Granulocytic ehrlichiosis in tick-immune guinea pigs

Abstract

We investigated whether Ixodes scapularis-mediated host immunity interrupts transmission of the agent of human granulocytic ehrlichiosis (aoHGE) to guinea pigs. Ticks infected with aoHGE readily transmitted aoHGE to tick-immune guinea pigs, despite incomplete tick engorgement and host attachment. Although tick immunity can prevent Lyme borreliosis, protection is not afforded against granulocytic ehrlichiosis.

FIG. 1

Effect of host tick immunity on duration of tick attachment. Ten aoHGE-infected nymphs were placed on the neck of each of the six tick-immune or six naive guinea pigs (from two sets of experiments), and tick attachment was monitored. Each point represents the average ± and standard deviation (error bars) of six observations.

FIG. 2

aoHGE infection in naive and tick-immune guinea pigs. (A) PCR amplification of 16S aoHGE rDNA fragment from blood from one experiment (comprising three naive and three tick-immune guinea pigs). Lane 1, blood from an aoHGE-infected mouse (positive control); lanes 2 to 4, blood from tick-immune guinea pigs; lanes 5 to 7, blood from naive guinea pigs; lane 8, blood from an uninfected guinea pig (negative control). (B) Sera from the animals described above were used to probe aoHGE lysates in the immunoblot. Lane 1, serum from an aoHGE-infected mouse (positive control); lanes 2 to 4, sera from tick-immune guinea pigs; lanes 5 to 7, sera from naive guinea pigs; lane 8, serum from an uninfected guinea pig (negative control).

FIG. 3

aoHGE is present in the salivary glands of unfed Ixodes nymphs. PCR amplification of aoHGE-specific 16S rDNA from gut and salivary gland total DNA was performed. Lane 1, molecular weight markers; lane 2, DNA (1.2 μg) from uninfected salivary glands; lane 3, DNA (1.2 μg) from aoHGE-infected salivary glands; lane 4, DNA (3.1 μg) from uninfected tick guts; lane 5, DNA (3.1 μg) from aoHGE-infected tick guts; lane 6, aoHGE DNA (positive control).