BackgroundInfection by two or more canine vector-borne disease (CVBD)-causing pathogens is common in subtropical and tropical regions where vectors are plentiful. Co-infections may potentiate disease pathogenesis, thereby altering clinical manifestations typically associated with singular infections. These factors complicate diagnosis, treatment and can adversely influence prognosis if the practitioner fails to suspect, document, and treat each concurrent infection. The spectrum of pathogens co-infecting dogs may change over time in a given practice location due to the rapid expansion of arthropods and their associated vectored agents, and international transit among pets and wild animals. This applies, for example, to Dirofilaria immitis and Leishmania infantum, the distributions of which have expanded from northern to southern Italy, and vice versa, respectively. Indeed, mixed infections by D. immitis and L. infantum have only been reported once in Italy, probably due to the fact that competent vectors for these infections do not usually occur in the same geographical areas. Thus, information that would help practitioners to identify clinical presentations in dogs co-infected by D. immitis and L. infantum and other CVBD-causing pathogens is scant.FindingsThis manuscript describes the clinical history and physical examination of findings for 7 CVBD co-infected dogs that were examined because of a spectrum of clinical signs. Five dogs were co-infected with L. infantum and Ehrlichia canis, one dog with L. infantum, E. canis and D. immitis and the remaining dog with L. infantum and D. immitis.ConclusionsThe clinical signs and haematological abnormalities associated with the diagnostic evaluation and treatment of these dogs is discussed. Also, the usefulness of bone marrow specimens for the molecular diagnosis of CVBDs and for the enhanced monitoring of treatment response is emphasized.

Canine vector-borne diseases (CVBDs) pose a diagnostic challenge, particularly when a dog is coinfected with more than one pathogen. The purpose of this study was to generate information about the diagnosis of CVBDs in young dogs following their first exposure to flea, tick, sand fly, louse, and mosquito vectors. From March 2008 to May 2009, 10 purpose-bred young naive beagle dogs and a cohort of 48 mixed-breed dogs living in an area to which CVBD is endemic in southern Italy were monitored using different diagnostic tests (cytology, serology, and PCR). Overall, PCR detected the highest number of dogs infected with Anaplasma platys, Babesia vogeli, and Ehrlichia canis, whereas seroconversion was a more sensitive indicator of exposure to Leishmania infantum. For A. platys infection, combining blood and buffy coat cytology in parallel enhanced the relative sensitivity (SE rel ) (87.3%). For B. vogeli, the best diagnostic combination was buffy coat cytology and serology used in parallel (SE rel , 67.5%), whereas serology and PCR used in parallel (SE rel , 100%) was the best combination for L. infantum. Overall, 12 (20.7%) dogs were coinfected; however, the percentage of new coinfections decreased from baseline (50%) to the first (33.3%) and second (16.6%) follow-up time points. Numbers of coinfections with A. platys and B. vogeli were significantly higher (P < 0.05) than coinfections with other pathogen combinations. The data generated in this study provide insights on the incidence of certain pathogens infecting young dogs in southern Italy, highlight important diagnostic testing limitations, and support the use of multiple diagnostic modalities when attempting to confirm a tick-borne infection in an individual dog or in a canine population.

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The most frequently used diagnostic methods were compared in a longitudinal survey with Leishmania infantum-infected asymptomatic dogs from an area of Italy where leishmaniasis is endemic. In February and March 2005, 845 asymptomatic dogs were tested by an immunofluorescence antibody test (IFAT), a dipstick assay (DS), and an enzyme-linked immunosorbent assay (ELISA) for L. infantum and by IFAT for Ehrlichia canis. Dogs seronegative for L. infantum were further parasitologically evaluated by microscopic examination of lymph node tissues and PCR of skin samples. A total of 204 animals both serologically and parasitologically negative for L. infantum at the first sampling were enrolled in the trial and were further examined for canine leishmaniasis (CanL) and canine monocytic ehrlichiosis in November 2005 (i.e., the end of the first sandfly season) and March 2006 and 2007 (1-and 2-year follow-ups, respectively). At the initial screening, the overall rates of L. infantum seroprevalence were 9.5% by IFAT, 17.1% by ELISA, and 9.8% by DS and the overall rate of E. canis seroprevalence was 15%. The rates of concordance between the results of IFAT and DS were almost equal, whereas the rate of concordance between the results of IFAT and DS and those of the ELISA was lower. The results of the annual incidence of Leishmania infection were variable, depending on the test employed, with the highest values registered for PCR (i.e., 5.7% and 11.4% at the 1-and 2-year follow-ups, respectively), followed by ELISA, IFAT, and DS. Over the 2 years of observation, 55 animals (i.e., 26.9%) became positive for L. infantum by one or more diagnostic tests at different follow-up times, with 12.7% showing clinical signs related to CanL, while the remaining 87.3% were asymptomatic. A diagnostic scheme for assessment of the L. infantum infection status in asymptomatic dogs is suggested.