Abstract
Tick-borne infectious diseases caused by obligate intracellular bacteria of the genus Rickettsia are a growing global problem to human and animal health. Surveillance of these pathogens at the wildlife interface is critical to informing public health strategies to limit their impact. In Australia, reptile-associated ticks such as Bothriocroton hydrosauri are the reservoirs for Rickettsia honei, the causative agent of Flinders Island spotted fever. In an effort to gain further insight into the potential for reptile-associated ticks to act as reservoirs for rickettsial infection, Rickettsia-specific PCR screening was performed on 64 Ambylomma albolimbatum ticks taken from shingleback skinks (Tiliqua rugosa) located in southern Western Australia. PCR screening revealed 92% positivity for rickettsial DNA. PCR amplification and sequencing of phylogenetically informative rickettsial genes (ompA, ompB, gltA, sca4, and 17kda) suggested that the single rickettsial genotype detected represented a novel rickettsial species, genetically distinct from but closely related to Rickettsia gravesii and within the rickettsia spotted fever group (SFG). On the basis of this study and previous investigations, it would appear that Rickettsia spp. are endemic to reptile-associated tick species in Australia, with geographically distinct populations of the same tick species harboring genetically distinct SFG Rickettsia species. Further molecular epidemiology studies are required to understand the relationship between these diverse Rickettsiae and their tick hosts and the risk that they may pose to human and animal health.
Highlights
Ticks are important vectors of infectious disease in humans and animals [1]
Of the 64 A. albolimbatum ticks screened by real-time PCR, 59 (92.2%) were positive for rickettsial DNA (Table 1)
DNA in A. albolimbatum ticks collected from the shingleback skink (T. rugosa) in the southern part of Western Australia
Summary
Ticks are important vectors of infectious disease in humans and animals [1]. Ticks preceded mosquitos as being the first arthropods ever associated with the transmission of infection to a healthy vertebrate animal (Texas cattle fever), as determined by TheobaldSmith and colleagues in 1889. Ticks are important vectors of infectious disease in humans and animals [1]. Of the most important groups of pathogens transmitted by ticks, the obligate intracellular bacteria of the order Rickettsiales are paramount. Knowledge of this group of bacteria has been transformed recently with the advent of molecular techniques, leading to the description of a growing diversity of emerging tick-borne rickettsioses [2]. Australia has a rich diversity of hard and soft tick species, with at least 70 commonly found across the continent [3]. It is perhaps not surprising that these ticks are reservoirs for a variety of novel Rickettsia species not described elsewhere, including rickettsiae recognized to cause infectious diseases in humans following a tick bite [4]
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