Bornavirus in parrots: PaBV, PDD and smart testing

10/06/2026

PaBV is the virus, PDD the disease. How to choose between PCR and serology (ELISA), from what age to test young birds, and what a positive result means.

Bornavirus in parrots: the PDD mystery unravelled

Bornavirus in parrots leaves many breeders uncertain. And rightly so: some birds become seriously ill, others appear perfectly healthy for years, and those same test results are interpreted very differently in practice. A workable testing strategy starts with a single distinction.

PaBV (Parrot Bornavirus) is the virus itself. PDD stands for Proventricular Dilatation Disease. PDD is the disease that can develop from a PaBV infection, not the virus itself.

A bird can therefore be PaBV-positive without being ill at that moment. Conversely, not every bird with undigested seeds, weight loss or neurological signs automatically has bornavirus. Targeted diagnostics remain necessary.

Which symptoms point to PDD?

PaBV can affect various peripheral nerves. As a result, the clinical pictures vary widely: gastrointestinal problems, neurological signs, or a vague combination.

Possible signs:

weight loss despite a normal appetite
undigested seeds in the droppings, regurgitation, slowed digestion
diarrhoea or a dilated proventriculus
balance disorders, tremors, blindness, loss of strength, epileptiform seizures
behavioural changes, self-mutilation
sudden death

These symptoms can also fit feeding problems, intoxications, parasites, bacterial infections, fungal or yeast infections (including Macrorhabdus), tumours or other viruses. A targeted differential approach is therefore the norm, not the exception.

How is PaBV transmitted?

For a long time, the focus was on spread via feather dust or oral/nasal uptake. That picture has been revised.

Horizontal transmission (bird to bird)

Horizontal transmission appears to be not particularly efficient. A single positive bird does not automatically infect the whole collection. We regularly find pairs or groups in which some birds are positive and others remain negative, including pairs that have been housed together for years.

What is strongly supported experimentally: transmission via wounds and skin lesions, followed by retrograde spread along peripheral nerves [1]. Bite wounds, foot-sole problems, poor perches, rough group changes and stress are therefore relevant risk factors in management. Oral or nasal infection remains theoretically possible, but is not supported by experimental studies as a reliable route of infection [2].

Vertical transmission (via the egg)

Vertical transmission has been demonstrated experimentally in Nymphicus hollandicus (cockatiel) [3]. PaBV RNA, and in certain groups also infectious virus, was found in eggs and embryos. The likelihood depends partly on the age at which the parent birds themselves became infected.

Important for breeders: positive parent birds do not automatically produce only positive young. Negative offspring are possible. Testing the young themselves is therefore essential, and clearing out a valuable bloodline is rarely the right first reflex.

Which test should you choose: PCR or serology (ELISA)?

Two tests, two stories.

PCR looks for viral material at the moment of sampling. Fast and practical, with one caveat: viral shedding is intermittent, and an infected bird can be PCR-negative at that moment.

Serology (an antibody test, often called ELISA or indirect immunofluorescence in practice) shows whether the bird has produced antibodies against PaBV, and therefore whether it has ever had contact with the virus. From here on, we consistently use the term serology.

Which combination, and when?

Strategy	What it delivers	For whom
PCR + serology, retest after 4-6 weeks	Highest certainty	Valuable breeding birds, purchase of expensive birds, import/export, rare species, collection screening
Serology + retest after 4-6 weeks	Good certainty, more cost-effective	Practical screening where PCR is financially unfeasible
Single serology	Strong first indication	Collection overview, screening at sale, large numbers
Single PCR	Detection of current shedding	Sick birds, deaths, post-mortem, situations where blood sampling is difficult

PCR detects active viral shedding at the moment of sampling. A positive PCR is always valuable and confirms a current infection. A negative PCR on its own, however, gives limited certainty: an infected bird does not shed the virus continuously, so a negative result does not fully rule out an infection.
Serology (ELISA) measures the antibodies the immune system produces in response to contact with the virus. A positive serology result indicates earlier contact with the virus. A negative serology shows that there was no contact with the virus up to a few weeks before sampling. If an infection occurred at the moment of sampling or just before, the serology can still be falsely negative: the antibodies have not yet had enough time to form. To rule this out as far as possible, we advise combining it with PCR in that case.

Which samples are needed?

PCR: blood, a cloacal swab, or the combination of a crop and cloacal swab. For screening live birds, we generally advise the crop + cloaca combination, as it increases the chance of detection.
Serology (ELISA): at least 0.5 ml of blood in a serum tube or an ordinary plastic tube. A blood capillary yields too little serum.

From what age should you test young birds for bornavirus?

For sick young birds: test regardless of age.

For healthy young birds that will be sold, moved or placed in a negative group: test from around 6 weeks. With larger parrots it is often more practical to test after weaning, or once the bird no longer has intensive contact with other birds. The reasoning: a test only has full value when you can subsequently keep the bird separated or protected from possible sources of infection.

For maximum certainty with valuable birds: PCR + serology from 6 weeks, retest 4 to 6 weeks later with the same combination.

How do you get your collection PaBV-negative?

Testing and separation plan:

Test all birds from weaning age, preferably with PCR + serology.
Strictly separate positive, doubtful and negative birds.
Retest negative birds after 4 to 6 weeks. Only place double-negative birds in the negative group.

Management that makes the difference:

Separate materials, nest boxes, gloves and care routes per group.
Care for negative birds first, positive birds last.
Prevent bite wounds, foot-sole problems and stress: these are the routes along which the virus spreads.
Do not automatically remove positive birds. For valuable or rare lines, negative offspring can be selected, provided there is strict follow-up.

How do you then keep that collection negative? Every new bird is a risk, even if it looks healthy. Test before introduction (PCR + serology on arrival, retest after 4 to 6 weeks) and maintain strict quarantine. Only introduce the bird once both the test results and the quarantine period are reassuring.

Is there a vaccine or treatment?

At present there is no commercially available vaccine and no treatment proven to eliminate the virus. Management is supportive: adapted, more easily digestible food, monitoring of weight and droppings, treatment of secondary problems and, where necessary, supportive medication for inflammatory or gastrointestinal problems under veterinary guidance. Immune-supporting products such as Immuno-Plus from NeorniPharma can be of use here, to support and promote immunity. With this kind of supportive care, some birds can remain stable for a long time or even remain healthy carriers, but this depends heavily on the stage of the disease.

The key message

PaBV is no reason to panic, but it is reason for a structured approach.

The highest certainty comes from PCR + serology with a retest after 4 to 6 weeks. If that is not feasible, serology with a retest or a single serology is a strong practical next step. A single PCR is useful as low-threshold screening, provided you know its limitations.

Test smartly, separate correctly, prevent injuries and don't make rushed decisions. Positive birds can produce negative young: you don't clear out a valuable bloodline without a plan.

References

[1] Heckmann J., Enderlein D., Gartner A.M., Bücking B., Herzog S., Heffels-Redmann U., Malberg S., Herden C., Lierz M. Wounds as the Portal of Entrance for Parrot Bornavirus 4 (PaBV-4) and Retrograde Axonal Transport in Experimentally Infected Cockatiels (Nymphicus hollandicus). Avian Diseases.

[2] Heffels-Redmann U., Enderlein D., Herzog S. et al. (2012). Occurrence of avian bornavirus infection in captive psittacines in various European countries and its association with proventricular dilatation disease. Avian Pathology, 41(2), 145–153.

[3] Heckmann J., Enderlein D., Piepenbring A.K. et al. Studies on vertical transmission of Parrot Bornavirus in Nymphicus hollandicus.