Thomas J. Quan

DYNAMICS OF PLAGUE IN A GUNNISON'S PRAIRIE DOG COLONY COMPLEX FROM NEW MEXICO

A plague (Yersinia pestis) epizootic spread through Gunnisons 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 Gunnisons prairie dogs, thirteen-lined ground squirrels, deer mice, and meadow voles (Microtus pennsylvanicus), we identified elevated serum titers against Y. pestis only in Gunnisons 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.

Serologic Survey for Selected Arboviruses and Other Potential Pathogens in Wildlife from Mexico

During 1988 and 1989, a serologic survey of wildlife was conducted in northeastern Mexico to determine the presence, prevalence, and distribution of arboviruses and other selected disease agents. Eighty mammal specimens were tested. Antibodies to vesicular stomatitis-Indiana, Venezuelan equine encephalitis–Mena II, Rio Grande virus, and vesicular stomatitis-New Jersey were detected predominately in small mammals. Deer and mouflon (Ovis musimon) had antibodies to bluetongue and epizootic hemorrhagic disease. Two species had serologic evidence of recent exposure to Francisella tularensis. A white-tailed deer (Odocoileus virginianus) had antibodies to Anaplasma marginale. All specimens tested for antibodies against Yersinia pestis and Brucella abortus were negative. Sera from 315 birds were tested for antibody against five equine encephalitis viruses and six avian pathogens. During 1988, antibodies to Venezuelan equine encephalitis–Mena II, Venezuelan equine encephalitis-TC83, St. Louis encephalitis, eastern equine encephalitis, and western equine encephalitis were detected in birds of several species. Antibodies to Pasteurella multocida and Newcastle disease virus were also detected. Birds from five species presented antibodies to Mycoplasma meleagridis. Specimens tested for M. gallisepticum, M. synoviae, and Chlamydia psittaci were negative. To the best of our knowledge, this survey represents the first serologic evidence of bluetongue, Cache Valley virus, epizootic hemorrhagic disease, Jamestown Canyon virus, vesicular stomatitis–Indiana, vesicular stomatitis–New Jersey, Rio Grande virus, and tularemia reported among wildlife in Mexico.

Serologic Survey for Selected Infectious Disease Agents in Swift and Kit Foxes from the Western United States

A serologic survey of swift fox (Vulpes velox) and kit fox (V. macrotis) from the western USA was conducted for 12 infectious diseases. Samples from swift fox were collected between 1987 and 1992 from Colorado (n = 44), Kansas (n = 10), and Wyoming (n = 9). Samples from kit fox were collected in California (n = 86), New Mexico (n = 18), Utah (n = 9), and Arizona (n = 6). Overall antibody prevalence rates were 33 of 110 (30%) for canine parvovirus (CPV), 9 of 72 (13%) for canine distemper virus (CDV), 23 of 117 (20%) for vesicular stomatitis New Jersey, 16 of 117 (14%) for vesicular stomatitis Indiana, six of 117 (5%) for Cache Valley virus, five of 117 (4%) for Jamestown Canyon virus, one of 97 (1%) for rabies virus, one of 117 (1%) for Colorado tick fever virus, and one of 117 (1%) for western equine encephalitis virus. In addition, antibodies were not found to Yersinia pestis, Francisella tularensis, and Borrelia burgdorferi in serum from 25 Colorado swift fox. Adult swift fox from Colorado had serologic evidence of exposure to CPV more often than juveniles. No juvenile swift fox from Colorado had serum antibodies to CDV. There were season-specific differences in serum antibody prevalence for CPV for swift fox from Colorado. No viruses were isolated from ectoparasites or fox from Colorado.

RECOVERY AND IDENTIFICATION OF PASTEURELLA MULTOCIDA FROM MAMMALS AND FLEAS COLLECTED DURING PLAGUE INVESTIGATIONS

During the 12-yr period, 1973–1984, 243 isolates of Pasteurella multocida were recovered or identified from specimens submitted for plague tests. Of the isolates, 79% were from rodents, 10% from lagomorphs, and 7% from carnivores; eight isolates were recovered from pools of rodent or carnivore fleas, and two were recovered from cat-bite wounds of human patients. No correlations of host or geographic sources, season, or biotypic or serotypic characteristics were found. Of the rodent strains serotyped, most were found to be serotypes 1A or 3A, which suggests a possible epizootiologic role for rodents in outbreaks of avian cholera that commonly involve these serotypes.

EXPERIMENTAL PLAGUE IN ROCK SQUIRRELS, SPERMOPHILUS VARIEGATUS (ERXLEBEN)

Experimental infections with Yersinia pestis were followed in groups of rock squirrels. Development of coagulopathy and pneumonia were observed in 2–4% and 11–12% of the test animals, respectively. Susceptibility to experimental infection was heterogeneous with some animals surviving inoculation with large numbers of organisms and others succumbing after inoculation with small numbers. Production and longevity of serum antibody titers, as measured by passive hemagglutination tests, were variable as well, and apparently unrelated to dose. The data presented attest to the need for care in interpreting serologic test results for individual animals.

Cloacal flora isolated from wild black-bellied whistling ducks (Dendrocygna autumnalis) in Laguna La Nacha, Mexico.

Cloacal swabs from 110 adult black-bellied whistling ducks trapped at Laguna La Nacha, Tamaulipas, Mexico, were cultured to determine the prevalence of normal and potentially pathogenic bacteria. Twenty-five gram-negative enterobacteria and four gram-positive cocci were isolated. The most common isolates included Escherichia coli (54%), Staphylococcus spp. (29%), Streptococcus spp. (22%), Aeromonas hydrophila (15%) Enterobacter cloacae (14%), and Micrococcus sp. (14%). The implications of whistling ducks as possible reservoirs of pathogenic bacteria are discussed.

Isolation of pathogens other than Yersinia pestis during plague investigations.

From 1975 to 1978, 37 isolates of Pasteurella multocida, 1 of Salmonella enteriditis, and 5 of Francisella tularensis were recovered from 42 mammalian specimens and 1 flea pool submitted for examination for evidence of infection with Yersinia pestis. Most of the specimens were collected during investigations of either a human plague infection or a reported epizootic among rodent populations. All specimens were of species regularly or occasionally involved in plague or tularemia cycles in nature and most were collected in areas of known plague or tularemia activity.

SEROLOGIC AND BACTERIOLOGIC STUDIES ON THE DISTRIBUTION OF PLAGUE INFECTION IN A WILD RODENT PLAGUE POCKET IN THE SAN FRANCISCO BAY AREA OF CALIFORNIA

Wild rodents involved in a plague epizootic were trapped on a bimonthly schedule at 15 trap sites distributed throughout the San Bruno Mountain plague pocket located in northern San Mateo County, California. The percentage of positive sera obtained from Microtus californicus varied from zero in two sites in which Y. pestis had not been recovered from rodent flea or tissue pools to as high as 90% to 97% positives in Microtus trapped in four sites in which Y. pestis was recovered. Analysis of the data available indicates that the rate of seropositive rodents, Peromyscus maniculutus and Microtus californicus, is correlated with gross numbers of fleas found per trapline.