Exposure to Agent Orange increases the risk of CLL, and exposure to hepatitis C virus may increase the risk. There is no clear association between ionizing radiation exposure and the risk of developing CLL. Blood transfusions have been ruled out as a risk factor. Diagnosis
The diagnosis of CLL is based on the demonstration of an abnormal population of B lymphocytes in the blood, bone marrow, or tissues that display an unusual but characteristic pattern of molecules on the cell surface. CLL is usually first suspected by a diagnosis of lymphocytosis, an increase in a type of white blood cell, on a complete blood count test. This frequently is an incidental finding on a routine physician visit. Most often the lymphocyte count is greater than 5000 cells per microliter (µl) of blood but can be much higher. The presence of lymphocytosis in a person who is elderly should raise strong suspicion for CLL, and a confirmatory diagnostic test, in particular flow cytometry, should be performed unless clinically unnecessary. Molecular examination of peripheral blood and flow cytometry
The combination of the microscopic examination of the peripheral blood and analysis of the lymphocytes by flow cytometry to confirm clonality and marker molecule expression is needed to establish the diagnosis of CLL. Both are easily accomplished on a small amount of blood. A flow cytometer instrument can examine the expression of molecules on individual cells in fluids. This requires the use of specific antibodies to marker molecules, with fluorescent tags recognized by the instrument.
In 1873, Otto Obermeier first described the disease-causing ability and mechanisms of spirochetes, but was unable to reproduce the disease in inoculated test subjects and thereby unable to fulfill Kochs postulates. The disease was not  successfully produced in an inoculated subject until 1874. In 1904 and 1905, a series of papers outlined the cause of relapsing fever and its relationship with ticks. Both Joseph Everett Dutton and John Lancelot Todd contracted relapsing fever by performing autopsies while working in the eastern region of the Congo Free State. Dutton died there on February 27, 1905. The cause of tick-borne relapsing fever across central Africa was named Spirillum duttoni. In 1984, it was renamed Borrelia duttoni. The first time relapsing fever was described in North America was in 1915 in Jefferson County, Colorado.Sir William MacArthur suggested that relapsing fever was the cause of the yellow plague, variously called pestis flava, pestis ictericia, buidhe chonaill, or cron chonnaill, which struck early Medieval Britain and Ireland, and of epidemics which struck modern Ireland in the famine. This is consistent with the description of the symptoms experienced by King Maelgwn of Gwynedd as recorded in words attributed to Taliesin and with the "great mortality in Britain" in 548 CE noted in the Annales Cambriae. See also
Lyme disease
Typhus
Continuous fever
Intermittent fever
Remittent fever

References
External links
CDC: Relapsing Fever