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Detection of the agents of human ehrlichioses in ixodid ticks from California
V L Kramer1, M P Randolph, L T Hui
1Division of Communicable Disease Control, California Department of Health Services, Sacramento 94234-7320, USA.
Abstract:
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.
Insights
Researchers detected Ehrlichia chaffeensis, the cause of human monocytic ehrlichiosis (HME), in California ticks for the first time. The study also found the HGE agent in Ixodes pacificus ticks across multiple counties.
Area of Science:
- Veterinary Entomology
- Infectious Diseases
- Molecular Diagnostics
Background:
- Human ehrlichioses, including human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE), are emerging tick-borne diseases.
- The prevalence and distribution of Ehrlichia species in ixodid ticks in California remain incompletely understood.
- Ixodid ticks are significant vectors for various pathogens affecting human and animal health.
Purpose of the Study:
- To estimate the prevalence and distribution of rickettsial agents causing HME and HGE in ixodid ticks in northern California.
- To identify tick species harboring Ehrlichia spp. in the study region.
- To establish baseline data for Ehrlichia infections in California tick populations.
Main Methods:
- Collection of over 650 ixodid ticks from 17 sites across six California counties over 15 months.
- Utilized nested polymerase chain reaction (PCR) for the detection of Ehrlichia chaffeensis (HME agent) and the HGE agent.
- Analyzed tick specimens including Ixodes pacificus, Dermacentor variabilis, and Dermacentor occidentalis.
Main Results:
- Ehrlichia chaffeensis was detected in Ixodes pacificus (MIR = 13.3%) and Dermacentor variabilis (infection rate = 20.0%) in Santa Cruz County.
- The HGE agent was identified in Ixodes pacificus adults in Alameda County (MIR = 4.7%) and Sonoma County (MIR = 6.7%).
- No evidence of Ehrlichia spp. infection was found in Dermacentor occidentalis adults or Ixodes pacificus nymphs.
Conclusions:
- This study marks the first detection of Ehrlichia chaffeensis in California ticks and the first report of Ehrlichia infection in Ixodes spp.
- The findings highlight the presence of HME and HGE agents in key tick vectors within California.
- Further research is needed to determine the coinfection and transmission capabilities of Ixodes pacificus with multiple disease agents, including those of human ehrlichioses and Lyme disease.
