Understanding what viruses are and how they function will help individuals develop a perspective of how viruses can affect birds.Viruses are the most basic of all organisms. They contain only nucleic acid (DNA or RNA) and a protein coat cover. Some more complex viruses are enclosed in a protective envelope derived from the infected cells own cell membrane. Viruses require the help of other cells to reproduce. Bacteria, fungi, chlamydia are more complex and have a nuclear body (DNA or RNA) and cytoplasm that contain components that convert nutrients into energy to drive the functions of the cell. These organisms can reproduce on their own. The nucleus of a cell can be viewed as the control center and the cytoplasm the factory. Viruses have a control center but no cytoplasm therefore a virus is dependent on the cell it infects to provide the factory it needs to produce energy or reproduce itself. Viruses are very small. For example, it would take 21,517 Psittacine Beak and Feather Disease (PBFD) viral particles to cover the tip of a needle. These tiny particles can survive in the environment for months to years and can be spread to other birds in a home or aviary via contaminated fingernails, skin, hair, jewelry, cloths, food bowls, perches etc.The general steps in viral reproduction are:
The protein coat has binding sites that recognize receptors on the cells of susceptible bird species. A bird is considered susceptible to a viral infection if a receptor on its cell allows the virus to attach. If this receptor is not present then the bird will not be infected even if it has been exposed to the virus. For example, a duck may not be susceptible to a parrot virus or vice versa but an Amazon parrot would be susceptible to a Macaw virus. Disinfectants work by destroying these sites on the virus thus preventing the virus from initially binding to the cell.A virus infection can cause disease in a bird in several ways:
The result of exposure to a virus depends on the age, species and condition of the bird and the characteristics of the particular virus. A healthy bird that is exposed to a virus to which it is susceptible can become infected. The infected bird may remain clinically normal or it can become obviously diseased. If the bird remains clinically normal and develops a subclinical infection, it may destroy the virus and be protected from future infections, or it may remain persistently infected (carrier state). Likewise, a clinically infected bird (showing obvious signs of disease) may mount an effective immunologic response to destroy the virus and develop protection from future infections, or it may recover from the disease and remain persistently infected (a carrier) or it may die. Young birds are more susceptible to viral infections because their immune system is not fully developed likewise very old birds are more susceptible due to an age related decrease in immune system function. Birds are most resistant to disease during their reproductively active years. If all other factors are equal, a healthy bird exposed to a small number of viral particles is less likely to become ill than the same bird exposed to a large number of particles. Maintaining numerous birds in close proximity will increase the likelihood that a virus can be transmitted from bird to bird. Depending on the type of infection, birds may or may not produce antibodies. Antibodies produced in response to viral infection help clear the infection and protect the body from future infections.Potential methods of viral transmission in birds:
Diseases are frequently caused by the interaction of more than one type of infectious agent, including bacteria, fungi, viruses and parasites. A virus may cause damage to a bird allowing other pathogens (particularly bacteria and fungi) to colonize damaged tissues. The bird may clear the viral infection that initiated the disease process, and it is a bacteria or fungi that is detected on diagnostic testing of the ill bird. In these cases, the virus is referred to as the PRIMARY infection and the bacteria is referred to as the SECONDARY infection. Therefore, many birds that are diagnosed with bacterial/fungal infections may have initially had a viral infection.
Clinical abnormalities, necropsy findings and microscopic abnormalities may suggest that a bird was infected by a virus; however, clinical signs or lesions that absolutely confirm that a particular type of viral infection occurred are rare. A thorough necropsy with collection of necessary diagnostic samples should be performed on any bird that dies. Diagnostic samples may include portions of tissues placed in formalin for microscopic evaluation, samples of blood for bacterial or viral isolation and swabs or samples of abnormal tissues for viral, bacterial or fungal isolation.Preventing Viral Infections
The goal of maintaining any bird in captivity is to insure that it is in the best possible condition. Few effective vaccines exist against the viruses that infect companion and aviary birds. Careless exposure of a single bird within a flock can result in viral outbreak that may affect the entire flock.Ways to prevent spread of virus:
Viruses are susceptible to inactivation when they are outside the bird's body. The destruction or removal of the virus from the bird's environment is one of the best methods for control of viral transmission. This can be achieved by a combination of:
Few vaccines have been developed and tested for use in companion and aviary birds. When a bird recovers from a viral infection, it does so because its immune system produces specific antibodies and specialized immune system cells that react to the surface proteins that compose a virus' coat or envelope. Vaccination is intended to induce a similar immune response. Depending on the particular virus, a vaccine may initiate an immune response that will prevent the virus from infecting the bird or it may allow a bird to be infected but produce a minor, rather than a severe, disease. In either case, the bird should develop an active immune response following vaccination. Over time, the response will decrease and administration of a booster vaccination will be necessary. Vaccines may fail to produce effective immune response if the vaccinate bird is immunocompromised, already infected, or undergoing immunosuppressive therapy (steroids, some antibiotics). Any vaccine may be expected to cause an inappropriate reaction in a certain percentage of birds. These reactions can vary in severity from a sore/scab at injection site to lethargy or rarely death.Definitions:
Active compound and trade names of common disinfectants.
|Chlorinated compounds||bleach, Clorox, Purex|
|Chlorhexidine gluconates||Hibitane, Hibistat, Nolvasan, Virosan|
|Glutaraldehydes||Banacide, Cidex, Cybact, MC-25, Sporocide, Sonacide, Sterol, Wavecide|
|Iodine||Betadyne, Scrubodyne, Povidone, Prepodyne, Virac, Wescodyne|
|Phenols||Avinol-3, LPH, Lysol, Matar, Amerse, One Stroke, Environ, O-Syl, Staphene|
|Quaternary Ammonium||A-33, Baraquat, Cetylcide, Floquat, Hitor, Merquat, Omega, Parvasol, Quintacide, Roccal, Zepharin|
|Wood tar distillates||Hexol, Pine-Sol|
From: Ritchie, WR. Avian Viruses: Function and Control. Wingers Publishing, INC. Lake Worth, Florida, 1995.
The majority of information in this article was obtained from Ritchie, WR. Avian Viruses: Function and Control. Wingers Publishing, INC. Lake Worth, Florida, 1995.
Psittacine Beak and Feather Disease (PBFD) is a chronic disease characterized by feather dystrophy and loss, beak deformity and ultimately, death. The cause of PBFD is a newly discovered virus in the family Circoviridae. The disease probably originated in Australia and spread to other continents as a result of the shipment of birds for the pet bird trade. The disease has been reported in Australia, North America, Europe and Asia. Most species of parrots are susceptible to the virus however the species most commonly affected are cockatoos, African Grey Parrots, Eclectus Parrots and Lovebirds. The first clinically detectable sign of PBFD is the appearance of necrotic, abnormally formed feathers. Generally, PBFD is a disease of young birds (up to 3 years of age) however, it has been reported in birds over 20 years old that had been clinically normal most of their life. Peracute, acute and chronic disease patterns occur.
The virus is spread from hen to the egg, hen to chicks being parent raised, and inhalation or ingestion of infected feather dust or feces. Viral particles in feather dust or dried feces can easily spread on clothing, nest materials, feeding formula or feeding utensils, nets, bird carriers, food dishes and air currents. The virus particles can remain viable in the environment for months, long after the infected bird is gone. Many birds infected with PBFD die with in 6-12 months of onset of clinical signs however, some birds have been known to survive 10-15 years. Death usually occurs from secondary bacterial, fungal, parasitic, chlamydial, or viral infections.
PBFD should be suspected in any bird that shows progressive feather loss and abnormal feather development. However one can not determine that a bird is infected with the virus just by examination of the feathers. Other disease processes can result in feathers with a similar appearance. Any factor that disrupts the blood supply to the developing feather, including trauma; bacterial or fungal infection of the feather follicles; other viral infections; malnutrition; hormone reactions; and some drug reactions, can cause feather changes similar to those seen with PBFD. Identical feather lesions to those caused by PBFD can be produced by pinching developing feathers at or near the level of the pulp cap. On the other hand, birds can carry the virus in their blood but have perfectly normal feathers. Until recently, the primary method of diagnosing PBFD was the demonstration of viral particles in the cells of the feather follicle and /or shaft. This required a surgical biopsy of the affected feather and its associated follicle. Since PBFD virus does not affect all feathers at the same time, this test could give a false negative result if the tissue sampled did not contain the virus. A more recent test, DNA probe analysis, tests for the presence of PBFD virus in the bird's blood. This is the only effective method available for detecting the PBFD virus in a bird before feather lesions are present. The test requires a small amount of blood. Some birds may become infected with the virus, test positive, remain infected but never show clinical signs. Other birds, become infected, test positive, fight off the infection and subsequently test negative. Therefore, it is recommended to retest any PBFD positive bird 90 days after the initial test. If this bird tests positive a second time then it is infected however if subsequent test is negative, then the bird was able to eliminate the virus and is not infected. Since the virus survives in the environment, the DNA probe can also be used to test samples of feces and/or feather dust taken from the surfaces in the environment.Management of a positive bird
If a bird from a breeding aviary tests positive for PBFD, remove the bird from the environment as quickly as possible. The bird can potentially shed large numbers of viral particles that can be spread to other birds by wind or on cloths, skin, hair or inanimate objects. All areas, supplies, and equipment should be cleaned, disinfected then tested with the DNA probe as mentioned above to determine if any infective material remains. In addition, I recommend testing of all birds exposed to the positive bird as well as any offspring of the infected bird. Retest the positive birds in 90 days to determine if the birds were permanently infected.
If a companion bird tests positive, then the bird should never be exposed to other birds outside of the household. Many infected birds can live a long life when provided a healthy, relatively stress free environment, good diet and regular veterinary care. Remember, you can carry the virus on your cloths.
To prevent spread of this disease, DNA probe testing is recommended on all cockatoos, Lovebirds, Eclectus Parrots, African Grey Parrots and any birds showing feather lesions consistent with PBFD as part of a routine pre-purchase examination, prior to sale from an aviary or pet shop and prior to entry in to a new home/aviary. Research is ongoing for development of a vaccine against PBFD.
The primary information source for this article was the text book written by Dr. Branson Ritchie, Avian Viruses: Function and Control published in 1995 from Wingers Publishing Inc., Lake Worth, Florida. Branson Ritchie, DVM, PHD is an Associate Professor of Avian and Zoologic Medicine at The University of Georgia in Athens. He and his associates have been primarily responsible for the research into the cause of PBFD and for development of testing procedures for detection of this virus and are presently working on a vaccine for prevention of this disease.