Molecular DNA Tests Identify New Bacterium

A molecular diagnostic test, combined with DNA sequencing, serology and culture have enabled the identification of a bacterium infecting humans with ehrlichiosis in areas where it was unknown.

A multidisciplinary team centered at the Mayo Clinic (Rochester, MN, USA), extracted DNA from 4,247 blood specimens from residents in 45 US states and tested them by means of a real-time polymerase chain reaction assay (rt-PCR) for bacteria of the family Anaplasmataceae and a nested PCR assay of the groEL gene. Serum and plasma specimens from patients with an atypical groEL PCR product were tested for immunoglobulin G (IgG)-class antibodies reacting to Ehrlichia chaffeensis or Anaplasma phagocytophilum with the use of a commercial indirect immunofluorescence assay (Focus Diagnostics, Cypress, CA, USA).

Of the 1,518 specimens obtained from residents of two US states, 163 (10.7%) were positive for A. phagocytophilum (35 from Wisconsin and 128 from Minnesota), whereas none were positive for E. chaffeensis or E. ewingii. Four residents had positive fluorescence resonance energy transfer PCR assays with a melting temperature that was outside the melting temperature range for E. chaffeensis, E. ewingii, and A. phagocytophilum. This atypical result was not found for the 2,729 specimens collected from the 43 other states. The Ehrlichia–Anaplasma real-time groEL PCR assay used in the investigation had the advantage of providing differential detection of Ehrlichia species Wisconsin from E. chaffeensis, E. ewingii, and A. phagocytophilum based on differences in DNA composition of the amplified fragment.

Genetically, the new bacterium bears closest similarity to another species known as E. muris, which infects small rodents and deer in Eastern Europe and Asia. E. muris rarely infects humans, and no cases have been reported in North America. Bobbi S. Pritt, MD, corresponding author of the study, said, "Before this report, human ehrlichiosis was thought to be very rare or absent in Minnesota and Wisconsin. Therefore, physicians might not know to look for Ehrlichia infections at all." Ehrlichia infect and kill white blood cells and may cause fever, body aches, headache, and fatigue. More severe disease may involve multiple organs such as the lungs, kidneys and brain, and require hospitalization, although ehrlichiosis rarely results in human death as it is easily treated. The study was published on August 4, 2011, in the New England Journal of Medicine (NEJM).

Related Links:
Mayo Clinic
Focus Diagnostics