Disinfection
by Emilie Evenson 

Hygiene is concerned with the maintenance of health.  The aim is to reduce the numbers of organisms that could cause disease, thereby providing a healthy environment for both animals and people.  Methods to eradicate disease-causing microorganisms are sterilization, chemical disinfection, physical disinfection and heat disinfection.

Sterilization is a process which results in the complete destruction of all living organisms.  Sterility is an absolute state: an object is either sterile or it is not.  Methods to sterilize items include autoclaving, gamma radiation, using powerful acids, and incinerating.  Sterilization is almost impossible to achieve in the non-institution setting, so we are stuck with disinfection.

Disinfection removes the causes of infectious disease.  It does not destroy all forms of pathogenic organisms, but will eradicate most.  The intention of disinfection is to reduce the numbers of organisms to levels where there are too few to cause disease.

To achieve hygienic conditions appropriate cleaning regimes must be applied in an appropriate way.  Inadequate attention to detail or the use of unsuitable cleaning agents will result in the spread of agents believed to be removed or destroyed.  Cleaning regimes have three major objectives: to remove, destroy or contain contaminated objects, to provide clean conditions for the animals and to provide conditions acceptable to people.  All cleaning processes involve moving dirt from one place to another.  The goal is to move the filth from inside to outside, via trash or drain.  Combinations of methods are used to clean.  Factors involved in the choice of methods are the desired state of cleanliness, such as sterile, disinfected or merely free from obvious dirt, properties of the surface being cleaned, like absorbency and resistance to scratching, availability of services, like water, drains and vacuum, and properties of chemicals used, such as toxicity, staining, corrosiveness and rinsing ability.

How often cages are changed is determined by many factors which include: cage size and design, where the cage is located, the numbers of rats in the cage, the individual behavior of the rats in the cage, the type of diet used and its presentation, the amount and type of bedding used, the likelihood of the presence of pests and parasites, and the effort involved in cleaning – both our own effort and the stress affect upon the rats.  The cleaning interval selected in a compromise between the factors listed.  For instance, it is important to provide a clean environment for their health, but changing cages too frequently disturbs them and takes up a lot of our time and money.

Physical disinfection can be done by hand, but it is difficult to do at home.  The best way available is to simply ‘clean cages.’  This involves removing the rats, dirty bedding, cleaning the materials and then putting in clean bedding.  Emptying bedding causes a release of allergens and pathogens into the air.  This is the time to avoid if you’re allergic to any part of owning rats.  Using vacuum cleaners with a high efficiency particulate air filter (HEPA filter) can reduce the problem.  If your reaction is very bad and you can handle the noise, run the vacuum while dumping out the bedding.  If you don’t react very badly, using the vacuum to clean up the room after you’re done dumping can make a big difference too.

Scrub the supplies with warm water, while taking off any organic material like feces, traces of food, or dirty bedding.  If you’d like, adding soap might help, especially if you’ve decided not to pursue an additional type of disinfectant.

This physical cleaning needs to be done even if you’re using another method to disinfect afterwards; most chemical disinfectants are inactivated by organic matter, and using heat can permanently fix some things to the supplies.  Although the physical removal of dirt will carry away vast numbers of micro-organisms and allergens, other more effective methods of destroying pathogens must be used regularly.  In order to work effectively the disinfection agent must come in contact with the organism it is intended to kill.  Any dirt, organic matter or air that prevents this contact could allow organisms to survive the treatment, so cleaning must precede disinfection.

Disinfection can be achieved by the application of heat.  The principle heating method available to us is immersion in boiling water.  This is often impractical for items like softer plastics, cages and other large items.

Routine chemical disinfection is often the easiest method to disinfect your rat room.  It is important to be aware to the limitations of disinfectants though; they should only be used in the way the manufacturers advise.  They must be freshly made up when used and excess disinfectant should be discarded.  All utensils used to apply the disinfectant should be cleaned after use with another type of disinfectant.  This prevents the establishment of resistant strains of micro-organisms.

Microorganisms have different levels of resistance to chemical disinfection.  Bacterial spores are the most difficult to destroy.  Spores are formed by some groups of bacteria when their environment becomes hostile; they are very resilient and can exist in spore form for very long periods.  Pinworm eggs are also difficult to remove, but we shouldn’t be in contact with those in our normal ratteries.  In descending order of resistance to chemical germicides, pathogens rank: bacterial spores, mycobateria, nonenveloped viruses like parvo and polio, rhinovirus, fungi - think ringworm, vegetative bacteria such as Salmonella or Staph, and enveloped viruses like Corona and HIV.  Enveloped viruses are those using and essentially surrounded by fat.  A disinfectant at a certain level of effectiveness should inactivate or kill all organisms at that level and on the lower levels of resistance.  If you found a disinfectant that would eliminate parvo, it would also clear rhino, fungi, bacteria and enveloped viruses.

In the US, the EPA registers commercially manufactured disinfectants.  If a product does not have an EPA registration number, then it should not be used for disinfection in an animal-care area.  Claims for disinfectants that are unregistered with the EPA may not be substantiated.  The EPA and other agencies classify chemical disinfectants by level.  A high-level disinfectant should eradicate all microbes except for bacterial spores.  An intermediate- level disinfectant should eradicate enveloped viruses and all the less-resistant microbes.  A low-level disinfectant must only kill three species of bacteria: Salmonella choleraesius, Staphlococcus aureus, and Pseudomonas aeruginosa.  There is also a category below that of low-level disinfectant called “hospital disinfectants”.  These must only kill S. coleraesius and S. aureus.

The properties of some of the major groups of disinfectants are given below.

Phenols and derivatives (e.g. Lysol, PineSol)

These agents are bactericidal, fungicidal and destroy enveloped viruses but they have no effect on bacterial spores.  Their activity is reduced by organic material and oils.  They are more active in an acid pH and also when in a hot solution.  They are stable when diluted according to manufacturer’s directions and have fair rinsing properties.  Phenolic compounds are toxic, extremely corrosive and have an unpleasant smell.  These products also cause human health isssues, from skin depigmentation to cancer.  Animals like rats and mice (along with cats and dogs) are particularly sensitive to the smell.  Phenols are used by applying these agents to surfaces following the removal of gross soiling.

Alcohols (e.g. alcohol)

These are bactericidal, fungicidal and virucidal but have no effect on bacterial spores.  They are easily inactivated by organic material and oil.  Normal use dilution is not stable due to vaporization.  (Absolute alcohol has no disinfectant properties.)  Contact time for some products can range up to several hours.  Alcohols can also damage rubber and plastic components. 

Iodophors (e.g. Provodine iodine, Betadine)

Iodophors are bactericidal, sporicidal, fungicidal and virucidal.  Activity is enhanced by an acid pH and heat.  They have low toxicity but have poor rising properties.  They are stable at use dilution of 1-2%, but is unstable with light exposure.  Iodine is a poor cleaner, requiring a use of another chemical to clean the surface and can permanently stain surfaces if not used properly. 

Chlorine (e.g. bleach)

Sodium hypochlorite is the active ingredient in bleach.  If used very carefully, it is very effective and inexpensive.  It is bactericidal, sporicidal, fungicidal and virucial.  Activity is reduced by a factor of 10 for every unit of pH above 7.  Increasing temperature increases activity.  Chlorine has low toxicity but is highly corrosive, especially on metals, concrete and clothing.  Compounds have good rinsing properties but are not very stable at the use dilution of 1-5%.  An organic soil load reduces effectiveness.  Bleach reacts with acids releasing highly toxic chlorine gas.  It also reacts with feces to produce potentially carcinogenic compounds.  One such compound, trihalomethane, can be released as a toxic gas.  Concerns about the efficacy of sodium hypochlorite have involved the percentage of active chlorine required to provide antimicrobial properties.  Prepared bleach solutions rapidly lose potency under regular conditions.  Sodium hypochlorite is highly reactive and degrades rather quickly.  Thus, bleach rapidly loses its effectiveness as sodium hypochlorite degrades.  A study done by the Quality Assurance Laboratory of Pharmacal Research Laboratories showed that the percentage of active sodium hypochlorite went from 18% at manufacture to 14% at 10 days after manufacture to 11% at 70 days after manufacture.  NOTE: Only a few manufacturers of household bleach have EPA-registered numbers for their products.  The other companies are making a product that will clean and brighten your clothes, but may not disinfect your rat room.  In fact, their percentage of active ingredients in these products may be too low for sanitizing.

Quaternary ammonium compounds (e.g. Roccal-D)

These are selectively bactericidal and bacteriostatic.  The newer generation, containing blends of ADBAC, will kill some nonenveloped viruses as well as enveloped viruses.  Some compounds are also fungicidal and virucidal.  Activity is reduced and even totally destroyed by detergents, hard water, rubber and plastics, oil and some metals.  It’s enhanced by an alkaline pH and heat.  Dilutions are generally stable.  They have low toxicity and poor rinsing properties.  Such compounds contain detergents which can remove fat from the skin.  Activity varies considerably between types.  They are relatively cost effective, easy to use and safer for animals and people than other disinfectants.

Peroxygen compounds:

The search for good disinfectants may lead to peroxygen products such as hydrogen peroxide.  Hydrogen peroxide is a sterilant at appropriate concentrations and use.  It is environmentally friendly, as disinfectants go, and it relatively low in toxicity.  Many products leave no residuals and have excellent germicidal activities with low contact times.

Amphoterics:

Amphterics are fungicidal and selectively bactericidal.  Activity is enhanced by heat.  Rinsing properties are poor, but the active residue left behind can be advantageous in certain situations.  Dilutions are generally stable.  There is low toxicity but the detergency properties can cause removal of fat from the skin.