Doxycycline levels and anti-Wolbachia antibodies in sera from dogs experimentally infected with Dirofilaria immitis and treated with a combination of ivermectin/doxycycline

•Doxycycline levels are compared in D. immitis-infected dogs treated alone vs. in combination with ivermectin.•Anti-Wolbachia antibodies are lower in both treatment groups compared to untreated controls.•Adulticide effect of a doxycycline/ivermectin combination is independent of doxycycline levels. Sera from Dirofilaria immitis-experimentally infected dogs treated with a combination of ivermectin/doxycycline were analysed for doxycycline levels by HPLC and anti-Wolbachia Surface Protein (rWSP) antibodies by ELISA and compared with sera from dogs treated with doxycycline alone. Results show that doxycycline levels were not statistically different between the two groups. Circulating anti-WSP antibody titres were markedly lower in both treatment groups when compared to control D. immitis infected dogs, indicating that doxycycline is able to reduce Wolbachia and prevent the immune response against the bacteria. The combination treatment protocol has been shown to be highly adulticidal and further studies are needed to better understand the interaction between doxycycline and ivermectin in D. immitis infected dogs.