Distemper is a contagious, inoculable fever, due to a specific microbe (the cocco-bacillus, or pasteurella of Lignieres), and is similar, if not identical, to that causing distemper in the dog. Krajewsky, Laosson, Lignieres, and others have experimentally demonstrated its. identity, but I have never observed the cat naturally giving the dog distemper, nor vice versa, and I believe this is the experience of most veterinary surgeons in this country.

The microbe of distemper - which belongs to the same class of micro-organisms, the pasteurella, that causes influenza in the horse, fowl cholera, swine-fever, guineapig distemper, etc. - is generally found in the blood, which it alters to such a degree as to make so profound an impression on the system as to diminish its natural resistance to the ordinary germs, which become, in consequence, increased in virulence, and cause the various phenomena by which we know the disease. It is difficult to detect in the body after about a week.

The disease varies in severity according to the degree of virulence of the microbe. If this is very virulent, it causes a very acute or septic disease, as is observed in the typhus or gastro-enteric outbreak, which kills off a large number of animals within a few days or even hours. If it is of a milder strength, we get the subacute form with localisations, such as we usually see in distemper. There is also a chronic form, which lasts a long time, and which tries the patience of the owner as well as the vitality of the sufferer. Finally, a chronic wasting or cachectic form is sometimes observed ; it resembles the " going light " in birds and other animals, and may be mistaken for starvation, which it simulates very much.

The microbe may exist in a healthy cat's body for weeks without causing it any disturbance until, perhaps, the animal catches cold, or is depressed in some other manner. However, an apparently healthy animal with this microbe in it may be infective for other cats.

Period Of Incubation

This varies according to the degree of virulency of the microbe and the state of the cat's system and the surroundings in which it is kept. A very virulent infection has a much shorter period of incubation than a mild infection. Whereas the former may cause distemper in from two to five days, the latter takes from one to three weeks. It seems doubtful whether the specific microbe causes the symptoms we usually see in distemper, or if these are due to a secondary infection resulting from the invasion of the normal microbes of the body, which have become virulent, and prey upon their hosts.

Duration Of The Disease

This, like the period of incubation, varies also according to the degree of virulence of the virus. A very virulent virus kills in a few days or even hours, or the animal recovers very quickly. It is not so with a virus of a milder degree of virulence, which may cause symptoms that take from one to five or six weeks to disappear, if the animal recover. In other cases the disease shows itself in so mild a form that it appears like an ordinary catarrh, and recovery is established within a few days.

In a few instances death takes place suddenly before any premonitory symptoms have had time to develop.

The principal sources of propagation of the infection are cat shows, catteries (especially those belonging to people who exhibit), homes for lost and stray cats, and institutions that take in these animals as boarders. The cat dealer's shop is not free from blame - many newly purchased kittens develop distemper a few days after purchase, contracted, no doubt, at the dealer's. Many cases have been traced to the cattery where the female has been sent to stud. Hampers, cages, and persons coming from infected catteries are so many media of contagion. Even if a cat has apparently recovered from the disease, it may still give off infection and contaminate other cats for a variable but uncertain period.

Although the disease may be seen at all times of the year, it is most prevalent during spring and autumn, especially if the weather is changeable and wet.

Moisture of the atmosphere favours the increase of distemper. Wet, following very dry weather, continuous dampness and rain, all predispose an animal to the disease. Where catteries or homes for lost and strays are continuously being washed out and not properly dried, especially in damp weather, before the cats are allowed into the rooms, distemper is very prevalent.

Where too many cats are crowded into a given space, especially if the place is badly lighted and not very well ventilated, this is favourable for the contamination of the inmates.

The mortality varies according to the breed of the animal, its surroundings, and the degree of virulence of the infection. Seasons and periods have also some bearing on it. Common-bred cats allowed to roam out in the open at their will are more likely to recover from the disease, but if confined to cages or in catteries, or in the house, the mortality is quite twenty-five per cent. The long-haired cats are less resistant against it, and as many as fifty percent, die. In the Siamese breed of cats, the fatality is as high as ninety out of every hundred. The younger the animals, the greater the death-rate ; yet, on the other hand, if old animals are very fat or anaemic from want of fresh air and exercise, the mortality is just as high.

Many cats are resistant at one time against the infection, others have it in a mild form, and yet others have it severely; but this does not always prevent them from having it again at some future period. My experience is that a cat may frequently have a recurrence of distemper at least two or three times, and then succumb to it.