Infection tests carried out on blood samples can diagnose various infectious diseases by identifying pathogens such as bacteria, viruses, fungi, protozoa and parasites. These tests can detect infections such as malaria, which is most commonly transmitted by mosquitoes, as well as candida yeast, which is caused by poor diet or strong drugs, and listeriosis. Special tests identify infectious agents or specific antibodies produced during or after illness. Antibody tests can also be used to assess the effectiveness of vaccination.