Diana R. Goldberg

Avian cholera in waterfowl: the role of lesser snow and ross's geese as disease carriers in the Playa Lakes Region.

We collected samples from apparently healthy geese in the Playa Lakes Region (USA) during the winters of 2000–01 and 2001–02 to determine whether carriers of Pasteurella multocida, the bacterium that causes avian cholera, were present in wild populations. With the use of methods developed in laboratory challenge trials (Samuel et al., 2003a) and a serotype-specific polymerase chain reaction method for identification of P. multocida serotype 1, we found that a small proportion of 322 wild birds (<5%) were carriers of pathogenic P. multocida. On the basis of serology, an additional group of these birds (<10%) were survivors of recent avian cholera infection. Our results confirm the hypothesis that wild waterfowl are carriers of avian cholera and add support for the hypothesis that wild birds are a reservoir for this disease. In concert with other research, this work indicates that enzootic infection with avian cholera occurs in lesser snow goose (Chen caerulescens caerulescens) populations throughout their annual cycle. Although fewer Rosss geese (Chen rossii) were sampled, we also found these birds were carriers of P. multocida. Even in the absence of disease outbreaks, serologic evidence indicates that chronic disease transmission and recent infection are apparently occurring year-round in these highly gregarious birds and that a small portion of these populations are potential carriers with active infection.

Pasteurella multocida Serotype 1 Isolated from a Lesser Snow Goose: Evidence of a Carrier State

Pharyngeal swabs were collected from 298 lesser snow geese (Chen caerulescens caerulescens) at Banks Island (Northwest Territories, Canada) in the summer of 1994. Pasteurella multocida serotype 1 was isolated from an adult male bird and P. multocida serotype 3 was isolated from an adult female goose. Pathogenicity of the serotype 1 isolate was confirmed by inoculation in Pekin ducks (Anas platyrhynchos). The serotype 3 isolate was non-pathogenic in Pekin ducks. This is the first documented isolation of pathogenic P. multocida serotype 1 from apparently healthy wild snow geese.

Persistence of Pasteurella multocida in Wetlands Following Avian Cholera Outbreaks

Avian cholera, caused by Pasteurella multocida, affects waterbirds across North America and occurs worldwide among various avian species. Once an epizootic begins, contamination of the wetland environment likely facilitates the transmission of P. multocida to susceptible birds. To evaluate the ability of P. multocida serotype-1, the most common serotype associated with avian cholera in waterfowl in western and central North America, to persist in wetlands and to identify environmental factors associated with its persistence, we collected water and sediment samples from 23 wetlands during winters and springs of 1996–99. These samples were collected during avian cholera outbreaks and for up to 13 wk following initial sampling. We recovered P. multocida from six wetlands that were sampled following the initial outbreaks, but no P. multocida was isolated later than 7 wk after the initial outbreak sampling. We found no significant relationship between the probability of recovery of P. multocida during resampling and the abundance of the bacterium recovered during initial sampling, the substrate from which isolates were collected, isolate virulence, or water quality conditions previously suggested to be related to the abundance or survival of P. multocida. Our results indicate that wetlands are unlikely to serve as a long-term reservoir for P. multocida because the bacterium does not persist in wetlands for long time periods following avian cholera outbreaks.

Are wetlands the reservoir for avian cholera

Wetlands have long been suspected to be an important reservoir for Pasteurella multocida and therefore the likely source of avian cholera outbreaks. During the fall of 1995–98 we collected sediment and water samples from 44 wetlands where avian cholera epizootics occurred the previous winter or spring. We attempted to isolate P. multocida in sediment and surface water samples from 10 locations distributed throughout each wetland. We were not able to isolate P. multocida from any of the 440 water and 440 sediment samples collected from these wetlands. In contrast, during other investigations of avian cholera we isolated P. multocida from 20 of 44 wetlands, including 7% of the water and 4.5% of the sediment samples collected during or shortly following epizootic events. Our results indicate that wetlands are an unlikely reservoir for the bacteria that causes avian cholera.

ANTIBODIES AGAINST PASTEURELLA MULTOCIDA IN SNOW GEESE IN THE WESTERN ARCTIC

To determine if lesser snow geese (Chen caerulescens caerulescens) are a potential reservoir for the Pasteurella multocida bacterium that causes avian cholera, serum samples and/or pharyngeal swabs were collected from >3,400 adult geese breeding on Wrangel Island (Russia) and Banks Island (Canada) during 1993–1996. Pharyngeal swab sampling rarely (>0.1%) detected birds that were exposed to P. multocida in these populations. Geese with serum antibody levels indicating recent infection with P. multocida were found at both breeding colonies. Prevalence of seropositive birds was 3.5% at Wrangel Island, an area that has no recorded history of avian cholera epizootics. Prevalence of seropositive birds was 2.8% at Banks Island in 1994, but increased to 8.2% during 1995 and 1996 when an estimated 40,000–60,000 snow geese were infected. Approximately 50% of the infected birds died during the epizootic and a portion of the surviving birds may have become carriers of the disease. This pattern of prevalence indicated that enzootic levels of infection with P. multocida occurred at both breeding colonies. When no avian cholera epizootics occurred (Wrangel Island, Banks Island in 1994), female snow geese (4.7%) had higher antibody prevalence than males (2.0%).

Mortality from duck plague virus in immunosuppressed adult mallard ducks

Environmental contaminants contain chemicals that, if ingested, could affect the immunological status of wild birds, and in particular, their resistance to infectious disease. Immunosuppression caused by environmental contaminants, could have a major impact on waterfowl populations, resulting in increased susceptibility to contagious disease agents. Duck plague virus has caused repeated outbreaks in waterfowl resulting in mortality. In this study, several doses of cyclophosphamide (CY), a known immunosuppressant, were administered to adult mallards (Anas platyrhynchos) to determine if a resultant decrease in resistance to a normally sub-lethal strain of duck plague virus would occur, and induce mortality in these birds. Death occurred in birds given CY only, and in birds given virus and CY, but not in those given virus only. There was significantly greater mortality and more rapid deaths in the duck plague virus-infected groups than in groups receiving only the immunosuppressant. A positively correlated dose-response effect was observed with CY mortalities, irrespective of virus exposure. A fuel oil and a crude oil, common environmental contaminants with immunosuppressive capabilities, were tested to determine if they could produce an effect similar to that of CY. Following 28 days of oral oil administration, the birds were challenged with a sub-lethal dose of duck plague virus. No alteration in resistance to the virus (as measured by mortality) was observed, except in the positive CY control group.

The occurrence of mycoplasmas in selected wild North American waterfowl

We determined the prevalence of mycoplasma infection in breeding mallard (Anas platyrhynchos) and canvasback (Aythya valisineria) hens and their broods from the central United States (1988 to 1990); and wintering American black duck (Anas rubripes) and mallard hens from the eastern United States (1990 to 1993). Mycoplasmas were isolated by culturing tracheal swabs from 656 live birds and tissue samples from 112 dead waterfowl. Nine (18%) of 51 mycoplasma isolates were identified as Mycoplasma anatis; M. anatis was recovered from four mallards, a black duck, and a gadwall (Anas strepera) duckling. Nineteen (37%) of 51 mycoplasma isolates were identified as Mycoplasma cloacale; these isolates were obtained from mallard, canvasback, and black duck adults, and from a mallard duckling. Additional unspeciated mycoplasmas were isolated from mallards, black ducks, and one canvasback.

Neckband retention for lesser snow geese in the western Arctic

Neckbands are commonly used in waterfowl studies (especially geese) to identify individuals for determination of movement and behavior and to estimate population parameters. Substantial neckband loss can adversely affect these research objectives and produce biased survival estimates. We used capture, recovery, and observation histories for lesser snow geese (Chen caerulescens caerulescens) banded in the western Arctic, 1993-1996, to estimate neckband retention. We found that neckband retention differed between snow goose breeding colonies at Wrangel Island, Russia, and Banks Island, Northwest Territories, Canada. Male snow geese had higher neckband loss than females, a pattern similar to that found for Canada geese (Branta canadensis) and lesser snow geese in Alaska. We found that the rate of neckband loss increased with time, suggesting that neckbands are lost as the plastic deteriorates. Survival estimates for geese based on resighting neckbands will be biased unless estimates are corrected for neckband loss. We recommend that neckband loss be estimated using survival estimators that incorporate recaptures, recoveries, and observations of marked birds. Research and management studies using neckbands should be designed to improve neckband retention and to include the assessment of neckband retention.

The dynamics of avian influenza in Lesser Snow Geese: implications for annual and migratory infection patterns

Wild water birds are the natural reservoir for low-pathogenic avian influenza viruses (AIV). However, our ability to investigate the epizootiology of AIV in these migratory populations is challenging and, despite intensive worldwide surveillance, remains poorly understood. We conducted a cross-sectional, retrospective analysis in Pacific Flyway Lesser Snow Geese, Chen caerulescens, to investigate AIV serology and infection patterns. We collected nearly 3000 sera samples from Snow Geese at two breeding colonies in Russia and Canada during 1993-1996 and swab samples from >4000 birds at wintering and migration areas in the United States during 2006-2011. We found seroprevalence and annual seroconversion varied considerably among years. Seroconversion and infection rates also differed between Snow Goose breeding colonies and wintering areas, suggesting that AIV exposure in this gregarious waterfowl species is likely occurring during several phases (migration, wintering, and potentially breeding areas) of the annual cycle. We estimated AIV antibody persistence was longer (14 months) in female geese compared to males (6 months). This relatively long period of AIV antibody persistence suggests that subtype-specific serology may be an effective tool for detection of exposure to subtypes associated with highly pathogenic AIV. Our study provides further evidence of high seroprevalence in Arctic goose populations, and estimates of annual AIV seroconversion and antibody persistence for North American waterfowl. We suggest future AIV studies include serology to help elucidate the epizootiological dynamics of AIV in wild bird populations.

Comparison of methods to detect Pasteurella multocida in carrier waterfowl.

We conducted laboratory challenge trials using mallard ducks (Anas platyrhynchos) to compare methods for detecting carriers of Pasteurella multocida, the bacterium that causes avian cholera, in wild birds. Birds that survived the initial infection were euthanized at 2–4 wk intervals up to 14 wk post challenge. Isolates of P. multocida were obtained at necropsy from 23% of the birds that survived initial infection. We found that swab samples (oral, cloacal, nasal, eye, and leg joint) were most effective for detecting carrier birds up to 14 wk post infection. No detectable differences in isolation were observed for samples stored in either 10% dimethysulfoxide or brain heart infusion broth. The frequency of detecting carriers in our challenge trials appeared to be related to mortality rates observed during the trial, but was not related to a number of other factors including time after challenge, time delays in collecting tissues postmortem, and route of infection. In our trials, there was little association between antibody levels and carrier status. We concluded that swabs samples collected from recently dead birds, stored in liquid nitrogen, and processed using selective broth provide a feasible field method for detecting P. multocida carriers in wild waterfowl.