Elimination of Dirofilaria immitis Infection in Dogs, Linosa Island, Italy, 2020-2022

Abstract

On Linosa Island, Italy, Dirofilaria immitis infection has been hyperendemic in dogs and seroprevalent among islanders. In 2020, we implemented a heartworm disease elimination program on Linosa Island. Of 54 dogs tested for D. immitis antigen and microfilariae, 28 had positive results and received treatment with oral doxycycline twice daily for 4 weeks plus topical imidacloprid/moxidectin monthly for 12 months. The 26 dogs with negative results received monthly topical imidacloprid/moxidectin as preventive. During month 1, the number of microfilaremic dogs was reduced by 76.5%. From month 2 on, all animals were microfilariae negative, and during months 3 to 9, the number of antigen-positive dogs decreased progressively. Treatment of positive dogs coupled with chemoprophylaxis for noninfected dogs was effective, protecting them from new infections. The elimination program reduced the risk for human infection, representing a One Health paradigm. Monitoring and chemoprophylaxis are advocated to maintain the status of heartworm disease-free area.

Keywords: Dirofilaria immitis; Italy; dog; elimination; heartworm disease; moxidectin; parasites; soft-kill treatment; vector-borne infections.

Figure 1

Schematic design of study of elimination of Dirofilaria immitis infection in dogs, Linosa Island, Italy, 2020, and follow-up examinations. G1, infected group; G2, noninjected group; T, time after start of elimination program, in months. Boldface indicates follow-up visits.

Figure 2

Linosa Island (Sicily, Italy) indicating the positions of infected dogs, noninfected dogs, and light traps used to capture mosquitoes. Inset shows location of Linosa Island.