First documentation of malaria parasites (genus Plasmodium) in the Saltmarsh Sparrow (Ammodramus caudacutus) and patterns of infection with mercury exposure
Date of Completion
Honors College Thesis
Saltmarsh Sparrow, endangered, malaria, Plasmodium, mercury
Avian malaria parasites, protist parasites of the genus Plasmodium, are extremely common in birds worldwide and have the ability to dramatically impact sensitive populations and species. Mercury, a heavy metal that accumulates in the tissues of birds, is a common environmental pollutant that may reduce immune system function and increase susceptibility to malaria parasite infection. I surveyed the endangered Saltmarsh Sparrow (Ammodramus caudacutus), a species with high exposure to mercury, for malaria parasites. Specifically, I investigated the presence, diversity, and distribution of malaria parasites in the species, the degree of sharing of parasite lineages with other bird species, and the relationship between blood mercury levels and infection status. Through collaboration with researchers at the Biodiversity Research Institute (BRI) and the University of New Hampshire (UNH), blood samples were collected from 290 individuals across the entire breeding range of the species from Maine to Maryland, U.S. By sensitive nested PCR methods, I screened each sample for malaria parasite infection and each positive infection was sequenced at the mitochondrial cytochrome b gene to identify parasite lineages, the standard gene used in defining Plasmodium lineages. Overall, 16.5% of Saltmarsh Sparrows were found to be infected with a total of six Plasmodium lineages. Prevalence and diversity of parasite lineages varied across the breeding range of the Saltmarsh Sparrow, with greater prevalence and diversity in northern states. The skewed distribution of prevalence and parasite diversity may be due to mosquito control measures, habitat type, or possibly climate change. All six parasite lineages were found to be shared with other passerine species including those also found to nest in or near saltmarshes. Blood mercury levels varied in the Saltmarsh Sparrow, ranging from 0.18 ppm to 2.52 ppm with a mean of 0.86 ppm. Although a positive correlation was expected between blood mercury levels and infection status because mercury negatively impacts an individual’s ability to fight infection, I found a negative correlation. These results suggest that individuals with low blood mercury levels are more likely to be infected with malaria parasites. The discovery of a relatively high prevalence and diversity of malaria parasites in the Saltmarsh Sparrow, a species in rapid decline across its range, and the negative correlation relationship between mercury exposure and malaria parasite infection status, suggest the need for continued study of malaria parasite dynamics in the species. Further research will help elucidate the link between environmental pollution and infectious disease risk, which is a pressing topic as environmental contamination combined with climate change may heavily impact host, vector, and parasite distributions and host-parasite dynamics.
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Neuhaus, Alyssa P.; Martinsen, Ellen; Schall, Joseph; Strong, Allan; Lane, Oksana; and Kovach, Adrienne, "First documentation of malaria parasites (genus Plasmodium) in the Saltmarsh Sparrow (Ammodramus caudacutus) and patterns of infection with mercury exposure" (2020). UVM Honors College Senior Theses. 355.