28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

Concepts and Importance of Disinfection

Mary B. Brown¹, Paul A. Klein² and Lori D. Wendland¹
Departments of Pathobiology¹ & Pathology, Immunology and Laboratory Medicine² University of Florida, Gainesville, Florida

Little is known about infectious diseases present within wild populations or the long-term impact of these diseases. This creates a major dilemma for scientists, wildlife biologists, conservationists, and public policy makers when trying to manage and ensure the survival of wildlife species. This is even more critical when the animal concerned is a keystone species such as the desert tortoise, which is critical to the health of its ecosystem and the survival of many additional species. As we seek to evaluate and monitor populations and individuals, we have come to realize that we may also present a risk in facilitation or potentiation of spread of disease in the very animals we hope to preserve. For the desert tortoise, the most widely studied disease is respiratory mycoplasmosis. However, this is only one infectious agent and other agents, particularly viruses, are even more likely to be spread unintentionally if appropriate disinfection measures are not used. It is also important to note that many of the newly recognized diseases affecting humans are caused by zoonotic agents with wildlife reservoirs or have resulted from large-scale ecological changes that may increase human exposure to insect vectors as well as to animal and environmental sources of disease. Thus, failure to use appropriate field disinfection techniques might also represent a risk to humans.

This talk will highlight some of the common concepts of disinfection. Disinfection refers to the inactivation of most pathogens (but not necessarily bacterial endospores) on inanimate objects. Factors which influence successful disinfection include number of microbes present, type of microbes, length of exposure to the chemical agent, concentration of the chemical, amount of organic matter present, type of material to be disinfected, and temperature. An antiseptic is used on or in a living tissue to inhibit or destroy microbes. Although an agent may be used as both a disinfectant and antiseptic there may be differences in formulation or concentrations, so care should be taken not to use disinfectants on living tissue unless a use for antisepsis is provided by the manufacturer.

A critical concern is contaminated fomites such as field equipment that might contribute to the spread of the organism, especially when mucous and organic contamination is present and proper disinfection techniques are not used. A fomite is an inanimate object that may be contaminated with infectious agents and serve in their transmission; for example field calipers, trapping or holding containers. Mycoplasmas lack a cell wall and are susceptible to desiccation; therefore, they do not normally persist in the natural environment for any appreciable length of time. However, other bacteria and many viruses, including herpes viruses, are extremely hardy and survive well in the environment. It is important to remember that disinfection is not just for mycoplasmas, but also for viruses, bacteria, fungi, and parasites. It is imperative that the disinfectant have the broadest spectrum of activity.

A number of compounds are available for disinfection. However, most have a limited spectrum of activity and many are poor against nonenveloped viruses. The agents with the broadest overall spectrum of activity are chlorine or bleach. Classes of disinfectants with poor to no activity against certain viruses include phenols (Cresl-400, Environ, Laro, Amphyl, Lysol), chlorhexidines (Vikron S), alcohol, quarternary ammonia compounds (Roccal, Germex, HiLethol, Sanofec, Zephiran). These are NOT effective against certain viruses and should not be used. Most hand sanitizers are alcohol based and therefore are not effective against viruses.

By far, the best overall choice of disinfectant is bleach. In fact, for maximum effectiveness in cleaning blood spills with potential infectious agents like HIV, CDC recommend a 1:10 dilution of 5.25% bleach, resulting in 5,000 ppm available Cl as the disinfectant of choice. For most microbes, 100-200 ppm is effective. For fie1d use, a 1:30 dilution of bleach should give 1667 ppm and be sufficient. There are a few caveats that need to be noted about bleach. First not all bleaches are 5.25% sodium hypochlorite, so check the label. Also, high organic load under field conditions can cause inactivation of bleach solutions. Therefore, instruments and containers should have dirt and organic material rinsed off and then sprayed with bleach solution for maximum effectiveness. Light inactivates bleach so it should be stored in opaque containers or covered. In addition, even opening of stock bleach bottle with normal use over 30d period can decrease the activity by 50%. Be sure to make fresh working solutions frequently (once a week or every 10 days). Finally, bleach can be corrosive to equipment. Despite this, it is still the most effective disinfectant. If alternate disinfectants are used, one must remember that a low organic load and a minimum contact time of 30 minutes are required. Although oxidizing agents (Novalsan) and aldehydes (Wavicide) have good activity against viruses, both require longer contact times (10 min to 10 hrs) than bleach. Wavicide is more effective if organic matter debris is present and could be used for example to soak drill bits, BUT contact time required for effective disinfection can be as long as 10 hours! Novalsan requires less contact time but is not effective when organic debris is present.

In summary, strict disinfection protocols should be followed to prevent spread of known and potentially unknown agents. Bleach is the most effective disinfectant, with a broad spectrum of activity. It is also highly cost effective. However, organic load should be minimized, field solutions should be made frequently and stored in opaque containers, and the active concentration of bleach solution used for disinfection should be 1667 ppm (1:30 dilution of 5.25% sodium hypochlorite).

More detailed information can be found at University of Nebraska Cooperative Extension website, http://www.ianr.unl.edu/pubs/animaldisease/g1410.htm or in Block. 2001. Disinfection, Sterilization and Preservation. Philadelphia: Lippincott Williams & Wilkins. p139.