CHAPTER XXIII.
PATHOGENIC BACTERIA OUTSIDE THE BODY.

Pathogenic bacteria may exist outside the body of the host under a variety of conditions as follows:

  1. I. In or on inanimate objects or material.
    1. (a) As true saprophytes.
    2. (b) As facultative saprophytes.
    3. (c) Though obligate parasites, they exist in a latent state.
  2. II. In or on other animals, or products from them:
    1. A. Susceptible to the disease.
      1. (a) Sick themselves. (As far as human beings are concerned these are mainly:
        1. 1. Other human beings for most diseases.
        2. 2. Rats for plague.
        3. 3. Dogs for rabies.
        4. 4. Horses for glanders.
        5. 5. Cattle, swine, parrots for tuberculosis).
      2. (b) Recovered from illness.
      3. (c) Never sick but “carriers.”
    2. B. Not susceptible.
      1. (d) Accidental carriers.
      2. (e) Serving as necessary intermediate hosts for certain stages of the parasite—this applies to protozoal diseases only, as yet.

I.

(a) The bacilli of tetanus, malignant edema and the organisms of “gas gangrene” are widely distributed. There is no evidence that their entrance into the body is at all necessary for the continuation of their life processes, or that one case of either of these diseases ever has any connection with any other case; they are true saprophytes. Manifestly it would be futile to attempt to prevent or eradicate such diseases by attacking the organism in its natural habitat. Clostridium botulinum, which causes a type of food poisoning in man, does not even multiply in the body, but the disease symptoms are due to a soluble toxin which is produced during its growth outside the body.

(b) Organisms like the bacterium of anthrax and the bacillus of black-leg from their local occurrence seem to be distributed from animals infected, though capable of a saprophytic existence outside the body for years. These can no more be attacked during their saprophytic existence than those just mentioned. Doubtless in warm seasons of the year and in the tropics other organisms pathogenic to animals may live and multiply in water or in damp soil where conditions are favorable, just as the cholera organism in India, and occasionally the typhoid bacillus in temperate climates do.

(c) Most pathogenic organisms, however, when they are thrown off from the bodies of animals, remain quiescent, do not multiply, in fact always tend to die out from lack of all that is implied in a “favorable environment,” food, moisture, temperature, light, etc. Disinfection is sometimes effective in this class of diseases in preventing new cases.

II. A.

(a) The most common infectious diseases of animals are transmitted more or less directly from other animals of the same species. Human beings get nearly all their diseases from other human beings who are sick; horses, from other horses; cattle, from other cattle; swine, from swine, etc. Occasionally transmission from one species to another occurs. Tuberculosis of swine most frequently results from feeding them milk of tuberculous cattle or from their eating the droppings of such cattle. Human beings occasionally contract anthrax from wool, hair and hides of animals dead of the disease or from postmortems on such animals; glanders from horses; tuberculosis (in children) from tuberculous milk; bubonic plague from rats; rabies practically always from the bites of dogs and other rabid animals, etc. The mode of limiting this class of diseases is evidently to isolate the sick, disinfect their discharges and their immediate surroundings, sterilize such products as must be handled or used, kill lower animals that are dangerous, and disinfect, bury properly, or destroy their carcasses.

Classes of the sick that are especially dangerous for the spread of disease are the mild cases and the undetected cases. These individuals do not come under observation and hence not under control.