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International Society for Infectious Diseases <http://www.isid.org>

Date: 17 Aug 2012
Source: <http://www.healthywildlife.ca/>

Epidemic disease in double-crested cormorants in Saskatchewan
An outbreak of a virus infection of the brain and spinal cord (encephalitis and myelitis) occurred in August 2012 at a large colony of double-crested cormorants (DCCO) on Dore Lake in the southern boreal forest of Saskatchewan. The cause of the outbreak was avian
paramyxovirus-1 (APMV-1), a virus that occurs in DCCO across their range in North America and regularly results in mortality of nearly full grown young-of-the year DCCO close to the end of the nesting season. Acutely-infected cormorants show a range of signs associated with damage to the central nervous system.

Many birds die during outbreaks, but some recover with various forms of paralysis. At affected colonies, it is common to see birds attempting to take off and fly with only one wing due to paralysis of the other wing, and birds "walking" on their wings or unable to dive due to leg paralysis. Total mortality appears to reach about 50 per cent of hatch year birds in some outbreaks. The surviving birds with paralysis also will die when winter arrives. Only young cormorants appear to suffer disease from APMV-1. Affected birds generally are 5-8 weeks of age; by 16 weeks of age, they no longer show signs of disease when they become infected.

APMV-1 infection has occurred on this same breeding colony many times since it was first noted in 1995. Although large numbers of American white pelicans nest here among the cormorants, and several species of gull, ravens, crows, and bald eagles regularly visit the colony and feed on the dead cormorants, significant mortality and clinical disease due to APMV-1 has only been seen in the cormorants.

Some strains of APMV-1 can cause severe disease in chickens and these strains are then referred to as "Newcastle disease" viruses. It has not yet been determined whether or not the 2012 virus in Saskatchewan DCCO falls into this category.

communicated by:
Christine Wilson
Canadian Cooperative Wildlife Health Centre

[Saskatchewan Province, Canada may be found on the interactive healthmap at <http://healthmap.org/r/2bqZ>.

A photograph of a cormorant may be viewed at <http://www.allaboutbirds.org/guide/double-crested_cormorant/id>.

There are 9 serotypes of avian paramyxovirus (APMV), including APMV-1, or Newcastle disease virus. Some sources report as many as 11 serotypes. These viruses, which are called either APMV-1 or Newcastle disease viruses (NDV), are members of the genus _Avulavirus_ in the family Paramyxoviridae. APMV-1 strains maintained in pigeon populations have some antigenic differences from other NDV isolates, and are sometimes called pigeon paramyxovirus type 1 (PPMV-1).

Newcastle disease primarily affects birds. Some avian species become ill, while others carry these viruses asymptomatically. Infections also occur in humans, but have not been reported in other species of mammals.

Virtually all birds are considered susceptible to infection with Newcastle diseases virus (NDV; Fam. Paramyxoviridae). NDV has been categorized into 5 pathotypes based on clinical signs in infected chickens, designated: a) viscerotropic velogenic, b) neurotropic velogenic, c) mesogenic, d) lentogenic or respiratory and e) subclinical enteric.

The clinical signs vary with the pathogenicity of the isolate and the species of bird. In chickens, lentogenic strains usually cause subclinical infections or mild respiratory disease with coughing, gasping, sneezing and rales. Mesogenic strains can cause acute respiratory disease and neurologic signs in some chickens, but the mortality rate is usually low. Lentogenic or mesogenic strains can produce more severe symptoms if the flock is co-infected with other pathogens.

Unfortunately, vaccination is not practical in wild birds. But the carcasses of any dead birds will have to be removed from the area or we will be hearing about a send die off due to avian botulism.

Portions of this comment were extracted from < <http://www.cfsph.iastate.edu/Factsheets/pdfs/newcastle_disease.pdf>
and from <http://www.jwildlifedis.org/content/46/2/481.abstract>. - Mod.TG]

[see also:
Newcastle disease, wild birds - USA: (MN) susp. 20120809.1237146
Paramyxovirus, pigeons - Australia (02): (VI) 20110921.2862 Paramyxovirus, pigeons - Australia: (VI) 20110908.2735] .................................................mhj/tg/sh/ll
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