Why can asymptomatic infections make Koch's postulates difficult to apply?

Robert Koch developed his famous postulates to establish a causal link between a specific microorganism and a disease. However, these criteria are not universally applicable to all pathogens.12

Asymptomatic infections present a significant challenge to the first and third postulates. Koch’s first postulate requires that the microorganism be present in diseased individuals but absent in healthy ones. In cases of asymptomatic infection, a host may carry and transmit the pathogen without exhibiting any clinical symptoms of the disease, effectively blurring the distinction between a diseased and a healthy individual.3

Furthermore, the third postulate requires that the cultured organism cause the same disease when introduced into a healthy host. Because asymptomatic carriers do not display the disease, it is difficult to satisfy the requirement that the organism must consistently produce the expected clinical symptoms in a new host. These limitations highlight that while Koch's work remains foundational to microbiology, modern science must often adapt these criteria to account for complex host-pathogen interactions.123