Sacramento-Yolo Counties Lyme Disease Surveillance 2004

Annual Report 2004, Sacramento-Yolo Mosquito and Vector Control District

Summary of Sacramento-Yolo MVCD 2003-2004 Tick Surveillance

Location          Total   Pools    Positive   Estimated Minimum
                  Ticks   Tested   Pools (b)  Infection Rate (a)
Yolo
Cache Creek        368      42         5              1.4%
Sacramento
Ancil Hoffman        0       0         0              N/A
Mississippi Bar     83      11         1              1.2%
Negro Bar          189      22         0              0.0%
Nimbus Dam          74      11         2              2.7%
Snipes Park         64      11         0              0.0%
Willow Creek        69      12         0              0.0%
Totals             847     109         3

a IFA-positive samples were tested by a PCR assay targeting the 5S(rrf)-23S(rrl) intergenic spacer region of B. burgdorferi.
b Minimum infection rate (%) = (#positive pools/#ticks tested) x (100). Assume a positive pool contains a minimum of one infected tick.

The bacterium that causes Lyme disease is called Borrelia burgdorferi. The primary vector for Lyme disease for Sacramento and Yolo Counties is Ixodes pacificus, also known as the western black-legged tick. The table (above) summarizes the Lyme disease surveillance data from Ixodes pacificus ticks collected from November 2003 through May 2004.

Tick specimens were collected by dragging a flannel sheet along the side of a trail, a technique called flagging. The ticks were pooled and tested by indirect immunofluorescence assay (IFA). A sample was considered positive by IFA if one or more fluorescently stained spiral-shaped bacteria were present. Some positive samples were confirmed using a polymerase chain reaction assay and by culture in liquid media.