Dirofilaria immitis and Dirofilaria repens infections in French working military dogs: Prevalence and factors associated with vector exposure

Dirofilaria (D.) immitis and D. repens are mosquito-borne nematodes that can cause heartworm disease and skin nodules, respectively in infected dogs. These parasites may also be responsible for minor zoonoses. Infections caused by these agents are widely distributed throughout the world and have already been reported in mainland France, especially in the south. Both parasites are associated with animal and public health concerns in France. Military working dogs are often exposed to them during their missions throughout the world, and prophylactic measures are therefore well established. To gain a better understanding of the situation among these dogs, a prevalence survey was carried out on a representative sample of 250 military working dogs. Blood samples were analyzed using a rapid test for the detection of D. immitis adult antigens, and modified Knott's test for microfilariae identification. Data on dog exposure to vectors and on their living behaviors were also collected with a survey questionnaire. For one dog (0.4 %), a positive result for D. immitis was obtained with the rapid diagnostic test, and another dog (0.4 %) was found to be positive for D. repens with the modified Knott's test. However, only D. repens infection was confirmed by polymerase chain reaction. These dogs were living in outdoor kennels, which could increase their exposure to mosquito vectors in enzootic areas, and thus to the parasites, further reinforced by their predominantly outdoor operational activities. Nevertheless, the low observed prevalences may reflect the effectiveness of stringent prevention measures in this specific population, or a generally low level of transmission in the general canine population in France—albeit insufficiently documented due to limited surveillance data—or again, limitations related to the imperfect diagnostic methods employed in this study.