Monocytic ehrlichiosis in people caused by the intracellular bacterium, 
Ehrlichia chaffeensis, is an emerging infectious disease transmitted by the lone 
star tick, Amblyomma americanum. Tick transmission disease models for 
ehrlichiosis require at least two hosts and two tick blood feeding episodes to 
recapitulate the natural transmission cycle. One blood feeding is necessary for 
the tick to acquire the infection from an infected host and the next feeding is 
needed to transmit the bacterium to a naïve host. We have developed a model for 
E. chaffeensis transmission that eliminates the entire tick acquisition stage 
while still producing high numbers of infected ticks that are also able to 
transmit infections to naïve hosts. Fully engorged A. americanum nymphs were 
ventrally needle-infected, possibly into the midgut, and following molting, the 
unfed adult ticks were used to infect naive deer and dogs. We have also 
described using the ticks infected by this method the transmission of both 
wild-type and transposon mutants of E. chaffeensis to its primary reservoir 
host, white tailed deer and to another known host, dog. The infection 
progression and IgG antibody responses in deer were similar to those observed 
with transmission feeding of ticks acquiring infection by natural blood feeding. 
The pathogen infections acquired by natural tick transmission and by feeding 
needle-infected ticks on animals were also similar to intravenous infections in 
causing persistent infections. Needle-infected ticks having the ability to 
transmit pathogens will be a valuable resource to substantially simplify the 
process of generating infected ticks and to study infection systems in 
vertebrate hosts where interference of other pathogens could be avoided.