Anaplasma phagocytophila is a recently described tick-borne pathogen that causes Human Granulocytic Ehrlichiosis. Anaplasma infects the neutrophils (immune system cells) of host organisms. Infection can lead to fever, chills, myalgia (muscle ache), headache, nausea, confusion, cough, and arthralgias (joint aches). Antibiotic treatment is usually sufficient to clear up infection, but if left untreated, infection can lead to fatality.

It has been demonstrated that a number of tick-borne pathogens must receive an appropriate “signal” before they can successfully be transmitted from a feeding tick to the host. Upon receiving this signal, the bacteria may need to multiply or convert to an “active” form before they can be transmitted. This process is termed “reactivation” and has been noted in a number of organisms. Rickettsia rickettsii-infected ticks that had not been fed and were homogenized and then injected into mice did not cause infection. But Rickettsia rickettsii-infected ticks that had fed for 48hr or had been incubated at 37^oC for 24hr and were then homogenized and injected into mice did cause infection. This suggested that the temperature of the feeding tick may play a role in the reactivation and transmission of Rickettsia rickettsii.

Brandon’s work with Anaplasma phagocytophila was aimed at elucidating the existence of such a “reactivation-factor” for this organism. It had been shown that after Anaplasma-infected ticks had been fed on a rabbit for 5 days, injection of tick salivary glands into laboratory mice caused infection. Brandon’s experiment involved feeding Anaplasma-infected ticks or incubating Anaplasma-infected ticks at 37^oC for varying time intervals (6hr, 12hr, 24hr, 48hr) and then injecting salivary glands from those ticks into mice to determine if they caused infection. He found that salivary glands from those ticks that had fed for 48hr caused infection. Salivary glands from ticks that fed for shorter periods of time did not cause infection. In addition, none of the salivary glands from ticks that were incubated at 37^oC caused infection. These results suggested that reactivation of Anaplasma may be dependent on a signal from the feeding of the tick and may not be dependent on temperature. They also suggest that transmission may be dose-dependent, requiring a certain number of reactivated organisms to be amassed before transmission can occur. This would explain why no infection with salivary glands from ticks that fed for less than 48 hours was noted.

Brandon hoped to continue this line of investigation by advising a study to confirm that salivary glands from naturally feeding ticks could cause infection when injected (specifically – ticks that had fed for 72hrs). He also hoped to investigate the potential existence of a chemical signal in the salivary glands themselves that prevents Anaplasma transmission before a certain time. This would be accomplished by combining Anaplasma culture with salivary glands of uninfected ticks that had fed for various time intervals and determining whether such injection mixtures cause infection.

This document was written by Lindsay Mitchell, an undergraduate student who worked with Brandon on this project.