Prevalence of Heartworm per 1,000 dogs examined*

LAKE COUNTY

Clear Lake/Clear Lake Oaks 52
Lakeport 81
Lower Lake 28
Middletown 49
Nice 200

MENDOCINO COUNTY

Ukiah 80
Willits 146

NAPA COUNTY

Angwin 86
Napa 45

SONOMA COUNTY

Cloverdale 95
Healdsburg 57
Petaluma 12
Santa Rosa 3
Sebastapol 9
Sonoma 22

* all dogs exposed to outdoors, no preventive meds, and no travel outside the county
Source: "Canine Filariasis in California ", J.H. Theis, R.G. Schwab, F. Stevens, C.E.
Franti, A.K. Chawla;  Merck AgVet, div Merck & Co., St. Louis, MO,  1995