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Epizootiology of Trypanosomes in Red Squirrels and Eastern Chipmunks
Author(s) -
Dorney Robert S.
Publication year - 1969
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1933695
Subject(s) - biology , epizootiology , population , zoology , trypanosomiasis , ecology , immunology , virology , demography , sociology
To determine the natural fluctuations of lewisi—like trypanosome populations in red squirrels (Tamiasciurus hudsonicus), I examined 151 stained blood slides over a 3—year period and found that parasitemias were almost absent (4% positive) in 1961, had significantly increased in 1962 (37% positive), and then decreased in 1963 (15% positive). This sharp rise in 1962 presumably may have been related to the original absence of immunity among members of the population, and the decline in 1963 related to an increase in the general level of immunity in the population in combination with a reduction in the recruitment of susceptible juveniles during the 1963 reproductive season. Fluctuations of trypanosome populations in eastern chipmunks (Tamias striatus) based on examination of 283 stained blood slides followed a pattern different from that in red squirrels. In 1961 animals with parasitements were common (42%), but then the declined in both 1962 (26%) and 1962 (12%). Consecutive blood histories on marked animals and analysis of population age structure suggested this 3—year decline was caused primarily by a decrease each year in the proportion of susceptible juveniles recruited into the population. Although parasitemias in both hosts tended to last only a few months, suggesting that immunity develops rapidly, occasional retained parasitemias through the winter into the next spring. Pathogenicity of these trypanosomes must be minimal since animals with parasitemias had similar rates to those of parasites. The pattern of annual fluctuation of trypanosomiasis observed in these two hosts suggested that the study area may have been a primary focus for the lewisi—like trypanosome in chipmunks and a secondary focus for that in the red squirrel. That the squirrels on the study area moved from winter nest sites under the snow to tree nests in summer also may account for the irruptive occurrence of trypanosomiasis in this host. Whatever the explanation, the occurrence of trypanosomes at Trout Lake exhibited extreme variability from year to year and from host to host. This points up the necessity, in epizootiological studies of blood protozoa in sciurids, to examine the host—parasite system over a period spanning many years.