Evaluation of host preferences by helminths and ectoparasites among black-tailed jackrabbits in northern California.

Fifty-four black-tailed jackrabbits (Lepus californicus) (five juvenile males, 22 adult males, five juvenile females, and 22 adult females) from Humboldt County, California (USA) were evaluated for sex and age-specific differences in parasite prevalences and intensities, 26 February through 30 October 1996. Nematodes found included Biogastranema leporis in 42 hares (78% prevalence), Rauschia triangularis in 26 hares (48%), Trichostrongylus calcaratus in 14 hares (26%), and Trichuris sylvilagi in two hares (4%). Cestodes found included Taenia sp. cysticerci in five hares (9%) and Taenia sp. coenurus found in one hare (2%). Ectoparasites found included the ticks Dermacentor variabilis on 10 hares (19%) and Ixodes spinipalpis (= Ixodes neotomae) on nine hares (17%), as well as the anoplurid louse Haemodipsus setoni on 12 hares (22%). No significant differences in the parasite prevalences or intensities were found between male and female jackrabbits; this was for all males and females collectively, juvenile males and females only, as well as adult males and females only. Combining male and female hosts, adult jackrabbits had a significantly higher prevalence of B. leporis and R. triangularis compared to juveniles. This is the first known report of Trichostrongylus calcaratus, Rauschia triangularis, Trichuris sylvilagi, and Dermacentor variabilis among black-tailed jackrabbits and the first known report of T. calcaratus and T. sylvilagi in the western USA. This is the first published report of I. spinipalpis, the vector for Lyme disease in California, on black-tailed jackrabbits.

Effect of ectoparasite removal procedures on recapture of Microtus californicus.

We tested the null hypothesis that anesthetizing meadow voles (Microtus californicus) and brushing them vigorously for ectoparasites would have no effect on the later recapture of these voles. Voles were trapped from 6 December 1993 to 10 January 1994 at Faye Slough Wildlife Area near Eureka, Humboldt County, California (USA). Alternate trapped voles were anesthetized with ethyl ether and brushed vigorously for ectoparasites. There was no significant difference in the frequency of recapture nor in the time to first recapture between those voles anesthetized and brushed, compared to control animals.

Recovery of Pasteurella multocida from experimentally-exposed freshwater snails.

We determined how long Pasteurella multocida could survive in experimentally-exposed freshwater snails. Physa virginea were collected from the Sacramento National Wildlife Refuge, Glenn County, California (USA), an enzootic site for avian cholera. Exposure to water containing up to 10(7) P. multocida per ml did not produce observable changes or mortality in snails. A minimum of 84 P. multocida per snail was necessary for detection among the normal snail bacterial flora. When snails were exposed to P. multocida in vials containing 10(7) bacteria per ml, P. multocida was detected for up to 72 hours in snails. When uninoculated snails were placed in aquaria containing 10(6) P. multocida per ml, P. multocida was not detected within the snails; further, P. multocida was detected in the water for only 24 hours at this level. Based on these results, we propose that P. virginea is not an effective reservoir for P. multocida.

Correlations of daily activity with avian cholera mortality among wildfowl.

We tested the hypothesis that wildfowl activities can influence the risk of avian cholera (Pasteurella multocida infection) for susceptible birds at Centerville, Humboldt County, California (USA). Avian cholera mortality characteristics from past epizootics were correlated with variations in flock size, habitat use and 11 feeding and nonfeeding behaviors among six empirically defined groups of wildfowl: American coots (Fulica americana), tundra swans (Cygnus columbianus), American wigeon (Anas americana), northern pintails (A. acuta), northern shovelers (A. clypeata)/mallards (A. platyrhynchos), and teal (A. discors, A. crecca, A. cyanoptera). The position of these wildfowl groups in past mortality sequences was directly correlated with mean flock size, time spent on land, and time spent grazing on land or in shallow water. We propose that variations in bird density, habitat use and frequency of grazing may serve as predisposing factors to avian cholera among wildfowl.

Epizootiology of avian cholera in wildfowl.

Pasteurella multocida, the cause of avian cholera, has naturally infected over 100 species of free-living birds. Among wild birds, avian cholera has its greatest impact on North American wildfowl. Epizootics usually are explosive in onset and may involve thousands of birds. The disease has been reported in every month of the year among wildfowl. Disproportionate mortality, with some species suffering proportionately greater mortality than others, has been a common feature of this disease. Presence of animal organic matter plays a significant role in the survival of P. multocida. There are conflicting reports or a lack of information on the role of host sex, age, body size, other physical features, genetic variation or behavioral differences, as predisposing factors to infection by P. multocida. There also are ambiguities on the relationship between season, precipitation, temperature, nutritional stress, water quality, other microorganisms, and environmental contaminants, and the occurrence of avian cholera in wildfowl. Two competing hypotheses for the year-round reservoir of wildfowl strains of P. multocida are ambient soil or water of enzootic sites, and carrier animals; most current evidence favors the role of carrier animals. Transmission most likely occurs by ingestion of contaminated water, inhalation of bacteria-rich aerosols, or both. While many techniques have been proposed to prevent or control avian cholera, none have been rigorously tested to determine their effectiveness.

The effects of six environmental variables on Pasteurella multocida populations in water.

The effects of protein, pH, temperature, sodium chloride (NaCl), clays, sucrose, and their interactions on the survival and growth of Pasteurella multocida were evaluated. Pasteurellae populations declined rapidly in waters maintained at 2 C, compared to 18 C. Increasing water soluble proteins by 175 micrograms/ml, and NaCl by 0.5%, greatly enhanced survival of P. multocida, whereas variations in pH, clays, and sucrose had relatively minor effects. Pasteurella multocida survived for over 1 yr in some samples of water. This is the longest known survival of these bacteria in water.

Epizootiological features of avian cholera on the north coast of California.

An avian cholera (Pasteurella multocida) epizootic was observed among wildfowl at the Centerville Gun Club, Humboldt County, California (USA) in January 1978. Compared to their live populations and use of the area, coots (Fulica americana) died in proportionately greater numbers than any other species. Coots collected by gunshot were evaluated for sex and age composition, and morphometry from November 1977 through mid-January 1978 at this site. There was no substantial difference in the sex, age or morphometry between birds dying of avian cholera and from those dying from gunshot. Assuming coots dying of gunshot are representative of the general population, it appears there was little selection among coots by P. multocida. There was evidence for a sequential mortality similar to that reported previously at this site: coots were the first birds to die, followed by American wigeon (Anas americana) and northern pintails (A. acuta acuta); northern shovelers (A. clypeata) and mallards (A. platyrhynchos) died late in the epizootic.

Serologic evidence of Yersinia pestis infection in small mammals and bears from a temperate rainforest of north coastal California.

From 1983 to 1985, 463 serum samples from 11 species of mammals in Redwood National Park (RNP) (California, USA) were evaluated for antibodies to Yersinia pestis by the passive hemagglutination method. Yersinia pestis antibodies occurred in serum samples from 25 (36%) of 69 black bears (Ursus americanus), one (50%) of two raccoons (Procyon lotor), five (3%) of 170 dusky-footed woodrats (Neotoma fuscipes), and one (less than 1%) of 118 deer mice (Peromyscus maniculatus). Two hundred seventy-three flea pools, consisting of 14 species of fleas, were collected from small mammals and woodrat nest cups. Viable Y. pestis were not isolated from any of the flea pools. Significant between-year variations in the frequencies of seropositive bear or small mammal sera were not observed. A significantly higher frequency of plague antibodies was observed in bear sera taken during September collections. Frequencies of seropositive bear sera did not vary significantly by sex or age group of bears. Significant differences were not observed in the frequencies of seropositive small mammals by forest habitat type in which they were captured. This is the first report of Y. pestis infection in Redwood National Park, and the first detailed report of Y. pestis activity in a temperate rainforest.

Isolation of Yersinia enterocolitica and Y. frederiksenii from forest soil, Federal Republic of Germany.

This is the first report of Yersinia frederiksenii from soil in Europe and of Yersinia enterocolitica sensu stricto from soil in the Federal Republic of Germany. These organisms were isolated from deciduous forest soil, but were not found in grassland soils.

Tick paralysis in a western harvest mouse.

An engorging female Ixodes pacificus was observed on a western harvest mouse (Reithrodontomys megalotis) in Humboldt County, California. The mouse demonstrated a flaccid paraplegia, but it appeared to recover fully after the tick was removed.

Yersiniae in the soil of an infected wapiti range.

Yersinia enterocolitica was isolated from 10 of 121 soil samples from an area inhabitated by infected wapiti (Cervus elaphus roosevelti) in northwest California. Significantly (p less than 0.05) more soil samples from a forest habitat were infected, compared to soil samples from prairie habitats. Soil was found infected with yersiniae only on dates for which rainfall in excess of 17 mm had occurred during the previous 7 days.

The January 1977 avian cholera epornitic in northwest California.

A total of 844 birds were observed dead at three sites in Humboldt County and an estimated 6750 birds died at three sites in Del Norte County, California. Coots were the primary species affected. The isolation of Pasteurella multocida from a snowy egret (Egretta thula) is the first reported case of avian cholera in this bird. There was evidence for a distinct sequence in the bird species dying at one site; American coots (Fulica americana) appeared to be the first species to die.

The 1975-76 avian cholera outbreaks in Humboldt County, California.

The 1975-76 avian cholera outbreaks were observed from 25 November 1975 to 17 February 1976 at three sites in Humboldt County, California. This is the first known occurrence of avian cholera on one of the sites (City of Arcata Oxidation Ponds).

Yersiniae in pond water and snails.

A Yersinia enterocolitica serotype 9 was isolated from pond water; Y. enterocolitica-like bacteria were also isolated from pond water and from three species of snails (Lymnaea palustris elodes, Helisoma sp., Oxyloma retusa) from the Edwin S. George Reserve in southeastern Michigan. There was evidence for biochemical stability among some of the organisms over a period of years. There also was evidence of transmission of these organisms to snails from the water.

Yersinae isolated from wapiti (Cervus canadensis roosevelti).

Yersinia enterocolitica and Yersinia enterocolitica-like bacteria were isolated from 22 of 90 fecal samples taken from five herds of wapiti studied in northwestern California. The serotypes included: (5), (6), (11), (16), (2,19), (4,16) and (6,15). In one herd, all of the organisms were isolated from within a one hectare area. A significantly higher (p < .02) prevalence of isolations was obtained during April and May.

Listeria monocytogenes isolated from wapiti (Cervus canadensis roosevelti).

Serotypes 1 and 4 Listeria monocytogenes were isolated from 14 of 72 wapiti among four of five herds studied in northwestern California. More isolations of Listeria were made during the summer months than during the other months of the study from one of the herds. The pathogenicity of the strains varied with their ability to ferment xylose and rhamnose.