Detection of Vector-Borne Agents in Lone Star Ticks, Amblyomma americanum (Acari: Ixodidae), From Mississippi

Abstract

In this study, we evaluated Amblyomma americanum (lone star tick) in Mississippi for the presence of Ehrlichia chaffeensis, causative agent of human monocytic ehrlichiosis; Ehrlichia ewingii, causative agent of human and canine granulocytic ehrlichiosis; Borrelia lonestari, putative agent of southern tick-associated rash illness; Francisella tularensis, the agent of tularemia; and Rickettsia spp., particularly R. amblyommii, a suspected pathogen. We collected adult A. americanum from four regions of Mississippi: Northeast, Northwest, Southeast, and East. Of the ticks collected, 192 were dissected and DNA was extracted for nested polymerase chain reaction (PCR) assays to detect the above bacteria. In all, 3% of tick extracts had evidence of Borrelia sp., 4% for E. chaffeensis, 6% for E. ewingii, and 44% for a Rickettsia species. As determined by sequencing, most Rickettsia spp. were R. amblyommii. In addition, extracts from 42 pools (total of 950) of larval A. americanum collected in Southwest Mississippi were tested for the presence of E. chaffeensis and Rickettsia species. Of these extracts from pools, nine of 37 (24%) were PCR positive for a Rickettsia sp., most often, R. amblyommii; none had evidence of E. chaffeensis, supporting the ability of lone star ticks to transovarially transmit R. amblyommii, but not E. chaffeensis. This study demonstrates E. chaffeensis, E. ewingii, "B. lonestari", and R. amblyommii in A. americanum by PCR for the first time in Mississippi. Understanding the prevalence and epidemiology of these agents in Mississippi should increase awareness of tick-borne disease in the medical community.

Spotted fever group Rickettsia infecting ticks (Acari: Ixodidae) in the state of Santa Catarina, Brazil

“…This rickettsial strain was recently found in the immature stages (5 larvae and 1 nymph) of A. longirostre collected from passerine birds in SP (Ogrzewalska et al 2008). Although different strains of R. amblyommii have been reported to infect different tick species of the New World (Labruna 2009, Castellaw et al 2010, Ogrzewalska et al 2010, Bermúdez et al 2011, the pathogenicity of R. amblyommii in humans remains to be demonstrated. Interestingly, there is serological evidence suggesting that it is a human pathogen in the United States (Apperson et al 2008).…”

Update on Tick-Borne Rickettsioses around the World: a Geographic Approach

“…Contemporary surveys of questing adult A. americanum ticks collected from several states in the eastern United States reported average infection frequencies of 45% in Georgia, 66% in Maryland, 13% in New Jersey, 42% in New York, and 60% in North Carolina (131)(132)(133)(134). Infections have also been detected commonly in larval-stage ticks (78,127,135,136 (72,139,140). "Candidatus Rickettsia amblyommii" has been implicated as a possible cause of mild or subclinical infection in humans in the United States (137,141); however, neither guinea pigs, meadow voles, nor rabbits exhibit any evidence of disease when inoculated with this SFG rickettsia (130), and there is no evidence of direct detection of "Candidatus Rickettsia amblyommii" in human clinical specimens (142).…”

Expanding Range of Amblyomma americanum and Simultaneous Changes in the Epidemiology of Spotted Fever Group Rickettsiosis in the United States

“…17,20,[34][35][36][37][38][39][40][41][42][43][44] Because of these large differences in prevalence, exposure to R. rickettsii may be rare relative to exposure to "Ca. Rickettsia amblyommii".…”