Background: Heartworm (Dirofilaria immitis) is mosquito-borne filarial nematode capable of causing serious cardiopulmonary disease in canines and felines, and pulmonary dirofilariasis in man. This research was conducted with the objectives of determining the incidence and assessing possible risk factors of canine heartworm in the southeast of Iran. Methods: In this experiment from October 2012 to September 2013, blood samples from 87 dogs from Zabol area in Sistan and Baluchestan and 33 dogs from Bam area in Kerman province were examined for detection of Dirofilaria immitis using modified knott test and serology. Results: Out of 120 dogs 29 (24.2%; 95%CI: 16.6-31.8%) were positive, serologically. The overall seroprevalence of D.immitis in dog in Zabol and Bam were 27.5% (95% CI: 24.7-32.5%) and 15.15% (95% CI: 12.3-20.7%), respectively. 28.8% of stray dogs and 20.6% of housed dogs in the study areas were seropositive. Seroprevalence of D. immitis was not significantly different between stray and housed dogs (P=0.295). Investigation of seasonal dynamic of infection with D.immitis in stray and housed dog showed that the proportion of infected dog in spring and summer was greater than colder season (autumn and winter) which was not significant. The prevalence of infection with D.immitis in >5 years old stray dogs (53.8%) was greater than other age categories while in housed dogs infection rate was greater in 3-5 years old (27.3%) . Conclusion: Based on our data, it is important to point out the increased incidence of canine heatrworm in Iran. In order to stop the spread of canine heartworm, preventive measures must be taken now.

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