To confirm a diagnosis of visceral leishmaniasis in this patient, the following laboratory researches are necessary:

1.Liver and spleen function tests: Liver and spleen enlargement and dysfunction are common in visceral leishmaniasis, so tests like liver function tests (LFTs) can help in assessing their function.Serological tests: Blood tests such as Enzyme-linked Immunosorbent Assay (ELISA) can detect antibodies against Leishmania to confirm the infection.2.3.4.5.