Dynamics of Plague in a Gunnison's Prairie Dog Colony Complex From New Mexico

Abstract

A plague (Yersinia pestis) epizootic spread through Gunnison's prairie dogs (Cynomys gunnisoni), and possibly other rodent species, in the Moreno Valley in north-central New Mexico between winter 1984-1985 and autumn 1987. We observed the progress of the epizootic and subsequent population recovery at four prairie dog towns within the valley during this period. At two towns (Midlake and Val Verde) the prairie dogs were marked prior to the epizootic. At two additional towns (Vega and South Entrance) prairie dogs were marked following the epizootic. In 1988, a second epizootic occurred at Vega. One hundred thirty-nine serum samples were collected from prairie dogs and other rodents and 1,750 fleas were collected from animals and burrows. Fleas infected with Y. pestis were collected from prairie dogs, deer mice (Peromyscus maniculatus), and thirteen-lined ground squirrels (Spermophilus tridecemlineatus). Prairie dog fleas included Oropsylla hirsuta, O. labis and O. tuberculata, deermouse associated fleas were Aetheca wagneri and Rhadinopsylla sectilis, and Oropsylla bacchi was associated with thirteen-lined ground squirrels. All of the above flea species were collected from prairie dog burrows. All rodent species shared some flea species. Thirteen-lined ground squirrels disappeared shortly before plague was identified in prairie dogs at Midlake. Meadow voles were rare following the epizootic at Vega in 1986, became abundant in 1987, and disappeared at the time of the second prairie dog epizootic in summer 1988. Although we collected serum from Gunnison's prairie dogs, thirteen-lined ground squirrels, deer mice, and meadow voles (Microtus pennsylvanicus), we identified elevated serum titers against Y. pestis only in Gunnison's prairie dogs. Prairie dog mortality at all towns affected by plague was in excess of 99%. Serum antibody titers indicate that more than 40% of the few prairie dogs left to establish colonies following epizootics survived plague infection.

No Evidence of Persistent Yersina pestis Infection at Prairie Dog Colonies in North-Central Montana

“…Barnes (1982) reported a recurrence of plague epizootics within 4 to 5 yr and Cully et al (1997) reported an epizootic again after 3 yr. Whether these cases in which the same colonies experience plague again represent a continued presence of infection among hosts in that area or a reintroduction of Y. pestis from surrounding areas is not known.…”

“…Lechleitner et al (1968) found antibodies to Y. pestis in only one of 108 deer mice (Peromyscus maniculatus) (the one seropositive animal was sampled during the active epizootic) and Cully et al (1997) only found antibodies in prairie dogs. In both studies, the epizootic appeared to diminish over the course of about a year.…”

“…Two previous studies (Lechleitner et al, 1968;Cully et al, 1997) followed the progression of plague epizootics among prairie dogs and demonstrated that, in general, Y. pestis positive fleas from prairie dogs, their burrows, and associated mammals are most likely to be collected during an epizootic. These studies also illustrated that one year following an epizootic, some Y. pestis positive fleas may still be present in prairie dog burrows, but after two years, there is little or no evidence of Y. pestis in the vector community.…”

“…Prairie dogs often repopulate colonies following epizootics (Menkens and Anderson, 1991;Cully et al, 1997) and these colonies may then persist for many years or experience a plague epizootic again. Barnes (1982) reported a recurrence of plague epizootics within 4 to 5 yr and Cully et al (1997) reported an epizootic again after 3 yr.…”

“…on ships from Asia (Eskey and Haas, 1940). Today, the range of the disease in North America includes areas west of the 100th meridian (Cully et al, 2000).…”