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Avian Borna virus (ABV)
Avian Borna Disease (ABD)
Proventricular Dilatation Disease (PDD)

 
Description:

Bornavirus is the causative agent of Borna disease. Borna disease virus (BDV) is a negative-stranded neurotropic RNA virus. A neurotropic virus is a virus which can infect nerve cells, or which does so preferentially. A few commonly known neurotropic viruses are Rabies, Herpes virus, Poliovirus, and Japanese Encephalitis.

Borna disease was first recognized in 1885 in cavalry horses in the town of Borna in Saxony, Germany. BDV, the virus that causes Borna Disease, appears to have a wide host range having been detected in birds, horses, cattle, sheep, dogs and foxes. In 1995, the virus was isolated from cats suffering from a "staggering disease". In 2000, a Swedish researcher isolated BDV from wild birds including mallards and jackdaws. BDV has also been found in ostrich farms in Australia. It is generally accepted that ADV causes a persistent infection of the central nervous system (CNS). This infection can be expressed in varying degrees from mild behavioral changes to severe neurological disease.

Bornavirus was first described in psittaciforms in 2008 by researchers at UCSF who were studying a group of five parrots suffering from Proventricular Dilatation Disease (PDD). Using microarray technology, the group isolated a negative-stranded RNA virus from three of the five birds. This virus was determined to be a member of the Bornaviridae family. The researchers named the avian strain 'Avian Bornavirus' (ABV).


It has long been believed that PDD is caused by an enveloped neurotropic virus that in some cases causes cytokine storm resulting from lymphocyte infiltration to the proventriculus (forestomach), ventriculus (gizzard), and areas of the small intestines. As a result of the damage, birds are unable to digest their food properly. In some birds with PDD, the severely dilated thin wall of the proventriculus may rupture, resulting in movement of undigested food into the abdominal cavity causing severe infection which many times leads to rapid death.

Research strongly suggests that ABV plays a pivotal role in the onset of PDD in birds. ABI has tested over 5000 samples from both suspect and non-suspect birds. Samples from over 500 cases of PDD diagnosed birds have been confirmed to have ABV antibodies as well as Borna virus RNA. However, there is also a large population of birds that have tested positive for ABV but have not developed any clinical signs of PDD.

New research confirms that cloacal swabs and fecal samples are not a reliable source of ABV RNA due to the inconsistent shedding of the virus and destructive forces like bacteria, enzymes and other contaminants found in the feces. This results in an unacceptable percentage of false negatives by PCR.

ABV has been found in samples from countries in Europe, Asia, African and South America.

ABV is also being studied as a possible causitive agent of conditions such as skin inflammation, feather plucking, self mutilation, major neurological problems, and chronic bacterial and fungal infections.

In May 2010, we recieved feather samples from 6 birds who are chronic feather pluckers. 5 of the 6 birds tested positive for ABV by rtPCR using feather samples. None of these birds were suffering from any weight problems as observed by the vetrinarian treating them.


Transmission:

Bornavirus transmission is not well understood. Bornavirus is thought to be primarily transferred from one individual to another through direct or intimate contact, or by exposure to infected fecal material. Avian Biotech is currently studying ABV transmission from an infected female to an egg and performing testing to determine embryonic infection of ABV. Additional work is being done to study ABV-specific antibody levels in the yolk of an egg laid by an infected bird. ABI is also studying cellular transmission and variations in specific ABV protein expression from one individual to another.


Symptoms:

Signs suggestive of PDD include weight loss over a period of weeks to months despite a good appetite, passage of undigested food, vomiting, abdominal distention, and impaction of the crop and proventriculus.
Neurological signs include intermittent shaking of the bird's head, feather plucking and mutilation, problems with balance, moaning or crying due to digestive problems, change in aggression, and seizures. Some or all of these signs may or may not be present.

It is also important to note that in many cases birds infected with ABV may not develop any symptoms of ABD or PDD for years or even decades before the onset of disease. It is still unknown if a percentage of birds may never develop any symptoms of disease but may continue to function as a reservoir for ABV and allow the virus to infect other birds.


Prevention:

In 2010 ABI began testing a sub-unit vaccine to prevent the spread of the disease and the results are looking very promising.

To disinfect areas that may have been contaminated by bornavirus, use an oxidizer solution such as diluted bleach: 50 parts water to 1 part bleach, plus a small amount of dish soap as a wetting agent.


Treatment:

There are no known treatments for ABV infections. ABI is looking forward to conducting experimental treatments using ABI's own parrot-specific gamma and alpha interferon, as well as combining these cytokins with specific anti-viral drugs. Proventricular Dilatation Disease (PDD


Diagnosis:

Complete ABV/PDD panel!!

Two methods of identifying ABV infection are available at ABI: serology (rELISA) which tests for immunological exposure to specific ABV antigens, and direct rtPCR which detects the presence of ABV-specific RNA. Our complete ABV panel includes both the rtPCR and the ELISA panel.

ABV ELISA panel consists of 4 AVB-specific proteins (P40, P24, P29, and matrix). A small serum sample is required for the rELISA panel.

ABV rtPCR panel is a multiplex assay that amplifies both conserved ABV M&N segment genes as well as two internal RNA controls (housekeeping genes). Internal controls are extremely important to confirm proper RNA isolation. For routine ABV screening using rtPCR, the most reliable samples are chest or breast contour feathers.

Cloacal or vent swabs as well as fecal samples are not recommended for routine screening due to the intermittent shedding of the virus, as well as bacterial and enzymatic degradation, that greatly reduce the reliability of this sample type. Because of the neurotropic nature of the virus, blood is also not recommended for rtPCR.

For postmortem detection of ABV RNA, samples from the brain, proventricular tissue, or crop biopsies stored in alcohol are preferred.

Animal Genetics' latest publication on ABV was submitted for publication to the Journal of Veterinarian Diagnostic Investigation. Our research paper describes current methods used by Animal Genetics for detection of ABV. This paper also demonstrates the effectiveness of testing for ABV from feathers, and compares the reliability of a feather sample with a cloacal swab and serum sample.


Sample:

Serum samples are currently accepted for ELISA. However, fecal samples and blood cards are being evaluated and could become an alternative sample for ELISA. Cloacal swabs are not considered an reliable source for ABV RNA and should not be submitted by them selfs for rtPCR. Due to the neurotropic nature of the virus, the calamus of 4-8 plucked chest or breast feathers provides the best source of viral RNA for screening of birds infected with ABV.

Postmortem testing requires a small brain tissue sample placed in alcohol. Detailed information has been submitted for publication in the "Journal of Veterinary Diagnostic Investigation". Proventricular Dilatation Disease (PDD)


Handling:

Samples should be submitted by overnight or two day air.


Limitations: Because of mutations occurring in ABV genome, it may be difficult to detect all subtypes. Proventricular Dilatation Disease (PDD
References:  
 
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