Studies of Leptospirosis in Natural Host Populations I. Small Mammals of Waipio Valley, Island of Hawaii

摘要

The small Indian mongoose, Herpestes auropunctalus(Carnivora: Viverridae), and the roof rat, Rattus rattus, and the Polynesianrat, Rattus exulans (both Rodentia: Muridae), are abundant in Waipio Valley,island of Hawaii. Two other murid rodents, the house· mouse, Mus musculus,and the Norway rat, Rattus norvegicus, are sporadic or rare in occurrence. Ascarriers of serotypes of the bacterium Leptospira interrogans (Spirochaetales:Treponemataceae), which is transmissible to humans, this assemblage ofintroduced mammals is of public health significance, for numerous cases ofleptospirosis, or Weil's disease, have been traced to the valley. Populationdensity of the mongoose was estimated at 2.3 per acre; for rats, it fluctuatedseasonally from I to 11 per acre. The serotypes icterohemorrhagiae and sejroewere found in the mongoose in a 40:60 ratio by the kidney culture method.Combined kidney culture and serological tests on 180 mongooses showed ahigh of 34 percent overall infection in winter and a summer low of 9.4 percent.Of 33 house mice tested by culture only, ballum was isolated from 21 andicterohemorrhagiae from two. One isolation of icterohemorrhagiae was madefrom four Norway rats examined. For 126 roof rats tested by serology andkidney culture, 68 percent of adults and 26 percent of young were infected; andfor 175 Polynesian rats, 34 percent of adults and 26 percent of young wereinfected. The Polynesian rat demonstrated a lesser persistence of the serumtiter phase of the disease than did the roof rat. Icterohemorrhagiae made up 95percent and ballum the remaining 5 percent of infections in the roof rat. Forthe Polynesian rat the ratio was 75: 25. Free-ranging rats under observationfor as long as 8 months acquired or lost infections, as determined by repeatedserological tests. The wet subtropical climate of Waipio Valley supportsconditions for transmission of leptospirosis among small mammals, andpossibly to humans, even in times of drought. No prominent differences wereobserved in the infection rates in the lower valley at 30 ft above sea level and1.7 miles inland at 120 ft. In the forested watershed of the valley rim at 3000 ft,conditions of infection by species of host and by serotype of L. interrogansmatched elosely those found on the valley floor. Tests of 152 water samplesfrom streams, ponds, and taro patches resulted in isolations only of saprophyticleptospires, although temperatures, salinities, and pH concentrationsappeared to be favorable for the support of pathogenic forms.