Steven Clark, Roche Vitamins Inc.
TurkeyDoc@aol.com
Reference: Clark, Steven. A Review of Avian Pneumovirus. In the:
Proceedings & Technical Supplement of the Roche Avian
Pneumovirus Workshop. ed. S.R. Clark and L.M. Ginsburg. Roche
Vitamins Inc., Parsippany NJ. RCD 9713. Pp. 21-24.
Diseases caused by avian pneumoviruses include Avian Pneumovirus
infection, which is now recognized in the United States (US), and
Turkey Rhinotracheitis (TRT), which is recognized everywhere else
in the world. Swollen Head Syndrome (SHS) of chickens is also
recognized throughout the world, except in the US, and is also
caused by an avian pneumovirus. The avian pneumovirus is a member
of the Pneumovirane subfamily from the Paramyxoviridae family of
viruses. The TRT and SHS viruses are classified as A and B
subgroups. The US isolates are presently not completely
characterized.
TRT affects chickens and turkeys of all ages and was first
described in South Africa in 1970s; yet the causative agent was
not identified until 1985. It has spread through Europe, South
America, Japan and the Middle East. In February 1997 the US
National Veterinary Services Laboratory (NVSL) isolated APV from
turkeys in Colorado with respiratory disease, designated as APV/CO.
Clinical disease was first recognized in May 1996. Colorado has
been free of APV since February 1998. The disease was first
recognized in Fall 1996 and subsequently APV was identified in
Minnesota, South Dakota and North Dakota. APV in the US is
distinct from TRT virus in other countries.
APV infection in turkeys causes a rapidly spreading respiratory
disease of all ages. Turkeys appear depressed and act chilled/seek
heat. Increased mortality (up to 30%) is associated with
secondary bacterial infections. It has been characterized as
"CRS" (cough, rhinitis and sinusitis). APV is
associated with high condemnations due to airsacculitis.
Mortality is more severe in young birds. Recovery takes 10-14
days in uncomplicated disease. Exceptions to these clinical signs
do occur in the field. Upon necropsy, in uncomplicated cases, the
birds show sinusitis, rhinitis, and mucoid tracheitis. In
complicated cases, pneumonia, airsacculitis, pericarditis and
perihepatitis is observed.
The rate of spread within a flock or between flocks may vary.
Management factors, such as stocking densities and ventilation,
affect severity of disease. Other concurrent infections, such as,
E. coli, Bordetella avium, Pasteurella, Newcastle disease virus
and Ornithobacterium rhinotracheale, also affect severity of
disease. In breeders, APV disease can cause a drop in egg
production.
In Minnesota, APV disease appears to be cyclical (occurring in
"waves"). The disease is associated with high
geographical density of turkeys. There have been a few reports of
clinical disease not spreading on a multi-age farm, serologically
positive flocks without clinical disease, serologically negative
flocks but PCR positive with clinical disease, and flocks
serologically positive but PCR negative. In 1997, APV resulted in
rapid spread, severe clinical disease, more treated flocks and
high, acute mortality in younger flocks. APV infections in 1998
have resulted in slower spread, mild clinical disease, fewer
treated flocks and low, chronic mortality in older flocks. These
differences between 1997 and 1998 may be associated with
variation in the virus and/or management changes.
APV is probably, but not yet proven, to be transmitted by the
movement of contaminated birds, equipment, people and/or litter.
Air-borne transmission is suspected (up to 1-2 miles). Egg
transmission is not documented. Wild birds and reservoirs are
also suspected in the spread of the virus. In the laboratory, the
virus can survive for at least 2 weeks at room temperature, and
at least 4 weeks refrigerated, and less than 72 hours at 37C (100F).
Clinical signs are not pathognomonic for a diagnosis of APV. A
diagnosis may be made by either serology, PCR or virus isolation.
Current serological tests include enzyme linked immunosorbent
assay (ELISA), virus neutralization (VN), and immunofluorescence
(FA). No commercial tests are available in the US. Laboratories
in the US presently providing serological testing are NVSL and
the University of Minnesota. ELISA is currently the preferred
diagnostic. The European subgroup A and B serological tests
detect APV/CO very poorly. The polymerase chain reaction (PCR)
procedure detects virus nucleic acid and is used to sample
respiratory tissues (such as, tracheal swabs and turbinates).
Samples should be fresh, refrigerated, and not frozen. Presently
the only US laboratory providing PCR is the University of
Minnesota. For any diagnostic test, sample both affected and
unaffected birds within a sick flock.
Virus isolation, by propagation in cell culture and
electronmicroscopy (EM) are other diagnostic tools. It is noted
that Tracheal Ring Organ Culture (TROC) is not applicable for the
APV/CO since this isolate is not ciliostatic (TROC relies on
ciliostasis as a diagnostic criterion). Other procedures, such as
Chick Embryo Yolk Sac and Chick Embryo Fibroblast cells, have
been used successfully for initially isolating APV/CO. After the
virus is isolated, it may be propagated in Vero Cells, BS-C-1,
CEF or QT-35 systems. Sample respiratory tissues (especially the
turbinates) early in the infection (before clinical signs).
Multiple host systems (i.e., virus isolation procedures) should
be used to maximize isolation of virus(es). Consult the
laboratory for specific sample submission procedures.
APV can resemble other respiratory diseases found in turkeys. A
differential diagnosis should include: MG (Mycoplasma
gallisepticum), MS (Mycoplasma synoviae), AI (avian influenza
virus), Fowl Cholera (Pasteurella multocida), NDV (Newcastle
disease virus), BART (Bordetella avium rhinotracheitis), ORT (Ornithobacterium
rhinotracheale) and all other respiratory diseases.
Researchers note that APV/CO is distinct from APV subgroups A and
B that cause TRT in other countries. It differs in both molecular
and antigenic characteristics. APV/CO is more closely related to
subgroup A, comparing F protein and virus neutralization. APV/CO
is distinct from A and B comparing M protein sequences. Further
research is ongoing to more fully characterize the US isolates of
APV.
Treatment of APV infections should focus on management practices
("tender loving care"). It is critical to adjust the
barn temperature for bird comfort. Optimize air quality in the
barn and be careful to avoid chilling birds. Suspend tilling of
litter and suspend all vaccinations to avoid stressing the flock.
Antibiotics such as chlortetracyclines, sulfas and
fluoroquinolones may be appropriate to control secondary
bacterial infections associated with mortality. Results are
highly variable. For best results, check antibiotic sensitivity
patterns of bacterial isolates.
To control APV spread, biosecurity procedures must be a priority.
Effective communication and cooperation among poultry growers
coupled with integrated poultry company management is essential.
If APV positive flocks are identified, isolate younger birds from
older flocks. Wild bird control is important, as free-living
birds are suspected in carrying the virus. Properly dispose of
contaminated litter and of dead birds is a must, so as not to
contaminate other farms. Proper loading and routing of live haul
trucks, especially when moving infected flocks, is important. To
insure compliance, audit all control measures. To minimize the
risk of spreading disease to other flocks, avoid introduction of
susceptible birds. It is suggested to delay multi-age farm
placements. Depopulation may be necessary to minimize virus
spread. Reduce the geographic density of turkeys through delayed
placements or depopulation and coordinating with local farms.
Proper cleaning, washing and disinfecting procedures (including
the proper use of formaldehyde) have been parts of successful
programs to minimize the spread of disease. Also minimize
stresses (management) and other complicating diseases (NDV, ORT,
BART). Another essential step is to avoid high stocking densities
especially in brooder barns (less than approximately 1 square
foot per bird). Optimizing barn temperature and ventilation is
important in controlling an outbreak within a flock.
In Europe, vaccination is helpful for controlling TRT. There are
vaccines that induce protective antibodies to A and B subgroups.
No vaccines are available in the US. Laboratory experiments show
that live subgroup A and B vaccines from Europe provide
protection against APV/CO. In Europe there is cross-protection
between A and B. Commercial birds are typically given a live
vaccine, via spray administration, at the hatchery. Vaccination
of commercial birds minimizes clinical disease and associated
mortality, yet vaccination reactions can be a problem. In
breeders, a live vaccine is given at 0, 6, and 10 weeks of age,
followed by a killed vaccine at 18 and 26 weeks of age. Breeder
vaccination minimizes egg drop, clinical disease and mortality.
The US industry has several needs relating to APV. The industry
might consider eliminating the virus, since this disease appears
limited to a specific geographic area. The industry must address
biosecurity "failures", such as with contaminated
employees and equipment moving between farms, inadequate barn
clean out practices, inadequate downtime, improper dead bird
disposal or wild bird control practices. The management of multi-age
farms might also need to be re-evaluated.
More research is needed to better understand APV. Proper sampling
protocol should be confirmed. There is much to be understood
about the stability of the virus, of potential reservoirs, and
how it is transmitted. Once the duration of virus shedding in the
field is known, then other questions may be answered, such as:
When is it safe to transport previously infected birds? When is
it safe to put birds onto a previously infected farm? More
information is needed to better characterize APV variation. This
will be invaluable for monitoring infections and developing
control programs. Vaccine research is needed with the US isolates.
Finally, diagnostic tests must be rapid, reliable, inexpensive
and easy-to-use.
Acknowledgements
I acknowledge all the participants of the "The Avian
Pneumovirus Workshop" and "The Avian Pneumovirus Grower
Luncheon", sponsored by Roche Vitamins Inc. in cooperation
with the Minnesota Turkey Growers Association (MTGA). These
events were held June 30 - July 1, 1998 in St. Cloud, Minnesota,
USA. More information is available from The Proceedings of The
Roche Avian Pneumovirus Workshop.