Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2004
Publication Date: 7/23/2004
Citation: Long, S.W., Pound, J.M., Yu, X. 2004. Ehrlichia prevelence in Amblyomma americanum, Central Texas. [letter]. Emerging Infectious Diseases. [serial online]. 10(7):1342-1343. Available: http://www.cdc.gov/ncidod/EID/vol10no7/03-0792.htm. Interpretive Summary: Ticks must obtain blood meals from host animals to gain nutrients and energy that support all of their bodily functions, including molting and reproduction, and it is this act of biting a host to obtain a blood meal that often results in transmission of microscopic disease agents to the hosts, which may include humans, livestock, and wildlife. Disease agents such as those causing Lyme disease, the human ehrlichioses, human babesiosis, Rocky Mountain spotted fever, and many others are transmitted in this manner. In many cases, disease agents are not known to exist in an area until clinical symptoms are diagnosed in patients, but in others preemptive epidemiological studies may be done to determine if agents are present in the ticks before the diseases actually are diagnosed in patients. The present study screened ticks from Kerr County, Texas to determine if they were infected with the disease agents Ehrlichia chaffeensis and E. ewingii that cause ehrlichiosis in humans, and while none were positive for E. chaffeensis, some ticks were positive for E. ewingii. This is the first record of the E. ewingii agents being found in any state in the U. S. other than North Carolina, Florida, or Missouri, and this information will increase the awareness of the medical community regarding the potential for cases of this disease in Texas.
Technical Abstract: DNA extracted from pooled halves of field-trapped adult lone star ticks, Amblyomma americanum, was evaluated using a nested species-specific 16S rRNA gene polymerase chain reaction (PCR) for Ehrlichia chaffeensis and E. ewingii, with E. canis as a negative control. DNA was extracted from individual tick halves from E. ewingii positive pools and the 16S rRNA gene cloned and analyzed for sequence variation. Five of the 66 ticks examined were positive for E. ewingii by comparison to the E. ewingii 16S rRNA gene sequence. No ticks were found to be infected with E. chaffeensis. Although no cases of E. ewingii infections have been reported for the state of Texas, this study presents conclusive evidence of the presence of this infective agent in ticks in Texas, and it also is the first record of E. ewingii infected ticks occurring in any state in the U.S. other than North Carolina, Florida, or Missouri