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Swine cell systems as interferon producers. IV. Comparative studies on the correlation between virulence of different Newcastle disease virus strains and their potency as interferon inducers.

Comparative studies concerning a correlation between virulence of various Newcastle virus strains and their interferon-inducing potency confirmed that such a correlation existed. The nearly avirulent La Sota strain of NDV was the poorest interferon inducer, the virulent Hertfordshire strain manifested a very good inducing potency. However, the most virulent J.B. strain virus was a poorer interferon inducer than the Hertfordshire strain. This should not be viewed as contradictory to the conclusion of the correlation between virulence and interferon-inducing ability of NDV since the highly virulent strain might destroy faster the interferon-producing cells, before the latter produced the maximum interferon quantity which they potentially could produce.

Animals↗

Newcastle disease virus in double-crested cormorants in Alabama, Florida, and Mississippi.

In order to understand the epidemiology of Newcastle disease (ND) outbreaks in double-crested cormorants (Phalacrocorax auritus), a study was conducted on wintering migratory cormorants (P. a. auritus) in Alabama and Mississippi (USA) and non-migratory cormorants (P. a. floridanus) that breed in Florida (USA). Antibodies against ND virus were detected by the hemagglutination-inhibition method in sera from 86 of 183 (47%) migratory cormorants over-wintering in eight roosting sites in Alabama and Mississippi between November, 1997 and April, 1999. Titers ranged from 5 to 40. Antibody prevalences in sera collected from females in early winter (November and December) (26%) and late winter (February and March) (56%) were significantly different (P = 0.0007). None of 45 serum samples from 1- to 7-wk-old nestlings from 11 colonies in Florida during the 1997-98 and 1998-99 breeding seasons was positive. However, antibodies were detected in yolk samples from 98 of 126 (78%) eggs collected in these same colonies. Titers ranged from 4 to 256. The prevalence of antibodies in eggs collected from fresh-water colonies (63% prevalence, n = 30) and salt-water colonies (82% prevalence, n = 96) was significantly different (P = 0.041). ND virus was not isolated from tissues of 18 cormorants and cloacal and tracheal swabs from 202 cormorants collected in Alabama and Mississippi; virus was also not isolated from cloacal and tracheal swabs from 51 nestlings from Florida.

Alabama↗

Use of sentinel chickens to evaluate the effectiveness of cleaning and disinfection procedures in noncommercial poultry operations infected with exotic Newcastle disease virus.

The use of sentinel chickens in establishing the negative status of commercial poultry flocks depopulated due to exotic Newcastle disease (END) is considered to be an economically beneficial process. However, the costs and benefits of using sentinel chickens in noncommercial operations are in question. The objective of this study was to use sentinel chickens to evaluate whether adequate cleaning and disinfection coupled with an appropriate time period without susceptible poultry species on the premises would eliminate END virus from a noncommercial poultry operation and preclude the need for placement of sentinels in previously infected operations before declaring them free of virus. Noncommercial poultry operations were selected from the 2002 to 2003 END outbreak database. Operations included in the study had one or more isolations of END virus (ENDV) from cloacal or oropharyngeal swabs of birds on the premises. A total of 546 birds were placed on 53 premises. All sentinel birds sampled after placements were negative by virus detection methods and serologic tests. Results of this study indicate that time and the application of appropriate cleaning and disinfection procedures will adequately mitigate the risk of viable virus persisting in noncommercial poultry operations. In the future, this information may eliminate the need for sentinel bird placement to ensure virus free status of premises before repopulation, thereby decreasing the costs of END eradication.

Animals↗