Prevention of Avian Polyomavirus Infections through Vaccination

Introduction
In non-budgerigar psittacines, avian polyomavirus-induced disease is most common in young birds (up to 150 days of age). However, despite a common misconception, adult birds are readily seusceptible to infection and can become ill Some affected birds die without developing any cilical signs of disease, while others die 12-to-48-hours after developing clinical signs that may include depression, loss of appetite, weight loss, delayed crop emptying, vomiting, diarrhea and bleeding under the skin. In contrast to many young that die, most infected adult birds develop transient lethargy, poor appetite and diarrhea with the surviving birds developing antibodes to the virus. Infections classified as "subclinical" (not obvious upon typical examination) are common in adult and young birds. In most aviaries and pet retail establishments, it is these subclinicaly infected birds that intiate a cycle of infection, and create an opportunity for the virus to be spread from bird to bird. Until recently, preventing birds from being infected with avian polyomavirus was limited to the arduous task of reducing potential exposure to the virus. Fortunately, an inacivated avian polyomavirus vaccine*, which has been shown to help prevent infection is now available.

Strategies for Vaccination
The strategies for using the avian polyomavirus vaccine are similar to those used to control cats. Preventing polomavirus infection within a flock requires the vaccination of two crucial groups of birds: the breeding flock and the young birds, before they leave the nursery.
To reduce polyomavirus infections within the aviary, it is essential to vaccinate the adult birds. There are only two known sources for polyomavirus infections enterign the nursery: either it is transported into the nursery during periods when infections (which usually go unnotieced are occuring in the breeding population or it is inroduced to the nursery by people who bring the virus in froms an outside source (Table 1). Once the breeding flock is vaccinated, the population of birds at risk (those taht could be infected) is substantially decreased, and the likelihood of a progressive cycle of transmission among these adult birds is reduced. This in turn lessends the chances that the adult population will serve as a source of virus for the exposure of neonates in the nursery.
If the flock is vaccinated and people do not inadvertently inroduce the virus to the nursery, it is unlikely that nay neonates will ve exposed to the virus. This logic is substantinated by observations of polyomavirus outbreaks. In several large aviaries, control of polomavirus-induced disease occured when the breeding adults and neonates were vaccinated. By contrast, aviculturists who attempted to control outbreaks by vaccinateing oly young birds decreased, but did not eliminate, the incidence of disease. These findings emphasize the importance of vaccinating the adults to prevent polyomavirus infeciton in the nursery. Once polyomavirus has been controlled within the flock, then it is crucial for yonhg birds that will be leaving the aviary to be protected before they are exposed in the pet trade to birds (particulary budgeriagars) which may be shedding the virus.

Recommendations for Vaccination
When using a vaccine or any threapeutic agent, the manufacturer's recommendations should be followed. The suggestions for vaccinations described below have been developed over 5 years of evlauations of an avian polyomavirus vaccine in experimental and field situations, and are provided to supplement the recommendations of the vaccine's manufacturer*.
Adults - breeding birds should be vaccined twice, with a two week inteval between vaccinations. It si best to vaccinate breeding birds in the non-breeding season. However, in flocks that are experiencing an outreak of disease, baccination can be performed during the breeding season. When vaccinating during an outbreak, it is important that the veterinary staff and aviary personned exercise extreme caution to prevent handling and injection procedures for becoming mode of virus transportation farom bird to bird. It should be noted that aviculturists wtih large breeding facilitied rarely handle or evaluate the overall health of their adults. The infrequent attention provided to these adults allows some problems such as liver disease, kidney disease, heart disease, obestity, cancers, bacterial infections, fungal infections and proventrical dilations disease to slowly progress unnoticed in what appear to be clinicaly normal birds. Many of these hidden problems may be detected or exacerbated during the handling necessary for vaccination. In the best managed aviaries in which adult birds are rarely handled during the vaccination process, pre-existing medical problems have been identified in from 2% to 4% of the adults.
Immature Birds - An avian veterinarian may adjust the schedule for vaccinationg neonates based on the risk of virus exposure in the nursery. These suggestions are based on the fact that the older a young bird is when it is vaccinated, the more likely it's immune system will respond
(Figure 1)
1. In the ideal aviary, where the avicultureists has vaccinated the breeding birds, does not have a history of polyomavirus-induced disease and sells only weaned birds, vaccination of young birds can be started about 4 weeks prior to weaning. These birds should be vaccinated twice with a 2 to 3 week interval between 40 to 50 days of age. These birds should be caccinate twice with a 2 to 3 week interval between doses. A bird should receive that last vaccination at least 2 weeks before leaving the aviary. The original certificate of vaccination, provided by the manufacturer* should be sent witht he young bird when it leaves the aviary.

2. IF an aviculturist has vaccinate the breeding birds, does not have a history of polyomavirus-induced disease but sells birds prior to weaning, vaccination of young birds should be started between 40 to 50 days of age. These birds should be vaccinated at least 2 to 3 week interval between doses. A bird should receive the last vaccination at least 2 weeks prior to leaving the aviary. The original certificate of vaccination, provided by the manufacturer, should be sent with the young bird when it leaves the aviary.

3. If necessary, young birds can be safely vaccinated starting at 20 days of age. These birds should rececive twi additional boosters with a 2 to 3 week interval between doses. A bird should receive the last vaccination at least 2 weeks prior to leaving the aviary. The original certificate of vaccination, provided by the manufacturer*, should be sent with the young bird when it leaves the aviary.
Companion birds - if a companion bird is maintained in complete isolation, which is not a very realistic scenario, it has minimal risk of beign exposed to polyomavirus. However, isolation means that the bird, and its keeper, never leaves the home to go to the veterinarian, grommer, club meetings or any where else where direct of indirect exposure to other birds might occur. It also means that all of the food, toys perches and enclosures for the bird are purchased from mail-order catalogs that shop form warehouses that do not house birds. These items may be contaminated with polyomavirus if they are kept in the same airspace with birds (particulary budgerigars). IT seems more logical to vaccinate companion birds thatn try to maintain such rigourous isolation, although isolation is the best method to reduce a bird's exposure to the infectious agents for which vaccines are not yet availabel. It is interesting to note that companion dogs and cats that are maintained in relative isolation (those that are confined to living) are routinely vaccinated to protect them from common infectious diseases. Why would one elect to afford a companion bird a lesser level of protection?

Establishing a Standard
During the past 25 years, the individuals who breed or enjoy the compan7y of dogs and cats have used vaccines to substantially decrease the incidence of many infectious diseases. By establishing requirements for vaccination, and other health monitoring techniques (for example, testing dogs for heart worms or cats for feline luekemia), quality dog and cat breeders and pet retailers have developed a positve reputation that separates them fromt he "puppy mills" that do not aspire to the same standard. Professional aviculturists and quality pet retailers can use the polyomavirus vaccine as one more tool to help separate themselves from the "birdie millers".
If you are a pet retailer, you now have a readily availble, safe method for reducing the probablity that a severe nad costly polyomavirus-induced outbread will occur within your establishment. Additionaly, as more consumers become aware of the polyomavirus vaccine, the demand for vaccinated birds will continue to increase. Look for bird breeders who are willing to vaccinate young birds before they leave the nursery, and request that a properly validated certificate of vaccination be sent with each young bird that you buy (Figure 2)
If you are a bird breeder, it is critical that you vaccinate your flock to reduce the chances of a polyomavirus outbreak, to protect your reputation and to separate your facility for the "birdie mills", which may choose not to vaccinate. Absolutley no bird should be added to you breeding facility that has not been vaccinated. Every bird that is transferred from you facility shoud be vaccinated to decrease its chances of being infected by the polyomavirus during transport of upon reaching its destination. The original vaccination certificate provided to you by your veterinarian should be included in the packet of infromation that you send with a bird. Transferring only vaccinated birds will reduce the chances that one of your birds will succumb to polyomavirus- induced disease, and will establish your aviary as a "state of the fart" avicultural facility. In several outbreaks of polyomavirus in per retail establishments, vaccinated birds survived while many unvaccinated birds have died. Retailers who experience these losses eventually seek sources of vaccinated birds. Make sure that once your flock has been vaccinated that your avian veterinarian registers your flock with the vaccines's manufacture*
If you are obtaining a bird from any source, insist that the bird be vaccinated. You should request that the original vaccination certificate accompany the bird. If a breeder is not willing to vaccinate you bird, you should consider finding a different source.

Evaluating a Vaccine
Prior to USDA registration of the avian polyomavirus vaccine, it was evaluated for:
(a) saftey - the lack of unacceptable local or systemic reactions.
(b)immunogenicy - the capacity of the vaccine to stimulate a measureable immune response
(c) efficacy - the capacity of the vaccine to induce an immune responce that protects a vaccinate from experimental challenge with live virus The saftey of the inacitvated avian polyomavirus vaccine has been evaluated in more that 80 species of psittacine birds including lovebirds, cockatiels, macaws, cockatoos, African grey parrots, Amazon parrots and eclectus parrots (figure 3). In an exprimental trial desinged to challenge tha safety of an inactivated avian polyomavirus vaccine, no adverse clinical changes occured when previously infected birds were vaccinated 5 times during a 49 day period. This finding suggests that vaccinaton is as safe for previously infected birds as it is for their previously uninfected conspecifics. In addition, an experimental group of 18 birds have been vaccinated 6 to 12 or a 5 year period to exacerbate the potential for an adverse reaction, and a group of approximately 300 birds have been vacinated 3 times over a 2 year period, with no adverse sode effects/ In fact with over 15,000 doses of the vaccine in use, in species as varied as lovebirds to hyacinth macaws, there have been no post-vaccination systemic reactions reported. The polyomavirus vaccine has been shown to be effective in protecting birds from infection. In multiple trials, the vaccine protected more than 90% of vaccinates from infection. This is in stark contrast to unvaccinated birds, where 97% were susceptible to infection.
Reactions at the site of a properly administered subcutaneous vaccine are minimal (slight discoloration of the skin in some birds). If the vaccine is administered intradermally, it may cause thickening of the skin or formation of a self-limiting knot. If you are an aviculturist who is obtaining vaccine from your veterinarian, make sure that you are clearly advised on how to use the vaccine. Many avian veterinarians who have extensively used the vaccine are confident enough in its safety that they will treat any local reaction might occur free-of-charge. If an adverse reaction occurs, it should be reported immediately to the vaccine's manufacturer*.

What is a "Carrier"?
It is occasionally suggested, albgiet incorrectly, that the avian polyomavirus vaccine is of limited value in adults because it does not eliminate the "carrier" state. The term "carrier" is frequently and loosely discussed in association with polyomavirus infections in companion birds. By defenition, a carrier is "an individual who harbors a specific organism and is capable of transmitting the infectious organisim that can cause a disease but shows no clinical signs". This is a simple definition for a rather complex interaction between infectious organisms and their host. It is a particularly simple definition with respect to avian polyomavirus. In scientific literature which discusses viral infections, the term "carrier" is rarely used. In its place, the term "persistant infection" is used to describel animals that are infected with a virus, shed the virus for an extended period of time and exhibit no easily observerd clinical signs. There are then two types of persistent infections: latent infections and chronic infections, and the characteristics of each must be understood when evaluating how to prevent avian polyomavirus infections. The characteristcs of these infections are listed in Table 2.
A common example of a latent infection is the herpes simplex virus that causes "cold sores" in humans. Once an individual is infected with this virus, he remains infected for life and intermittently sheds the virus. More than 10 years ago, it was demonstrated that budgerigars psittacine birds may shed the virus for a certain period, but they appear able to mount an approriate immune response which conrols the infection and eventually stops the bird form shedding the virus. The most improtant consideration for preventing polyomavirus within a flock is to reduce the opportunity for these temporary shedders to infect other birds. Toward this ed, vaccinating a flock helps to protect uninfected birds from the virus and inhibits the amplification of virus activity throught the susceptible birds within a flock. Additionally, the polyomavirus vaccine has not been shown to have any adverse affect on a bird that has already been infected with the virus, making flock vaccination both practical and safe.
The propensity of non- budgerigar psittacine birds to develop transient polyomavirus infections is critical to control of the virus within an aviary. By vaccinting the breeding birds, the cycle of transmission can be reduced, and over time, it should be possible to functionally "eradicated" the virus from a particular aviary. Even if non-budgerigar psittacine birds were to develop latent infections, vaccination may still be a valuable method of perventing disease. Vaccination programs in other species (humans, cats, dogs, cattle, etc) have been very effective in controlling many virus that are known to cause latent infections.
Because budgerigar respond differently to polyomavirus infections thatn do non-bugerigar psittacine birds, the recommendations for controlling infections in non-budgerigar psittacines may not apply to budgerigars. Research is currently under way to determine how to effectively vaccinate budgerigars for polyomavirus. It is important that unvaccinated psittacine birds not come in direct or indirect contact with budgerigars.

Controlling a Polyomavirus Outbreak
As is the case with many viral-induced diseases in companion animals, vaccination will play a pivotal role in reducing the incidence of avian polyomavirus infections. However, because no vaccine is 100% effective, vaccination should not be expected to compensate for the deleterious effects of poor management or hygiene. The techniques recommended for decreasing the occruence of any infectious disease are listed in Table 3
Controlling polyomavirus in an outbreak requires vaccinating the adults and neonates to stimulate flock immunity, as well as cleaning and disinfecting of the contaminated facility. While vaccinating during a polyomavirus outbreak has been shown to be advantageous, it should be stressed that deaths may continue in neonates until flock immunity has been increased. generally 2 to 3 weekds after the last booster vaccination. Once an outbreack has occured, it is important that the nursery be thouroughly cleaned and disinfected to prevent virus contaminating this enviroment from infedcting neonates before the time that their immune systems will respond to vaccinations. It is crucial during an outbreak that the adults be vaccinated to reduce the amplification of the virus activity in the adult population, thus decreasing the chances of the virus entering the nursery.
A DNA probe-based assay** is extremely valuable for identifying birds that are shedding virus in their excrement during an outbreak. Birds that are sheeding the virus can be separated from others in a nursery to reduce further virus transmission, while vaccinated birds are developing antibodies to the virus. Birds that are clinically ill, are found to be shedding polyomavirus, or are in direct contact with birds that are clinically ill or shedding polyomavirus, should be isolated (placed in a separate geographic location and serviced by separate aviary personnel) from birds that are clinically normal and not shedding virus.

Acknowlagments
Major sustained contributionsthat have made this work possiblwe have been provided by the Cowan Avian Health Foundation, the International Avian Research Foundation, Veterinary Medical Experiment Station, Joe and Sue Still, Terry Clyne, Richard and Luanne Porter, Knick Enterprises, Kathleen Szabo, Allen Berk, Bobbi Brinker, International Aviculterist's Society. Avian Research Associates, Midwest Avian Research Exposition, National Aviary, Puerto Rican DNR, Ann Arbor Cage Bird Club, Aviary and Cage Bird Club of South Florida, Avicultrual Society of Puget Sound, Central Indiana Cage Bird Club, Charlotte Metrolina Cage Bird Club Society, Cream City Featherd Friends, Dallas Cage Bird Society, Feathered Friends Society, Gateway Parrot Club, Greater Brandon Avian Society, Hookbill Hobbyists of Southern California. Kentuckian Bird Society, Louisiana Aviculture Society, Northwest Ohio Exotic Bird Club, South Jersey Bird Club, Wasatch Avian Education Society, West Valley Bird Society, Lafeber Inc, and Ziegler Brothers Inc. Hundreds of aviculturists, bird clubs and veterinarians have also made significant contributions.

This information was brought to you by the following:

Branson W. Richie DVM, PhD
Nancy Pritchard BS
Denise Pesti MS
Kenneth Latimer DVM, PhD P
Phil D. Lukert DVM, PhD
Joan Leonard*,PhD
Cheryl B. Greenacre,DVM
Raymond Campagnoli, MS

Psittacine Disease Research Group
University of GeorgiaCollege of Veterinary MedicineAthens, Ga 30602
*Biomune 8906 Rosehill Rd Lenexa, Ks 66215

Reprinted in part with permission from:
Avian Viruses; Function and Control and Advances in Exotic Companion Animal Medicine and Surgery, Wingers Publishing, Lake Worth. Fl 33466.

Articles are Copyright Up At Six and cannot be reprinted without the written permission of Up At Six and the author.

Last Revised: Tue Jul 29 18:49:30 2008 ( Damian )
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