West Nile virus transmission and ecology in birds.

The ecology of the strain of West Nile virus (WNV) introduced into the United States in 1999 has similarities to the native flavivirus, St. Louis encephalitis (SLE) virus, but has unique features not observed with SLE virus or with WNV in the old world. The primary route of transmission for most of the arboviruses in North America is by mosquito, and infected native birds usually do not suffer morbidity or mortality. An exception to this pattern is eastern equine encephalitis virus, which has an alternate direct route of transmission among nonnative birds, and some mortality of native bird species occurs. The strain of WNV circulating in the northeastern United States is unique in that it causes significant mortality in exotic and native bird species, especially in the American crow (Corvus brachyrhynchos). Because of the lack of information on the susceptibility and pathogenesis of WNV for this species, experimental studies were conducted at the USGS National Wildlife Health Center. In two separate studies, crows were inoculated with a 1999 New York strain of WNV, and all experimentally infected crows died. In one of the studies, control crows in regular contact with experimentally inoculated crows in the same room but not inoculated with WNV succumbed to infection. The direct transmission between crows was most likely by the oral route. Inoculated crows were viremic before death, and high titers of virus were isolated from a variety of tissues. The significance of the experimental direct transmission among captive crows is unknown.

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.

American woodcock (Scolopax minor) mortality associated with a reovirus.

A virus isolate associated with a 1989-90 die-off in American woodcock (Scolopax minor) was identified as a reovirus. Emaciation was a consistent necropsy finding in the woodcock involved in this die-off. This reovirus infection appeared to be systemic, had the potential for fecal oral virus transmission, and was associated with deterioration of body condition. To our knowledge this is the first report of a virus isolate from wild American woodcock. A survey conducted in 1990-92 indicated that this virus was not present at detectable levels in the woodcock breeding and wintering population.

Epithelial intracytoplasmic herpes viral inclusions associated with an outbreak of duck virus enteritis.

Several muscovy ducks from a free-roaming flock of 65 muscovy and mallard ducks died over a 3-week period. Three muscovy ducks were necropsied. Gross and microscopic changes were compatible with duck virus enteritis, and the virus was isolated. In addition to intranuclear viral inclusion bodies in several tissues, intracytoplasmic inclusion bodies were present in esophageal and cloacal epithelium. By electron microscopy, the membrane-bound intracytoplasmic inclusions were found to contain enveloped herpesvirus, and nuclei contained herpes viral nucleocapsids.

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 hen's 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.

Microcontaminants and reproductive impairment of the Forster's tern on Green Bay, Lake Michigan--1983.

For the 1983 nesting season, Forster's tern (Sterna forsteri) reproductive success was significantly impaired on organochlorine contaminated Green Bay, Lake Michigan compared to a relatively uncontaminated inland location at Lake Poygan, Wisconsin. Compared with tern eggs from Lake Poygan, eggs from Green Bay had significantly higher median concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), other polychlorinated dibenzo-p-dioxins (PCDDs), total polychlorinated biphenyls (PCBs), total (three congeners) non-ortho, ortho' PCBs, five individual PCB congeners known to induce aryl hydrocarbon hydroxylase (AHH) and several other organochlorine contaminants. Conversions of analytical concentrations of TCDD and PCB congeners based on relative AHH induction potencies allowed for estimation of total 2,3,7,8-TCDD equivalents. Two PCB congeners, 2,3,3',4,4'- and 3,3',4,4',5-pentachlorobiphenyl (PeCB) accounted for more than 90% of the median estimated TCDD equivalents at both Green Bay and Lake Poygan. The median estimated TCDD equivalents were almost 11-fold higher in tern eggs from Green Bay than in eggs from Lake Poygan (2175 and 201 pg/g). The hatching success of Green Bay sibling eggs from nests where eggs were collected for contaminant analyses was 75% lower at Green Bay than at Lake Poygan. Hatchability of eggs taken from other nests and artificially incubated was about 50% lower for Green Bay than for Lake Poygan. Among hatchlings from laboratory incubation, those from Green Bay weighed approximately 20% less and had a mean liver weight to body weight ratio 26% greater than those from Lake Poygan. In both field and laboratory, mean minimum incubation periods were significantly longer for eggs from Green Bay compared to Lake Poygan (8.25 and 4.58 days, respectively). Mean minimum incubation time for Green Bay eggs in the field was 4.37 days longer than in the laboratory. Hatchability was greatly improved when Green Bay eggs were incubated by Lake Poygan adults in an egg-exchange experiment, but was sharply decreased in Lake Poygan eggs incubated in Green Bay nests. Nest abandonment and egg disappearance were substantial at Green Bay but nil at Lake Poygan. Thus, not only factors intrinsic to the egg, but also extrinsic factors (parental attentiveness), impaired reproductive outcome at Green Bay. The epidemiological evidence from this study strongly suggested that contaminants were a causal factor. AHH-active PCB congeners (intrinsic effects) and PCBs in general (extrinsic effects) appeared to be the only contaminants at the concentrations measured in eggs, capable of producing the effects that were observed at Green Bay.

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).

A solitary case of duck plague in a wild mallard.

Duck plague was diagnosed on the basis of pathology and virus isolation in a wild female mallard Anas platyrhynchos found dead near Saskatoon, Saskatchewan. Day-old Pekin ducklings and one of two adult mallards died with lesions typical of duck plague following inoculation of tissue from the wild bird. This is believed to be the only reported case of duck plague in a wild bird since a major outbreak occurred in South Dakota in 1973, and the fourth such report in North America.

Mortality of captive whooping cranes caused by eastern equine encephalitis virus.

Of 39 captive whooping cranes (Grus americana), 7 died during a 7-week period (Sept 17 through Nov 4, 1984) at the Patuxent Wildlife Research Center, Laurel, Md. Before their deaths, 4 cranes did not develop clinical signs, whereas the other 3 cranes were lethargic and ataxic, with high aspartate transaminase, gamma-glutamyl transferase, and lactic acid dehydrogenase activities, and high uric acid concentrations. Necropsies indicated that the birds had ascites, intestinal mucosal discoloration, fat depletion, hepatomegaly, splenomegaly, and visceral gout. Microscopically, extensive necrosis and inflammation were seen in many visceral organs; the CNS was not affected. Eastern equine encephalitis (EEE) virus was isolated from specimens of the livers, kidneys, lungs, brains, and intestines of 4 of the 7 birds that died, and EEE virus-neutralizing antibody was detected in 14 (44%) of the 32 surviving birds. Other infectious or toxic agents were not found. Morbidity or mortality was not detected in 240 sandhill cranes (Grus canadensis) interspersed among the whooping cranes; however, 13 of the 32 sandhill cranes evaluated had EEE virus-neutralizing antibody. Of the 41 wild birds evaluated in the area, 3 (4%) had EEE virus-neutralizing antibody. Immature Culiseta melanura (the most probable mosquito vector) were found in scattered foci 5 km from the research center.

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.

Isolation of a herpesvirus from a bald eagle nestling.

Cloacal swabs collected from wild bald eagle nestlings (Haliaeetus leucocephalus) were tested for viruses. A virus isolated from one of these samples had a lipid coat and contained DNA. Electron microscopy confirmed that it was a herpesvirus. This appears to be the first report of a herpesvirus isolation from a wild bald eagle.

Inclusion body disease of cranes: a serological follow-up to the 1978 die-off.

A herpesvirus was isolated from captive cranes involved in a 1978 die-off. Neutralizing antibody to this virus was detected in this captive population as early as 1975 and consistently thereafter through 1979. Exposure to the virus evidently occurred at least 2 1/2 years before the die-off, without causing any mortality diagnosed as being caused by inclusion body disease of cranes (IBDC). Overcrowding and environmental conditions in 1978 may have contributed to the deaths of certain species of cranes in one area and not in another. Mortality ratios and serological data suggest that crane species vary in their response to IBDC virus.

Failure of naturally acquired rhinovirus infections to produce temporal immunity to heterologous serotypes.

Nine naturally acquired rhinovirus infections in 31 asthmatic and nonasthmatic children were succeeded rapidly (2 to 26 days) by infections with heterologous rhinovirus.