Branson W. Ritchie, DVM, PhD
University of Georgia
College of Veterinary Medicine
Control of Viruses and Bacteria while Outside the Host
The goal of maintaining any bird in captivity, whether it is a single companion bird or a functional member of a large breeding aviary, is to assure that the bird remains in the best possible condition. Preventing infectious disease is of fundamental importance to this sustained health. Elsewhere in veterinary medicine, widespread uses of multivalent vaccines are used to create “herd immunity” and thereby reduce the unimpeded amplification of a virus through a respective population of hosts. If vaccine is not available for a particular virus, then stopping the host from being exposed can only prevent infections by this virus. Attempts to control the spread of viruses in the absence of vaccines require absolute vigilance in establishing and maintaining closed aviaries, correct use and interpretation of screening assays and assuring exceptional personal and aviary cleanliness. For many bacterial and fungal organisms, sanitation is currently the only way to reduce the accumulation and spread of these microbes within an aviary.
In general, the cleaner a bird’s environment, the healthier a bird is likely to be. However, one should be aware the excessive or improper use of even the safest of cleaners or disinfectants could create health hazards for the user, the environment or the animals that they are intended to protect. While some cleaning and disinfecting agents can be considered safer to use than others, it should be remembered that if a disinfectant is to be effective it must be capable of destroying life and thus. Safe is a relative term.
A virion that does not enter a bird, or come in contact with a target cell within the bird, will not replicate and will eventually become inactivated. Thus, complete cleaning to remove a virus from a host’s environment is an effective method for reducing virus spread. Disinfectants can be used in conjunction with thorough cleaning to inactivate any residual virions not removed by cleaning. Once an item has been cleaned, it should be rinsed before being placed in disinfectant solution. Thorough rinsing helps prevent the cleaning agent from reacting with, and possibly inactivating, the disinfectant. It should be noted that disinfectants couldn’t be used in lieu of cleaning to reduce the spread of infectious agents. Epornitics are frequently linked to veterinarians, pet retailers and aviculturists who become careless in routine cleaning and attempt to compensate with disinfectants or drugs.
The capacity of a disinfectant to destroy a virus varies with the type of virus, the type of disinfectant, the concentration of the disinfectant, the quantity of the virus and the material in which the virus is contained. For disinfection to occur there must be direct contact for the necessary time between effective disinfectant and the agent to be destroyed. Disinfectants may require minutes to hours of contact time to be effective. However, in many applications, disinfectants may come in contact with an agent for only seconds. For example, wiping an inanimate surface with a disinfectant-laden cloth provides a particularly short time of interaction between the disinfectant and contaminating viral particles. Soaking and object in a disinfectant provides longer contact time, but many disinfectants are corrosive and may damage metals or plastics.
Hospital personnel should choose a disinfectant based on which an item for disinfection can be cleaned, the practical amount of time the item can remain in contact with the disinfectant, the time and type (direct or indirect) of exposure that personnel or animals will have with the disinfectant, the disposal options available for the waste disinfectant and when known, the type of organism for which the disinfectant is intended. For personnel, animal and environmental health, it is best to thoroughly clean an object and then use the lowest concentration of the least aggressive disinfectant that will destroy residual target microbes.
Soaps and Detergents
Soaps and detergents reduce the attraction of greases and dirt to an object. In some cases, specific chemical disinfectants are combined with a soap or detergent. These agents are used to facilitate the cleaning and disinfecting of areas or objects that are contaminated with large quantities of blood, feces, food, or mucus.
Household detergents are excellent for cleaning bowls, enclosures, perches and nets that may be contaminated with food, excrement or secretions. As is the case with any chemical, surfaces and objects washed should be thoroughly rinsed and dried before coming in contact with the bird.
Sodium hypochlorite (bleach) is the most common chlorinated compound used as a disinfectant. Bleach is an extremely powerful oxidizer that, depending on concentration, can destroy many, if not most, microorganisms including bacteria, viruses, and chlamydia. In general, a 1:32 dilution (1/2-cup bleach per gallon water) is effective in inactivating many infectious agents.
Bleach solutions are rapidly inactivated by organic debris, extremes in pH, exposure to sunlight or evaporation. They require frequent mixing (every several hours) to maintain an active solution. Unfortunately, bleach solutions and the fumes they produce are toxic to living tissues. Irritation of mucous membranes including watery eyes, nasal discharge and sneezing may be noted in birds exposed to bleach fumes. Use of bleach in poorly ventilated areas can result in fatal tracheitis and pneumonia in birds.
Stabilized chlorine dioxide
Like bleach, stabilized chlorine dioxide is an extremely powerful oxidizer that can destroy many microorganisms including bacteria, viruses, fungi and protozoa. Some studies suggest that in many applications chlorine dioxide may be a superior disinfectant to sodium hypochlorite. At working dilutions, stabilized chlorine dioxide is considered of low toxicity to humans and animals. Solutions containing stabilized chlorine dioxide and the fumes it produces are toxic to living tissue, including skin, eyes, and lungs. Organic debris and exposure to sunlight rapidly inactivate it. It evaporates quickly and requires frequent mixing to maintain active solution.
Chlorhexadine-containing compounds are frequently used as disinfectants and for wound cleaning. They are considered relatively nontoxic and noncorrosive, and safe for use around birds. They have good activity against many bacteria, yeast (particularly Candida) and some enveloped viruses. It has limited use against some bacteria, spores produced by mycobacteria and nonenveloped viruses. In general, it should not be considered viracidal. It is ineffective in the presence of organic debris and has limited stability. It must be made fresh at least once per day.
Glutaraldehydes rapidly inactivate many microbial agents including bacteria (including mycobacteria), many viruses, and chlamydia. They are effective against viruses even in the presence of organic debris and are stable as a working solution from 2 weeks up to 1 month. However, they are infrequently used as general-purpose disinfectants because they cause irritation to eyes, respiratory tract and skin. The product information provided by the manufacturer will list the corrosive properties of a particular glutaraldehyde disinfectant.
Most commercially available iodine-containing disinfectants are iodophors (iodines mixed with detergents) or “tamed” iodines. Iodine-containing disinfectants generally produce limited toxic vapors, are available mixed with detergents to both clean and disinfect, and are effective for many bacteria, some viruses, and fungi. However, they can be expensive, toxic if ingested, cause drying and cracking of skin, are not effective against all strains of Pseudomonas and are not effective against some viruses.
Sodium orthophenol is the active ingredient in most phenol-containing disinfectants. Phenols can inactivate many bacteria (including Pseudomonas and mycobacteria), fungi and some viruses. They vary in activity based on the presence of organic matter and the temperature, concentration, and pH of the disinfectant solution. They are inexpensive and easy to rinse. They are toxic to many tissues and may be particularly toxic to cats and reptiles.
Quaternary ammonium compounds
Adding organic compounds to ammonia produces these. They function as a detergent. They are inexpensive at working dilution, are relatively nontoxic, and inactivate many types of bacteria, some viruses and chlamydia.
Organic debris and contact with soaps may inactivate these disinfectants. They are not considered effective for spores, mycobacteria or fungi, and may have reduced efficacy against many nonenveloped viruses and Pseudomonas. They are difficult to rinse and may leave a slimy residue. Ingestion, and possibly inhalation, can cause respiratory paralysis and death. These agents are recommended for objects that will not come in direct contact with birds.
Seventy- percent ethyl alcohol inactivates many bacteria and viruses when contact time approaches 20 minutes. Parvoviruses and some enteroviruses are resistant to inactivation by it. Alcohols may dissolve plastics, rubbers and glues.
Formalin and formaldehyde are extremely dangerous, toxic compounds that should not be used as disinfectant. Formaldehyde will inactivate most viruses, but require up to one hour of contact time. It is very irritating to mucous membranes and should be thought of as a powerful carcinogen.