Ixodes holocyclus Tick-Transmitted Human Pathogens in North-Eastern New South Wales, Australia

Abstract

A group of 14 persons who live in an area of Australia endemic for the Australian paralysis tick, Ixodes holocyclus, and who were involved in regularly collecting and handling these ticks, was examined for antibodies to tick-transmitted bacterial pathogens. Five (36%) had antibodies to Coxiella burnetii, the causative agent of Q fever and three (21%) had antibodies to spotted fever group (SFG) rickettsiae (Rickettsia spp). None had antibodies to Ehrlichia, Anaplasma, Orientia, or Borrelia (Lymedisease) suggesting that they had not been exposed to these bacteria. A total of 149 I. holocyclus ticks were examined for the citrate synthase (gltA) gene of the SFG rickettsiae and the com1 gene of C. burnetii; 23 (15.4%) ticks were positive for Rickettsia spp. and 8 (5.6%) positive for Coxiella spp. Sequencing of fragments of the gltA gene and the 17 kDa antigen gene from a selection of the ticks showed 99% and 100% homology, respectively, to Rickettsia australis, the bacterium causing Queenslandtick typhus. Thus, it appears that persons bitten by I. holocyclus in NE NSW, Australia have an approximate one in six risk of being infected with R. australis. Risks of Q fever were also high in this region but this may have been due to exposure by aerosol from the environment rather than by tick bite. A subset of 74 I. holocyclus ticks were further examined for DNA from Borrelia spp., Anaplasma spp. and Ehrlichia spp. but none was positive. Some of these recognised human bacterial pathogens associated with ticks may not be present in this Australian tick species from northeastern New South Wales.

Tick‐borne infectious diseases in Australia

“…Although often a mild condition involving fever, rash and eschar and readily treated with a short course of doxycycline, the infection may be severe 21 , 22 or fatal, 23 and may have unusual feaures 24 . In north‐eastern New South Wales, 15.4% of paralysis ticks contained R. australis 13 . Hence, being bitten by this tick, in this location, appears to offer a 1 in 6 risk of being infected with the rickettsia.…”

“…Many different bacteria have been detected in Australian tick species, 8 ‐ 13 mostly using molecular techniques. Some are known human pathogens or are closely related phylogenetically to known human pathogens; others are unique bacteria that are part of the tick microbiome.…”

“…This bacterium causes Q fever and usually infects humans by inhalation of infectious aerosols from carrier vertebrate animals such as goats, sheep, cattle and domestic pets. However, it is present in both paralysis ticks 13 and ornate kangaroo ticks, 37 , 38 and although, anecdotally, there are other cases of Q fever being transmitted by ticks, there is only one published case where the patient developed pericarditis, a rare presentation of Q fever, after being bitten by an ornate kangaroo tick 39 …”

“…In north‐eastern NSW, 5.6% of paralysis ticks contained the com1 gene of C. burnetii 13 . This bacterium has been isolated from the bandicoot tick ( Haemaphysalis humerosa ) from both sides of Australia, 40 , 41 although it is unlikely that this tick species bites humans.…”

Laboratory diagnosis of human infections transmitted by ticks, fleas, mites and lice in Australia

“…(i) Rickettsia australis is found in at least two different Australian tick species (Ixodes holocyclus 4 and I. tasmani) and various native mammals (e.g. bandicoots), causing Queensland Tick Typhus 5,6 when they bite humans.…”