 marked increase is unlikely to be fully attributable to climate change given the complexities of vector life cycles, disease prevalence, and human interactions (well discussed by Ogden 2017), neither can the contribution of climate change be discounted. Thus, concern is reasonable.
The interactions between climate, vectors, and pathogens are complex. For example, for certain mosquitoes increased temperatures boost the rate of reproduction and feeding, lengthen the breeding season, and shorten the maturation time for the pathogens they carry (Patz et al. 1996; Epstein et al. 1998; Epstein 2005). However, such complex relationships vary by locale and species. Temperatures that benefit mosquitoes may be detrimental to ticks; flooding may wash away larval stages of mosquitoes; drought may contribute to a decline in tick numbers. Rodent vectors, such as deer mice that carry Hantavirus, demonstrate equally variable relationships (Mordecai et al. 2012, 2017, 2019).
According to the Centers for Disease Control and Prevention (CDC), Lyme disease is the most common vector-borne illness in the US, with approximately 300,000 total cases diagnosed annually (CDCa undated). Lyme disease is most prevalent in the Northeast, but has been spreading westward and northward into the Midwestern states and farther into Canada. The main vector, the deer or blacklegged tick, is not found in arid parts of the West, requiring more moisture to thrive. Although Lyme disease is the most common tick-borne disease in Montana—averaging 10 cases per year—all cases reported through 2018 came from people infected outside of Montana (MTDPHHSb undated).
West Nile virus
West Nile virus, first reported in the United States in 1999, is found in nearly every country and is the most common mosquito-borne illness in the United States, with 2647 cases and 167 deaths reported in 2018 (CDCb undated). West Nile virus is considered the most important cause of viral encephalitis globally (Chancey et al. 2015; Paz 2015), with increased spread projected with climate change (Paz 2015). Drier weather, especially drought, leads to higher rates of West Nile virus infection in people (Wang et al. 2010; Paull et al. 2016).
In the last several years, the northwest region of the US has seen an increase in some infectious diseases, including West Nile virus. The Washington Department of Health’s vector surveillance program observed earlier arrival of West Nile virus-carrying mosquitoes than some other states (likely associated with higher temperatures), and an increasing number of human infections, including some resulting in fatalities (WSDOH 2018).
Montana had no cases of West Nile virus until 2002. By 2018, the Montana Department of Public Health and Human Services (MTDPHHS) reported 51 cases across 18 counties. Nine counties reported mosquito pools that tested positive for West Nile virus out of 30 counties tested (Figure 3-9). Three people have died from West Nile virus in Montana since it was first detected (MTDPHHSc undated). MCA projects longer droughts, warmer temperatures, and minimal change in average annual precipitation, likely concentrated in fewer precipitation events (Whitlock et al. 2017; also see Section 2), factors that favor both the virus and the primary vector, the Culex spp. mosquito (Epstein 2001; Harrigan et al. 2014; Paull et al. 2017). Thus, concern exists for climate change resulting in increased numbers of West Nile virus infections in Montana.
Climate Change and Mental Well-being—Perspectives from Montana Farmers and Ranchers
Meredith Howard, Selena Ahmed, Paul Lachapelle, and Mark B. Schure
While the physical and economic implications of climate change have been studied widely, including effects on agricultural systems, the mental health implications have been largely overlooked. Farmers and ranchers—who contribute to local, national, and global food security—represent an especially vulnerable and critical population for consideration. Montana State University researchers surveyed farmers and ranchers (n=125) in Montana using a mixed-method approach 