Douglas E. Docherty

Isolation and Characterization of a Reovirus from Common Eiders (Somateria mollissima) from Finland

SUMMARY. Samples of brain, intestine, liver, lung, spleen, and bursa of Fabricius were collected from five common eider (Somateria mollissima) duckling carcasses during a die-off in the western Gulf of Finland (59°50′N, 23°15′E) in June 1996. No viral activity was observed in specific-pathogen-free chicken embryos inoculated with tissue suspensions, but samples of bursa of Fabricius from three birds were positive when inoculated into Muscovy duck (Cairina moschata) embryo fibroblasts. The isolates were characterized as nonenveloped RNA viruses and possessed several characteristics of the genus Orthoreovirus. Virus particles were icosahedral with a mean diameter of 72 nm and were stable at pH 3.0; their genome was separated into 10 segments by polyacrylamide gel electrophoresis. Mallard (Anas platyrhynchos) ducklings experimentally infected with the eider reovirus showed elevated serum activities of aspartate aminotransferase, creatine kinase, and lactate dehydrogenase enzymes and focal hemorrhages in the liver, spleen, and bursa of Fabricius. During 1997–99, the prevalence of neutralizing antibodies to the isolated virus ranged from 0 to 86% in 302 serum samples collected from incubating eider hens at three nesting areas along coastal Finland. The highest seroprevalence was found in Hanko in 1999, just weeks before reports of an uninvestigated mortality event resulting in the death of an estimated 98% of ducklings at that location. These findings raise the question of potential involvement of the virus in poor duckling survival and eider population declines observed in several breeding areas along coastal Finland since the mid-1980s.

Diagnosis of Duck Plague in Waterfowl by Polymerase Chain Reaction

A recently developed polymerase chain reaction (PCR) assay was used for diagnosis of duck plague in waterfowl tissues from past and current cases of waterfowl mortality and to identify duck plague virus in combined cloacal/oral-pharyngeal swab samples from healthy mallards (Anas platyrhynchos) after a disease outbreak. The PCR was able to detect viral DNA from all the individual or pooled tissues assayed from 10 waterfowl, including liver and spleen samples from three Muscovy ducks (Cairina moschata domesticus) that did not yield virus isolates. The strong staining intensity of the PCR products from the waterfowl tissues indicated that large amounts of virus were present, even when virus was not isolated. Duck plague DNA was also detected in a cloacal swab sample from a wood duck (Aix sponsa) carcass submitted for diagnosis. The PCR assay identified duck plague DNA in 13 swab samples that produced virus isolates from carrier mallards sampled in 1981 after a duck plague die-off. The duck plague PCR clearly demonstrated the ability to quickly diagnose duck plague in suspect mortality cases and to detect virus shed by carrier waterfowl.

Diagnostic findings in the 1992 epornitic of neurotropic velogenic Newcastle disease in double-crested cormorants from the upper midwestern United States

Neurotropic velogenic Newcastle disease (NVND) occurred in juvenile double-crested cormorants, Phalacrocorax auritus, simultaneously in nesting colonies in Minnesota, North Dakota, South Dakota, and Nebraska and in Lakes Michigan, Superior, Huron, and Ontario during the summer of 1992. Mortality as high as 80%-90% was estimated in some of the nesting colonies. Clinical signs observed in 4- to 6-wk-old cormorants included torticollis, tremors, ataxia, curled toes, and paresis or weakness of legs, wings or both, which was sometimes unilateral. No significant mortality or unusual clinical signs were seen in adult cormorants. Necropsy of 88 cormorants yielded no consistent gross observations. Microscopic lesions in the brain and spinal cord were consistently present in all cormorants from which Newcastle disease virus (NDV) was isolated. Characteristic brain lesions provided rapid identification of new suspect sites of NVND. Lesions were also present in the heart, kidney, proventriculus, spleen, and pancreas but were less consistent or nonspecific. NDV was isolated at the National Wildlife Health Center from 27 of 93 cormorants tested. Virus was most frequently isolated from intestine or brain tissue of cormorants submitted within the first 4 wk of the epornitic. Sera collected from cormorants with neurologic signs were consistently positive for NDV antibody. The NDV isolate from cormorants was characterized as NVND virus at the National Veterinary Services Laboratories, Ames, Iowa. The NVND virus was also identified as the cause of neurologic disease in a North Dakota turkey flock during the summer of 1992. Although no virus was isolated from cormorants tested after the first month of submission, brain and spinal cord lesions characteristic of NVND were observed in cormorants from affected sites for 2 mo, at which time nesting colonies dispersed and no more submissions were received. Risk to susceptible populations of both wild avian species and domestic poultry makes early recognition and confirmation of NVND in wild birds a priority.

INFECTIOUS BURSAL DISEASE VIRUS ANTIBODIES IN EIDER DUCKS AND HERRING GULLS

Abstract We measured antibodies to infectious bursal disease virus (IBDV) in blood of nesting Common Eider (Somateria mollissima) females and immature Herring Gulls (Larus argentatus) in the Baltic Sea, and in blood of Spectacled Eider (Somateria fischeri) females nesting in a remote area of western Alaska. Positive (≥ 1:16) IBDV titers occurred in 75% of the eiders and 45% of the Herring Gull chicks. In eiders, the prevalence of positive titers differed among locations. We found no evidence that IBDV exposure impaired the immune function of Herring Gull chicks, based on their response to inoculation of sheep red blood cells. We suggest that eider ducks and Herring Gulls have been exposed to IBDV, even in locations where contact with poultry is unlikely. The presence of this virus in wild bird populations is of concern because it causes mortality of up to 30% in susceptible poultry.

Isolation of poxvirus from debilitating cutaneous lesions on four immature grackles (Quiscalus sp.)

Poxvirus was isolated from nodules on four immature grackles (Quiscalus sp.) collected in two residential areas of Victoria, Texas. All of the birds were emaciated and had nodules on the eyelids, bill, legs, toes, and areas of the skin on the wings, neck, and ventral abdomen. These pox nodules were extensive and probably interfered with both sight and flight. The preliminary diagnosis was confirmed by virus isolation, histopathology, and electron microscopy. Poxvirus was isolated on the chorioallantoic membrane of embryonated hens eggs and in Muscovy duck embryo fibroblast cell culture. Phaenicia calliphoridae (blowfly) larvae were found in one of the pox nodules, raising the possibility of mechanical transmission of the virus by contaminated adult blowflies.

A SURVEY OF NORTH AMERICAN MIGRATORY WATERFOWL FOR DUCK PLAGUE (DUCK VIRUS ENTERITIS) VIRUS

A survey of migratory waterfowl for duck plague (DP) virus was conducted in the Mississippi and Central flyways during 1982 and in the Atlantic and Pacific flyways during 1983. Cloacal and pharyngeal swabs were collected from 3,169 migratory waterfowl in these four flyways, principally mallards (Anas platyrhynchos L.), black ducks (Anas rubripes Brewster), and pintails (Anas acuta L). In addition 1,033 birds were sampled from areas of recurrent DP outbreaks among nonmigratory and captive waterfowl, and 590 from Lake Andes National Wildlife Refuge, the site of the only known major DP outbreak in migratory waterfowl. Duck plague virus was not found in any of the samples. Results support the hypothesis that DP is not established in North American migratory waterfowl as an enzootic disease.

Post-epizootic surveys of waterfowl for duck plague (duck virus enteritis).

Surviving birds from nine duck plague outbreaks in urban and confined waterfowl were sampled for duck plague (DP) virus and DP antibody during 1979-86. Duck plague virus was found in combined oral and cloacal swabs of birds from three outbreaks, and DP-neutralizing antibody was demonstrated in some birds from all nine outbreaks. Greater prevalence of DP antibody and higher titers were found in survivors from confined populations than from free-flying urban populations. Free-flying waterfowl from within 52 km of four DP outbreak sites were also sampled; virus was not found in any birds, but DP antibody was found in urban waterfowl in the vicinity of an outbreak in Potterville, Michigan. No evidence of exposure to or shedding of DP virus in migratory waterfowl was found in two regions where DP appears enzootic in urban and confined waterfowl (Eastern Shore of Maryland and the vicinity of Sacramento, California).

Isolation of a poxvirus from a house finch, Carpodacus mexicanus (Muller)

(33%) originating from the Alaska Peninsula and nine samples (23%) from the Susitna area. Positive titers ranged from 1:16 to 1:128. Six samples (6%) were seropositive to IBRV, with four (10%) being from the Susitna area and two (17%) from the Alaska Peninsula. All positive titers were at the 1:16 dilution. Antibodies to IBRV in moose have been reported previously for 14% of 14 moose sampled in Alberta (Zarnke and Yuill, 1981, J. Wildl. Dis. 17: 453-461) although none were found in a previous study (Thorsen and Henderson, 1971, J. Wildl. Dis. 7: 93-95). Unpublished studies on serologic reactivity to IBRV and BVDV apparently have shown seroreactive moose in Alaska (Dieterich, 1981, op. cit.) although evaluation of 73 Alaskan Dall’s sheep (Ovis dalli) failed to detect serologic reactivity to either virus (Foreyt et al., 1983, J. Wild]. Dis. 19: 136-139) nor did an evaluation of 39 moose from Alaska result in the detection of antibodies to BVDV or IBRV (Zarnke et al., 1983, op. cit.). The detection of serologic reactivity to these two viruses in the present study indicates that contact with domestic cattle or other seropositive wild ruminants may have occurred. Further studies appear warranted to determine the role of moose in the epidemiology of these infectious diseases and the significance of these findings to moose health.

An adenovirus associated with intestinal impaction and mortality of male common eiders (Somateria mollissima) in the Baltic Sea.

We examined 10 common eider (Somateria mollissima) males found dead in 1998 during a die-off in the northern Baltic Sea off the southwestern coast of Finland. We diagnosed impaction of the posterior small intestine with mucosal necrosis as the cause of death in all 10 and isolated adenoviruses from cloacal samples of six birds. The adenovirus isolates were not neutralized by reference antisera to group I, II, or III avian adenoviruses. Cloacal swabs from 22 apparently healthy eider females nesting at the mortality area were negative for viruses. An adenovirus isolated from one of the eiders caused clinical signs of illness and gastrointestinal pathology in experimentally infected mallard (Anas platyrhynchos) ducklings. These findings suggest that the adenovirus contributed to the mortality of common eider males in the Finnish archipelago.

An Adenovirus Linked to Mortality and Disease in Long-Tailed Ducks (Clangula hyemalis) in Alaska

Abstract SUMMARY. An adenovirus was isolated from intestinal samples of two long-tailed ducks (Clangula hyemalis) collected during a die-off in the Beaufort Sea off the north coast of Alaska in 2000. The virus was not neutralized by reference antiserum against known group I, II, or III avian adenoviruses and may represent a new serotype. The prevalence of the virus was determined in live-trapped long-tailed ducks at the mortality site and at a reference site 100 km away where no mortality was observed. Prevalence of adenovirus antibodies in serum samples at the mortality site was 86% compared to 10% at the reference site. Furthermore, 50% of cloacal swabs collected at the mortality site and only 7% of swabs from the reference site were positive for adenoviruses. In 2001, no mortality was observed at either of the study areas, and virus prevalence in both serum and cloacal samples was low, providing further evidence that the adenovirus was linked to the mortality event in 2000. The virus was used to infect long-tailed ducks under experimental conditions and resulted in lesions previously described for avian adenovirus infections and similar to those observed in long-tailed duck carcasses from the Beaufort Sea. The status of long-tailed ducks has recently become a concern in Alaska due to precipitous declines in breeding populations there since the mid-1970s. Our findings suggest that the newly isolated adenovirus is a disease agent and source of mortality in long-tailed ducks, and thus could be a contributing factor in population declines.