Introduction

In non-budgerigar psittacines, avian polyomavirus-induced disease is most common in young birds (up to 150 days of age). 1-4 However, despite a common misconception, adult birds are readily susceptible to infection, can become ill and some may die. 5-10 Some affected birds die without developing any clinical 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. 1-3, 11, 12 Many affected young birds die, while most infected adult birds develop transient lethargy, a poor appetite and diarrhea with the surviving birds developing antibodies to the virus. Infections classified as "subclinical" (not obvious upon typical examination) are common in adult and young birds. 1, 2, 12-15

In most aviaries and pet retail establishments, it is these subclinically infected birds that initiate a cycle of infection, and create an opportunity for the virus to be spread from bird to bird. Until recently, attempting to prevent birds from being infected with avian polyomavirus was limited to the arduous task of reducing potential exposure to the virus. Fortunately, an inactivated avian polyomavirus vaccine*, which has been shown to help prevent infections, is now available. The strategies for using the avian polyomavirus vaccine are similar to those used to control infectious diseases of other companion animals, like parvovirus in dogs or panleukopenia virus in cats. Preventing polyomavirus infections within a flock requires the vaccination of two crucial groups of birds: the breeding flock and the young birds, before they leave the nursery. Adults are vaccinated to reduce the spread of the virus among the resident population in an aviary or home. Neonates are vaccinated to protect chicks they leave the aviary and are exposed in the pet trade to birds (particularly budgerigars) which may be shedding the virus.

Recommendations for Vaccination

When using a vaccine, or any therapeutic agent, the manufacturer's recommendations should be followed. The suggestions for vaccination described below have been developed during 5 years of evaluating an avian polyomavirus vaccine in experimental and field situations, and are provided to supplement the recommendations of the vaccine's manufacturer*.

It is best to vaccinate adult birds during the non-breeding season. However, vaccination can be performed during the breeding season in flocks that are experiencing an outbreak of disease.16 If an outbreak of disease is occuring, neonates can be vaccinated as early as 10 to 20 days of age. Chicks that are vaccinated this early should receive two additional vaccinations with a 2 week interval between doses. If an outbreak is not occuring, then the vaccination process should be started when chicks are greater than 40 to 50 days of age (the older the better). These chicks should be vaccinated twice with a 2 to 3 week interval between doses. A bird should receive the last vaccination at least 2 weeks before leaving the aviary.

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 completely combat the deleterious effects of poor management or hygiene.

Controlling polyomavirus in an outbreak requires vaccinating the adults and neonates to stimulate flock immunity, as well as cleaning and disinfecting the contaminated facility. 16,17 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 weeks after the last booster vaccination.16

Once an outbreak has occurred, it is important that the nursery be thoroughly cleaned and disinfected to prevent virus contaminating this environment from infecting neonates before the time that their immune systems will respond to vaccination. Contaminated nest boxes must be replaced. It is crucial during an outbreak that the adults be vaccinated to reduce the spread of the virus among the adults, thus decreasing the chances of the virus entering the nursery.

A DNA probe-based assay (for additional information, write to Dr. Ritchie) is valuable for identifying birds that are shedding virus in their excrement during an outbreak. Birds that are shedding the virus can be separated from others in a nursery to reduce further virus transmission, while vaccinated birds are developing antibodies to the virus.

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