Tsutsugamushi Disease (Scrub or Mite-Borne Typhus) in the Philippine Islands during American Re-Occupation in 1944–45 1

Abstract

Summary 1. Cases of scrub typhus have occurred in troops during actions on the Islands of Leyte, Samar, Mindoro, Luzon, Negros and Mindanao. Japanese troops were reported to have encountered the disease on Mindanao. The largest epidemics occurred on Mindoro and Samar; widest distribution was encountered on Luzon. 2. The clinical and laboratory findings were in agreement with previous military experience with this disease. The case fatality rate was 4.5 per cent. 3. A strain of Rickettsia orientalis was recovered in laboratory mice from a patient on Samar and has been carried for 7 passages. Cross immunity with known strains of scrub typhus isolated in other geographic areas has been demonstrated. 4. As in previous experience, environments where infections have been contracted have varied. Focal areas have been encountered in fields of the common Philippine grasses, “talahib” (Saccharum) and “kogan” (Imperator), as well as neglected coconut groves with scrub undergrowth overlying both sandy and corraline floors. Most infections were contracted at or just above beach levels but some came from mountain scrub areas as high as 3000 feet. (Outbreaks appeared to be more referrable to exigencies of military operations than to detectable seasonable influence.) 5. Rats indigenous to focal areas have been identified as Rattus mindanensis, R. rattus umbrivenier and a small rat of the exulans group, R. vigoratus. The first appeared to be the most important mite host. 6. Trombicula deliensis, a known mite vector was taken from rats of all the above islands except Leyte. The other proved vector, T. akamushi, was identified from rats on Luzon and Negros. Eight other species of mites have been found on Philippine rats. 7. Incontrovertible evidence of the presence of tsutsugamushi disease (scrub typhus) in the Philippine Archipelago has been forthcoming for the first time during military operations on several islands in 1944–45.