Rapid screening with a recombinant antigen (rK39) for diagnosis of visceral leishmaniasis using dipstick

OBJECTIVE

To evaluate the diagnostic value of the recombinant antigen of 39 amino acid repeats encoded by a kinesin-like gene of Leishmania changasi (rK39) in serodiagnosis of visceral leishmaniasis (VL).

METHODS

In Kashi, Xinjiang, 13 VL patients with splenomegaly and bone marrow aspirate culture positive were subjected to dipstick assay. A drop of whole blood or serum from patient was placed at the absorbing pad at the bottom of the dipstick. Flooding of the bottom protein with buffer allows serum proteins to migrate upwards, producing the positive band and Western blot analysis of rK39 subsequently performed with the sera collected.

RESULTS

The end-point titers of anti-rK39 antibodies of these sera were determined by ELISA and found to fall within the range of 10(-2) to 10(-4), which were consistent with the intensity of their reaction with rK39 in dipstick assay. The positive sera could also recognize the specific rK39 band as analyzed by Western blot analysis.

CONCLUSION

The rK39 dipstick assay is more rapid, specific, sensitive and less invasive than the conventional methods of diagnosis for VL in the areas of low endemicity.

Cloning and characterization of cDNA sequences encoding two novel alpha-like-toxin precursors from the Chinese scorpion Buthus martensii Karsch

According to a relative conserved fragment of alpha-scorpion toxins, a degenerate primer was designed and synthesized. Two full-length cDNAs encoding the precursors of two novel putative alpha-like-toxins were then amplified from the total cDNAs of venomous glands of the Chinese scorpion Buthusmartensi Karsch using 3' and 5' RACE (rapid amplification of cDNA ends). The precursors were both composed of 85 amino acid residues, including a putative signal peptide of 19 residues and a mature toxin of 66 residues, respectively. The predicted amino acid sequences of these two toxins show a homology of 82% with each other, and of 55-70% with other BmK-originated alpha-like-toxins. Interestingly, it is rarely seen in other alpha or alpha-like-toxins that: (1) Met residue but not a basic amino acid residue (Arg or Lys) is located on position 58 for BmKalpha2; (2) both toxins are ended with double Gly in the C-terminus.

Diagnosis of kala-azar by nested PCR based on amplification of the Leishmania mini-exon gene

To diagnose visceral leishmaniasis (kala-azar), we have developed a nested PCR method based on amplification of the mini-exon gene, which is unique and tandomly repeated in the Leishmania genome. Nested PCR was sufficiently sensitive for the detection of DNA in an amount equivalent to a single Leishmania parasite or less. We examined the usefulness of this PCR method using bone marrow aspirates and buffy coat cells collected from kala-azar patients who had or had not received chemotherapy in northwest China. We obtained PCR positivity for all of the parasitologically positive bone marrow samples from the patients. Some ambiguities with the primary PCR results were eliminated by the subsequent nested PCR. The buffy coat samples from 7 of 12 patients with splenomegaly were positive by the nested PCR, although only 2 of them were positive for parasites by culture. However, buffy coat samples from nine children, whose splenomegaly has been reduced and clinically cured by antimony treatment, were all negative. Thus, this nested PCR method represents a new tool for the diagnosis of kala-azar with patient blood samples instead of bone marrow or spleen aspirates obtained by more invasive procedures.