An Acarologic Survey and Amblyomma americanum Distribution Map with Implications for Tularemia Risk in Missouri

Abstract

Abstract. In the United States, tickborne diseases occur focally. Missouri represents a major focus of several tickborne diseases that includes spotted fever rickettsiosis, tularemia, and ehrlichiosis. Our study sought to determine the potential risk of human exposure to human-biting vector ticks in this area. We collected ticks in 79 sites in southern Missouri during June 7-10, 2009, which yielded 1,047 adult and 3,585 nymphal Amblyomma americanum , 5 adult Amblyomma maculatum , 19 adult Dermacentor variabilis , and 5 nymphal Ixodes brunneus . Logistic regression analysis showed that areas posing an elevated risk of exposure to A. americanum nymphs or adults were more likely to be classified as forested than grassland, and the probability of being classified as elevated risk increased with increasing relative humidity during the month of June (30-year average). Overall accuracy of each of the two models was greater than 70% and showed that 20% and 30% of the state were classified as elevated risk for human exposure to nymphs and adults, respectively. We also found a significant positive association between heightened acarologic risk and counties reporting tularemia cases. Our study provides an updated distribution map for A. americanum in Missouri and suggests a wide-spread risk of human exposure to A. americanum and their associated pathogens in this region.

Environmental, Climatic, and Residential Neighborhood Determinants of Feline Tularemia

“…Dry forested areas in that study were estimated using normalized difference vegetation index estimates, and their finding was attributed to potential for higher tick prevalence in this type of land cover. Forested areas in general were more likely to be associated with Amblyoma americanum, a tick host for tularemia in an acarologic survey study conducted in the state of Missouri (Brown et al 2011). Land cover types other than grassland vegetation were not significantly associated with case status in the present study.…”

“…The role of physical environmental characteristics, such as dry forests (Eisen et al 2008), and the potential for different climatic influences (Brown et al 2011, Clark et al 2012) on human tularemia have been documented. It is highly likely for the same or similar factors to play an influential role in tularemia outcomes in pet cats as well.…”

Modeling the Present and Future Geographic Distribution of the Lone Star Tick, Amblyomma americanum (Ixodida: Ixodidae), in the Continental United States

“…105 As such, the summer months represent the portion of the year when all three life stages are actively seeking hosts and may be most vulnerable to desiccation stress. In modeling the distribution of A. americanum within Missouri, Brown and others 106 found that RH in July was a significant predictor of nymphal and adult abundance. Similarly, James and others 34 modeled the climatic niche of the American dog tick (Dermacentor variabilis) and found a strong effect of normalized difference vegetation index in July, which they posited is an indicator of humidity levels on the ground.…”

Tick-Borne Zoonoses in the United States: Persistent and Emerging Threats to Human Health

“…The highly infectious organism has been shown to infect hundreds of animal species and also to survive in water and soil; multiple tick species are likely involved in maintenance of F. tularensis in nature (Hopla 1974; Jellison 1974; Parker et al 1951). Tick bites are one of several possible modes of transmission of F. tularensis to humans, and A. americanum nymphs and adults have been implicated as important vectors in the south-central United States (Brown et al 2011; Eisen 2007a). …”