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Volume 15, Number 4—April 2009
Letter

Correlation between Buruli Ulcer and Vector-borne Notifiable Diseases, Victoria, Australia

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To the Editor: Buruli ulcer (BU) is a destructive skin disease caused by the toxin-producing environmental pathogen Mycobacterium ulcerans. Since the 1980s, BU has emerged as a major public health problem in rural West and Central Africa (1), where some researchers have suggested a role for aquatic insects as either reservoirs or vectors of M. ulcerans (2,3). However, this hypothesis remains unproven (4).

In contrast to the emerging BU–endemic areas in tropical rural West Africa, the climate of the Australian state of Victoria is temperate, yet locally acquired BU also has increased there in recent years (5). In addition, notifications have varied markedly from year to year for reasons not yet explained.

During the investigation of a new outbreak of BU in Victoria, we demonstrated that M. ulcerans is detectable by PCR in mosquitoes and that being bitten by mosquitoes increases the odds of being diagnosed with BU (6,7). However, M. ulcerans–positive mosquitoes might reflect only the presence of M. ulcerans in the local environment and play no role in transmission. To further investigate links between BU and mosquitoes, we compared patterns of notifications of BU with other notifiable diseases in Victoria. In particular, we were interested in any association between BU and the locally transmitted vector-borne alphaviruses Ross River virus (RRV) and Barmah Forest virus (BFV). Areas of BU and RRV/BFV endemicity overlap geographically, but areas with RRV and BFV are more extensive and include inland river systems where BU has not so far been reported.

Notification data for RRV, BFV, and other notifiable infections in Victoria are publicly available (8). Although BU was not made notifiable until January 2004 (before which notification was voluntary), since early 2000, most diagnoses were confirmed by culture or PCR at the Victorian Infectious Diseases Reference Laboratory, from which we obtained data for this report.

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Thumbnail of Numbers of cases per 100,000 inhabitants for selected notifiable diseases, Victoria, Australia, 2000–2008. Buruli ulcer is shown on the right y axis, other diseases on the left y axis. RRV, Ross river virus; BFV, Barmah Forest virus; TB, tuberculosis.

Figure. Numbers of cases per 100,000 inhabitants for selected notifiable diseases, Victoria, Australia, 2000–2008. Buruli ulcer is shown on the right y axis, other diseases on the left y axis. RRV, Ross...

Our analysis showed that in the last 7 years (2002–2008), BU notifications correlated with combined RRV/BFV notifications (r2 = 0.52, p = 0.06) (Figure). During the same period, no correlation was observed with tuberculosis, the other important mycobacterial disease in Victoria (r2 = 0.12, p = 0.43); legionellosis, caused by a nonvectored water-associated pathogen (r2 = 0.04, p = 0.66); or any other notifiable infectious disease (data not shown).

Although the environmental reservoir and mode of transmission of M. ulcerans remain unknown, mosquitoes are well known for transmitting RRV and BFV to humans, and year-to-year variation in incidence of these vector-borne viral infections is linked to changes in mosquito numbers (9,10). We are not implying that M. ulcerans, RRV, and BFV are transmitted simultaneously from the same reservoir species to the same humans or by the same mosquitoes. Also, environmental conditions that promote outbreaks of RRV/BFV infection might promote BU outbreaks without any other connection. However, we believe the correlation we have identified between BU and other mosquito-borne diseases is striking and further strengthens the link between mosquitoes and the transmission of M. ulcerans in Victoria.

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Acknowledgment

This study was performed with funding assistance from the Victorian Department of Human Services (Public Health Research Grant).

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Paul D.R. JohnsonComments to Author  and Caroline J. Lavender
Author affiliations: Austin Health, Melbourne, Victoria, Australia (P.D.R. Johnson); World Health Organization Collaborating Centre for Mycobacterium ulcerans (Western Pacific Region); Victorian Infectious Diseases Reference Laboratory, North Melbourne, Victoria, Australia (P.D.R. Johnson, C.J. Lavender)

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References

  1. Johnson  PD, Stinear  T, Small  PL, Pluschke  G, Merritt  RW, Portaels  F, Buruli ulcer (M. ulcerans infection): new insights, new hope for disease control. [erratum in PLoS Med. 2005:2:e173]. PLoS Med. 2005;2:e108. DOIPubMedGoogle Scholar
  2. Marsollier  L, Robert  R, Aubry  J, Saint Andre  J, Kouakou  H, Legras  P, Aquatic insects as a vector for Mycobacterium ulcerans. Appl Environ Microbiol. 2002;68:46238. DOIPubMedGoogle Scholar
  3. Portaels  F, Elsen  P, Guimaraes-Peres  A, Fonteyne  P, Meyers  W. Insects in the transmission of Mycobacterium ulcerans infection. Lancet. 1999;353:986. DOIPubMedGoogle Scholar
  4. Benbow  ME, Williamson  H, Kimbirauskas  R, McIntosh  MD, Kolar  R, Quaye  C, Aquatic invertebrates as unlikely vectors of Buruli ulcer disease. Emerg Infect Dis. 2008;14:124754. DOIPubMedGoogle Scholar
  5. Johnson  PD, Hayman  JA, Quek  TY, Fyfe  JA, Jenkin  GA, Buntine  JA, Consensus recommendations for the diagnosis, treatment and control of Mycobacterium ulcerans infection (Bairnsdale or Buruli ulcer) in Victoria, Australia. Med J Aust. 2007;186:648.PubMedGoogle Scholar
  6. Johnson  PD, Azuolas  J, Lavender  CJ, Wishart  E, Stinear  TP, Hayman  JA, Mycobacterium ulcerans in mosquitoes captured during an outbreak of Buruli ulcer, southeastern Australia. Emerg Infect Dis. 2007;13:165360.PubMedGoogle Scholar
  7. Quek  TY, Athan  E, Henry  MJ, Pasco  JA, Redden-Hoare  J, Hughes  A, Risk factors for Mycobacterium ulcerans infection, southeastern Australia. Emerg Infect Dis. 2007;13:16616.PubMedGoogle Scholar
  8. Department of Human Services. Notifications of infectious diseases [cited 2009 Jan 31]. Available from http://www.health.vic.gov.au/ideas/downloads/daily_reports/statewide/rptVictorianSummary.pdf
  9. Dhileepan  K. Mosquito seasonality and arboviral disease incidence in Murray Valley, southeast Australia. Med Vet Entomol. 1996;10:37584. DOIPubMedGoogle Scholar
  10. Passmore  J, O’Grady  KA, Moran  R, Wishart  E. An outbreak of Barmah Forest virus disease in Victoria. Commun Dis Intell. 2002;26:6004.PubMedGoogle Scholar

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Cite This Article

DOI: 10.3201/eid1504.081162

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Table of Contents – Volume 15, Number 4—April 2009

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Please use the form below to submit correspondence to the authors or contact them at the following address:

Paul D.R. Johnson, Infectious Diseases Department, Austin Health, PO Box 5555, Heidelberg 3084, Melbourne, Victoria, Australia

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Page created: December 10, 2010
Page updated: December 10, 2010
Page reviewed: December 10, 2010
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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