Fig. 1.

Distribution of canine and feline heartworm in the province of Madrid (Spain). The dark grey area corresponds to the city of Madrid, while the pale grey area corresponds to the metropolitan and adjacent area included in the study. The main rivers are illustrated as thick black lines. The positive animals are marked as follows: red circles (heartworm positive dogs); green squares (antibodies-seropositive cats); blue asterisk (antigens-positive cat). The municipalities with higher prevalences and seroprevalences are indicated as: 1, Aranjuez; 2, Alcalá de Henares; and 3, Majadahonda