Avian Viruses...

What They Are and How They Cause Disease
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:
Attachment of virus to a receptor on the bird’s cell
Penetration into the interior of the bird’s cell
Uncoating or removal of the protein coat releasing the viral nucleic acid into the infected cell
Transcription/translation of the virus’ nucleic acid, resulting in the infected cell producing new copies of the viral protein coat and nucleic acid
Assembly of protein coat and nucleic acid into a new viral particle
Release of the new viral particle from the cell.
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 virus can directly induce lesions in an organ by causing the rupture of infected cells
The virus may stimulate the bird’s immune response, which then destroys the virus-infected cells
The virus may damage the bird’s cells causing them to become neoplastic (cancer).
The virus may establish itself in the bird such that the infected bird becomes a persistently infected carrier of the virus.
Viruses may damage host cells in several ways:
The virus uses the cell’s metabolic functions exclusively for the virus therefore the host cell starves.
The virus produces products that are toxic to the cell.
The virus ruptures the cell membrane thus destroying the cell.
The virus alters the cell wall causing the cell to loose vital fluid and die.
The virus may change the DNA of the cell causing it to become cancerous.
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:
Preening
Rubbing
Inhalation of aerosols
coitus (mating)
insect or animal bites
contamination of egg
ingestion of contaminated feces
contact with contaminated fomites
ingestion of contaminated food or water
ingestion by neonates of regurgitated food from infected parent
fighting related injuries
insects-mechanical vector/biologic vector
from infected hen to egg in utero (while egg is in the reproductive tract)
contamination of egg by infected hen immediately after laying
Diagnosing Viral Infections
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:
Use clean, disinfected feeding utensil for each bird
Quarantine all new birds minimum 30 days if captive bred; 90 days for all others
Isolated any sick birds ASAP
Do not allow fecal contamination of food/water bowels
Disinfect food/water bowls daily
Disinfect cage area as often as possible
Limit outside visitation of aviary
Use disinfectant foot baths on entry/exit from aviary
Veterinary evaluation of sick birds
Necropsy examination of dead birds - Place bird in refrigerator as soon after death as possible - DO NOT FREEZE REMAINS - this damages tissues making microscopic evaluation difficult.

Limit exposure to noxious fumes esp. cigarette smoke.
Provide nutritionally, complete diet.
Relatively stress free environment
>Do not overcrowd
Do not mix babies from different nests/parents
Wash hands between handling birds
Eliminate vermin
Maintain good air circulation
Reduce fecal and food accumulations
Cleaning and Disinfection
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:
Washing - to remove viral particles from the environment
Painting - permanently fixes virus to the surface
Disinfection - destroys the receptors that allow a virus to bind to a cell or destroys the viral nucleic acid
The presence of soil, feces, food, blood, mucous, or bedding material can interfere with the disinfection process in two ways: it can inactivate the disinfectant or it can prevent the disinfectant from contacting the virus. The contact time between virus and disinfectant is also important to allow complete inactivation.

Common Disinfectants
Chlorinated compounds - widely available, inexpensive, low residual toxicity. In general a 1:32 dilution (1/2 cup bleach per gallon water) is sufficient. These compounds are rapidly inactivated by organic material and sunlight, require frequent mixing-every few hours-to maintain an active solution. The solutions and fumes they produce can be irritating to skin, eyes and respiratory tract therefore should only be used in well ventilated areas.

Chlorine dioxide - similar to bleach and in some studies may be superior to bleach but is rapidly inactivated by organic material and sunlight.
Chlorhexidine gluconate - relitively non-toxic to skin, often used to cleanse wounds, non-corrosive and good activity against many bacteria, yeast (Candida) and some enveloped viruses, however, should not be considered a reliable viricide. Inactive in presence of organic material and limited stability.
Glutaraldehyde - rapidly inactivate many bacteria (including mycobacteria-avian tuberculosis), viruses and chlamydia, active in presence of organic debris, and stable as working solution from 2-4 weeks. These compounds are infrequently used because of widespread side effects of irritation to skin, respiratory tract and eyes especially following long term exposure. Iodines - used for cleaning wounds and skin and is effective against many bacteria (not Pseudomonas), some viruses and fungi. Rapidly inactivated by organic material.
Phenols - inactivate many bacteria (including mycobacteria and Pseudomonas), fungi and some viruses, inexpensive but are irritating to skin, eyes and respiratory tract, toxic to cats and reptiles. Quaternary Ammonium Compounds - inexpensive, relatively safe, and inactivate many bacteria, some viruses and chlamydia. May be inactivated by organic debris, and are ineffective against spores, mycobacteria, fungi, nonenveloped viruses and Pseudomonas. Hard to rinse from some surfaces and leave a slimy residue. Not recommended for use on objects that would be in direct contact with birds i.e. feeding utensils, food or water bowls.

Wood tar distillates - low toxicity but poor disinfectant.
Alcohols - 70% ethyl alcohol inactivates many bacteria and viruses but require minimum of 20 minutes contact time. Dissolve plastics, glues, and rubber.
Vaccines
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:
Infection - process of a virus entering a bird’s cell and reproducing
Disease - abnormal changes that occur in the bird’s cells as a result of infection. The severity of the disease that occurs depends on the bird’s age, nutritional status, stress level and environmental conditions.
Carrier state - a subcliniclly infected bird that shows no outward signs of virus infection but can spread the virus to other birds.
Types of Infection:
Subclinical - No signs of disease. Immune system controls infection and birds develop antibodies.
Peracute - Very rapid progression of disease. Infected birds recover or die within hours to days of infection. Recovered birds usually develop antibodies.
Acute - Rapid progression of disease. Infected birds recover or die within days to weeks after infection. Recovered birds usually develop antibodies.
Persistent - Chronic, Latent, or Slow
Chronic - Long-term infection with persistent shedding of virus. May persist for months to years. Birds may or may not develop antibodies.
Latent - Long-term infection with intermittent shedding of virus. May persist for months to years. Birds may or may not develop antibodies. No disease or shedding of virus during dormant state. Birds shed virus and may develop disease when virus is activated.
Slow - Progressive disease over months to years eventually causing the death of the bird. Virus reproduces over a long time period. No signs of disease early on.
Fomite - Inanimate object responsible for spread of disease i.e. cage toy, cleaning utensils, feeding syringes, clothing, human skin.
Biologic vector - living organism that becomes infected with virus from bird then carries that virus to another bird i.e. Western Equine Encephalitis infects mosquito when mosquito bites horse then infects bird when same infected mosquito bites a bird.
Mechanical vector - living organism that spreads virus by carrying it on its body from one bird to another i.e. poxvirus infections
Disinfectant - will destroy many disease causing organisms on the surface of inanimate objects. Some organisms and heat-resistant spores may be resistant.
Sterilant - will destroy all microbial organisms including heat resistant spores. Achieved by autoclaving, boiling or exposure to toxic chemicals.
Germicide - Kills a specific group of organisms when used as directed.
Sanitizer - reduces surface microorganisms to an acceptable level on inanimate objects.
Antiseptic - reduces surface microorganisms to an acceptable level on skin.
Active compound and trade names of common disinfectants.
ACTIVE COMPOUND PRODUCTS
Chlorinated compounds bleach, Clorox, Purex
Chlorine dioxide Dent-A-Gene
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.