Clinical, serologic, and parasitologic follow-up after long-term allopurinol therapy of dogs naturally infected with Leishmania infantum

Canine leishmaniasis usually is treated with antimony compounds, but freque nt relapses, adverse effects, high costs, and development of resistance to long-term antimonial therapy emphasize the importance of searching for alte rnative antileishmanial drugs. Allopurinol was used at a dosage of 10 mg/kg /day PO to treat 10 dogs naturally infected with Leishmania infantum for a period of 2-24 months. Nine dogs recovered within 2-6 months of chemotherap y, and no relapses were observed during the treatment of up to 20 months. H owever, 3 of 4 dogs relapsed after treatment was discontinued. These dogs a gain recovered clinically when therapy was resumed. Parasite-specific immun oglobulin concentrations (IgG2) were high in all dogs before therapy and re mained high even in clinically cured dogs during or after therapy. On the o ther hand, specific IgG1 reactions, which have been shown to be detectable in symptomatic animals, persisted in 7 dogs for long periods after clinical recovery. Three of these dogs relapsed within 2-4 weeks after interrupting therapy. However, 1 dog with no detectable specific IgG1 reaction at the e nd of therapy did not relapse in the following 4 months. Parasites could be detected in 8 of 9 dogs after clinical improvement by in vitro cultivation or polymerase chain reaction (PCR) testing of lymph node aspirates. In 4 o f these dogs, parasites also were detected in blood samples by PCR. Hence, these clinically cured dogs must be regarded as reservoirs of Leishmania an d allopurinol cannot be recommended in endemic areas.