Disease-free rats?

By | April 13, 2018

This article was written in response to a growing interest in specially bred pathogen-free laboratory rats as pets. As SPF rats have no natural immunity, I feel strongly that they do not make ideal pets. This article first appeared in the now defunct rat-related webzine Squeak! in 1998 (the link is to the archived version courtesy of www.archive.org).
Most rat owners at some point have wished for the ultimate — the disease free rat that could live the longest possible natural life. As virtually all rats are infected with the mycoplasma organism, and many die of related respiratory disease, we often assume that a rat free from such infections would be a desirable goal. In this paper I intend to explain why I feel there is no advantage (and many disadvantages) to eradicating respiratory disease from the pet rat population.Disease-free rats?

In more recent years, fanciers and pet owners have become aware of SPF (Specific Pathogen Free) rats bred in laboratory conditions to be free from specific diseases. One misconception is that all (or even most) rats of laboratory origin are free from respiratory disease. This is not the case: SPF rats are only used in laboratories when the interference of respiratory illness could influence the results of an experiment. So that respiratory disease is not transmitted from mother to offspring, babies are delivered by caesarean section and hand-reared by humans (the mother is routinely destroyed). Such rats have no immunity to common respiratory disease as they have never come into contact with them, and can only survive in strictly maintained sterile conditions. Were such a rat to meet another of his species from the pet or wild population, he would very likely be killed by minor infections that our rats take for granted and have immunity against.

When Europeans first came to North America, Australia and Africa they carried with them transmittable diseases that the indigenous populations of those countries had no immune defences against. Millions of aboriginal peoples died from what in European terms were minor infections — colds and ‘flu. European immune systems had had hundreds if not thousands of years to develop immunity to these diseases, whereas the aboriginal peoples’ immune systems, having never before encountered these pathogens, had no defence against infection.

The case with rats and respiratory disease is similar: as virtually all rats (in fact all pet, wild and lab except for those SPF lab specimens delivered by C-section) carry respiratory infections in much the same way as we carry the common cold. These infections are airborne and there is no way for a pet rat to avoid contact with them. Even if every rat in the pet population was SPF we would still have the worry of infection through wild rats, who, because the pertinent respiratory disease causing pathogens are airborne (aka aerosol infections), a wild rat passing beneath your floorboards, or past an open window could, at least in theory, infect a pet rat. Many of these respiratory diseases are also zoonotic — transferable between species — notably transferable from mice and other small mammals. Rather than breed rats that are not infected by a specific pathogen, and having to keep them in isolation from other non-SPF rats, breeders should focus on only breeding from rats which exhibit no symptoms of respiratory disease, and show no signs of other illness throughout their lives.

A reputable breeder will only breed from stock that is thoroughly robust and entirely healthy. This has its rewards. Angela Horn and myself have had a line of pure-bred English Badger rats that, through years of only breeding from only the soundest stock, appear to have developed a strong immunity to respiratory disease. No rats from this line have shown symptoms of respiratory disease for several generations, and those on whom Post-mortems have been done have showed no sign of lung tissue scarring or other damage associated with respiratory disease. This type of selection and the bother (and cost) of post-mortem verification of the ability to fight off respiratory infection, belie the myth that Fancy rat breeders are only concerned with coat and colour. For some of us health and temperament come first!

The robust immune system of the pure-bred English Badger line can be carried into other lines with some success, but the two “badger outcross” lines that I have do not yet show the same across the board ability to fight off infection, but are still better than many lines. There is always room for improvement, and one disease resistant line is only a start.

It is probably a red herring to assume that the average lab rat is in any way healthier than the average fancy rat. Other than specific experiments for longevity, the lifespan of lab rats is considered of little importance except in relative terms (i.e. rats fed “X” lived 12 months, while rats from the same litter fed “Y” lived 13 months). As virtually all rats are destroyed at the end of an experiment — often at only a few months of age, little care is put into deliberately breeding long-lived or particularly healthy lab rats, although some specific experiments for longevity are documented.

Lab rats are, sadly, a product designed to serve a purpose. As long as they live long enough to serve this purpose both suppliers and labs are happy. As so many are destroyed far before the end of their natural life, there is very little reliable evidence about the “average” lab rat lifespan. Laboratory longevity experiments are not particularly useful for pet owners, as the conditions (i.e. near starvation and no use of energy) the animals are kept in cannot translate into a normal pet environment. By all accounts lab rats can make great pets, and may be more robust than a pet or fancy rat from a poor background, but on a par with those bred by conscientious breeders or pet shops.


Every pet rat lover should keep in main point to keep your rat healthy and happy is rat cage bedding.

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