Prevalence ofEhrlichia,Borrelia, andRickettsialAgents inAmblyomma americanum(Acari: Ixodidae) Collected from Nine States

Abstract

Ambyomma americanum (L.) (Acari: Ixodidae) is an aggressive tick that feeds on humans during all postembryonic life stages. In many regions of the United States, it is the tick most commonly found attached to humans. Public health interest has grown recently, due to the recognition of new human pathogens transmitted by A. americanum and the expanding distribution of the tick. A. americanum is a vector of several bacteria pathogenic to humans. Ehrlichia chaffeensis and Ehrlichia ewingii cause moderate-to-severe febrile illness. "Rickettsia amblyommii," a member of the spotted fever group Rickettsia, also has recently been implicated as a possible human pathogen based on serologic evidence from persons recovering from illness after a tick bite. We have determined the prevalence of infection of Ehrlichia chaffeensis, E. ewingii, "Borrelia lonestari", and R. amblyommii within A. americanum ticks from 29 sites in nine states. Overall infection prevalences were 4.7% for E. chaffeensis (range, 0-27%), 3.5% for E. ewingii (range, 0-18.6%), 2.5% for B. lonestari (range, 0-12.2%), and 41.2% for R. amblyommii (range, 0-84.0%). In addition, 87 ticks (4.3%) were infected with two or more bacteria. This report documents new distribution records for E. ewingii, B. lonestari, and R. amblyommii and underscores the nonhomogeneous distribution of pathogen foci of infection. Additional surveillance throughout the range ofA. americanum is warranted to increase physician and public awareness of the risk of disease to humans from exposure to the agents transmitted by this tick.

Cultivation of Rickettsia amblyommii in tick cells, prevalence in Florida lone star ticks (Amblyomma americanum)

“…The average prevalence of Rickettsia in all parks over the three-year collection period was 57.1% of individual host-seeking LSTs (845/1479). This is similar to previously reported prevalence of the organism in LSTs in other geographic areas in the southeastern United States [1]. R. amblyommii was the only Rickettsia spp.…”

“…This organism has been identified in many species of Amblyomma ticks including Amblyomma americanum, Amblyomma maculatum and Amnlyomma cajennense. The preferred tick host in the United States appears to be the lone star tick (LST), A. americanum, and has been identified in 41.2% [1] to 64.5% [2] of host-seeking A. americanum collected from diverse geographic regions of the United States. The organism was reportedly highly prevalent (89%) in pools of the immature life stages of A. americanum by polymerase chain reaction (PCR) [3] and was detected in 66.5% to 80.5% of A. americanum pools that were directly parasitizing humans [4].…”

Antibiotic Treatment of the Tick Vector Amblyomma americanum Reduced Reproductive Fitness

“…(AF031496 and AY3888929) from A. americanum . Moreover, Mixson et al reported that “ R. amblyommi ” was transovarially transmitted and had a prevalence in A. americanum that was similar to what we found in our present and previous studies [27].…”

High prevalence of “Candidatus Rickettsia andeanae” and apparent exclusion of Rickettsia parkeri in adult Amblyomma maculatum (Acari: Ixodidae) from Kansas and Oklahoma

“…R. andeanae” (from 64–69%) have been reported in specimens of Amblyomma parvum collected in Argentina and Brazil (Pacheco et al, 2007 and Nieri-Bastos et al, 2014). These percentages are also consistent with the frequency of R. amblyommii , a vertically-transmitted rickettsial symbiont (Ponnusamy et al, 2014) detected in 37–57% of Amblyomma americanum ticks collected in Florida (Mixson et al, 2006 and Sayler et al, 2014), 45–60% in Georgia (Mixson et al, 2006 and Clay et al, 2008), 60–65% in Kentucky (Clay et al, 2008 and Jiang et al, 2010), 66–71% in Maryland (Jiang et al, 2010 and Zhang et al, 2012), 55–60% in North Carolina (Mixson et al, 2006, Clay et al, 2008 and Smith et al, 2010) and 70–82% in Virginia (Jiang et al, 2010 and Nadolny et al, 2014). …”