PLAGUE (BUBONIC AND PNEUMONIC) i. Infective Agent.—Bacterium pestis.
2. Source of Infection.—Typical and atypical plague (acute and chronic) in rats and other rodents, including the native ground squirrels in California. In pneumonic plague man serves as the source of infection. The disease normally, how ever, is one of rodents.
3. Portal of Exit.—The blood of infected rats abstracted by fleas, or the sputum of pneumonic plague patients.
4. Route of Transmission.—In bubonic and septicemic plague the bacillus is conveyed from rat to man or from rat to rat or other rodent, by the agency of either the tropical rat flea (Loemopsylla clteopis) or the temperate zone rat flea (Cerato plzyllas fasciatus) (Fig. 84). Their action is purely mechanical. The plague bacilli produce an intestinal obstruction in the flea, so that an infected flea when attempting to feed regurgi tates plague bacilli from his stomach into the punctured wound. Bed bugs (Cimex lectularius) may also transmit the bacilli.
In pneumonic plague the bacilli are transferred from man to man by direct or indirect contact.
5. Portal of Entrance.—The fleas may introduce the bacilli into the subcutaneous tissues of any part of the body, usually into the lower extremities.
In pneumonic infection the bacilli are introduced into the body either through the mouth, nose or conjunctiva.
6. Incubation Period.—Commonly from three to seven days, though sometimes prolonged to eight or even fourteen days.
7. Period of Communicability.—(a) Man: Until convales cence is well established, period undetermined.
(b) Rat: In chronic or latent cases the infectivity may be prolonged, but the period is uncertain.
8. Methods of Control. The Infected Person.—(a) Diagno sis: Clinical manifestations confirmed by bacteriological ex amination of blood, glandular exudate or sputum.
(b) Isolation: 1. Bubonic plague: Hospitalize if possible, place patient in a vermin free, screened room.
2. Pneumonic plague: Rigid isolation must be employed and attendants must exercise great care for their own protection. Masks should be worn.
(c) immunization: Yersin produced a serum by the in jection of horses at first with a plague vaccine and later com pleting the immunization by the use of living cultures. The therapeutic value of the serum is appreciable. Active immu nization with Haffkine's vaccine apparently confers protection. The Indian experience appears to indicate that the likelihood of subsequent infection after its use is reduced four fifths, while among the proportion who do contract infection, the chances of recovery are much increased. It should be administered to those persons whose activities favor their exposure.
(d) Quarantine: Of contacts for seven days.
(e) Concurrent Disinfection: Of all discharges and articles soiled therewith.
(f) Terminal Disinfection: Thorough cleaning followed by thorough disinfection.
General Illeasures.—(a) Extermination of rats and vermin within the infected area, paying especial attention to the brown or Norway rat by employing: i. Fumigation with HCN, SO2, CO or CS2.
2. Trapping.
3. Poisoned bait.
(b) Rat exclusion.
i. By rat proofing homes, outhouses, and business buildings (Figs. 86, 87, 88, 89).
2. By removing accumulations of refuse in which rats can harbor, and of garbage upon which they can feed.
3. By exterminating rats on ships.
4. By preventing rats on ships from coming ashore, or those on shore from entering ships (Fig. 90). The marine migrations of rats, accomplished by the aid of shipping, have in the last twenty five years distributed plague over the entire world.
(c) Flea destruction by fumigation. This should be em ployed in infected foci.
(d) Delimitation of an infected area: General rat trapping operations should be carried out all over an infected area. All rats caught and all found dead should be examined for evi deuce of plague infection. The locality where each infected rat is found should be regarded as a focus of infection. Since permanent measures of rat exclusion and eradication are pensive and procede slowly, it is not always practicable, in the face of existing plague, to enforce these generally with the hope of eradicating the disease. A more practicable method is to confine the earliest operations, at any rate, to the infected foci until the disease is brought under control. The method veloped by Heiser in Manila for this purpose is as follows: Five radiating equidistant lines are drawn from each point where a plague rat is found. Starting at the center, rat catch ing operations are carried out along each. The most distant points along each line at which plague rats are found are con nected by lines. Thus the circumference of the infected area is outlined (See Fig. goa). As a rule its radius is seldom more than a few blocks from the original focus. Rat catching is then be gun along the periphery and proceeds toward the center, after which rat proofing operations are begun at the periphery and proceeds centrally. Thus the rodents in each focus are ex terminated and the place made uninhabitable for them. This method has not been employed in combatting plague in the United States.
(e) In California considerable effort is being made to eradi cate the ground squirrels in infected rural areas by use of poi soned grain, trapping, and asphyxiation of the squirrels in their burrows by carbon bisulphide.
(f) House to house inspection for the detection of unreported cases may be necessary. All dying during the epidemic should be autopsied.
(g) Cremation or burial in quick lime is advisable.