Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2010

Thesis Director

Jeff Laursen

Thesis Committee Member

Eric Bollinger

Thesis Committee Member

Charles Costa

Abstract

Parasitism often shows seasonal variation in their hosts and has been associated with host densities, host stress levels or transmission strategies (Moller et al 2003, Andersen and May 1982 ). This study was designed to evaluate the role of direct versus indirect life cycle transmission strategies, using Isospora and haemosporidians; and the impact of proposed ecological (winter) and physiological (breeding) stresses on parasitism levels. Coccidia have direct life cycles and infect gut tissues and are passed by fecal-oral transmission. Haemosporidians are blood parasites with an indirect life cycle that requires blood-feeding insects for transmission. If parasitemias are influenced by host stress, we hypothesized that prevalence and/or intensity of Isospora and haemosporidians would increase during the two points of stress, winter and the summer. If parasitemias are more strongly influenced by vector abundance, then malaria should increase during the breeding season and not during the winter.

Haemosporideans were only present in 3% of all birds. The overall prevalence of Isospora in adults was 77%. Isospora prevalence varied significantly by season when sexes were pooled (p=0.020) with winter significantly lower than spring (p=0.01), summer (p=0.01) and fall (p=0.005). There was a significant difference in mean intensity scores between seasons (p=0.002). The mean intensity score in summer was significantly higher than spring.

Haemosporidian prevalence in our house sparrow population was too small (3%) to test the hypothesis. The prevalence of Isospora spp. in house sparrows (Passer domesticus) showed a significant seasonal distribution, seemingly due to exposure. The coccidian mean intensity scores also showed a significant seasonal distribution, but this did not seem to be due only to exposure rates. It is likely that stress associated with seasonal breeding affected mean intensity scores. The patterns were subtle, but there was evidence that both winter and summer were periods of stress.

This study also monitored the prevalence of West Nile Virus in central Illinois during fall and winter. Viremia levels should be lowest during these seasons due to a lack of mosquito vectors. In fall, prevalence in adult birds was 4.3%. No infected juveniles were found in the fall. Viral prevalence in this study (4.3% in fall and 0% in winter) was smaller than previously reported for 2002 (Ringia et.al. 2004), which may be an effect of mosquito control programs.

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