Bornavirus in birds represents a complex health concern within avian populations, impacting various species globally. The virus, particularly Avian Bornavirus (ABV), can lead to a range of outcomes, from asymptomatic infection to severe and often fatal disease. Its unpredictable nature makes it a challenging pathogen for bird owners and veterinarians alike. Ongoing research aims to better understand its transmission and the factors influencing disease development.
Understanding Bornavirus in Birds
Avian Bornavirus (ABV) is an RNA virus belonging to the Bornaviridae family. There are multiple strains of ABV, with at least 17 identified in birds, including seven found specifically in parrots. Psittacines, including parrots, macaws, cockatoos, and conures, are widely susceptible to ABV infection. Canaries, finches, and various waterfowl species like geese, ducks, and swans are also affected.
The primary modes of ABV transmission include direct contact and exposure to infected fecal material. Virus can be shed in various bodily fluids, including feces, urine, tears, and oral secretions. Ingestion of contaminated food or water is a likely route of infection. Airborne transmission through aerosolized particles is also a suspected route. Vertical transmission, from an infected parent bird to its offspring through the egg, is another suspected pathway.
Signs of Infection and Diagnosis
Avian bornavirus infection can manifest as Proventricular Dilatation Disease (PDD), a condition that primarily affects the nervous system, particularly those nerves controlling the gastrointestinal tract. Birds with PDD may exhibit gastrointestinal symptoms such as weight loss despite a normal or increased appetite, regurgitation, and the passage of undigested food in their droppings. Other digestive signs include delayed crop emptying and a dilated proventriculus, which is the glandular stomach.
Beyond digestive issues, neurological signs can also occur, sometimes independently of gastrointestinal problems. These can include ataxia (loss of balance), head tremors, seizures, partial paralysis, and even blindness. The symptoms of PDD are not unique to bornavirus, so veterinarians often need to rule out other conditions like lead toxicity, fungal or bacterial infections, or parasites.
Diagnosing ABV infection and PDD can be challenging because not all infected birds develop clinical signs, and viral shedding can be intermittent. Veterinarians often use a combination of methods. Polymerase Chain Reaction (PCR) testing can detect viral RNA in samples such as cloacal swabs, fecal matter, blood, or feathers. Biopsies, particularly of the crop, are considered a reliable diagnostic tool to look for characteristic inflammatory changes in nerve tissue. Post-mortem examination, including histological analysis of tissues like the proventriculus, ventriculus, brain, and spinal cord, can provide a definitive diagnosis.
Managing Infected Birds and Prevention
Currently, there is no specific cure for avian bornavirus infection or Proventricular Dilatation Disease (PDD), but management focuses on supportive care and alleviating symptoms. Anti-inflammatory medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like celecoxib, have been suggested. Research into antiviral treatments is ongoing.
Preventing the spread of bornavirus in avian populations relies heavily on stringent biosecurity measures. Key strategies include:
- Thorough cleaning and disinfection of enclosures and feeding utensils using effective disinfectants like phenols, formaldehyde, or hypochlorites.
- Quarantining new birds for a period before introducing them to an existing flock.
- Regular testing of birds in a flock, using both PCR and serology, and separating infected individuals.
- Avoiding contact with birds of unknown health status.
Bornavirus and Other Species
Avian bornavirus (ABV) is not known to pose a risk to humans and is not considered a zoonotic disease. Similarly, there is no evidence that avian bornaviruses can infect other non-avian domestic animals.
Other types of bornaviruses exist that affect different mammalian species. For example, Borna Disease Virus 1 (BoDV-1) is a distinct bornavirus known to cause neurological disorders in horses and sheep, predominantly in central Europe. Another mammalian bornavirus, Variegated Squirrel Bornavirus 1 (VSBV-1), has been linked to lethal infections in humans.