In our experience, covering a large number of rabbits, we have found that the condition known as snuffles falls into different types, the acute and fatal, symptomatic of some underlying infection such as septicemia or pneumonia; and the intermittent, and the chronic. The intermittent and the chronic types considered in this paper are those most commonly present in laboratory stocks.
Our observations point to a widespread prevalence of the disease among rabbits kept under laboratory conditions. This statement might be questioned had the stock we examined been derived from a single source. But the animals were procured from dealers who obtain rabbits in New York, Pennsylvania, Ohio, and as far west as Michigan. The same dealers supply the stock of most of the laboratories in the East. Hence we believe that this disease is found generally prevalent in this part of the country.
We have demonstrated that practically all rabbits with intermittent or chronic snuffles reveal old chronic inflammatory processes of the upper nasal passages associated with thick inspissated pus in one or more sinuses. Moreover, these conditions are also present in about one-tenth of carefully selected, supposedly normal stock rabbits and in one-fourth of a casually selected group, free, during long periods of observation, from any of the symptoms of active snuffles. The peculiar anatomy of the animal's nose which predisposes to the ready formation of enclosed pockets of purulent material may be the cause for the chronicity of upper nasal affections. When the animal's resistance is lowered, the long standing, inflammatory process can flare up into an acute exacerbation, and then show itself as typical snuffles. Various means can effect this: chilling the body, the intravenous injection of foreign proteins such as killed vaccines, or the intranasal inoculation of microorganisms of divers species. Bacteriological examination of the nasal secretions or sinus pus from animals with snuffles and those apparently free of the disease shows the presence in both cases of various microorganisms—Staphylococcus albus, Bacillus bronchisepticus, Bacillus lepisepticus, and others, in order of frequency. Different bacteria may be found in different sinuses in the same animal.
A lack of recognition of these factors has led, we believe, to erroneous conclusions with regard to the inciting agent of the disease. Bacillus lepisepticus and Bacillus bronchisepticus have been declared the incitants of snuffles. Our experiments, in which an attempt was made to induce the disease de novo with these microorganisms, failed. In all cases (with a single exception) in which snuffles followed, there was evidence of an infection which, judging from the condition of the nasal passages and from the cells in the exudates or secretions, had existed before the inoculations were made. Furthermore, the microorganisms recovered from the nasal passages had as a rule no relationship to those in the material inoculated. We attempted also to produce snuffles by inoculating intranasally the unfiltered and filtered suspensions of the ground nasal mucous membranes from typical cases of the disease occurring in stock rabbits. These attempts also failed.
It appears, therefore, that intermittent and chronic snuffles, as it attacks rabbits kept under laboratory conditions, is, as a rule, a sign of an underlying condition—an exacerbation of a chronic inflammatory process in the upper nasal passages, associated with a purulent paranasal sinusitis. The microorganisms recovered are to be looked upon as tending to maintain such conditions but we have still been unable to reproduce typical snuffles with them, employing supposedly normal stock rabbits for the purpose. One may presume that some agent, as yet undetermined, diminishes the resistance of the nasal mucosa, allowing different bacteria to invade and multiply there, thus causing disturbance. In this respect perhaps an analogous condition exists to that which prevails in epidemic influenza and common colds in man.
It is obvious that further work along these lines cannot be properly carried out with rabbits whose antecedent history is unknown. The problem of the incitant of snuffles can best be studied in a breeding stock which is well controlled, one affording an opportunity to observe the animals from an early period of life.