The relapsing fevers are divided, as usual, into louse-borne and tick-borne types. It is well stated that the epidemiology of the louse-borne type is similar to that of the louse-borne form of typhus. It is correctly stated that transmission by the louse is not by bite but through the medium of the crushed louse. In comparing the two types, it is stated that the tick-borne type is “more endemic in nature.” It is endemic, never epidemic. The statements that “infection occurs most often by the penetration of the spirochete through an abrasion of the skin” and that “transmission can also occur by bite” are misleading. For the most part, infection takes place through the medium of the secretions of the salivary glands while the tick is feeding. The general statement that: “One factor dominates the epidemiology—the transovarial transmission of the spirochete through several generations of ticks” is unwarranted. In 0. turicata, transovarial transmission (up to 100 per cent) has been shown.

We investigate multi-level parallelism on GPU clusters with MPI-CUDA and hybrid MPI-OpenMP-CUDA parallel implementations, in which all computations are done on the GPU using CUDA. We explore efficiency and scalability of incompressible flow computations using up to 256 GPUs on a problem with approximately 17.2 billion cells. Our work addresses some of the unique issues faced when merging fine-grain parallelism on the GPU using CUDA with coarse-grain parallelism that use either MPI or MPI-OpenMP for communications. We present three different strategies to overlap computations with communications, and systematically assess their impact on parallel performance on two different GPU clusters. Our results for strong and weak scaling analysis of incompressible flow computations demonstrate that GPU clusters offer significant benefits for large data sets, and a dual-level MPI-CUDA implementation with maximum overlapping of computation and communication provides substantial benefits in performance. We also find that our tri-level MPI-OpenMP-CUDA parallel implementation does not offer a significant advantage in performance over the dual-level implementation on GPU clusters with two GPUs per node, but on clusters with higher GPU counts per node or with different domain decomposition strategies a tri-level implementation may exhibit higher efficiency than a dual-level implementation and needs to be investigated further.

An aberrant strain of Borrelia parkeri is reported from Oregon. This strain is transmitted regularly by Ornithodoros parkeri from Washington, erratically by Ornithodoros turicata from New Mexico, Oklahoma, Texas, and Kansas but not by O. turicata from Mexico. The reason for the irregular and finally all but discontinued transmission by O. turicata was made clear by the dark-field examination of the tick tissues from time to time. Initially, the spirochetes were found in the salivary glands, as well as in the coxal organs and the central ganglion, while later they were found, for the most part, only in the central ganglion. In O. turicata, which was carrying B. turicatae, and in O. parkeri, which was carrying the Oregon spirochete, the spirochetes were found regularly in the salivary glands.

Three pairs of ticks, each pair of which at times occupies the same habitat and presumably feeds on the same host, have been tested for the transmission of spirochetes native to each. These were Ornithodoros turicata and O. talaje, O. erraticus and O. normandi, and O. talaje and O. rudis. As O. rudis and O. normandi spirochetes were not available for this study, the results were supplemented by reports from other sources. There was the same degree of tick-spirochete specificity as has thus far been reported for the Western Hemisphere.