Prevalence and incidence of canine visceral leishmaniasis and its clinical–immunological features in an endemic area of the Brazilian Amazon

BACKGROUND: A cohort study for 2 years period analysed the prevalence, incidence and clinical–immunological features of canine Leishmania (L.) chagasi‐infection in 316 mongrel dogs in a visceral leishmaniasis‐endemic area in Pará State, Brazil. OBJECTIVE/METHODS: Diagnosis of infection was performed by the indirect fluorescent antibody test (IFAT‐IgG), the leishmanin skin test (LST) and a parasite search (from the popliteal lymph node aspiration) at the beginning of the study and at 6, 12 and 24 months intervals. RESULTS: IFAT/LST revealed three immune profiles of infection: (I) IFAT((+))/LST((−)) (81), (II) IFAT((−))/LST((+)) (17) and (III) IFAT((+))/LST((+)) (13). Prevalence of profiles I, II and III were 25.6, 5.4 and 4.1%, and an overall prevalence 35.1%. Incidence of profiles I, II and III were 5.4, 0.3 and 0.0%, and an overall incidence 5.7% dogs per month. Incidence at the age ranges <1 year, ≥1 year, <7 years and ≥7 years evidenced a highest rate in the age range <1 year (6.6% dogs per month). Parasitological diagnosis was positive in 19% dogs at the prevalence (85.7% profile I), and in 11% at the incidence (100% profile I). The clinical picture of 179 infected dogs showed 145 (81%) of profile I (82% subclinical); 21 (11.7%) of profile II (100% subclinical); and 13 (7.3%) of profile III (84.6% subclinical). Conversion from subclinical to sick dogs was higher (p < 0.05) in profile I (40.2%) than in profiles II (5.8%) and III (9%). Immunological conversion showed that only 3.2% of profile I dogs (prevalence) converted to LST((+)) (two at the end of the first 6 months and 1 after 24 months), while 82.3% of profile II dogs converted to IFAT((+)) (11 in the first 6 months, whereas three after 12 months). A 100% death rate was observed in dogs from profile I alone. CONCLUSION: These results reinforce the need of adopting preventive strategies against CVL as early as in the first semester of the dog's life.