K 39 antigen is used in diagnosis of:
Rapid Diagnostic Test: Now a rapid dipstick test based on the recombinant K39 protein is available for rapid diagnosis of kala-azar. K39 is an epitope apparently conserved on amastigotes of Leishmania species that cause visceral infection; by use of laboratory ELISA testing, circulating anti-K39, IgG is detectable in 95%- 100% of patients who have kala-azar, irrespective of geographic region. Ref:
Malaria
Typhus fever
Kala azar
Enteric fever