Volume 29, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Rocky Mountain () and eastern () cottontails were examined for their susceptibility to virulent and avirulent strains of the spotted fever agent, . Both species of rabbits responded to inoculation of yolk sac suspensions containing 500 egg LD of either virulent or avirulent rickettsiae, with rickettsemias detectable as early as 3 days after inoculation and lasting up to 7 days. When fed upon by infected ticks, only one of three Rocky Mountain and one of four eastern cottontails developed rickettsemias detectable in embryonated hens' eggs. Rickettsial concentrations in the peripheral blood of Rocky Mountain cottontails, infected either by syringe or by bites of one or more ticks harboring virulent , were sufficient to infect simultaneously feeding normal larvae of this tick species. However, infection rates were low and did not exceed 11.7%. In a single experiment, the bites of , infected with an avirulent strain of , did not produce rickettsemias sufficient to infect normal larvae. These laboratory findings suggest that cottontail rabbits, although susceptible to , do not serve as efficient reservoirs for infecting ticks.


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