the ticks on 
the patients of this study to be I. holocyclus and then show the presence of B. 
burgdorferi sensu stricto infection in erythema migrans biopsies. I. holocyclus 
has not previously been associated with erythema migrans or Lyme disease. Two 
patients presented to the lead author's medical practice with erythema migrans 
in mid and late 2012. The morphology and cytochrome oxidase 1 and ITS2 genes of 
the two ticks were studied. The skin at the attachment site was sampled by 
central biopsy for both real time and endpoint Borrelia polymerase chain 
reaction (PCR) analysis and subsequent sequencing. Morphologically, the two 
ticks were either I. holocyclus or I. cornuatus. Molecular studies and 
nucleotide sequencing revealed that both ticks were I. holocyclus. Real time and 
endpoint PCR on the central tissue biopsy samples returned positive results for 
B. burgdorferi DNA. Our results are evidence for transmission of B. burgdorferi 
sensu stricto species to humans by the tick I. holocyclus in Australia. I. 
holocyclus is commonly associated with human tick bites on virtually the entire 
eastern coastline of Australia.