No description available.

Effects of infective stage density, host density and surface area available for transmission on the rate of transmission of the nematode Heligmosomoides polygyrus were investigated in a controlled environment where naive CD1 outbred mice were naturally infected. Within a range of densities of infective larvae (500-6000/cage), randomly spread on damp peat moss, a linear increase was observed in the mean number of fourth stage larvae embedded in the intestinal mucosa per host. As host density increased (1-6 mice/cage), but exposure dose held constant (8000L$ sb3$), the mean number of L$ sb4$ recovered per mouse decreased at a faster rate than expected assuming a constant per capita rate of transmission. In an attempt to interpret the experimental data, mathematical models were generated. Although the inclusion of a death rate of infective larvae dependent on mouse density did improve the fit of the mathematical model based on a constant per capita rate of transmission, the best fit was provided by a model assuming a per capita rate of transmission dependent on mouse density. An independent experiment exploring the impact of surface area available for transmission on the relationship between host density and the rate of infection confirmed the adequacy of the mouse density-dependent per capita rate of transmission hypothesis.

The importance of host heterogeneity in generating aggregation was investigated using Heligmosomoides polygyrus (Nematoda) in laboratory mice. The protocol compared parameters of infection between inbred and outbred mice, primary and challenge infections, and gavage and natural exposure, to investigate the relative effects of innate resistance, acquired resistance and behaviour, respectively. The results show that heterogeneity in acquired resistance is the most consistent factor contributing to the variability and aggregation of H. polygyrus. When groups of mice did not acquire resistance, either in certain inbred strains or when mice were immunosuppressed, variability after the challenge was comparable with that after a primary infection. Heterogeneity in host behaviour, particularly in behaviours enhancing skin contact with larvae, frequently increased aggregation above that detected in both primary and challenge infections. Surprisingly, inconsistent results were obtained when inbred and outbred groups of mice were compared. The results suggest that the relative contribution of these three factors is likely to vary spatially and temporally.

The parasitic mites on mammals living in the chaparral community of Utah are practically unknown ecologically. Keegan (1953) was the first to publish on parasitic mites from Utah. He listed mites of 12 species and 9 genera from Tooele and Juab counties from hosts which included one Peromyscus truei, five P. crinitus, and 20 P. maniculatus. Brennan and Beck (1955) published on the chiggers of Utah and included a key to 38 species. Allred (1954, 1956, 1957, 1958) studied the geographical distribution, seasonal occurrence, and biology of mites found on mice of the genus Peromyscus in Utah.

No description available.

The Genus Trichinella is currently thought to consist of 8 seperate species. Several methods have been used to help differentiate these. In this study the ability of three of these species, T. spiralis, T. pseudospiralis, and T. sp. 3 to idependantly infect MRL++ mice was compared at 5, 7, 11, 18 and 20 days post infection ( dpi) with the hope of discovering new distinguishing characteristics. Of interest was the development of inflammation through the accumulation of neutrophils associated with larvae of Trichinella in mouse skeletal muscle. This was evaluated with routine histological stains, endogenous peroxidase staining and immunohistochemical staining specific for neutrophil myeloperoxidase. The inflammatory response in skeletal muscle varied considerably among these three species with neutrophil accumulation being very heavy in the later stages of T. spiralis infection , mild in T. sp. 3 and virtually nonexistant in T. pseudospiralis infections. Also, the appearance of neutrophils was closely correlated with the development of a nurse cell or cyst in the larvae that develop these structures. In T. pseudospiralis where cyst formation is absent, there consistently was a lesser degree of inflammation. These results suggest a possible role of neutrophils involved in inflammation or the process of inflammation itself in the production of nurse cell formation as well as confirming previously described antiinflammatory capabilities of T. sp. 3 and T. pseudospiralis.

Subclinical infections with the nematode Heligmosomoides polygyrus affect the behaviour and spatial learning of CD-1 mice in a Morris water maze. In early trials testing their ability to find and land on a hidden, submerged platform, uninfected mice displayed normal stress-related behaviours, such as avoiding the central areas of the circular maze and overswimming the platform. Infected mice manifested few such behaviours. Although both acquired the task, there were substantial differences between infected and uninfected mice in their patterns of task acquisition and execution. Although infected mice eventually reached comparable levels of competency, higher cognitive behaviours which suggest familiarity with the location of the platform, such as straight-line swimming, appeared earlier among uninfected mice. Other orientation behaviours, such as paddling and floating, occurred at higher levels among uninfected mice. These behavioural differences are discussed in terms of their adaptive significance to the survival of the host and the transmission of the parasite.

No description available.

Graduation date: 1995

No description available.