Subacute sclerosing panencephalitis, a rare, progressive, fatal central nervous 
system disease of children, is caused by measles virus. Clinical signs occur 
months to several years after recovery from acute measles infection. It is not 
known where the virus persists while the disease is inapparent. Involvement of 
organs outside the central nervous system has rarely been documented. To search 
for possible peripheral reservoirs of measles virus we used in situ 
hybridization to probe for measles virus RNA and immunocytochemical studies to 
localize measles virus antigens ina variety of organs taken at autopsy from 
confirmed cases of subacute sclerosing panencephalitis. Seven of 9 cadavers were 
found to contain measles virus RNA or antigens, or both, in at least one 
location outside the central nervous system. These sites included lymphoid 
organs such as thymus, spleen, lymph nodes, and tonsil, suggesting a role for 
lymphocytes in disease pathogenesis. Virus was also detected in kidney, lung, 
and glandular tissues such as pancreas, adrenal, and pituitary. These reservoirs 
may provide the antigenic stimulus leading to the elevated response 
characteristic for subacute sclerosing panencephalitis.