SAO PAULO/BRAZIL, (11 May 2009) – Paulo Henrique da Costa Pinheiroa and his team from Federal University of São Paulo used enzyme-linked immunosorbent assays (ELISA) to test for reactivity in delayed-type hypersensitivity responses of dogs from an endemic region of visceral leishmaniasis in Piauí State, Brazil. Amastigote or promastigote extracts were assayed for comparison.

In Veterinary Parasitology, the team reports that the sensitivity for detection of specific antibodies to L. (L.) chagasi using rLdccys1, a recombinant protein produced by expression of the gene encoding a 30 kDa cysteine proteinase, was 96%. Lysates from L. (L.) chagasi promastigotes and amastigotes achieved a sensitivity of 68% and 69%, respectively.

Among 106 sera from symptomatic dogs and 22 from non-infected controls, no false negatives and only two false positive sera were found for rLdccys1, they note. In contrast, amastigote lysates yielded 11 false positives and 13 false negatives, whereas the corresponding numbers for promastigote lysates were 17 and 16.

Continuing, they write that delayed-type hypersensitivity responses were determined after intradermal injection of rLdccys1 or amastigote extract. The induration area was measured at 24, 48 and 72 h after injection.

All asymptomatic dogs showed a positive intradermal response to rLdccys1 (>10 mm) which peaked at 48 h, whereas no significant reactivity to the recombinant antigen was found in the symptomatic group, the researchers outline their results. Histological analysis of the intradermal induration showed a predominance of necrotic and hemorrhagic areas in sections from asymptomatic dogs injected with L. (L.) chagasi amastigote extract, whereas a typical granulomatous reaction mediated by mononuclear cells was observed in sections from asymptomatic animals injected with rLdccys1.

By grouping data from ELISA and delayed-type hypersensitivity assays with rLdccys1 and L. (L.) chagasi amastigote extracts they found that humoral and cellular responses were inversely correlated during the development of canine visceral leishmaniasis. Overall, they conclude, these findings indicate that L. (L.) chagasi recombinant cysteine proteinase is potentially useful for diagnosis of canine visceral leishmaniasis, as well as for the discrimination of clinical and subclinical forms of the disease.

References

• Veterinary Parasitology, Volume 162, Issues 1-2, 26 May 2009, Pages 32-39