Gross Findings: On external examination, numerous lice are present, and there is moderate staining of feathers around the vent with urates. On internal examination, there is adequate subcutaneous, visceral, and epicardial fat. A small number of hair-like, red nematodes (Syngamus trachea) are present in the trachea. No other abnormalities are seen. 

Histopathological Findings: In the brain, the following are present: multifocal perivascular lymphocytic cuffing; multiple foci of gliosis; neuronal necrosis; neuronophagia; and multifocal to focally extensive leptomeningeal lymphocytic infiltrates (Fig 1A through 1D).  These changes are widespread and mild to moderate; they are most marked in the cerebrum and midbrain. In the spinal cord, there is multifocal, mild, perivascular lymphocytic cuffing.

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Morphologic Diagnosis: Acute to subacute, mild to moderate, multifocal, lymphocytic meningomyeloencephalitis with neuronophagia and neuronal necrosis. 

Disease: Newcastle Disease (ND).

Etiology: Virulent Newcastle Disease virus/Avian paramyxovirus-1.

Distribution: Newcastle Disease has a world-wide distribution. In the USA, outbreaks in double-crested cormorants occur most often in the upper Midwest. 

Seasonality: In DCCO, outbreaks of ND occur in juvenile birds during the breeding season, which stretches from April through August in North America.

Host range: Newcastle Disease is one of the most economically important diseases of poultry worldwide. Double-crested cormorants are the only known wild bird species that carry and act as a reservoir for virulent ND virus in the USA. They are also the only wild bird species in the USA that has been definitively diagnosed with ND as a cause of morbidity and mortality. Transmission from infected cormorants to poultry is uncommon, likely due to a lack of contact between them. However, DCCO were believed to be the source of virus for a 1992 ND outbreak in turkeys in North Dakota.

Transmission: ND virus/APMV-1 can be transmitted through either inhalation or ingestion of viral particles, which may be shed in feces, in body fluids, and in eggs. The virus can remain infective for long periods of time under the right environmental conditions, and infection from exposure to fomites is also possible. 

Clinical signs: In general, clinical signs in DCCO are referrable to the central nervous system. Ataxia, torticollis, and paralysis of one or both wings are typical; however complete paralysis of the wings and legs can occur. Some birds may only show weakness or prostration.  

Pathology: Grossly, there are usually no visible abnormalities in DCCO with ND. Histopathologic lesions primarily involve the central nervous system but may also be seen in the kidney. Nonsuppurative meningomyeloencephalitis with gliosis and neuronal necrosis are typical; vasculitis and neuronophagia may also occur. In the kidney, nonsuppurative interstitial nephritis with scattered tubular epithelial cell necrosis may be seen.

Diagnosis: An outbreak of neurologic disease in juvenile DCCO, with the presence of the histopathologic lesions described above, is highly suspicious for ND. However, laboratory confirmation is required for a definitive diagnosis. In general, viral RNA is extracted from swabs or tissue samples and tested by a PCR test that can detect all types of avian paramyxoviruses including Newcastle Disease. Follow-up nucleotide sequencing can be performed to determine if the ND virus is virulent.

Public health concerns: Newcastle Disease virus may cause conjunctivitis in people. Symptoms can be severe but generally are short-lived, with no residual damage. People at risk are those who have close contact with infected birds. 

Wildlife population impacts: In DCCO, APMV-1 viruses primarily infect nestlings and fledglings. In an affected nesting colony, morbidity and mortality in these age groups due to ND can exceed 90%. However, DCCO populations in the USA remain stable and this species is not considered to be threatened or endangered.

Management: Due to the potential for ND virus to infect domestic poultry, it is important to practice good biosecurity measures to keep the virus contained on cormorant breeding islands, particularly if domestic poultry flocks are nearby. Wear boots, gloves, and outer clothing that can be cleaned and disinfected, bagged and washed, or bagged and thrown away. It is preferable for any carcasses collected from this site to be disposed of on-site (by burying or incineration) rather than transported to other locations for disposal. Equipment, including transportation vehicles, that come in contact with the contaminated environment site should be washed to remove organic material and mud, then disinfected with 10% household bleach solution (9 parts water:1 part bleach) or other suitable disinfectant such as Virkon as soon as possible after use. Limiting contact with pet birds and poultry for 5 days is advised for any personnel that have recently handled contaminated animals or materials. 

References:              

Brown VR, Bevins SN. 2017. A review of virulent Newcastle disease viruses in the United States and the role of wild birds in viral persistence and spread. Vet Res 48:68. doi: 10.1186/s13567-017-0475-9. Erratum in: Vet Res 2017 48:77. doi: 10.1186/s13567-017-0485-7. 

Dimitrov KM, Ramey AM, Qiu X, Bahl J, Afonso CL. 2016. Temporal, geographic, and host distribution of avian paramyxovirus 1 (Newcastle disease virus). Infect Genet and Evol 39:22-34. doi.org/10.1016/j.meegid.2016.01.008.

Kuiken T, Leighton FA, Wobeser G, Danesik KL, Riva J, Heckert RA. 1998. An epidemic of Newcastle disease in double-crested cormorants from Saskatchewan. J Wild Dis 34:457–471. doi: 10.7589/0090-3558-34.3.457.

Kuiken T, Wobeser G, Leighton FA, Haines DM, Chelack B, Bogdan J, Hassard L, Heckert RA, Riva J. 1999. Pathology of Newcastle disease in double-crested cormorants from Saskatchewan, with comparison of diagnostic methods. J Wildl Dis. 35:8-23.doi: 10.7589/0090-3558-35.1.8. PMID: 10073341.

Mixson MA, Pearson JE. 1992. Velogenic neurotropic Newcastle disease (VNND) in cormorants and commercial turkeys, FY 1992. In: Proceedings of the 96th Annual Meeting of the United States Animal Health Association. Louisville, KY. p. 35–60.

White CL, Ip HS, Meteyer CU, Walsh DP, Hall JS, Carstensen M, Wolf PC. 2015. Spatial and temporal patterns of avian paramyxovirus-1 outbreaks in double-crested cormorants (Phalacrocorax auritus) in the USA.  J Wildl Dis 51:101-112. doi: 10.7589/2014-05-132