The objectives were (1) to determine seroprevalence of Anaplasma marginale and Babesia bovis in adult lactating dairy cattle (2) to assess associations of geographical and farm management factors with the seroprevalence of A. marginale and B. bovis in commercial dairy farms, and (3) to identify ecologic factors associated with the abundance and spatial distribution of Rhipicephalus (Boophilus) microplus larvae in Puerto Rico (PR). Serum samples were obtained from 2,414 adult lactating cattle from 76 commercial dairy farms between August 2005 and December 2006. Ninety-six sites were sampled for tick larvae during the dry season (March 4-18, 2007) and the rainy season (August 13-26, 2007). Data on farm management factors were obtained by an interviewer-administered questionnaire. Farm seroprevalence for A. marginale ranged from 2.8 to 100% with an overall animal seroprevalence of 27%. Risk factors significantly associated with A. marginale included pasture grazing as the main source to feed cattle (OR= 6.4, 95% CI=1.3-33), observed monkeys on the premises (OR= 14, 95% CI=1.4- 137), use of 11% permethrin (Atroban® ; OR= 14, 95% CI=1.9-98), farmers who attended an acaricide certification program (OR= 0.17, 95% CI=0.04-0.72), and lack of fly control methods (OR= 5.7, 95% CI=1.3-25). Farm seroprevalence for B. bovis ranged from 0 to 52% with an overall animal seroprevalence of 26%. Risk factors significantly associated with B. bovis included farms located in the north coastal region (OR= 0.21, 95% CI=0.05-0.86), dairy farms with calf raising facilities (OR= 16, 95% CI=3.0-86), having more than four neighbors with cattle (OR= 17, 95% CI=1.6-176), same producer owing more than one farm (OR= 7.3, 95% CI=1.7-32), and use of government services to apply amitraz on cattle (OR= 5.5, 95% CI=1.5- 20). Moran’s I indicated that the spatial pattern of A. marginale and B. bovis seroprevalence is neither clustered nor dispersed. Risk factors significantly associated with the presence of R.(Boophilus) microplus larvae in PR during the dry season included average wind speed of 2.6 to 10.0 mph (OR= 0.07, 95% CI=0.01-0.63), more than 25% bushes and shrubs on the site (OR= 11, 95% CI=1.6-71), and presence of cattle on the site (OR= 26, 95% CI=3.4-188).
