Diagnosis of leishmaniasis in Maltese dogs with the aid of the polymerase chain reaction

Abstract

Visceral leishmaniasis due to infection with Leishmania infantum (a member of the L. donovani complex) has been known in Malta since the beginning of the century. In 1946, when human diseases became compulsorily notifiable on the islands, the leishmaniasis figures were 1264 visceral cases, 36 cutaneous cases and 5 unspecified. Five cases of cutaneous infection were reported in 1997 and 23 cases of cutaneous and 3 of visceral infection in January–October 1998. There may be considerable underreporting of the disease. Figures of between 18% and 47% have been reported for canine leishmaniasis. This large discrepancy between reservoir and human hosts suggests that the canine reservoir could be a serious threat and is worthy of careful examination. This pilot study was carried out to determine the proportion of dogs serologically positive for leishmaniasis in order to assess the necessity for a possible control programme in Malta. Using 60 canine blood samples from the Maltese islands, we tested for deoxyribonucleic acid (DNA) of the L. donovani complex using the polymerase chain reaction (PCR). The samples had all been subjected to the indirect immunofluorescent antibody test (IFAT) and a direct comparison was made. DNA was extracted using the phenol/chloroform method and amplified with primers specific for kinetoplast minicircle DNA of the L. donovani complex and L. major, Southern blotted and hybridized with a radiolabelled probe specific for the L. donovani complex. Twelve of the samples gave positive results in the IFAT, whilst 37 (62%) were positive by PCR and hybridization. All samples from 36 dogs from a non-endemic area in the UK were negative by PCR. Five of the 12 samples positive by IFAT gave negative PCR results.