Whooping cough eight weeks, or sometimes longer. A gradual transition then occurs to the convalescent stage, which usually lasts one to four weeks. This stage is marked by a decrease in paroxysms of coughing, although paroxysms may occur with subsequent respiratory infection for many months after the onset of pertussis. The time between exposure and the development of symptoms is on average 7–14 days (range 6–20 days), rarely as long as 42 days. Pertussis is caused by the bacterium "Bordetella pertussis". It is an airborne disease (through droplets) that spreads easily through the coughs and sneezes of an infected person. Uncertainties have
Tay–Sachs disease Researchers are looking at gene therapy or enzyme replacement therapy as possible treatments. Tay–Sachs disease is typically first noticed in infants around 6 months old displaying an abnormally strong response to sudden noises or other stimuli, known as the "startle response". There may also be listlessness or muscle stiffness (hypertonia). The disease is classified into several forms, which are differentiated based on the onset age of neurological symptoms. Until the 1970s and 1980s, when the disease's molecular genetics became known, the juvenile and adult forms of the disease were not always recognized as variants of Tay–Sachs disease. Post-infantile Tay–Sachs was