Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) infection in Amblyomma americanum (Acari: Ixodidae) at Aberdeen Proving Ground, Maryland.

Human monocytic ehrlichiosis (HME) is a sometimes fatal, emerging tick-borne disease caused by the bacterium Ehrlichia chaffeensis. It is frequently misdiagnosed because its symptoms mimic those of the flu. Current evidence indicates that Amblyomma americanum (L.), the lone star tick, is the major vector of HME. To determine if E. chaffeensis is present in ticks at Aberdeen Proving Ground, MD, questing A. americanum ticks were collected from 33 sites. Nucleic acid was extracted from 34 adult and 81 nymphal pools. Sequences diagnostic for E. chaffeensis from three different loci (16S rRNA, 120-kDa protein, and a variable-length polymerase chain reaction [PCR] target, or VLPT) were targeted for amplification by the PCR. Fifty-two percent of the collection sites yielded pools infected with E. chaffeensis, confirming the presence and widespread distribution of E. chaffeensis at Aberdeen Proving Ground. Analysis with the both the 120-kDa protein primers and the VLPT primers showed that genetic variance exists. A novel combination of variance for the two loci was detected in two tick pools. The pathogenic implications of genetic variation in E. chaffeensis are as yet unknown.

Detection of the agents of human ehrlichioses in ixodid ticks from California.

A study was conducted in northern California to estimate the prevalence and distribution in ixodid ticks of the rickettsial agents of human monocytic (HME) and human granulocytic (HGE) ehrlichioses. More than 650 ixodid ticks were collected from 17 sites in six California counties over a 15-month period. Ehrlichia chaffeensis, the causative agent of HME, was detected by a nested polymerase chain reaction (PCR) in Ixodes pacificus (minimum infection rate [MIR] = 13.3%) and Dermacentor variabilis (infection rate=20.0%) from a municipal park in Santa Cruz County. The HGE agent was detected by nested PCR in I. pacificus adults from a heavily used recreational area in Alameda County (MIR = 4.7%) and a semirural community in Sonoma County (MIR = 6.7%). Evidence of infection with Ehrlichia spp. was not detected in D. occidentalis adults or I. pacificus nymphs. This study represents the first detection of E. chaffeensis in California ticks and the first report of infection in Ixodes spp. The competency of I. pacificus to be coinfected with and to transmit multiple disease agents, including those of human ehrlichioses and Lyme disease, has yet to be determined.