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16 - Emerging and emergent tick-borne infections
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- By S. R. Telford, Division of Infectious Diseases Cummings School of Veterinary Medicine Tufts University 200 Westboro Road North Grafton MA 01536 USA, H. K. Goethert, Division of Infectious Diseases Cummings School of Veterinary Medicine Tufts University 200 Westboro Road North Grafton MA 01536 USA
- Edited by Alan S. Bowman, University of Aberdeen, Patricia A. Nuttall
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- Book:
- Ticks
- Published online:
- 21 August 2009
- Print publication:
- 04 December 2008, pp 344-376
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- Chapter
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Summary
INTRODUCTION
Human activities continue to change the landscape vastly, altering faunal associations and thereby contact with arthropod vectors, producing circumstances that serve as the basis for the emergence of a vector-borne infection. However, few ‘emerging’ tick-borne infections are novel. Many (ehrlichiosis, babesiosis) have long been recognized as veterinary health problems. Some rickettsioses may be due to agents that were once thought to be tick endosymbionts. Others, such as the agents of bartonellosis, may form paratenic or dead-end associations with ticks. Some recently identified agents (deer tick virus, Borrelia lonestari) are ‘in search of an emerging disease’. Emergent epidemiological associations (Masters' disease) are in search of an agent. Finally, apparently well-characterized tick-borne infections, such as Rocky Mountain spotted fever, tularaemia and tick-borne encephalitis, remain neglected by researchers but retain the potential for resurgence. We briefly review the diversity of these infectious agents, identify aetiological enigmas that remain to be solved, and provide a reminder about ‘old friends’ that should not be forgotten in our pursuit of novelty. We suggest that newly recognized agents or tick–pathogen associations receive careful scrutiny before being declared as potential public health burdens.
REDISCOVERED, BETTER CHARACTERIZED, OR NEW?
Modern approaches to identifying and characterizing infectious agents, using nucleic acid amplification and molecular phylogenetic algorithms, are very powerful (Relman, 2002). However, there are fallacious assumptions that: (1) data accumulated by older (‘classical’) methods are not as precise and thus not to be trusted; and (2) a DNA or RNA sequence represents something novel if it does not match one that is already present in GenBank or other genetic information databases.
Emerging tick-borne infections: rediscovered and better characterized, or truly ‘new’?
- S. R. TELFORD, H. K. GOETHERT
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- Journal:
- Parasitology / Volume 129 / Issue S1 / October 2004
- Published online by Cambridge University Press:
- 19 April 2005, pp. S301-S327
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The emergence of Lyme borreliosis as a public health burden within the last two decades has stimulated renewed interest in tick-borne infections. This attention towards ticks, coupled with advances in detection technologies, has promoted the recognition of diverse emergent or potentially emerging infections, such as monocytic and granulocytic ehrlichiosis, local variants of spotted fever group rickettsioses, WA-1 babesiosis, or a Lyme disease mimic (Masters' Disease). The distribution of pathogens associated with well-described tick-borne zoonoses such as human babesiosis due to Babesia microti or B. divergens seems wider than previously thought. Bartonellae, previously known to be maintained by fleas, lice or sandflies, have been detected within ticks. Purported ‘new’ agents, mainly identified by sequencing of PCR products and comparison with those sequences present in GenBank, are being increasingly reported from ticks. We briefly review the diversity of these infectious agents, identify aetiological enigmas that remain to be solved, and provide a reminder about ‘old friends’ that should not be forgotten in our pursuit of novelty. We suggest that newly recognised agents or tick/pathogen associations receive careful scrutiny before being declared as potential public health burdens.
What is Babesia microti?
- H. K. GOETHERT, S. R. TELFORD
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- Journal:
- Parasitology / Volume 127 / Issue 4 / October 2003
- Published online by Cambridge University Press:
- 17 October 2003, pp. 301-309
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Babesia microti (Apicomplexa: Piroplasmida) has historically been considered a common parasite of Holarctic rodents. However, human babesiosis due to this species has generally been limited to the northeastern seaboard of the United States and Minnesota and Wisconsin. The absence of reports of B. microti babesiosis from sites where the agent is enzootic, such as in western Europe, remains unexplained. Previous work focusing on the 18S rDNA demonstrates little sequence diversity among samples from allopatric host populations across a wide geographical area. It may be that genetic diversity is underestimated due to sample size or the gene analysed. Accordingly, we collected blood or spleen samples from American or Eurasian animals with parasites that were morphologically consistent with B. microti, amplified the 18S rDNA and beta-tubulin gene, and conducted phylogenetic analysis. Surprisingly, what was considered to be ‘B. microti’ by microscopy appears to be a diverse species complex. We identify 3 distinct clades within this complex, including parasites from non-rodent hosts. Rodent parasites comprise 2 clades, one representing zoonotic isolates, and the other apparently maintained in microtine rodents, and therefore their morphological detection within animals from a site does not necessarily imply a risk to public health.