Because the canine parvovirus is not enveloped in a delicate but necessary covering of fat the way the distemper virus is, canine parvovirus is especially hardy in the environment. It is readily carried on shoes or clothing to new areas (which accounts for its rapid worldwide spread shortly after its original appearance). It is able to overwinter freezing temperatures in the ground outdoors, plus many household disinfectants are not capable of killing it indoors.
Given that this is such a tough virus to destroy, many people want to know exactly what they must do to disinfect an area that has contained an infected dog or how long they must wait before safely introducing a new dog to a previously contaminated area.
Here is what we know about how contaminated an environment is likely to be:
- Infected dogs shed virus (in their stool) in gigantic amounts during the 7 to 10 days following exposure. Because such enormous amounts of virus are shed, there is a HUGE potential for environmental contamination when an infected dog has been there.
- It is important to realize that because the canine parvovirus is so hardy in the environment, it is considered ubiquitous. This means that no environment is free from this virus unless it is regularly disinfected.
A parvoviral infection can be picked up anywhere, although it is easier to pick up an infection in an area where an infected dog has been simply because of the larger amounts of virus in a contaminated area.
- Whether an individual dog gets infected or not depends on the number of viral particles the dog experiences, what kind of immune experience the dog has had with the virus before (vaccinated? previously infected? how much past exposure?), and how strong the individual dog is (stress factors, diet, etc.)
A typical/average infectious dose for an unvaccinated dog is 1000 viral particles. For some dogs far less is needed. For other dogs, far more is needed. An infected dog sheds 35 million viral particles (35,000 TIMES the typical infectious dose) per OUNCE of stool.
- Indoors, virus loses its infectivity within one month (assuming room temperature or higher is maintained); therefore, it should be safe to introduce a new puppy indoors one month after the active infection has ended.
- Freezing is completely protective to the virus. If the outdoors is contaminated and is frozen, you must wait for it to thaw out and warm up before safely introducing a new puppy.
- Shaded areas should be considered contaminated for seven months.
- Areas with good sunlight exposure should be considered contaminated for five months.
Of course, the above presupposes that no decontamination steps (other than waiting) have been taken. In most households, owners want to know how to disinfect their homes to create a safer environment for the other dogs there or to create a safe environment for a new or replacement puppy.
Here's what we know about disinfection:
- Despite the introduction of new cleaners with all sorts of claims, parvovirus remains virtually impossible to completely remove from an environment. The goal of decontamination is to reduce the number of viral particles to an acceptable level.
- The best and most effective disinfectant against viruses, including parvoviruses, is BLEACH. One part bleach is mixed with 30 parts water and is applied to bowls, floors, surfaces, toys, bedding, and anything contaminated that is colorfast or for which color changes are not important. At least 10 minutes of contact time with the bleach solution is needed to kill the virus. Steam cleaning is also able to kill the virus.
Bleach completely kills parvovirus.
- Disinfection becomes problematic for non-bleachable surfaces such as carpet or lawn. Outdoors, if good drainage is available, thorough watering down of the area may dilute any virus. For carpet, disinfection is about temperature. If the temperature on the floor and in the carpet is at least room temperature then the virus should die off in approximately one month.
When in doubt, make the new puppy an older individual (16 weeks or so) who has already completed her vaccination series.