Assessing the Relative Contribution of Pre‐Deployment Abroad Versus In‐Mission Dirofilaria immitis Infections in French Military Working Dogs Screened Post‐Mission: A Quantitative Risk Assessment

ABSTRACT

Dirofilaria immitis ( D. immitis ) is a mosquito‐borne nematode responsible for canine cardiopulmonary dirofilariasis, a parasitic infection widely distributed worldwide and established in mainland France, particularly in southern regions. Military working dogs (MWDs) may be at increased risk of exposure to vector‐borne pathogens because of their predominantly outdoor lifestyle and frequent missions abroad. Nevertheless, D. immitis infection remains sporadic in this population, likely due to well‐implemented medical prophylaxis. The aim of this study was to investigate the likely origin of D. immitis infections detected in MWD during post‐mission screening using a quantitative risk analysis approach. Scenario trees were developed to describe the sequences of events leading to the return of an infected dog from a mission abroad, accounting for parasite biology, prophylactic measures, and compliance. The model estimated a mean annual number of 4.25 infected MWD returning from missions out of an average annual population of 466 returning dogs, of which 79% were detected through post‐mission screening. Most infections were likely acquired before deployment, either during previous missions, at the breeding facility before purchase, or within mainland France. Only 7.9% of infections acquired during missions were expected to be detected by testing performed at the end of the post‐mission quarantine period. Alternative scenarios highlighted the effectiveness of chemoprophylaxis, as its absence was associated with a 3.2‐fold increase in the number of infected dogs. Simulations also showed that extending the interval between return and testing would substantially improve the detection of mission‐acquired infections. These findings support the continued use of preventive measures while questioning the adequacy of current post‐mission screening alone for identifying D. immitis infections acquired during deployment.