Antibiotic Treatment of the Tick Vector Amblyomma americanum Reduced Reproductive Fitness

Abstract

BackgroundThe lone star tick Amblyomma americanum is a common pest and vector of infectious diseases for humans and other mammals in the southern and eastern United States. A Coxiella sp. bacterial endosymbiont was highly prevalent in both laboratory-reared and field-collected A. americanum. The Coxiella sp. was demonstrated in all stages of tick and in greatest densities in nymphs and adult females, while a Rickettsia sp. was less prevalent and in lower densities when present.Methodology/Principal FindingsWe manipulated the numbers of both bacterial species in laboratory-reared A. americanum by injecting engorged nymphs or engorged, mated females with single doses of an antibiotic (rifampin or tetracycline) or buffer alone. Burdens of the bacteria after molting or after oviposition were estimated by quantitative polymerase chain reaction with primers and probes specific for each bacterial species or, as an internal standard, the host tick. Post-molt adult ticks that had been treated with rifampin or tetracycline had lower numbers of the Coxiella sp. and Rickettsia sp. and generally weighed less than ticks that received buffer alone. Similarly, after oviposition, females treated previously with either antibiotic had lower burdens of both bacterial species in comparison to controls. Treatment of engorged females with either antibiotic was associated with prolonged time to oviposition, lower proportions of ticks that hatched, lower proportions of viable larvae among total larvae, and lower numbers of viable larvae per tick. These fitness estimators were associated with reduced numbers of the Coxiella sp. but not the Rickettsia sp.Conclusion/SignificanceThe findings indicate that the Coxiella sp. is a primary endosymbiont, perhaps provisioning the obligately hematophagous parasites with essential nutrients. The results also suggest that antibiotics could be incorporated into an integrated pest management plan for control of these and other tick vectors of disease.

Coinfection of Dermacentor silvarum Olenev (Acari: Ixodidae) by Coxiella-Like, Arsenophonus-Like, and Rickettsia-Like Symbionts

“…3) (27) and Reinhardt et al (29) reported that Ornithodoros moubata hosted two kinds of symbionts, namely, Rickettsia-like and Francisellalike symbionts. Besides, it has been previously reported that Amblyomma americanum simultaneously harbored Coxiella-like symbionts, which are primary and are closely related to host reproduction (30,31), and Rickettsia-like and Arsenophonus-like symbionts (21). In this study, we found an important coinfection phenomenon in D. silvarum, which provides a new model and clue for elucidating the issues about the interaction and interrelationship between symbionts and their hosts.…”

“…Previous studies have suggested that the Coxiella-like symbiont in A. americanum is a primary symbiont because of its ubiquitous distribution (21,30), vertical transmission (13,21), infection of specific tissues (13), loss of fitness with antibiotic treatment (31), and reduced genome (30). In this study, we found that CLS-Ds exhibited vertical infection and infected specific tissues.…”

Localization and Visualization of aCoxiella-Type Symbiont within the Lone Star Tick,Amblyomma americanum

“…It is also possible that the Amblyommaassociated Coxiella could negatively impact the host tick through reproductive parasitism, similarly to Wolbachia (58). The ability of A. americanum to survive and/or molt without Amblyomma-associated Coxiella could be tested by using heat or antibiotics to clear the bacteria, similar to the method described in a recent report (62).…”

Coxiella-like Endosymbionts

“…Although little is known about functions of symbiotic Coxiella -like bacteria in ticks, it has been hypothesized that they synthesize various nutrients that are required by arthropod hosts (Moran et al 2003 ;Douglas 2007 ;Zhong et al 2007 ;Baumann et al 1995 ;Faria e Silva et al 1994 ) . Ticks that feed entirely on blood are a virtual breeding ground for symbiotic partnerships because vertebrate blood rarely contains suf fi cient quantities of amino acids and B-vitamins.…”