Hi!
If there is increased infection and the body cannot fight it, the WBC start going down as the pathogen start engulfing them. However, if there is no fever, it is not due to infection. Chemotherapy, and radiation therapy are the other causes. Other common causes of low WBC are flu, lupus, Hodgkin's lymphoma, some types of cancer, typhoid, malaria, tuberculosis, dengue, enlarged spleen or hyper-spleenism, and folate deficiency.