Assessing plague risk and presence through surveys of small mammal flea communities
Friggens, M. M.1, Ford, P. L.1, Parmenter, R. R.3, Boyden, M.4, Gage, K.5
(1) Northern Arizona University; (2) USDA Forest Service, Rocky Mountain Research Station; (3) Valles Caldera National Preserve,
NM; (4) University of New Mexico; (5) Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention
333 Broadway Suite 115, Albuquerque NM 87102, meganfriggens@fs.fed.us
Key Words: Small mammals, Plague, Y. pestis
Introduction: Plague, caused by the bacterium Yersinia pestis, remains a threat to human and wildlife populations in
the Western United States (Gage and Kosoy 2005). Several rodent species have been implicated as important
maintenance hosts in the U.S., including Peromyscus maniculatus and Dipodomys spp. Fleas are a critical component of
plague foci (Gage and Kosoy 2005). Transmission of plague increases with flea abundance and prevalence (Eisen et al.
2006; Lorange 2005). Prairie dogs (Cynomys gunnisoni) which have little innate immunity experience mortality in
excess of 99% when exposed to plague (Gage and Kosoy 2005). Because prairie dogs outbreaks are conspicuous, it is
possible to record the conditions and risk factors associated with plague outbreaks. Information gathered on prairie dog
outbreaks may help identify risk factors for plague transmission in other communities. Here we present the results of a
3-year survey of flea and rodent communities surrounding prairie dog colonies in New Mexico.
Materials & Methods: Fleas and blood samples were collected from small mammals captured from two grassland sites
in New Mexico: Sevilleta National Wildlife Refuge (Sevilleta) and the Valles Caldera National Preserve (VCNP) from
May 2004 to October 2006. Every month, we trapped mammals using 300 Sherman livetraps set in 15 transects along
an elevational gradient. We also conducted biannual (spring/fall) surveys at upper and lower elevation sites using an
additional 854 traps/session. Site descriptions and procedures for the detection of Y. pestis antibodies (blood samples)
and DNA (flea samples) are described elsewhere (Friggens et al. 2010).
Results & Discussion: Prairie dog plague Table 1. Characteristics of rodent and flea communities of two sites in NM.
outbreaks occurred in VCNP in 2004. Rodents
Rodent Community
Prairie dogs
inhabiting the VCNP carried higher flea loads and
Sevilleta
VCNP
Sevilleta
VCNP
more flea species than animals residing within the
No.
captured
965
989
16
128
Sevilleta (Table 1). Plague was detected in fleas
and rodents in 2 of 3 years in the VCNP and during
Rodent Richness
19
12
---2006 in the Sevilleta. Plague positive fleas were
Flea Richness
24
28
1
4
pulled from Cynomys gunnisoni (11), Peromyscus
Flea Intensity
0.23
0.77
1.38
3.99
maniculatus (2), Neotoma mexicana (1) and
Spermophilus spilosoma (1) in the VCNP and from
Y. pestis in rodents
No
Yes (<1%)
No
Yes (7%)
Dipodomys spectabilis (2), N. albigula (1), and
Y. pestis in fleas
Yes (4)
Yes (20)
No
Yes (4)
Onychomys arenicola (1) on the Sevilleta. Flea and
rodent community dynamics are important determinants of Y. pestis transmission. We detected plague in fleas
throughout this study, but rarely found evidence of plague exposure in rodents.
Conclusions: Data gathered on fleas accurately reflected an increased risk of Y. pestis transmission in the VCNP and
provided the most consistent information regarding the presence of Y. pestis at both sites. Thus, information gained
through flea surveys may be the most useful for ecological studies of Y. pestis.
References:
Eisen, R.J., Bearden, S.W., Wilder, A.P. Montenieri, J.A Antolin, M.F.,Gage, K. L. 2006. Early-phase transmission of
Yersinia pestis by unblocked fleas as a mechanism explaining rapidly spreading plague epizootics. Proc Nat
Acad Science 103: 15380-15385.
Friggens, M.M., Parmenter, R.R., Ford, P.L., Gage, K., Keim, P. 2010. Flea abundance, diversity, and plague in
Gunnison's prairie dogs (Cynomys gunnisoni) and their burrows in montane grasslands in northern New
Mexico. J Wild Dis 46: 356-367.
Gage, K., Kosoy, M. 2005. Natural History of Plague: Perspectives from more than a century of research. Ann Review
Entomol 50: 505-528.
Lorange, E.A. 2005. Poor vector competence of fleas and the evolution of hypervirulence in Yersinia pestis. J Infect Dis
191: 1907-1912.
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