Acute phase protein response in heartworm-infected dogs after adulticide treatment

•Infected dogs showed increased concentrations of APPs before stating the treatment.•Decrease of APPs on day 60 could be due to reduction of Wolbachia and microfilariae.•The increases in APPs could be due to pulmonary inflammation and thromboembolism.•Dogs with high parasite burden had greater increase in CRP and Hp during the treatment.•As the pathology disappears, there is an improvement in the concentrations of APPs. During the adulticide treatment of Dirofilaria immitis the worms die releasing fragments of parasites and causing pulmonary thromboembolisms which could exacerbate the clinical condition. To determine the utility of acute phase proteins (APPs) to monitor the progression of the treatment, different positive [C-reactive protein (CRP), haptoglobin (hp)] and negative [albumin, paraoxonase-1(PON-1)] APPs were measured in 15 heartworm-infected dogs (5 with high and 10 with low parasite burden) following adulticide treatment. The results showed increased concentrations of CRP, decreased concentrations of haptoglobin and PON-1 in infected dogs before starting the treatment. Progressive but not significant increases were observed in PON-1 activity and albumin concentration along the treatment. After the treatment with doxycycline and ivermectine a decrease in CRP and Hp levels was experienced, which could reflect a reduction of the vascular inflammation caused by the elimination of Wolbachia and reduction of microfilariae. Fifteen days after the first melarsomine injection, marked increases in CRP and Hp were observed, which could be due to pulmonary inflammation and thromboembolism caused by the post-adulticide death of the worms. This increase was greater in dogs with high parasite burden. As the pathology disappeared, there was an improvement in the concentrations of CRP and Hp, returning into reference values in dogs with low parasite burden at the end of the treatment. The measurement of CRP and Hp could be a resource of support to evaluate the magnitude of the post-adulticide complications during the adulticide treatment of D. immitis.