Avian Bornavirus / PDD (Neurological)

Avian bornavirus infection represents one of the most significant viral diseases affecting psittacine birds, capable of causing devastating neurological disease through inflammation of the brain, spinal cord, and peripheral nerves. While avian bornavirus is most commonly associated with proventricular dilatation disease affecting the gastrointestinal system, the neurological manifestations of infection can occur independently or in combination with digestive symptoms, representing a distinct clinical presentation that poses significant diagnostic and management challenges. The neurological form of avian bornavirus disease occurs when the virus triggers an immune-mediated inflammatory response targeting neural tissues, resulting in progressive neurological dysfunction that varies widely in severity and presentation among affected individuals. This condition affects primarily psittacine species, with particularly high prevalence in macaws, cockatoos, African grey parrots, and Amazon parrots, though infections have been documented across a wide range of bird species.

Avian bornavirus is transmitted between birds through fecal-oral routes and potentially through feather dust and other secretions, though the exact mechanisms and efficiency of transmission continue to be studied and debated within the avian veterinary community. The virus appears to be widespread in captive psittacine populations, with seroprevalence studies indicating that a substantial percentage of birds have been exposed to the virus, yet only a portion of infected birds develop clinical disease. The factors that determine whether an infected bird remains asymptomatic, develops primarily gastrointestinal disease, or manifests neurological symptoms are not fully understood but likely involve complex interactions between viral factors, host genetics, immune response, and environmental stressors. This unpredictability makes bornavirus infection particularly challenging for bird owners and veterinarians to manage.

The impact of neurological avian bornavirus disease on affected birds can be profound and life-altering, affecting their ability to perch, fly, eat, and engage in normal behaviors. Neurological signs may include ataxia, tremors, seizures, blindness, and progressive paralysis depending on which areas of the nervous system are most affected by the inflammatory process. Quality of life considerations become paramount as owners and veterinarians work together to determine appropriate levels of treatment and intervention. The progressive nature of the disease in many cases requires ongoing reassessment of whether affected birds are maintaining acceptable quality of life or whether palliative care or humane euthanasia should be considered. The emotional toll on dedicated bird owners watching their companions decline neurologically cannot be underestimated.

Treatment for neurological avian bornavirus disease focuses on managing inflammation and providing supportive care, as no cure exists and the virus cannot be eliminated from infected birds. Anti-inflammatory medications, particularly non-steroidal anti-inflammatory drugs, represent the primary therapeutic intervention and can provide significant clinical improvement in many cases, sometimes maintaining acceptable quality of life for extended periods. However, treatment effectiveness varies among individuals, and some birds progress despite aggressive therapy. Early detection and intervention may improve outcomes, though the insidious onset of many cases means significant neurological damage may have occurred before symptoms become apparent. Working closely with an experienced avian veterinarian who understands this complex disease provides the best opportunity for successful long-term management of affected birds.

The primary cause of neurological avian bornavirus disease is infection with parrot bornavirus, a member of the family Bornaviridae, with subsequent immune-mediated inflammatory damage to neural tissues. Multiple genotypes of avian bornavirus have been identified, with some evidence suggesting that certain genotypes may be more commonly associated with neurological manifestations while others more frequently cause gastrointestinal disease, though birds infected with any genotype can potentially develop either or both forms of disease. The virus establishes persistent infection in neural tissues, and disease manifestation appears to result not from direct viral damage but from the host's own immune response attacking infected cells within the nervous system. This immune-mediated mechanism explains the variable and often delayed relationship between infection and clinical disease development.

Genetic and species-related factors significantly influence susceptibility to neurological avian bornavirus disease. Certain psittacine species, particularly macaws and African grey parrots, appear to develop clinical disease more frequently than others, though whether this reflects true species susceptibility differences, differences in viral exposure, or variations in how disease manifests remains unclear. Individual genetic factors likely determine the nature and intensity of immune responses to infection, with some birds mounting aggressive inflammatory responses that cause clinical disease while others tolerate infection without apparent illness. These individual variations make predicting disease outcomes in infected birds extremely challenging and complicate decisions about testing, quarantine, and management of positive birds.

Environmental and husbandry factors may influence both the likelihood of exposure to avian bornavirus and the progression from infection to clinical disease. Stress appears to play a role in disease development or progression, with some birds remaining stable while unstressed but developing clinical signs during periods of environmental change, breeding activity, or other stressors. Housing conditions that facilitate viral transmission between birds increase exposure risk within collections. Dietary factors and overall health status may affect immune function in ways that influence disease manifestation. The specific environmental triggers that cause some infected birds to develop neurological disease while others remain asymptomatic have not been definitively identified, though management strategies typically include stress reduction as a component of comprehensive care.

Risk factors for developing neurological avian bornavirus disease include known exposure to infected birds, housing in multi-bird environments where the virus may circulate, and belonging to species with high disease prevalence. Birds from breeding facilities or rescue situations where testing is incomplete may have unknown infection status. Stress from any source, including changes in environment, diet, social structure, or concurrent illness, may trigger disease progression in previously stable infected birds. Advanced age may be associated with increased disease risk in some populations, though birds of any age can develop clinical disease. Pre-existing conditions that compromise immune regulation may affect how infected birds respond to the virus and whether they develop inflammatory disease.

The mechanism of neurological disease development in avian bornavirus infection involves complex immunopathological processes rather than direct viral destruction of neural tissue. The virus infects neurons and glial cells throughout the central and peripheral nervous system, establishing persistent infection that may remain clinically silent for extended periods. In birds that develop disease, the immune system recognizes viral antigens within neural tissues and mounts an inflammatory response targeting infected cells. This lymphoplasmacytic ganglioneuritis, characterized by infiltration of inflammatory cells into neural structures, damages neurons and disrupts nervous system function. The location and extent of inflammatory lesions determine the clinical manifestations, with brain involvement causing central neurological signs and peripheral nerve involvement causing weakness and dysfunction in affected body regions.

Early warning signs of neurological avian bornavirus disease are often subtle and may be attributed to other causes or overlooked entirely. Initial indicators may include mild changes in coordination, occasional loss of balance, or subtle alterations in gait that owners might attribute to aging or minor injury. Personality changes such as increased quietness, decreased interest in activities, or altered sleep patterns may precede more obvious neurological signs. Some birds develop visual problems early in the disease course, which may manifest as difficulty navigating their environment, reduced interest in visually stimulating activities, or failure to track moving objects normally. Because avian bornavirus typically causes slowly progressive disease, early symptoms may be present for weeks to months before they become severe enough to prompt veterinary consultation, during which time significant neurological damage may occur.

Common symptoms of neurological avian bornavirus disease include a constellation of neurological deficits reflecting damage to various components of the nervous system. Ataxia, or incoordination, is one of the most frequently observed signs, manifesting as an unsteady gait, difficulty perching, and inability to coordinate movements accurately. Head tremors may be present, often becoming more pronounced during intentional movements such as reaching for food. Abnormal head posture, including head tilt or head bobbing, suggests involvement of vestibular pathways or brain structures. Some birds develop seizure activity ranging from subtle focal seizures to generalized convulsions. Vision problems are common and may progress to complete blindness as the optic nerves or visual processing areas of the brain become affected.

Behavioral changes associated with neurological avian bornavirus disease reflect both direct effects on brain function and the bird's response to declining neurological abilities. Affected birds may become withdrawn, showing decreased interest in social interaction and environmental stimulation. Changes in vocalization patterns, including decreased talking in species that talk, altered call quality, or unusual silence, may occur. Some birds exhibit behavioral changes suggestive of cognitive dysfunction, including apparent confusion, failure to recognize familiar people or environments, and altered responses to normal stimuli. Appetite may decrease due to difficulty eating, reduced interest in food, or nausea associated with vestibular involvement. Sleep disturbances commonly develop as neurological dysfunction progresses.

Physical signs of neurological avian bornavirus disease extend beyond the primary neurological deficits to include secondary changes resulting from disease progression. Weight loss is common and may result from decreased appetite, difficulty eating due to coordination problems, or concurrent gastrointestinal disease. Muscle wasting develops when neurological deficits prevent normal activity. Birds may show abnormal posture, with altered positioning of head, wings, or body reflecting neurological impairment. Feather quality may decline due to reduced preening ability and overall health compromise. In birds with concurrent gastrointestinal disease, whole undigested seeds may be visible in droppings, and regurgitation may occur. Physical examination findings may include abnormal reflexes, decreased response to positional changes, and other neurological deficits detectable by veterinary assessment.

Symptom progression in neurological avian bornavirus disease typically follows a slowly progressive course, though the rate of progression varies considerably among individuals. Some birds show gradual decline over months to years, with symptoms slowly worsening and new deficits appearing over time. Others may have relatively stable periods interrupted by episodes of more rapid decline, potentially triggered by stress or other factors. Acute deterioration can occur when previously compensated birds lose the ability to manage their deficits, or when inflammation affects critical neural structures. The gastrointestinal form of the disease may develop in birds initially presenting with only neurological signs, potentially adding digestive symptoms to the clinical picture. Monitoring disease progression helps guide treatment decisions and quality of life assessments.

Emergency symptoms requiring immediate avian veterinary care include sudden onset of severe neurological signs such as inability to stand or perch, active seizures, apparent sudden blindness, or rapid deterioration in neurological function. Signs of concurrent severe illness including profound weakness, collapse, or respiratory distress require urgent attention. Birds that become unable to eat or drink due to neurological impairment need immediate intervention to prevent dehydration and starvation. Any sudden change in a bird previously stable on treatment warrants prompt veterinary evaluation to assess whether the change represents disease progression, medication complications, or a new problem entirely. Because neurological avian bornavirus disease is incurable, emergency situations also prompt discussions about quality of life and appropriate intervention levels.

The initial veterinary examination for suspected neurological avian bornavirus disease combines thorough history-taking with comprehensive physical and neurological assessment. The avian veterinarian will inquire about the bird's background, including origin, exposure to other birds, any testing history, the onset and progression of symptoms, diet, husbandry conditions, and any concurrent health issues. Physical examination assesses overall body condition and identifies signs of systemic illness or concurrent gastrointestinal disease. The neurological examination systematically evaluates mental status, cranial nerve function, posture, gait, coordination, reflexes, and sensory responses to characterize the nature and distribution of neurological deficits. This clinical assessment helps localize lesions within the nervous system and guides selection of appropriate diagnostic tests.

Diagnostic tests for avian bornavirus infection include both direct testing for the virus and evaluation of the immune response to infection. Polymerase chain reaction testing, known as PCR, detects viral genetic material in samples including whole blood, cloacal swabs, and crop swabs, though intermittent shedding means that negative results do not definitively exclude infection. Serology testing detects antibodies against avian bornavirus, with positive results indicating exposure to the virus, though antibodies may persist for extended periods and positive serology alone does not confirm active disease. Combining PCR and serology increases diagnostic sensitivity. Additional blood tests including complete blood count and biochemistry panel assess overall health status and identify concurrent conditions. Radiographs may reveal signs of concurrent gastrointestinal disease and help rule out other conditions causing similar symptoms.

Differential diagnosis for neurological signs in birds is broad and requires systematic evaluation to distinguish avian bornavirus disease from other possible causes. Other infectious diseases affecting the nervous system include paramyxovirus, polyomavirus, and various bacterial and fungal infections that can cause encephalitis. Heavy metal toxicosis, particularly lead and zinc poisoning, commonly causes neurological symptoms and must be excluded through blood metal testing. Nutritional deficiencies, metabolic disorders, and organ failure can cause neurological dysfunction. Neoplasia affecting the nervous system produces progressive neurological signs similar to bornavirus disease. Trauma can cause acute neurological deficits. The presence of positive bornavirus testing combined with consistent clinical signs strengthens the presumptive diagnosis, though definitive diagnosis requires demonstration of characteristic histopathological lesions in neural tissue.

Diagnosis confirmation for neurological avian bornavirus disease involves integrating clinical findings, test results, and response to treatment to reach a working diagnosis, recognizing that definitive diagnosis in living birds is often not possible. Birds presenting with progressive neurological signs, positive bornavirus testing by either PCR or serology, and no evidence of other neurological disease are presumptively diagnosed with avian bornavirus-associated neurological disease. Response to anti-inflammatory treatment supports the diagnosis, as improvement suggests immune-mediated disease consistent with bornavirus pathophysiology. Definitive diagnosis requires histopathological examination of neural tissue demonstrating characteristic lymphoplasmacytic ganglioneuritis, which can only be obtained through biopsy, which is rarely performed in living birds, or post-mortem examination. Treatment is typically initiated based on presumptive diagnosis without awaiting definitive confirmation.

Emergency and immediate treatment for birds presenting with acute or severe neurological signs associated with avian bornavirus disease focuses on stabilization and initiating anti-inflammatory therapy. Birds in crisis require supportive care including warmth, fluid therapy if dehydrated, and placement in a safe environment where neurological deficits will not lead to injury. Anti-inflammatory medication, typically a non-steroidal anti-inflammatory drug such as meloxicam or celecoxib, is initiated promptly as this represents the primary therapeutic intervention for bornavirus-associated neurological disease. Seizure control with appropriate anticonvulsant medications may be needed for birds experiencing active seizures. Nutritional support addresses any deficits that have developed and may require assisted feeding for birds unable to eat independently due to coordination problems or concurrent gastrointestinal disease.

Medical management of neurological avian bornavirus disease centers on long-term anti-inflammatory therapy to suppress the immune-mediated inflammation damaging neural tissues. Non-steroidal anti-inflammatory drugs, particularly COX-2 selective inhibitors like celecoxib, have shown effectiveness in managing clinical signs and are typically prescribed for continuous long-term use. Meloxicam offers an alternative anti-inflammatory option and may be easier to administer for some owners. The choice of medication, dosing, and administration schedule is individualized based on the bird's response and any medication tolerance issues. Some protocols incorporate additional immunomodulatory approaches, though evidence for these is limited. Treatment typically continues indefinitely, as discontinuation often results in clinical relapse. Regular monitoring ensures medications remain effective and identifies any adverse effects.

Surgical options play no direct role in treating neurological avian bornavirus disease, as the condition involves diffuse inflammatory processes throughout the nervous system rather than discrete lesions amenable to surgical intervention. Surgical procedures may be needed to address complications or concurrent conditions, such as crop surgery for birds with severe proventricular dilatation disease affecting the digestive tract. Biopsy of accessible neural tissues could theoretically provide definitive diagnosis but is rarely performed due to the invasive nature of the procedure and the reliability of presumptive diagnosis based on clinical presentation and testing. The focus of intervention remains medical rather than surgical for the neurological manifestations of bornavirus disease.

Supportive care constitutes an essential component of management for birds with neurological avian bornavirus disease and addresses the practical challenges of living with neurological deficits. Environmental modifications protect birds from injury related to their neurological impairment, including lowering perches, providing padded surfaces, and ensuring easy access to food and water. Nutritional support maintains body condition despite any eating difficulties, with assisted feeding provided as needed. Physical assistance may be required for birds with significant balance problems. Maintaining social interaction and environmental enrichment supports psychological wellbeing despite physical limitations. Regular monitoring tracks clinical status and identifies any deterioration requiring treatment adjustment or quality of life reassessment.

Alternative and complementary treatments for neurological avian bornavirus disease have limited evidence but may be considered as adjuncts to conventional anti-inflammatory therapy. Omega-3 fatty acid supplementation may provide additional anti-inflammatory effects and support neural tissue health. Vitamin E and other antioxidants may help protect neural tissues from inflammatory damage. Some practitioners have explored other immunomodulatory supplements or approaches, though controlled studies demonstrating efficacy are lacking. Any complementary treatments should be discussed with the avian veterinarian to ensure they do not interfere with primary treatment and are appropriate for avian patients. These approaches should supplement rather than replace proven anti-inflammatory therapy.

Treatment decisions for neurological avian bornavirus disease require careful consideration of prognosis, quality of life, and practical factors. While treatment can often improve clinical signs and maintain quality of life for extended periods, the disease is incurable and most birds eventually progress despite treatment. Initial response to anti-inflammatory therapy helps predict long-term outcomes, with birds showing substantial improvement having better prognoses than those with minimal response. Quality of life assessment considers the bird's ability to eat, engage in normal behaviors, and show apparent contentment despite neurological deficits. Owner factors including ability to provide required care, administer long-term medications, and manage the emotional challenges of caring for a chronically ill bird influence treatment planning. Honest discussions about realistic expectations help owners make informed decisions about treatment intensity and duration.

Recovery timelines for neurological avian bornavirus disease differ from conditions with curative treatments, as the goal is disease management rather than cure. Birds started on anti-inflammatory therapy typically show initial response within one to two weeks, with clinical improvement continuing over the following weeks to months as inflammation is suppressed and any reversible neurological dysfunction recovers. The degree of improvement depends on how much permanent damage has occurred before treatment initiation, with birds treated early in the disease course generally achieving better outcomes than those with advanced disease at presentation. Some birds achieve substantial improvement, with neurological signs reduced to minimal levels that allow near-normal function. Others show partial improvement but retain significant deficits. A subset of birds fail to respond meaningfully to treatment despite appropriate therapy.

Post-treatment care for neurological avian bornavirus disease is essentially ongoing management, as treatment continues indefinitely rather than having a defined endpoint followed by post-treatment period. Medication administration continues as prescribed, typically for the remainder of the bird's life. Regular veterinary monitoring assesses treatment effectiveness and watches for adverse effects from long-term medication use. Environmental modifications established during acute disease management often remain in place permanently if residual neurological deficits persist. Diet optimization supports overall health and may help reduce disease activity. Stress minimization remains important as stress can trigger disease flares even in birds otherwise well-controlled on medication. Owner education ensures understanding of the chronic nature of the disease and the importance of consistent long-term management.

Prognosis factors for neurological avian bornavirus disease include the severity of disease at presentation, the response to initial treatment, and the presence or absence of concurrent gastrointestinal disease. Birds presenting with mild to moderate neurological signs and showing good response to anti-inflammatory therapy have the most favorable prognosis for maintaining quality of life on long-term treatment. Advanced neurological disease with severe deficits, poor response to treatment, or concurrent severe gastrointestinal disease carry worse prognosis. Individual variation in disease behavior means that some birds remain stable for years on treatment while others progress despite aggressive therapy. The unpredictable nature of the disease requires ongoing vigilance and flexibility in management approach.

Long-term outlook for birds with neurological avian bornavirus disease ranges from maintained quality of life for years to progressive decline leading to euthanasia. Best-case scenarios involve birds that achieve substantial improvement on medication, remain stable long-term, and live comfortably with minimal residual deficits for years. Many birds achieve intermediate outcomes, with some improvement but persistent deficits requiring accommodation, and gradual slow progression over time that eventually compromises quality of life. Some birds progress despite treatment, experiencing stepwise decline with episodes of deterioration, eventually reaching states incompatible with acceptable quality of life. Regular quality of life assessment helps guide decisions about treatment intensity and timing of humane euthanasia when appropriate. Emotional support for owners managing this challenging disease helps them navigate the difficulties of caring for a chronically ill companion.

Environmental prevention of avian bornavirus infection centers on biosecurity measures to prevent exposure, though the widespread prevalence of the virus in captive psittacine populations makes complete prevention challenging. Closed aviaries that do not introduce new birds avoid the primary route by which infection enters established collections. Air filtration and separation of potentially infected birds from susceptible populations reduce aerosol transmission risk. Disinfection protocols address fomite transmission, though bornavirus is susceptible to most common disinfectants when properly applied. Avoiding shared equipment, food dishes, and contact between birds of unknown status limits transmission opportunities. Complete prevention may not be realistic given the prevalence of infection, but thoughtful biosecurity reduces exposure risk.

Quarantine protocols for new birds help identify infected individuals before they can transmit virus to established collections. Extended quarantine periods of ideally ninety days or longer allow time for testing and observation of incoming birds. Testing during quarantine should include both PCR to detect viral shedding and serology to detect antibody evidence of exposure, with testing repeated at intervals during quarantine to account for intermittent shedding. Birds testing positive should not be introduced to collections of negative birds. The challenge with bornavirus testing is that positive results indicate infection or exposure but do not predict whether clinical disease will develop, complicating decisions about how to manage positive birds. Some owners choose to maintain separate positive and negative populations rather than mixing birds of different status.

Dietary prevention does not prevent bornavirus infection but supports overall immune function and may influence disease progression in infected birds. A complete, balanced diet appropriate for the species provides nutrients needed for healthy immune function. Avoiding nutritional deficiencies eliminates one potential stressor that could contribute to disease progression. Some evidence suggests that certain dietary factors may influence inflammation, though specific dietary interventions to prevent bornavirus disease progression have not been established. Maintaining optimal body condition supports the bird's overall ability to manage chronic infection and treatment.

Health maintenance through regular veterinary care supports early detection of disease in infected birds and optimal management once disease develops. Baseline testing for avian bornavirus allows birds to be categorized according to their infection status, though the interpretation of results requires understanding of testing limitations. Regular wellness examinations may detect subtle neurological changes before they progress to obvious clinical disease. Monitoring body weight and condition identifies changes that might indicate disease progression. Prompt veterinary consultation when any concerning symptoms develop allows early intervention that may improve outcomes. Established relationships with avian veterinarians experienced in bornavirus disease management ensure access to current treatment approaches.

Early intervention when clinical signs first appear provides the best opportunity to limit neurological damage and maintain quality of life. Bird owners should be educated about early signs of neurological disease and encouraged to seek veterinary evaluation promptly when changes are observed. Testing birds showing any neurological symptoms expedites diagnosis and treatment initiation. Starting anti-inflammatory treatment early in the disease course, before extensive irreversible damage has occurred, may result in better outcomes than delayed treatment. For known positive birds, heightened awareness of early symptoms allows particularly rapid response. The goal of early intervention is to suppress inflammation before permanent neurological damage accumulates, maximizing the chance of achieving good long-term disease control.

Daily management of birds with neurological avian bornavirus disease revolves around consistent medication administration, environmental safety, and monitoring for changes. Anti-inflammatory medication must be given reliably according to the prescribed schedule, typically once or twice daily depending on the specific medication. Many owners find that incorporating medication into daily routines, such as giving it at the same time as morning feeding, improves consistency. Food and water access should be optimized for birds with coordination problems, with dishes positioned for easy access and potentially multiple stations to ensure availability regardless of the bird's position. Daily observation notes any changes in neurological status, appetite, activity level, or behavior that might indicate disease progression or medication issues.

Home environment modifications create safe spaces for neurologically impaired birds while maintaining quality of life. Cage setup should minimize fall hazards, with perches lowered or replaced with platforms for birds with significant balance problems. Padding surfaces the bird might fall onto reduces injury risk. Cage location should allow for social interaction while protecting the bird from disturbances that might cause startling and falls. Environmental enrichment appropriate to the bird's abilities maintains psychological wellbeing despite physical limitations. For birds with visual impairment, maintaining consistent cage arrangement helps them navigate their environment using spatial memory. Temperature management may be important for birds with impaired thermoregulation.

Quality of life considerations are central to managing birds with neurological avian bornavirus disease and require ongoing assessment throughout the bird's care. Indicators of acceptable quality of life include apparent contentment, maintained interest in social interaction and environment, ability to eat and drink, and absence of apparent distress or pain. Birds showing these positive indicators can often enjoy meaningful lives despite neurological deficits. Warning signs of declining quality of life include persistent distress, inability to rest comfortably, loss of interest in previously enjoyed activities, significant difficulty eating, and apparent frustration with physical limitations. Quality of life assessments should be performed regularly and whenever clinical changes occur, with honest evaluation of whether the bird's experience remains positive overall.

Monitoring and ongoing care requirements for birds with neurological avian bornavirus disease include regular veterinary follow-up and at-home observation. Veterinary rechecks, typically every few months for stable birds, assess clinical status, monitor for medication side effects, and provide opportunity to adjust treatment as needed. Weight monitoring detects changes in nutritional status. Documentation of neurological function over time identifies trends that might not be apparent from individual observations. Blood tests may be performed periodically to monitor for organ effects from long-term medication use. Any sudden changes in neurological status or overall condition warrant prompt veterinary consultation rather than waiting for scheduled appointments.

Caregiver support resources help bird owners cope with the challenges of managing a bird with chronic neurological disease. Online communities specifically focused on avian bornavirus connect owners facing similar challenges, providing practical advice and emotional support. Avian veterinary teams offer medical guidance and can help with difficult decisions about treatment intensity and quality of life. Mental health support may be appropriate for owners struggling with the emotional burden of caring for a chronically ill companion with uncertain prognosis. Financial planning helps manage the ongoing costs of treatment, which continue indefinitely. Preparing emotionally for the possibility of eventual decline helps owners face difficult decisions when they arise. Open communication between owners and veterinary teams ensures that care decisions align with the bird's best interests and the owner's values and capabilities.

High-risk species for neurological avian bornavirus disease include psittacines that show particularly high infection prevalence and clinical disease rates. Macaws of various species have been identified as having high bornavirus infection rates and frequently develop clinical disease when infected. African grey parrots show high susceptibility and often develop severe disease. Cockatoos, including sulphur-crested, umbrella, and other species, are commonly affected. Amazon parrots represent another frequently affected group. Conures of various species have significant infection rates. The concentration of disease in these popular psittacine species means that a large proportion of companion birds are at risk. Within high-risk species, individual susceptibility to developing clinical disease varies, and many infected birds remain asymptomatic.

Moderate-risk species include other psittacines and some non-psittacine species in which bornavirus infection has been documented. Eclectus parrots, lovebirds, budgerigars, and cockatiels can be infected and develop disease, though some studies suggest lower clinical disease rates than in the highest-risk species. Poicephalus parrots including Senegals and Meyer's parrots are susceptible. Ring-necked parakeets and other Asiatic parakeet species have documented infections. Non-psittacine species including certain finches, geese, and waterfowl have been found infected with related bornaviruses, though disease in these species is less well characterized. The expanding recognition of bornavirus across species suggests that more populations may be at risk than previously appreciated.

Screening recommendations for avian bornavirus depend on the circumstances and goals of testing. New birds being introduced to established collections should be tested during quarantine, with testing including both PCR and serology to maximize detection sensitivity. Breeding birds should be tested to inform breeding decisions and prevent vertical transmission. Birds showing any neurological or gastrointestinal symptoms suggestive of bornavirus disease should be tested diagnostically. Routine screening of asymptomatic pet birds is controversial, as positive results create management dilemmas given that many positive birds never develop clinical disease. The decision to screen asymptomatic birds should be made in consultation with an avian veterinarian, considering the specific circumstances and the owner's ability to manage the information provided by testing.

Commonly co-occurring conditions with neurological avian bornavirus disease most notably include the gastrointestinal form of bornavirus disease, proventricular dilatation disease, which may occur simultaneously or develop sequentially in birds initially presenting with only neurological signs. The combined presentation of neurological and gastrointestinal disease creates additional management challenges and typically indicates more extensive disease involvement with worse prognosis than isolated neurological disease. Secondary complications of neurological impairment including aspiration pneumonia from coordination problems during eating, injuries from falls, and nutritional compromise from difficulty eating may develop as disease progresses. Immunosuppression associated with chronic illness may predispose to secondary infections. Concurrent diseases unrelated to bornavirus may occur and can be more difficult to diagnose and manage in birds already dealing with bornavirus disease.

Conditions with similar symptoms that must be differentiated from neurological avian bornavirus disease include other causes of neurological dysfunction in birds. Heavy metal toxicosis from lead or zinc causes neurological symptoms that can mimic bornavirus disease and should be excluded through blood metal testing in all birds presenting with neurological signs. Other viral diseases affecting the nervous system including paramyxovirus and polyomavirus produce neurological symptoms. Bacterial, fungal, and parasitic infections affecting the central nervous system cause encephalitis with varied neurological presentations. Brain tumors produce progressive neurological signs. Metabolic conditions including hepatic encephalopathy can cause neurological dysfunction. Vitamin deficiencies, particularly of vitamin E and thiamine, affect nervous system function. Trauma can cause acute neurological deficits. Thorough diagnostic evaluation helps distinguish bornavirus disease from these alternatives.

Potential complications of neurological avian bornavirus disease include both direct consequences of progressive neurological deterioration and secondary problems resulting from impaired function. Aspiration pneumonia represents a serious risk when coordination problems affect the ability to swallow safely, potentially causing life-threatening respiratory infection. Injuries from falls due to balance problems may cause fractures or soft tissue trauma. Nutritional compromise develops when neurological deficits impair eating ability, leading to weight loss and muscle wasting. Pressure sores may form in birds unable to shift position normally. Development of gastrointestinal disease in birds initially presenting with only neurological signs represents progression of viral effects on the nervous system. Quality of life may eventually decline to unacceptable levels as complications accumulate and neurological function deteriorates despite treatment.