EPIDEMIOLOGY, DISTRIBUTION
AND TRANSMISSION

The vector: In Mediterranean countries, phlebotomus sandflies are active from May to November. The presence of the vector has increased and has extended its distribution to the Alps in Italy, the Pyrenees in France, and the North of Spain. This has significantly increased the prevalence of the disease. From an epidemiological viewpoint, two concepts are to be considered nowadays.

The first concept is that, while infection is extensive in endemic areas, not all infected animals develop the disease. Studies using PCR methods have shown that the prevalence of infection in dogs is much higher than the proportion of dogs that actually develop clinical disease. Infected animals may present with either one of two patterns of disease progression: some dogs show severe clinical signs shortly after infection; conversely, most dogs will remain infected for life but will prevent the onset of clinical signs unless certain factors (disease, medication) awaken the dormant infection.

The second concept is that, under favorable conditions (high dog or sandfly densities), the disease can rapidly and effectively spread to the entire canine population. For instance, seroprevalence values of up to 34.6% have been reported in the area of Málaga (Spain). These two concepts show that clinical leishmaniasis in endemic areas is just the tip of the iceberg and that most of the population is actually infected.

Canine leishmaniasis is commonly transmitted through sandfly bites. Both symptomatic and asymptomatic dogs are potential transmitters of the disease –with greater infectivity potential found in symptomatic animals. While phlebotomi are the only vectors that have adapted to the transmission of Leishmaniasis, other routes of transmission such as the transplacental (vertical), venereal or blood transfusion routes have been described. Dog-to-dog direct transmission through bites or injuries could be another –yet unproven– route of transmission.