DOMESTIC RATS, FLEAS and NATIVE RODENTS
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DOMESTIC RATS, FLEAS and NATIVE RODENTS In Relation To Plague In The United States By Entomologist Carl 0. Mohr INTRODUCTION and finally to the lungs causing pneumonic plague. ubonic plague is a rodent and rodent - Pneumonic plague is extremely fatal and flea disease caused by the plague bacil highly infectious when sputum droplets pass Blus Pasturella pest is which is transmitted direct from person to person. The death from animal to animal and thence to man by rate due to it is practically 100 percent. fleas. It is highly fatal. At least half Plague is dreaded particularly where of the human cases result in death without living conditions are such as to bring modern medication. (Table I — last two human beings into close contact with large columns). Because of their close associa* oriental-rat-flea populations, and where tion with man, domestic rats* and their crowded conditions permit rapid pneumonic fleas, especially the oriental rat flea transmission from man to man. Xenopsylla cheopis, are responsible for most human epidemics. Only occasional cases ANCIENT AMERICAN DISEASE OR RECENT are caused by bites of other fleas or by INTRODUCTION direct infection from handling rodents. Infection due to bites of fleas or due to Two widely different views exist con direct contact commonly results in swollen cerning the arrival of plague in North lymph glands, called buboes, hence the name America. The prevalent view is that it was bubonic plague. Infection may progress to introduced from the Orient into North the blood stream causing septicemic plague, America at San Francisco through ship- * Rattus rattus and Rattus norvegicus. **Dr. Mohr is Chief of the Ectoparasite Branch, Entomology Division, Communicable Disease Center, Atlanta, Georgia. urtesy of the David J. Sencer CDC Museum 2 borne rats and their fleas about 1900. therefore, may have been present there Facts supporting this view: from ancient times. The following instances may be cited: 1. The first cases were recognized in the a. In 1908 a case in Los Angeles Chinese section of San Francisco re County, California was the first gion during that year. warning of its existence there. 2. Succeeding human cases were recognized, b. Hie death of a sheepherder and an first near San Francisco, and, as the epizootic among sylvan rodents in years went by, at increasingly greater ■ Lake County, Oregon, in 1934 was distances as plague presumably spread more than 200 miles north of the northward and inland. previously suspected area south of 3. Results of plague surveys in wild the Sacramento River. rodents revealed the presence of plague c. A case of bubonic plague in south in an ever-widening area after its west Utah in 1935 was the first original recognition in California. indication of the presence of plague For example, in 1935, after it was there. learned that animals in other western d. In 19 37 a human case near Lake states were infected, examinations Tahoe, in Nevada, was the first were extended to all of the Rocky indication of its presence in that Mountain states as far as the great s t « plains. No infection was found in the e. During 1935, plague was found by plains states until after a lapse of federal personnel studying rodent several years. diseases in Montana far removed 4. Plague occurred in Pensacola, Florida; from any areas in which plague was in New Orleans; and at Beaumont, Port previously suspected. Arthur and Galveston from 1914 to 1921, apparently having been introduced HISTORY OF HUMAN CASES by shipping, thus giving support to the theory that the San Francisco out pidemics of plague have struck in North break had occurred in the same way. E America in the past and can strike again The other view, perhaps not so widely if protection is relaxed in present danger held, is that plague is a characteristic zones or is not extended promptly to new disease of colonial rodents in North danger spots as they develop. America’s America, for i t is also found in very recent record has been good in this respect. closely-related species in Asia. Therefore, During the 21 years between 1925 and 1946, it must have been present on this continent only 21 reported human cases occurred in in those rodents and their fleas thousands the vast western half of this continent of years before modern shipping. Facts (see back cover) where plague was known to supporting this view: be present among wild rodents. (Table I). 1. It is a common occurrence for diseases No human cases have been reported in the as well as parasites to accompany their eastern states since 1921. This fine hosts into new territory. Mammalogists rapport has not always existed; our earlier generally agree that ground squirrels plague history illustrates how outbreaks and meadowmice are Asiatic in origin. can take place if watchfulness is relaxed Since plague is a common disease of and protection not provided in danger areas. these animals in Asia it may therefore Its manner of striking in the future may have arrived with them during pre resemble that of the past. historic times. As previously stated, the disease was 2. A considerable number of single human first recognized in North America during cases or epizootics have occurred in 1900 (Hampton 1945) in the San Francisco areas far in advance of those in which area. From that date until 1924, it struck plague had been suspected. Plague, repeatedly and disastrously in California ourtesy of the David J. Sencer CDC Museum 3 TABLE I CASES OF, AND DEATHS FROM, PLAGUE IN THE UNITED STATES (HAMPTON, 1945) YEAR CASES TOTALS CALIF. WASH. LA. FLA. TEX. OREGON UTAH NEV. IDAHO CASES DEATHS 1900 22 22 22 1901 30 30 26 1902 41 41 41 1903 17 17 17 1904 10 10 8 1905-06 0 0 1907 178 3 181 90 1908 8 8 5 1909 3 3 1 1910 3 3 1 1911 4 4 1 1912 0 0 1913 2 2 2 1914 1 30 31 10 1915 1 1 2 1 1916-18 0 0 1919 13 15 28 18 1920 1 7 10 33 51 27 1921 3 3 6 4 1922 2 2 0 1923 1 1 0 1924 41 41 34 1925 1 1 0 1926 0 0 1927 1 1 1 1928 3 3 2 1929-32 0 0 1933 1 1 1 1934 1 1 2 1 1935 0 0 1936 3 1 4 0 1937 1 1 2 1 1938 0 0 1939 1 1 0 1940 1 1 1 1941 2 2 2 1942 1 1 . 0 1943 1* 1 1 1944 1 1 0 1945-46** 0 0 TOTAL 397 3 5b 10 33 1 2 1 1 504 318 * Case acquired in laboratory ** 1945-1946 data from Public Health Reports for 1945, 1946, and 1947, One case occurred in California in 1947 Courtesy of the David J. Sencer CDC Museum 4 Roof rat. Domestic rats, being closely associated with man and b e a r i n g at least one highly p 1ag u e - susceptible flea, are largely responsible for most epidemics. until the general public and public offi SOURCES OF PLAGUE OUTBREAKS cials became sufficiently aware of the hazard to support protective measures. From DIRECTLY FROM NATIVE RODENTS OR FLEAS 10 to 41 cases occurred annually in San Plague among rodents of fields and woods is Francisco up to 1904. Then for two years known as sylvatic plague. Sixty-six human none was recognized and the city was infections in rural western areas (with declared to be free of detectable plague. a 63 percent death rate) have been traced During 1907, however, plague struck that to contact with rodents or to bites from city again. Total cases numbered 178, of their ectoparasites (Meyer 1947). Many which 87 were fatal. Eight cases were of these cases were traced to non-domestic reported from San Francisco in 1908; since rodents. From 1934 through 1943, cases then, none has been detected in that city*. were reported only in California, Oregon, However a few human plague cases were Idaho, Utah, and Nevada. reported from California nearly every year One outbreak due to contact with ground until 1919 when 13 recorded cases of squirrels is described as occurring in pneumonic plague occurred in Oakland. All Oakland in 1919. The f ir s t patient in patients died. A 41-case epidemic, 34 fatal, the series is thought to have acquired occurred in Los Angeles during 1924. From plague from squirrels which he had shot that date onward, control and good fortune and prepared for eating. The disease have held the rate down, as noted above. developed pneumonic phases. Thirteen of While California —chiefly in San Fran the persons who visited or attended him cisco and surrounding cities —was having acquired the pneumonic infection from these difficulties, New Orleans, Pensacola-, him, became ill with the disease, and Port Arthur, Beaumont, and Galveston also died. Deaths included two doctors and had outbreaks. Thirty cases of plague occur two nurses. red in New Orleans during 1914. After years Most of the sylvan-acquired plague has of survey and control measures, the last not, however, spread beyond the first con reported case occurred during 1921. Florida tact, (principally because the patients and Texas cities had a few cases during are more or less isolated) and pneumonic 1920, but having been forewarned by the plague has not resulted. experience of San Francisco and New Orleans, DIRECTLY FROM DOMESTIC RATS OR THEIR they quickly instituted sufficient control FLEAS. Domestic rats dying from plague measures and eliminated plague from their are the most common sources of infection.