Epidemiology
The virus is very common in the general population, infecting 70 to 90 percent of humans; most people acquire JCV in childhood or adolescence. It is found in high concentrations in urban sewage worldwide, leading some researchers to suspect contaminated water as a typical route of infection.
Minor genetic variations are found consistently in different geographic areas; thus, genetic analysis of JC virus samples has been useful in tracing the history of human migration. 14 subtypes or genotypes are recognised each associated with a specific geographical region. Three are found in Europe (a, b and c). A minor African type - Af1 - occurs in Central and West Africa. The major African type - Af2 - is found throughout Africa and also in West and South Asia. Several Asian types are recognised B1-a, B1-b, B1-d, B2, CY, MY and SC.
An alternative numbering scheme numbers the genotypes 1-8 with additional lettering. Types 1 and 4 are found in Europe and in indigenous populations in northern Japan, North-East Siberia and northern Canada. These two types are closely related. Types 3 and 6 are found in sub-Saharan Africa: type 3 was isolated in Ethiopia, Tanzania and South Africa. Type 6 is found in Ghana. Both types are also found in the Biaka Pygmies and Bantus from Central Africa. Type 2 has several variants: subtype 2A is found mainly in the Japanese population and native Americans (excluding Inuit); 2B is found in Eurasians; 2D is found in Indians and 2E is found in Australians and western Pacific populations. Subtype 7A is found in southern China and South-East Asia. Subtype 7B is found in northern China, Mongolia and Japan Subtype 7C is found in northern and southern China. Subtype 8 is found in Papua New Guinea and the Pacific Islands.
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