Thirty-seven subadult and adult coyotes (Canis latrans), collected Aug
ust 1992 through December 1996 from a coastal foothill area in norther
n California (USA), were examined for adult heartworm (Dirofilaria imm
itis). During 1992 through 1993, at the end of a 6 yr drought, none of
four coyotes examined were infected with heartworms. However, during
1994 through 1996, after the drought had ended, prevalences were 91% i
n 23 adult coyotes and 40% in 10 subadult coyotes. Heartworm intensity
did not differ by sex of coyote, and averaged (+/- SE) 19.4 +/- 3.8 a
mong adults; one subadult had >238 heartworms. The prevalence and inte
nsity of heartworm infection in coyotes reported here for 1994 through
1996 are the highest reported anywhere in the United States.