Rickettsia australis
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Alphaproteobacteria
Order: Rickettsiales
Family: Rickettsiaceae
Genus: Rickettsia
Species group: Spotted fever group
Species:
R. australis
Binomial name
Rickettsia australis
Philip, 1950

Rickettsia australis is a bacterium that causes a medical condition called Queensland tick typhus.[1][2] The probable vectors are the tick species, Ixodes holocyclus and Ixodes tasmani. Small marsupials are suspected reservoirs of this bacterium.[3]

Early Scientific History

In 1946 this bacterium was discovered and isolated as a new tick-borne illness that began to present in Australian soldiers stationed in northern Queensland. This illness was designated as the North Queensland tick typhus. From here, researchers began to continue this work. After many experiments were completed, such as cross-protection and serological assays in guinea pigs, it was concluded that the isolate previously seen in 1946 was a new addition to the spotted fever group. Although it wasn’t until 1950 when the organism was officially discovered and named Rickettsia australis by a scientist with the surname Philip.[4]

Role in Human Disease

Rickettsia australis causes Queensland tick typhus (QTT).[4] This disease was first identified in 1946, although the specific bacterium was not identified until 1950. Rickettsia australis produces a spectrum of symptoms ranging from headaches and fever but can ultimately lead to sepsis and vital organ failure.[5]

Biology

Rickettsia

The Rickettsia genus contain a distinct collection of intracellular gram-negative bacteria.[2] They are serologically categorized into two major classes:

  1. the spotted fever group[6]
    • Subsets: the ancestral group & the transitional group[6]
  2. the typhus group[6]

Rickettsia australis belongs to the category of the spotted fever group and the subset of transitional group. Together these organisms encompass more than 36 tick-borne species, 15 of these species are known causal agents of human illnesses.[5] Of the vector-borne disease these zoonoses are among the oldest known.[7]

Genome

Rickettsia australis is a distinct pathogen that belongs in the Rickettsial spotted fever group. It genome is sequences and is approximately 1.29 Mb (mega–base-pairs). It is also highly similar to Rickettsia akari which is the closest known phylogenetic neighbor. The chromosome has a predicted size of 1,297,390 bp. It is also known that the chromosome itself contain 1,110 genes with approximately 855 genes function to encode proteins with putative functions and 255 encode hypothetical proteins and proteins of known function. To see the whole genome project on the database Genbank the accession number is AKVZ00000000.[2]

Vectors

The three tick species that have been identified as vectors of R. australis are Ixodes tasmani, Ixodes holocyclus, and Ixodes cornuatus.[8] The species of ticks known to harbor R. australis typically reside along the eastern coastline ranging from the Torres Strait islands to Queensland and Victoria.

Mechanism

Once the infected tick bites an individual, the Rickettsiae bacteria can spread throughout the bloodstream. It begins by targeting the endothelium and will eventually start to target the vascular smooth muscle cells (VSMCs). Once in the bloodstream, the Rickettsia Australias can immediately begin multiplying by binary fission. If left in the body long enough without treatment, it will parasitize healthy cells and create lasting damage.[9]

Prevalence

Rickettsia australis and its associated disease Queensland Tick Typhus are an ever changing diseases with growing public health importance.[5]

References

  1. ↑ Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. p. 1130. ISBN 978-1-4160-2999-1.
  2. 1 2 3 Dong X, El Karkouri K, Robert C, Raoult D, Fournier PE (September 2012). "Genome sequence of Rickettsia australis, the agent of Queensland tick typhus". J. Bacteriol. 194 (18): 5129. doi:10.1128/JB.01117-12. PMC 3430325. PMID 22933759.
  3. ↑ Definition: Rickettsia Australis, Medilexicon
  4. 1 2 Sexton, Daniel; Dwyer, Brian; Kemp, Richard; Graves, Stephen (September–October 1991). "Spotted Fever Group Rickettsial Infections in Australia". Clinical Infectious Diseases. 13 (5): 876–886. doi:10.1093/clinids/13.5.876. JSTOR 4456108. PMID 1962102 – via JSTOR.
  5. 1 2 3 Stewart, Adam; Armstrong, Mark; Graves, Stephen; Hajkowicz, Krispin (2017-06-20). "Clinical Manifestations and Outcomes of Rickettsia australis Infection: A 15-Year Retrospective Study of Hospitalized Patients". Tropical Medicine and Infectious Disease. 2 (2): 19. doi:10.3390/tropicalmed2020019. ISSN 2414-6366. PMC 6082078. PMID 30270878.
  6. 1 2 3 Pickens, E. G.; Bell, E. J.; Lackman, D. B.; Burgdorfer, W. (1965-06-01). "Use of Mouse Serum in Identification and Serologic Classification of Rickettsia Akari and Rickettsia Australis". The Journal of Immunology. 94 (6): 883–889. ISSN 0022-1767. PMID 14332634.
  7. ↑ Smalley, Claire; Bechelli, Jeremy; Rockx-Brouwer, Dedeke; Saito, Tais; Azar, Sasha R.; Ismail, Nahed; Walker, David H.; Fang, Rong (2016-06-30). "Rickettsia australis Activates Inflammasome in Human and Murine Macrophages". PLOS ONE. 11 (6): e0157231. Bibcode:2016PLoSO..1157231S. doi:10.1371/journal.pone.0157231. ISSN 1932-6203. PMC 4928923. PMID 27362650.
  8. ↑ Dehhaghi, Mona; Kazemi Shariat Panahi, Hamed; Holmes, Edward C.; Hudson, Bernard J.; Schloeffel, Richard; Guillemin, Gilles J. (2019-01-28). "Human Tick-Borne Diseases in Australia". Frontiers in Cellular and Infection Microbiology. 9: 3. doi:10.3389/fcimb.2019.00003. ISSN 2235-2988. PMC 6360175. PMID 30746341.
  9. ↑ Walker, David H. (1996), Baron, Samuel (ed.), "Rickettsiae", Medical Microbiology (4th ed.), Galveston (TX): University of Texas Medical Branch at Galveston, ISBN 978-0-9631172-1-2, PMID 21413251, retrieved 2021-12-09
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