Working in the South Valley, Dr. Merchant was able to gain extensive experience in parasitic disease, and observe the long term effects of chronic parasitic disease. He observed patients with parasitic disease had reduced absorption of nutrients, lowered immunity, recurrent infection, and ultimately developed a chronic disease. He recognized, whether parasite or pathogen, the patients experienced an infectious cascade. Acute infection became a chronic infection, and chronic infection evolved into a chronic disease over years or decades. His experience in the South Valley was the beginning of understanding the origin of disease, which through experience, observation, and successes in treating chronic disease, over decades, became a central organizing principle in chronic disease which is now described in The Origin of Disease: The War Within.