On October 3rd,2002
exotic Newcastle disease was diagnosed in a poultry flock in Southern
California. This disease causes serious
illness and death in most bird species.
Pigeons can be infected with exotic Newcastle disease virus, and when
infected, they will show clinical signs, such as depression, diarrhea, and
sudden death. Like infected chickens
and turkeys, all ages are susceptible and can experience very high mortality
(up to 90%). There is some confusion
over the relationship between pigeon paramyxovirus and Newcastle disease
virus. Currently, we know that they are
very closely related but not identical (for additional information on pigeon paramyxovirus
and Newcastle disease see Twins or Cousins—Paramyxovirus type 1 of Pigeons
and Fowl, California Poultry Letter, Mar/Apr 2001,
http://animalscience.ucdavis.edu/Avian/cplbackissues.htm). Vaccination for either Newcastle disease or
paramyxovirus will not protect pigeons or other birds from either becoming
infected with the virus or showing the clinical signs of Newcastle disease.
Pigeon
lofts experiencing excessive mortality should immediately seek veterinary
advice, submit birds to a local diagnostic laboratory, and stop all human and
bird traffic in and out of suspect lofts.
At this time, there is no evidence that pigeons are involved in the
current disease outbreak in California although the investigation is not yet
complete.
Dr.
Joan Jeffrey, University of California, Davis presented a talk on Paramyxovirus
type 1 (PMV-1) or Newcastle disease virus.
Dr. Jeffrey relayed the diagnostic challenge that exists for
differentiating pigeon paramyxovirus (PPMV-1) from Newcastle disease virus
which is also a paramyxovirus type 1.
Newcastle virus has a worldwide distribution and affects most bird
species. It is a common virus of
chickens and turkeys that can cause anything from mild respiratory disease to
deadly infections with high mortality in 24 hours. These would be called low pathogenic and highly pathogenic
viruses, respectively.
California
suffered from an outbreak of highly pathogenic NDV in 1971, which had
devastating effects on the California poultry industry. Vaccination of commercial poultry against
NDV is almost universal, but it cannot protect against highly pathogenic
strains of the virus. Dr. Jeffrey
showed that depending upon which diagnostic tests are used PPMV-1 and ND virus
may appear alike. A standardized test,
called the intracerebral pathogenicity index (ICPI) is one of several tests
that are used to gauge the pathogenicity of paramyxoviruses. Both PPMV-1 and highly pathogenic Newcastle
viruses rank greater than 0.7 on the ICPI test. Dr. Jeffrey pointed out that this could raise concerns about the
protection of commercial chickens and turkeys (with the vaccination programs currently used). She quoted a study performed by J. Gelb et
al. that tested the ability of pigeon viruses to harm chickens vaccinated
with B1 Hitchner and LaSota strains of NDV (the most commonly used strains for
vaccination). This trial showed
complete protection against the pigeon PMV-1 viruses with ICPI scores of 0.84
or above.
Dr.
Jeffrey relayed that the danger of PPMV-1 to U.S. poultry producers was in
affecting the ability of the industry to export products outside of the
USA. Currently, rules are pending
approval by the International Organization of Epizootics (O.E.I.), for determining
what is considered a highly pathogenic PMV-1.
The O.I.E. is a group made up of over 200 member nations, that makes
international rules aimed at preventing
the spread of dangerous diseases across international borders. The O.I.E. has stated that any PMV-1 virus
with an ICPI of greater than 0.7 will be considered a highly pathogenic
virus. Any country that identifies such
a virus will be subject to export bans.
Dr. Jeffrey concluded that pigeon PMV-1 and Newcastle disease virus are
related, but appear to have differences in disease-causing potential for
commercial poultry. The problem is,
that if they are judged by the ICPI test, pigeon PMV-1's could have a negative
impact on the export of all poultry products from California and the U.S.A.