|
|
Letter
Potential for Zoonotic Transmission
of Brachyspira pilosicoli
David J. Hampson,*
Sophy L. Oxberry,* and Tom La*
*Murdoch University, Murdoch, Western Australia, Australia
Suggested
citation for this article
To the Editor: Anaerobic intestinal spirochetes of the genus Brachyspira
colonize the large intestine (1). Most Brachyspira
species have a restricted host range, whereas Brachyspira (formerly
Serpulina) pilosicoli colonizes a variety of animal and
bird species and humans. B. pilosicoli is an important colonic
pathogen of pigs and chickens (2). It occurs at
high prevalence rates in humans in developing countries and in male homosexuals
and HIV-positive persons in industrialized countries (3).
Its potential as a human pathogen was emphasized after its identification
in the bloodstream of a series of debilitated persons (4).
B. pilosicoli isolates from humans and other species have been
used experimentally to colonize chicks, piglets, and mice (5–7).
While these results indicate that the B. pilosicoli strains used
lacked host-species specificity, few data exist on whether natural zoonotic
spread of B. pilosicoli strains occurs. In 1 study that used pulsed-field
gel electrophoresis (PFGE) to type isolates from Papua New Guinea, 2 dogs
were colonized with B. pilosicoli isolates with the same PFGE types
as those from villagers. However, the higher prevalence of colonization
with B. pilosicoli in humans than dogs suggested that the dogs
were infected with human isolates, probably through consumption of human
feces (8).
Multilocus enzyme electrophoresis (MLEE) has been used to study variation
in B. pilosicoli isolates; most studies have focused on isolates
from only 1 or 2 host species (8–10). Generally,
B. pilosicoli isolates are diverse, and a lack of linkage disequilibrium
in the MLEE data for human isolates suggests that the species is recombinant
(8).
We used MLEE to investigate relationships between 107 B. pilosicoli
isolates of diverse geographic and host-species origins and the B.
aalborgi type strain (NCTC 11492T). Isolates were selected
on the basis of their diverse origins and availability in the Murdoch
University culture collection. They originated from feces of 34 pigs,
19 chickens, 13 ducks, 1 rhea, 25 humans, and 4 dogs; from 7 human blood
samples; and from 4 water sources frequented by waterfowl. Isolates originated
from Australia, Canada, France, Italy, the Netherlands, Oman, Papua New
Guinea, the United Kingdom, and the United States.
The MLEE method used was as previously described (8–10);
the electrophoretic mobility of 15 constitutive enzymes was analyzed.
Variations in electrophoretic mobility were interpreted as representing
products of different alleles at each enzyme locus. Isolates with identical
enzymatic profiles at 15 loci were grouped into an electrophoretic type
(ET). Genetic distance between ETs was calculated as the proportions of
loci at which dissimilar alleles occurred. PHYLIP version 3.51c (Phylogeny
Inference Package, University of Washington, Seattle, WA, USA) was used
to analyze data and generate a dendrogram by using the unweighted pair-group
method with arithmetic mean clustering fusion strategy. Genetic diversity
(h) was calculated for the number of ETs as (1 – Σpi2)(n/n
– 1), where pi is the frequency of the indicated allele and n is
the number of ETs.
B. pilosicoli isolates were divided into 80 ETs (mean 1.35 isolates
per ET) (Figure). B. aalborgi NTCC 11492T
was distinct in ET81. The B. pilosicoli isolates were diverse,
with an h value of 0.41. Generally, they did not cluster according to
host species of origin, and isolates from a given species were distributed
throughout the dendrogram. Isolates from birds were more diverse than
those from humans and pigs. Eight ETs contained multiple isolates, in
each case from the same host species (either chickens or pigs). In 4 cases
these originated from different countries: ET47 contained 2 Australian
porcine isolates and 2 from the United States; ET53 contained 2 Australian
porcine isolates and Scottish porcine type strain P43/6/78T;
ET54 contained 2 Australian and 2 Canadian porcine isolates; ET65 contained
1 Dutch and 1 US chicken isolate.
Although human isolates did not share an ET with isolates from other
species, they were frequently closely related, differing in 1 allele.
This occurred with US and Australian pig isolates in ET47 and a human
isolate from Oman in ET48; an Australian pig isolate in ET61 and a UK
human isolate in ET62; an isolate from an Australian HIV-positive person
in ET64, and 1 Dutch and 1 US chicken isolate in ET65; and a Papua New
Guinea canine isolate in ET68 and a French human blood isolate in ET69.
The distribution continuum of isolates of diverse host species and geographic
origin was consistent with a lack of species specificity and suggests
that B. pilosicoli isolates naturally have the potential to be
transmitted between species. Even should there be some unexpected species-specific
barrier preventing "true" animal or bird isolates from colonizing
humans, animals have been colonized by human isolates, and thus could
act as a reservoir of these for subsequent retransmission to humans. The
results suggest that zoonotic transfer of B. pilosicoli isolates
likely occurs in nature, e.g., after exposure to infected animals or birds,
their feces, or contaminated water.
References
- Stanton TB. Physiology of ruminal and intestinal spirochaetes.
In: Hampson DJ, Stanton TB, editors. Intestinal spirochaetes in domestic
animals and humans. Wallingford (UK): CAB International; 1997. p. 7–45.
- Hampson DJ, Duhamel GE. Porcine colonic spirochetosis/intestinal spirochetosis.
In: Straw B, Zimmerman JJ, D’Allaire S, Taylor DJ, editors. Diseases
of swine. 9th ed. Ames (IA): Iowa State University Press; 2006. p. 755–67.
- Hampson DJ. Intestinal spirochaetes. In: McIver CJ, editor. A compendium
of laboratory diagnostic methods for common and unusual enteric pathogens–an
Australian perspective. Sydney: ASM Publications; 2005. p. 101–8.
- Trott DJ, Jensen NS, Saint Girons I, Oxberry SL, Stanton TB, Lindquist
D, Hampson DJ. Identification
and characterization of Serpulina pilosicoli isolates from the
blood of critically-ill patients. J Clin Microbiol. 1997;35:482–5.
- Trott DJ, McLaren AJ, Hampson DJ. Pathogenicity
of human and porcine intestinal spirochaetes in day-old specific pathogen
free chicks: an animal model of intestinal spirochetosis. Infect
Immun. 1995;63:3705–10.
- Trott DJ, Huxtable CR, Hampson DJ. Experimental
infection of newly weaned pigs with human and porcine strains of Serpulina
pilosicoli. Infect Immun. 1996;64:4648–54.
- Sacco RE, Trampel DW, Wannemuehler MJ. Experimental
infection of C3H mice with avian, porcine, or human isolates of Serpulina
pilosicoli. Infect Immun. 1997;65:5349–53.
- Trott DJ, Mikosza ASJ, Combs BG, Oxberry SL, Hampson DJ. Population
genetic analysis of Serpulina pilosicoli and its molecular epidemiology
in villages in the Eastern Highlands of Papua New Guinea. Int J
Syst Bacteriol. 1998;48:659–68.
- Lee JI, Hampson DJ, Lymbery AJ, Harders SJ. The
porcine intestinal spirochaetes: identification of new genetic groups.
Vet Microbiol. 1993;34:273–85.
- McLaren AJ, Trott DJ, Swayne DE, Oxberry SL, Hampson DJ. Genetic
and phenotypic characterization of intestinal spirochetes colonizing
chickens, and allocation of known pathogenic isolates to three distinct
genetic groups. J Clin Microbiol. 1997;35:412–7.
Suggested citation
for this article:
Hampson DJ, Oxberry
SL, La T. Potential for zoonotic transmission of Brachyspira pilosicoli
[letter]. Emerg Infect Dis [serial on the Internet]. 2006 May [date
cited]. Available from http://www.cdc.gov/ncidod/EID/vol12no05/05-1180.htm
|
